rfc8829xml2.original.xml   rfc8829.xml 
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<?rfc rfcedstyle="no" ?> <link href="urn:issn:2070-1721" rel="alternate"/>
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<rfc category="std" docName="draft-ietf-rtcweb-jsep-26"
ipr="trust200902">
<front> <front>
<title abbrev="JSEP">JavaScript Session Establishment <title abbrev="JSEP">JavaScript Session Establishment Protocol (JSEP)</title
Protocol</title> >
<seriesInfo name="RFC" value="8829" stream="IETF"/>
<author fullname="Justin Uberti" initials="J." surname="Uberti"> <author fullname="Justin Uberti" initials="J." surname="Uberti">
<organization>Google</organization> <organization showOnFrontPage="true">Google</organization>
<address> <address>
<postal> <postal>
<street>747 6th St S</street> <street>747 6th Street South</street>
<city>Kirkland</city> <city>Kirkland</city>
<region>WA</region> <region>WA</region>
<code>98033</code> <code>98033</code>
<country>USA</country> <country>United States of America</country>
</postal> </postal>
<email>justin@uberti.name</email> <email>justin@uberti.name</email>
</address> </address>
</author> </author>
<author fullname="Cullen Jennings" initials="C." <author fullname="Cullen Jennings" initials="C." surname="Jennings">
surname="Jennings"> <organization showOnFrontPage="true">Cisco</organization>
<organization>Cisco</organization>
<address> <address>
<postal> <postal>
<street>400 3rd Avenue SW</street> <street>400 3rd Avenue SW</street>
<city>Calgary</city> <city>Calgary</city>
<region>AB</region> <region>AB</region>
<code>T2P 4H2</code> <code>T2P 4H2</code>
<country>Canada</country> <country>Canada</country>
</postal> </postal>
<email>fluffy@iii.ca</email> <email>fluffy@iii.ca</email>
</address> </address>
</author> </author>
<author fullname="Eric Rescorla" initials="E.K." surname="Rescorla" <author fullname="Eric Rescorla" initials="E." surname="Rescorla" role="edit
role="editor"> or">
<organization>Mozilla</organization> <organization showOnFrontPage="true">Mozilla</organization>
<address> <address>
<postal>
<street>331 Evelyn Ave</street>
<city>Mountain View</city>
<region>CA</region>
<code>94041</code>
<country>USA</country>
</postal>
<email>ekr@rtfm.com</email> <email>ekr@rtfm.com</email>
</address> </address>
</author> </author>
<date /> <date month="01" year="2021"/>
<area>RAI</area> <keyword>webrtc</keyword>
<abstract> <keyword>sdp</keyword>
<keyword>negotiation</keyword>
<t>This document describes the mechanisms for allowing a <keyword>signaling</keyword>
<keyword>peerconnection</keyword>
<keyword>api</keyword>
<keyword>ice</keyword>
<keyword>rtp</keyword>
<keyword>offer</keyword>
<keyword>answer</keyword>
<abstract pn="section-abstract">
<t indent="0" pn="section-abstract-1">This document describes the mechanis
ms for allowing a
JavaScript application to control the signaling plane of a JavaScript application to control the signaling plane of a
multimedia session via the interface specified in the W3C multimedia session via the interface specified in the W3C
RTCPeerConnection API, and discusses how this relates to existing RTCPeerConnection API and discusses how this relates to existing
signaling protocols.</t> signaling protocols.</t>
</abstract> </abstract>
<boilerplate>
<section anchor="status-of-memo" numbered="false" removeInRFC="false" toc=
"exclude" pn="section-boilerplate.1">
<name slugifiedName="name-status-of-this-memo">Status of This Memo</name
>
<t indent="0" pn="section-boilerplate.1-1">
This is an Internet Standards Track document.
</t>
<t indent="0" pn="section-boilerplate.1-2">
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
</t>
<t indent="0" pn="section-boilerplate.1-3">
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
<eref target="https://www.rfc-editor.org/info/rfc8829" brackets="non
e"/>.
</t>
</section>
<section anchor="copyright" numbered="false" removeInRFC="false" toc="excl
ude" pn="section-boilerplate.2">
<name slugifiedName="name-copyright-notice">Copyright Notice</name>
<t indent="0" pn="section-boilerplate.2-1">
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
</t>
<t indent="0" pn="section-boilerplate.2-2">
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(<eref target="https://trustee.ietf.org/license-info" brackets="none
"/>) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
</t>
</section>
</boilerplate>
<toc>
<section anchor="toc" numbered="false" removeInRFC="false" toc="exclude" p
n="section-toc.1">
<name slugifiedName="name-table-of-contents">Table of Contents</name>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="section-to
c.1-1">
<li pn="section-toc.1-1.1">
<t indent="0" pn="section-toc.1-1.1.1"><xref derivedContent="1" form
at="counter" sectionFormat="of" target="section-1"/>.  <xref derivedContent="" f
ormat="title" sectionFormat="of" target="name-introduction">Introduction</xref><
/t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
n-toc.1-1.1.2">
<li pn="section-toc.1-1.1.2.1">
<t indent="0" keepWithNext="true" pn="section-toc.1-1.1.2.1.1"><
xref derivedContent="1.1" format="counter" sectionFormat="of" target="section-1.
1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-ge
neral-design-of-jsep">General Design of JSEP</xref></t>
</li>
<li pn="section-toc.1-1.1.2.2">
<t indent="0" keepWithNext="true" pn="section-toc.1-1.1.2.2.1"><
xref derivedContent="1.2" format="counter" sectionFormat="of" target="section-1.
2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-ot
her-approaches-considered">Other Approaches Considered</xref></t>
</li>
<li pn="section-toc.1-1.1.2.3">
<t indent="0" keepWithNext="true" pn="section-toc.1-1.1.2.3.1"><
xref derivedContent="1.3" format="counter" sectionFormat="of" target="section-1.
3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-co
ntradiction-regarding-bun">Contradiction regarding bundle-only "m=" sections</xr
ef></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.2">
<t indent="0" pn="section-toc.1-1.2.1"><xref derivedContent="2" form
at="counter" sectionFormat="of" target="section-2"/>.  <xref derivedContent="" f
ormat="title" sectionFormat="of" target="name-terminology">Terminology</xref></t
>
</li>
<li pn="section-toc.1-1.3">
<t indent="0" pn="section-toc.1-1.3.1"><xref derivedContent="3" form
at="counter" sectionFormat="of" target="section-3"/>.  <xref derivedContent="" f
ormat="title" sectionFormat="of" target="name-semantics-and-syntax">Semantics an
d Syntax</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
n-toc.1-1.3.2">
<li pn="section-toc.1-1.3.2.1">
<t indent="0" pn="section-toc.1-1.3.2.1.1"><xref derivedContent=
"3.1" format="counter" sectionFormat="of" target="section-3.1"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-signaling-model">Signa
ling Model</xref></t>
</li>
<li pn="section-toc.1-1.3.2.2">
<t indent="0" pn="section-toc.1-1.3.2.2.1"><xref derivedContent=
"3.2" format="counter" sectionFormat="of" target="section-3.2"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-session-descriptions-a
nd-st">Session Descriptions and State Machine</xref></t>
</li>
<li pn="section-toc.1-1.3.2.3">
<t indent="0" pn="section-toc.1-1.3.2.3.1"><xref derivedContent=
"3.3" format="counter" sectionFormat="of" target="section-3.3"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-session-description-fo
rmat">Session Description Format</xref></t>
</li>
<li pn="section-toc.1-1.3.2.4">
<t indent="0" pn="section-toc.1-1.3.2.4.1"><xref derivedContent=
"3.4" format="counter" sectionFormat="of" target="section-3.4"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-session-description-co
ntrol">Session Description Control</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.3.2.4.2">
<li pn="section-toc.1-1.3.2.4.2.1">
<t indent="0" pn="section-toc.1-1.3.2.4.2.1.1"><xref derived
Content="3.4.1" format="counter" sectionFormat="of" target="section-3.4.1"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-rtptransce
ivers">RtpTransceivers</xref></t>
</li>
<li pn="section-toc.1-1.3.2.4.2.2">
<t indent="0" pn="section-toc.1-1.3.2.4.2.2.1"><xref derived
Content="3.4.2" format="counter" sectionFormat="of" target="section-3.4.2"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-rtpsenders
">RtpSenders</xref></t>
</li>
<li pn="section-toc.1-1.3.2.4.2.3">
<t indent="0" pn="section-toc.1-1.3.2.4.2.3.1"><xref derived
Content="3.4.3" format="counter" sectionFormat="of" target="section-3.4.3"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-rtpreceive
rs">RtpReceivers</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.3.2.5">
<t indent="0" pn="section-toc.1-1.3.2.5.1"><xref derivedContent=
"3.5" format="counter" sectionFormat="of" target="section-3.5"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-ice">ICE</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.3.2.5.2">
<li pn="section-toc.1-1.3.2.5.2.1">
<t indent="0" pn="section-toc.1-1.3.2.5.2.1.1"><xref derived
Content="3.5.1" format="counter" sectionFormat="of" target="section-3.5.1"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-ice-gather
ing-overview">ICE Gathering Overview</xref></t>
</li>
<li pn="section-toc.1-1.3.2.5.2.2">
<t indent="0" pn="section-toc.1-1.3.2.5.2.2.1"><xref derived
Content="3.5.2" format="counter" sectionFormat="of" target="section-3.5.2"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-ice-candid
ate-trickling">ICE Candidate Trickling</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn
="section-toc.1-1.3.2.5.2.2.2">
<li pn="section-toc.1-1.3.2.5.2.2.2.1">
<t indent="0" pn="section-toc.1-1.3.2.5.2.2.2.1.1"><xref
derivedContent="3.5.2.1" format="counter" sectionFormat="of" target="section-3.
5.2.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="nam
e-ice-candidate-format">ICE Candidate Format</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.3.2.5.2.3">
<t indent="0" pn="section-toc.1-1.3.2.5.2.3.1"><xref derived
Content="3.5.3" format="counter" sectionFormat="of" target="section-3.5.3"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-ice-candid
ate-policy">ICE Candidate Policy</xref></t>
</li>
<li pn="section-toc.1-1.3.2.5.2.4">
<t indent="0" pn="section-toc.1-1.3.2.5.2.4.1"><xref derived
Content="3.5.4" format="counter" sectionFormat="of" target="section-3.5.4"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-ice-candid
ate-pool">ICE Candidate Pool</xref></t>
</li>
<li pn="section-toc.1-1.3.2.5.2.5">
<t indent="0" pn="section-toc.1-1.3.2.5.2.5.1"><xref derived
Content="3.5.5" format="counter" sectionFormat="of" target="section-3.5.5"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-ice-versio
ns">ICE Versions</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.3.2.6">
<t indent="0" pn="section-toc.1-1.3.2.6.1"><xref derivedContent=
"3.6" format="counter" sectionFormat="of" target="section-3.6"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-video-size-negotiation
">Video Size Negotiation</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.3.2.6.2">
<li pn="section-toc.1-1.3.2.6.2.1">
<t indent="0" pn="section-toc.1-1.3.2.6.2.1.1"><xref derived
Content="3.6.1" format="counter" sectionFormat="of" target="section-3.6.1"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-creating-a
n-imageattr-attri">Creating an imageattr Attribute</xref></t>
</li>
<li pn="section-toc.1-1.3.2.6.2.2">
<t indent="0" pn="section-toc.1-1.3.2.6.2.2.1"><xref derived
Content="3.6.2" format="counter" sectionFormat="of" target="section-3.6.2"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-interpreti
ng-imageattr-attr">Interpreting imageattr Attributes</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.3.2.7">
<t indent="0" pn="section-toc.1-1.3.2.7.1"><xref derivedContent=
"3.7" format="counter" sectionFormat="of" target="section-3.7"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-simulcast">Simulcast</
xref></t>
</li>
<li pn="section-toc.1-1.3.2.8">
<t indent="0" pn="section-toc.1-1.3.2.8.1"><xref derivedContent=
"3.8" format="counter" sectionFormat="of" target="section-3.8"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-interactions-with-fork
ing">Interactions with Forking</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.3.2.8.2">
<li pn="section-toc.1-1.3.2.8.2.1">
<t indent="0" pn="section-toc.1-1.3.2.8.2.1.1"><xref derived
Content="3.8.1" format="counter" sectionFormat="of" target="section-3.8.1"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-sequential
-forking">Sequential Forking</xref></t>
</li>
<li pn="section-toc.1-1.3.2.8.2.2">
<t indent="0" pn="section-toc.1-1.3.2.8.2.2.1"><xref derived
Content="3.8.2" format="counter" sectionFormat="of" target="section-3.8.2"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-parallel-f
orking">Parallel Forking</xref></t>
</li>
</ul>
</li>
</ul>
</li>
<li pn="section-toc.1-1.4">
<t indent="0" pn="section-toc.1-1.4.1"><xref derivedContent="4" form
at="counter" sectionFormat="of" target="section-4"/>.  <xref derivedContent="" f
ormat="title" sectionFormat="of" target="name-interface">Interface</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
n-toc.1-1.4.2">
<li pn="section-toc.1-1.4.2.1">
<t indent="0" pn="section-toc.1-1.4.2.1.1"><xref derivedContent=
"4.1" format="counter" sectionFormat="of" target="section-4.1"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-peerconnection">PeerCo
nnection</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.4.2.1.2">
<li pn="section-toc.1-1.4.2.1.2.1">
<t indent="0" pn="section-toc.1-1.4.2.1.2.1.1"><xref derived
Content="4.1.1" format="counter" sectionFormat="of" target="section-4.1.1"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-constructo
r">Constructor</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.2">
<t indent="0" pn="section-toc.1-1.4.2.1.2.2.1"><xref derived
Content="4.1.2" format="counter" sectionFormat="of" target="section-4.1.2"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-addtrack">
addTrack</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.3">
<t indent="0" pn="section-toc.1-1.4.2.1.2.3.1"><xref derived
Content="4.1.3" format="counter" sectionFormat="of" target="section-4.1.3"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-removetrac
k">removeTrack</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.4">
<t indent="0" pn="section-toc.1-1.4.2.1.2.4.1"><xref derived
Content="4.1.4" format="counter" sectionFormat="of" target="section-4.1.4"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-addtransce
iver">addTransceiver</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.5">
<t indent="0" pn="section-toc.1-1.4.2.1.2.5.1"><xref derived
Content="4.1.5" format="counter" sectionFormat="of" target="section-4.1.5"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-onaddtrack
-event">onaddtrack Event</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.6">
<t indent="0" pn="section-toc.1-1.4.2.1.2.6.1"><xref derived
Content="4.1.6" format="counter" sectionFormat="of" target="section-4.1.6"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-createdata
channel">createDataChannel</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.7">
<t indent="0" pn="section-toc.1-1.4.2.1.2.7.1"><xref derived
Content="4.1.7" format="counter" sectionFormat="of" target="section-4.1.7"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-ondatachan
nel-event">ondatachannel Event</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.8">
<t indent="0" pn="section-toc.1-1.4.2.1.2.8.1"><xref derived
Content="4.1.8" format="counter" sectionFormat="of" target="section-4.1.8"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-createoffe
r">createOffer</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.9">
<t indent="0" pn="section-toc.1-1.4.2.1.2.9.1"><xref derived
Content="4.1.9" format="counter" sectionFormat="of" target="section-4.1.9"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-createansw
er">createAnswer</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.10">
<t indent="0" pn="section-toc.1-1.4.2.1.2.10.1"><xref derive
dContent="4.1.10" format="counter" sectionFormat="of" target="section-4.1.10"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-sessiond
escriptiontype">SessionDescriptionType</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn
="section-toc.1-1.4.2.1.2.10.2">
<li pn="section-toc.1-1.4.2.1.2.10.2.1">
<t indent="0" pn="section-toc.1-1.4.2.1.2.10.2.1.1"><xre
f derivedContent="4.1.10.1" format="counter" sectionFormat="of" target="section-
4.1.10.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="
name-use-of-provisional-answers">Use of Provisional Answers</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.10.2.2">
<t indent="0" pn="section-toc.1-1.4.2.1.2.10.2.2.1"><xre
f derivedContent="4.1.10.2" format="counter" sectionFormat="of" target="section-
4.1.10.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="
name-rollback">Rollback</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.4.2.1.2.11">
<t indent="0" pn="section-toc.1-1.4.2.1.2.11.1"><xref derive
dContent="4.1.11" format="counter" sectionFormat="of" target="section-4.1.11"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-setlocal
description">setLocalDescription</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.12">
<t indent="0" pn="section-toc.1-1.4.2.1.2.12.1"><xref derive
dContent="4.1.12" format="counter" sectionFormat="of" target="section-4.1.12"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-setremot
edescription">setRemoteDescription</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.13">
<t indent="0" pn="section-toc.1-1.4.2.1.2.13.1"><xref derive
dContent="4.1.13" format="counter" sectionFormat="of" target="section-4.1.13"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-currentl
ocaldescription">currentLocalDescription</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.14">
<t indent="0" pn="section-toc.1-1.4.2.1.2.14.1"><xref derive
dContent="4.1.14" format="counter" sectionFormat="of" target="section-4.1.14"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-pendingl
ocaldescription">pendingLocalDescription</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.15">
<t indent="0" pn="section-toc.1-1.4.2.1.2.15.1"><xref derive
dContent="4.1.15" format="counter" sectionFormat="of" target="section-4.1.15"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-currentr
emotedescription">currentRemoteDescription</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.16">
<t indent="0" pn="section-toc.1-1.4.2.1.2.16.1"><xref derive
dContent="4.1.16" format="counter" sectionFormat="of" target="section-4.1.16"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-pendingr
emotedescription">pendingRemoteDescription</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.17">
<t indent="0" pn="section-toc.1-1.4.2.1.2.17.1"><xref derive
dContent="4.1.17" format="counter" sectionFormat="of" target="section-4.1.17"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-cantrick
leicecandidates">canTrickleIceCandidates</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.18">
<t indent="0" pn="section-toc.1-1.4.2.1.2.18.1"><xref derive
dContent="4.1.18" format="counter" sectionFormat="of" target="section-4.1.18"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-setconfi
guration">setConfiguration</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.19">
<t indent="0" pn="section-toc.1-1.4.2.1.2.19.1"><xref derive
dContent="4.1.19" format="counter" sectionFormat="of" target="section-4.1.19"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-addiceca
ndidate">addIceCandidate</xref></t>
</li>
<li pn="section-toc.1-1.4.2.1.2.20">
<t indent="0" pn="section-toc.1-1.4.2.1.2.20.1"><xref derive
dContent="4.1.20" format="counter" sectionFormat="of" target="section-4.1.20"/>.
 <xref derivedContent="" format="title" sectionFormat="of" target="name-onicecan
didate-event">onicecandidate Event</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.4.2.2">
<t indent="0" pn="section-toc.1-1.4.2.2.1"><xref derivedContent=
"4.2" format="counter" sectionFormat="of" target="section-4.2"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-rtptransceiver">RtpTra
nsceiver</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.4.2.2.2">
<li pn="section-toc.1-1.4.2.2.2.1">
<t indent="0" pn="section-toc.1-1.4.2.2.2.1.1"><xref derived
Content="4.2.1" format="counter" sectionFormat="of" target="section-4.2.1"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-stop">stop
</xref></t>
</li>
<li pn="section-toc.1-1.4.2.2.2.2">
<t indent="0" pn="section-toc.1-1.4.2.2.2.2.1"><xref derived
Content="4.2.2" format="counter" sectionFormat="of" target="section-4.2.2"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-stopped">s
topped</xref></t>
</li>
<li pn="section-toc.1-1.4.2.2.2.3">
<t indent="0" pn="section-toc.1-1.4.2.2.2.3.1"><xref derived
Content="4.2.3" format="counter" sectionFormat="of" target="section-4.2.3"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-setdirecti
on">setDirection</xref></t>
</li>
<li pn="section-toc.1-1.4.2.2.2.4">
<t indent="0" pn="section-toc.1-1.4.2.2.2.4.1"><xref derived
Content="4.2.4" format="counter" sectionFormat="of" target="section-4.2.4"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-direction"
>direction</xref></t>
</li>
<li pn="section-toc.1-1.4.2.2.2.5">
<t indent="0" pn="section-toc.1-1.4.2.2.2.5.1"><xref derived
Content="4.2.5" format="counter" sectionFormat="of" target="section-4.2.5"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-currentdir
ection">currentDirection</xref></t>
</li>
<li pn="section-toc.1-1.4.2.2.2.6">
<t indent="0" pn="section-toc.1-1.4.2.2.2.6.1"><xref derived
Content="4.2.6" format="counter" sectionFormat="of" target="section-4.2.6"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-setcodecpr
eferences">setCodecPreferences</xref></t>
</li>
</ul>
</li>
</ul>
</li>
<li pn="section-toc.1-1.5">
<t indent="0" pn="section-toc.1-1.5.1"><xref derivedContent="5" form
at="counter" sectionFormat="of" target="section-5"/>.  <xref derivedContent="" f
ormat="title" sectionFormat="of" target="name-sdp-interaction-procedures">SDP In
teraction Procedures</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
n-toc.1-1.5.2">
<li pn="section-toc.1-1.5.2.1">
<t indent="0" pn="section-toc.1-1.5.2.1.1"><xref derivedContent=
"5.1" format="counter" sectionFormat="of" target="section-5.1"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-requirements-overview"
>Requirements Overview</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.5.2.1.2">
<li pn="section-toc.1-1.5.2.1.2.1">
<t indent="0" pn="section-toc.1-1.5.2.1.2.1.1"><xref derived
Content="5.1.1" format="counter" sectionFormat="of" target="section-5.1.1"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-usage-requ
irements">Usage Requirements</xref></t>
</li>
<li pn="section-toc.1-1.5.2.1.2.2">
<t indent="0" pn="section-toc.1-1.5.2.1.2.2.1"><xref derived
Content="5.1.2" format="counter" sectionFormat="of" target="section-5.1.2"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-profile-na
mes-and-interoper">Profile Names and Interoperability</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.5.2.2">
<t indent="0" pn="section-toc.1-1.5.2.2.1"><xref derivedContent=
"5.2" format="counter" sectionFormat="of" target="section-5.2"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-constructing-an-offer"
>Constructing an Offer</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.5.2.2.2">
<li pn="section-toc.1-1.5.2.2.2.1">
<t indent="0" pn="section-toc.1-1.5.2.2.2.1.1"><xref derived
Content="5.2.1" format="counter" sectionFormat="of" target="section-5.2.1"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-initial-of
fers">Initial Offers</xref></t>
</li>
<li pn="section-toc.1-1.5.2.2.2.2">
<t indent="0" pn="section-toc.1-1.5.2.2.2.2.1"><xref derived
Content="5.2.2" format="counter" sectionFormat="of" target="section-5.2.2"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-subsequent
-offers">Subsequent Offers</xref></t>
</li>
<li pn="section-toc.1-1.5.2.2.2.3">
<t indent="0" pn="section-toc.1-1.5.2.2.2.3.1"><xref derived
Content="5.2.3" format="counter" sectionFormat="of" target="section-5.2.3"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-options-ha
ndling">Options Handling</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn
="section-toc.1-1.5.2.2.2.3.2">
<li pn="section-toc.1-1.5.2.2.2.3.2.1">
<t indent="0" pn="section-toc.1-1.5.2.2.2.3.2.1.1"><xref
derivedContent="5.2.3.1" format="counter" sectionFormat="of" target="section-5.
2.3.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="nam
e-icerestart">IceRestart</xref></t>
</li>
<li pn="section-toc.1-1.5.2.2.2.3.2.2">
<t indent="0" pn="section-toc.1-1.5.2.2.2.3.2.2.1"><xref
derivedContent="5.2.3.2" format="counter" sectionFormat="of" target="section-5.
2.3.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="nam
e-voiceactivitydetection">VoiceActivityDetection</xref></t>
</li>
</ul>
</li>
</ul>
</li>
<li pn="section-toc.1-1.5.2.3">
<t indent="0" pn="section-toc.1-1.5.2.3.1"><xref derivedContent=
"5.3" format="counter" sectionFormat="of" target="section-5.3"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-generating-an-answer">
Generating an Answer</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.5.2.3.2">
<li pn="section-toc.1-1.5.2.3.2.1">
<t indent="0" pn="section-toc.1-1.5.2.3.2.1.1"><xref derived
Content="5.3.1" format="counter" sectionFormat="of" target="section-5.3.1"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-initial-an
swers">Initial Answers</xref></t>
</li>
<li pn="section-toc.1-1.5.2.3.2.2">
<t indent="0" pn="section-toc.1-1.5.2.3.2.2.1"><xref derived
Content="5.3.2" format="counter" sectionFormat="of" target="section-5.3.2"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-subsequent
-answers">Subsequent Answers</xref></t>
</li>
<li pn="section-toc.1-1.5.2.3.2.3">
<t indent="0" pn="section-toc.1-1.5.2.3.2.3.1"><xref derived
Content="5.3.3" format="counter" sectionFormat="of" target="section-5.3.3"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-options-ha
ndling-2">Options Handling</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn
="section-toc.1-1.5.2.3.2.3.2">
<li pn="section-toc.1-1.5.2.3.2.3.2.1">
<t indent="0" pn="section-toc.1-1.5.2.3.2.3.2.1.1"><xref
derivedContent="5.3.3.1" format="counter" sectionFormat="of" target="section-5.
3.3.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="nam
e-voiceactivitydetection-2">VoiceActivityDetection</xref></t>
</li>
</ul>
</li>
</ul>
</li>
<li pn="section-toc.1-1.5.2.4">
<t indent="0" pn="section-toc.1-1.5.2.4.1"><xref derivedContent=
"5.4" format="counter" sectionFormat="of" target="section-5.4"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-modifying-an-offer-or-
answe">Modifying an Offer or Answer</xref></t>
</li>
<li pn="section-toc.1-1.5.2.5">
<t indent="0" pn="section-toc.1-1.5.2.5.1"><xref derivedContent=
"5.5" format="counter" sectionFormat="of" target="section-5.5"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-processing-a-local-des
cript">Processing a Local Description</xref></t>
</li>
<li pn="section-toc.1-1.5.2.6">
<t indent="0" pn="section-toc.1-1.5.2.6.1"><xref derivedContent=
"5.6" format="counter" sectionFormat="of" target="section-5.6"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-processing-a-remote-de
scrip">Processing a Remote Description</xref></t>
</li>
<li pn="section-toc.1-1.5.2.7">
<t indent="0" pn="section-toc.1-1.5.2.7.1"><xref derivedContent=
"5.7" format="counter" sectionFormat="of" target="section-5.7"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-processing-a-rollback"
>Processing a Rollback</xref></t>
</li>
<li pn="section-toc.1-1.5.2.8">
<t indent="0" pn="section-toc.1-1.5.2.8.1"><xref derivedContent=
"5.8" format="counter" sectionFormat="of" target="section-5.8"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-parsing-a-session-desc
ripti">Parsing a Session Description</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.5.2.8.2">
<li pn="section-toc.1-1.5.2.8.2.1">
<t indent="0" pn="section-toc.1-1.5.2.8.2.1.1"><xref derived
Content="5.8.1" format="counter" sectionFormat="of" target="section-5.8.1"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-session-le
vel-parsing">Session-Level Parsing</xref></t>
</li>
<li pn="section-toc.1-1.5.2.8.2.2">
<t indent="0" pn="section-toc.1-1.5.2.8.2.2.1"><xref derived
Content="5.8.2" format="counter" sectionFormat="of" target="section-5.8.2"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-media-sect
ion-parsing">Media Section Parsing</xref></t>
</li>
<li pn="section-toc.1-1.5.2.8.2.3">
<t indent="0" pn="section-toc.1-1.5.2.8.2.3.1"><xref derived
Content="5.8.3" format="counter" sectionFormat="of" target="section-5.8.3"/>.  <
xref derivedContent="" format="title" sectionFormat="of" target="name-semantics-
verification">Semantics Verification</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.5.2.9">
<t indent="0" pn="section-toc.1-1.5.2.9.1"><xref derivedContent=
"5.9" format="counter" sectionFormat="of" target="section-5.9"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-applying-a-local-descr
iptio">Applying a Local Description</xref></t>
</li>
<li pn="section-toc.1-1.5.2.10">
<t indent="0" pn="section-toc.1-1.5.2.10.1"><xref derivedContent
="5.10" format="counter" sectionFormat="of" target="section-5.10"/>. <xref deriv
edContent="" format="title" sectionFormat="of" target="name-applying-a-remote-de
scripti">Applying a Remote Description</xref></t>
</li>
<li pn="section-toc.1-1.5.2.11">
<t indent="0" pn="section-toc.1-1.5.2.11.1"><xref derivedContent
="5.11" format="counter" sectionFormat="of" target="section-5.11"/>. <xref deriv
edContent="" format="title" sectionFormat="of" target="name-applying-an-answer">
Applying an Answer</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.6">
<t indent="0" pn="section-toc.1-1.6.1"><xref derivedContent="6" form
at="counter" sectionFormat="of" target="section-6"/>.  <xref derivedContent="" f
ormat="title" sectionFormat="of" target="name-processing-rtp-rtcp">Processing RT
P/RTCP</xref></t>
</li>
<li pn="section-toc.1-1.7">
<t indent="0" pn="section-toc.1-1.7.1"><xref derivedContent="7" form
at="counter" sectionFormat="of" target="section-7"/>.  <xref derivedContent="" f
ormat="title" sectionFormat="of" target="name-examples">Examples</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
n-toc.1-1.7.2">
<li pn="section-toc.1-1.7.2.1">
<t indent="0" pn="section-toc.1-1.7.2.1.1"><xref derivedContent=
"7.1" format="counter" sectionFormat="of" target="section-7.1"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-simple-example">Simple
Example</xref></t>
</li>
<li pn="section-toc.1-1.7.2.2">
<t indent="0" pn="section-toc.1-1.7.2.2.1"><xref derivedContent=
"7.2" format="counter" sectionFormat="of" target="section-7.2"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-detailed-example">Deta
iled Example</xref></t>
</li>
<li pn="section-toc.1-1.7.2.3">
<t indent="0" pn="section-toc.1-1.7.2.3.1"><xref derivedContent=
"7.3" format="counter" sectionFormat="of" target="section-7.3"/>.  <xref derived
Content="" format="title" sectionFormat="of" target="name-early-transport-warmup
-exam">Early Transport Warmup Example</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.8">
<t indent="0" pn="section-toc.1-1.8.1"><xref derivedContent="8" form
at="counter" sectionFormat="of" target="section-8"/>.  <xref derivedContent="" f
ormat="title" sectionFormat="of" target="name-security-considerations">Security
Considerations</xref></t>
</li>
<li pn="section-toc.1-1.9">
<t indent="0" pn="section-toc.1-1.9.1"><xref derivedContent="9" form
at="counter" sectionFormat="of" target="section-9"/>.  <xref derivedContent="" f
ormat="title" sectionFormat="of" target="name-iana-considerations">IANA Consider
ations</xref></t>
</li>
<li pn="section-toc.1-1.10">
<t indent="0" pn="section-toc.1-1.10.1"><xref derivedContent="10" fo
rmat="counter" sectionFormat="of" target="section-10"/>. <xref derivedContent=""
format="title" sectionFormat="of" target="name-references">References</xref></t
>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
n-toc.1-1.10.2">
<li pn="section-toc.1-1.10.2.1">
<t indent="0" pn="section-toc.1-1.10.2.1.1"><xref derivedContent
="10.1" format="counter" sectionFormat="of" target="section-10.1"/>.  <xref deri
vedContent="" format="title" sectionFormat="of" target="name-normative-reference
s">Normative References</xref></t>
</li>
<li pn="section-toc.1-1.10.2.2">
<t indent="0" pn="section-toc.1-1.10.2.2.1"><xref derivedContent
="10.2" format="counter" sectionFormat="of" target="section-10.2"/>.  <xref deri
vedContent="" format="title" sectionFormat="of" target="name-informative-referen
ces">Informative References</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.11">
<t indent="0" pn="section-toc.1-1.11.1"><xref derivedContent="Append
ix A" format="default" sectionFormat="of" target="section-appendix.a"/>.  <xref
derivedContent="" format="title" sectionFormat="of" target="name-sdp-abnf-syntax
">SDP ABNF Syntax</xref></t>
</li>
<li pn="section-toc.1-1.12">
<t indent="0" pn="section-toc.1-1.12.1"><xref derivedContent="" form
at="none" sectionFormat="of" target="section-appendix.b"/><xref derivedContent="
" format="title" sectionFormat="of" target="name-acknowledgements">Acknowledgeme
nts</xref></t>
</li>
<li pn="section-toc.1-1.13">
<t indent="0" pn="section-toc.1-1.13.1"><xref derivedContent="" form
at="none" sectionFormat="of" target="section-appendix.c"/><xref derivedContent="
" format="title" sectionFormat="of" target="name-authors-addresses">Authors' Add
resses</xref></t>
</li>
</ul>
</section>
</toc>
</front> </front>
<middle> <middle>
<section title="Introduction" anchor="sec.introduction"> <section anchor="sec.introduction" numbered="true" toc="include" removeInRFC
="false" pn="section-1">
<t>This document describes how the W3C WEBRTC RTCPeerConnection <name slugifiedName="name-introduction">Introduction</name>
<t indent="0" pn="section-1-1">This document describes how the W3C Web Rea
l-Time Communication (WebRTC) RTCPeerConnection
interface interface
<xref target="W3C.webrtc"></xref> is used to control the setup, <xref target="W3C.webrtc" format="default" sectionFormat="of" derivedConte
management and teardown of a multimedia session.</t> nt="W3C.webrtc"/> is used to control the setup,
<section title="General Design of JSEP" management, and teardown of a multimedia session.</t>
anchor="sec.general-design-of-jsep"> <section anchor="sec.general-design-of-jsep" numbered="true" toc="include"
removeInRFC="false" pn="section-1.1">
<t>WebRTC call setup has been designed to focus on controlling <name slugifiedName="name-general-design-of-jsep">General Design of JSEP
the media plane, leaving signaling plane behavior up to the </name>
<t indent="0" pn="section-1.1-1">WebRTC call setup has been designed to
focus on controlling
the media plane, leaving signaling-plane behavior up to the
application as much as possible. The rationale is that application as much as possible. The rationale is that
different applications may prefer to use different protocols, different applications may prefer to use different protocols,
such as the existing SIP call signaling protocol, or something such as the existing SIP call signaling protocol, or something
custom to the particular application, perhaps for a novel use custom to the particular application, perhaps for a novel use
case. In this approach, the key information that needs to be case. In this approach, the key information that needs to be
exchanged is the multimedia session description, which exchanged is the multimedia session description, which
specifies the necessary transport and media configuration specifies the transport and media configuration
information necessary to establish the media plane.</t> information necessary to establish the media plane.</t>
<t indent="0" pn="section-1.1-2">With these considerations in mind, this
<t>With these considerations in mind, this document describes document describes
the JavaScript Session Establishment Protocol (JSEP) that the JavaScript Session Establishment Protocol (JSEP), which
allows for full control of the signaling state machine from allows for full control of the signaling state machine from
JavaScript. As described above, JSEP assumes a model in which a JavaScript. As described above, JSEP assumes a model in which a
JavaScript application executes inside a runtime containing JavaScript application executes inside a runtime containing
WebRTC APIs (the "JSEP implementation"). The JSEP WebRTC APIs (the "JSEP implementation"). The JSEP
implementation is almost entirely divorced from the core implementation is almost entirely divorced from the core
signaling flow, which is instead handled by the JavaScript signaling flow, which is instead handled by the JavaScript
making use of two interfaces: (1) passing in local and remote making use of two interfaces: (1) passing in local and remote
session descriptions and (2) interacting with the ICE state session descriptions and (2) interacting with the Interactive
machine. The combination of the JSEP implementation and the Connectivity Establishment (ICE) state
machine <xref target="RFC8445" format="default" sectionFormat="of" deriv
edContent="RFC8445"/>. The combination of the JSEP implementation and the
JavaScript application is referred to throughout this document JavaScript application is referred to throughout this document
as a "JSEP endpoint".</t> as a "JSEP endpoint".</t>
<t indent="0" pn="section-1.1-3">In this document, the use of JSEP is de
<t>In this document, the use of JSEP is described as if it scribed as if it
always occurs between two JSEP endpoints. Note though in many always occurs between two JSEP endpoints. Note, though, that in many
cases it will actually be between a JSEP endpoint and some kind cases it will actually be between a JSEP endpoint and some kind
of server, such as a gateway or MCU. This distinction is of server, such as a gateway or Multipoint Control Unit (MCU). This dist inction is
invisible to the JSEP endpoint; it just follows the invisible to the JSEP endpoint; it just follows the
instructions it is given via the API.</t> instructions it is given via the API.</t>
<t indent="0" pn="section-1.1-4">JSEP's handling of session descriptions
<t>JSEP's handling of session descriptions is simple and is simple and
straightforward. Whenever an offer/answer exchange is needed, straightforward. Whenever an offer/answer exchange is needed,
the initiating side creates an offer by calling a createOffer() the initiating side creates an offer by calling a createOffer
API. The application then uses that offer to set up its local API. The application then uses that offer to set up its local
config via the setLocalDescription() API. The offer is finally configuration via the setLocalDescription API. The offer is finally
sent off to the remote side over its preferred signaling sent off to the remote side over its preferred signaling
mechanism (e.g., WebSockets); upon receipt of that offer, the mechanism (e.g., WebSockets); upon receipt of that offer, the
remote party installs it using the setRemoteDescription() remote party installs it using the setRemoteDescription
API.</t> API.</t>
<t indent="0" pn="section-1.1-5">To complete the offer/answer exchange,
<t>To complete the offer/answer exchange, the remote party uses the remote party uses
the createAnswer() API to generate an appropriate answer, the createAnswer API to generate an appropriate answer,
applies it using the setLocalDescription() API, and sends the applies it using the setLocalDescription API, and sends the
answer back to the initiator over the signaling channel. When answer back to the initiator over the signaling channel. When
the initiator gets that answer, it installs it using the the initiator gets that answer, it installs it using the
setRemoteDescription() API, and initial setup is complete. This setRemoteDescription API, and initial setup is complete. This
process can be repeated for additional offer/answer process can be repeated for additional offer/answer
exchanges.</t> exchanges.</t>
<t indent="0" pn="section-1.1-6">Regarding ICE
<t>Regarding ICE <xref target="RFC8445" format="default" sectionFormat="of" derivedConten
<xref target="RFC8445"></xref>, JSEP decouples the ICE state t="RFC8445"/>, JSEP decouples the ICE state
machine from the overall signaling state machine, as the ICE machine from the overall signaling state machine. The ICE
state machine must remain in the JSEP implementation, because state machine must remain in the JSEP implementation because
only the implementation has the necessary knowledge of only the implementation has the necessary knowledge of
candidates and other transport information. Performing this candidates and other transport information. Performing this
separation provides additional flexibility in protocols that separation provides additional flexibility in protocols that
decouple session descriptions from transport. For instance, in decouple session descriptions from transport. For instance, in
traditional SIP, each offer or answer is self-contained, traditional SIP, each offer or answer is self-contained,
including both the session descriptions and the transport including both the session descriptions and the transport
information. However, information. However,
<xref target="I-D.ietf-mmusic-trickle-ice-sip" /> allows SIP to <xref target="RFC8840" format="default" sectionFormat="of" derivedConten
be used with trickle ICE t="RFC8840"/> allows SIP to
<xref target="I-D.ietf-ice-trickle" />, in which the session be used with Trickle ICE
<xref target="RFC8838" format="default" sectionFormat="of" derivedConten
t="RFC8838"/>, in which the session
description can be sent immediately and the transport description can be sent immediately and the transport
information can be sent when available. Sending transport information can be sent when available. Sending transport
information separately can allow for faster ICE and DTLS information separately can allow for faster ICE and DTLS
startup, since ICE checks can start as soon as any transport startup, since ICE checks can start as soon as any transport
information is available rather than waiting for all of it. information is available rather than waiting for all of it.
JSEP's decoupling of the ICE and signaling state machines JSEP's decoupling of the ICE and signaling state machines
allows it to accommodate either model.</t> allows it to accommodate either model.</t>
<t indent="0" pn="section-1.1-7">Although it abstracts signaling, the JS
<t>Through its abstraction of signaling, the JSEP approach does EP approach
require the application to be aware of the signaling process. requires that the application be aware of the signaling process.
While the application does not need to understand the contents While the application does not need to understand the contents
of session descriptions to set up a call, the application must of session descriptions to set up a call, the application must
call the right APIs at the right times, convert the session call the right APIs at the right times, convert the session
descriptions and ICE information into the defined messages of descriptions and ICE information into the defined messages of
its chosen signaling protocol, and perform the reverse its chosen signaling protocol, and perform the reverse
conversion on the messages it receives from the other side.</t> conversion on the messages it receives from the other side.</t>
<t indent="0" pn="section-1.1-8">One way to make life easier for the app
<t>One way to make life easier for the application is to lication is to
provide a JavaScript library that hides this complexity from provide a JavaScript library that hides this complexity from
the developer; said library would implement a given signaling the developer; said library would implement a given signaling
protocol along with its state machine and serialization code, protocol along with its state machine and serialization code,
presenting a higher level call-oriented interface to the presenting a higher-level call-oriented interface to the
application developer. For example, libraries exist to adapt application developer. For example, libraries exist to provide
the JSEP API into an API suitable for a SIP or XMPP. Thus, JSEP implementations of the SIP <xref target="RFC3261" format="default" secti
onFormat="of" derivedContent="RFC3261"/> and Extensible Messaging
and Presence Protocol (XMPP) <xref target="RFC6120" format="default" sec
tionFormat="of" derivedContent="RFC6120"/> signaling
protocols atop the JSEP API.
Thus, JSEP
provides greater control for the experienced developer without provides greater control for the experienced developer without
forcing any additional complexity on the novice developer.</t> forcing any additional complexity on the novice developer.</t>
</section> </section>
<section title="Other Approaches Considered" <section anchor="sec.other-approaches-consider" numbered="true" toc="inclu
anchor="sec.other-approaches-consider"> de" removeInRFC="false" pn="section-1.2">
<name slugifiedName="name-other-approaches-considered">Other Approaches
<t>One approach that was considered instead of JSEP was to Considered</name>
<t indent="0" pn="section-1.2-1">One approach that was considered instea
d of JSEP was to
include a lightweight signaling protocol. Instead of providing include a lightweight signaling protocol. Instead of providing
session descriptions to the API, the API would produce and session descriptions to the API, the API would produce and
consume messages from this protocol. While providing a more consume messages from this protocol. While providing a more
high-level API, this put more control of signaling within the high-level API, this put more control of signaling within the
JSEP implementation, forcing it to have to understand and JSEP implementation, forcing it to have to understand and
handle concepts like signaling glare (see handle concepts like signaling glare (see
<xref target="RFC3264" />, Section 4).</t> <xref target="RFC3264" sectionFormat="comma" section="4" format="default
" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-4" derivedContent="RFC
<t>A second approach that was considered but not chosen was to 3264"/>).</t>
<t indent="0" pn="section-1.2-2">A second approach that was considered b
ut not chosen was to
decouple the management of the media control objects from decouple the management of the media control objects from
session descriptions, instead offering APIs that would control session descriptions, instead offering APIs that would control
each component directly. This was rejected based on the each component directly. This was rejected based on the
argument that requiring exposure of this level of complexity to argument that requiring exposure of this level of complexity to
the application programmer would not be beneficial; it would the application programmer would not be beneficial; it would
result in an API where even a simple example would require a (1) result in an API where even a simple example would require a
significant amount of code to orchestrate all the needed significant amount of code to orchestrate all the needed
interactions, as well as creating a large API surface that interactions and (2) create a large API surface that
needed to be agreed upon and documented. In addition, these API would need to be agreed upon and documented.
In addition, these API
points could be called in any order, resulting in a more points could be called in any order, resulting in a more
complex set of interactions with the media subsystem than the complex set of interactions with the media subsystem than the
JSEP approach, which specifies how session descriptions are to JSEP approach, which specifies how session descriptions are to
be evaluated and applied.</t> be evaluated and applied.</t>
<t indent="0" pn="section-1.2-3">One variation on JSEP that was consider
<t>One variation on JSEP that was considered was to keep the ed was to keep the
basic session description-oriented API, but to move the basic session-description-oriented API but to move the
mechanism for generating offers and answers out of the JSEP mechanism for generating offers and answers out of the JSEP
implementation. Instead of providing createOffer/createAnswer implementation. Instead of providing createOffer/createAnswer
methods within the implementation, this approach would instead methods within the implementation, this approach would instead
expose a getCapabilities API which would provide the expose a getCapabilities API, which would provide the
application with the information it needed in order to generate application with the information it needed in order to generate
its own session descriptions. This increases the amount of work its own session descriptions. This increases the amount of work
that the application needs to do; it needs to know how to that the application needs to do; it needs to know how to
generate session descriptions from capabilities, and especially generate session descriptions from capabilities, and especially
how to generate the correct answer from an arbitrary offer and how to generate the correct answer from an arbitrary offer and
the supported capabilities. While this could certainly be the supported capabilities. While this could certainly be
addressed by using a library like the one mentioned above, it addressed by using a library like the one mentioned above, it
basically forces the use of said library even for a simple basically forces the use of said library even for a simple
example. Providing createOffer/createAnswer avoids this example. Providing createOffer/createAnswer avoids this
problem.</t> problem.</t>
</section> </section>
<section numbered="true" removeInRFC="false" toc="include" pn="section-1.3
">
<name slugifiedName="name-contradiction-regarding-bun">Contradiction reg
arding bundle-only "m=" sections</name>
<t indent="0" pn="section-1.3-1">Since the approval of the WebRTC specif
ication documents, the IETF has become
aware of an inconsistency between the document specifying JSEP and the document
specifying BUNDLE (this RFC and <xref target="RFC8843" format="default" sectionF
ormat="of" derivedContent="RFC8843"/>, respectively). Rather than delaying publ
ication further to come to a resolution, the documents are being published as th
ey were originally approved. The IETF intends to restart work on these technolo
gies, and revised versions of these documents will be published as soon as a res
olution becomes available.</t>
<t indent="0" pn="section-1.3-2">The specific issue involves the handlin
g of "m=" sections that are designated as bundle-only, as discussed in <xref tar
get="sec.pc-constructor" format="default" sectionFormat="of" derivedContent="Sec
tion 4.1.1"/> of this RFC. Currently, there is divergence between JSEP and BUNDL
E, as well as between these specifications and existing browser implementations:
</t>
<ul bare="false" empty="false" indent="3" spacing="normal" pn="section-1
.3-3">
<li pn="section-1.3-3.1">JSEP prescribes that said "m=" sections shoul
d use port zero and add an "a=bundle-only" attribute in initial offers, but not
in answers or subsequent offers.</li>
<li pn="section-1.3-3.2">BUNDLE prescribes that these "m=" sections sh
ould be marked as described in the previous point, but in all offers and answers
.</li>
<li pn="section-1.3-3.3">Most current browsers do not mark any "m=" se
ctions with port zero and instead use the same port for all bundled "m=" section
s; one follows the JSEP behavior.</li>
</ul>
</section>
</section> </section>
<section title="Terminology" anchor="sec.terminology"> <section anchor="sec.terminology" numbered="true" toc="include" removeInRFC=
"false" pn="section-2">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL <name slugifiedName="name-terminology">Terminology</name>
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and <t indent="0" pn="section-2-1">The key words "<bcp14>MUST</bcp14>", "<bcp1
"OPTIONAL" in this document are to be interpreted as described in 4>MUST NOT</bcp14>",
"<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>",
<xref target="RFC2119"></xref>.</t> "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>",
"<bcp14>SHOULD NOT</bcp14>",
"<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are
to be interpreted as described in BCP 14 <xref target="RFC2119" format="defa
ult" sectionFormat="of" derivedContent="RFC2119"/>
<xref target="RFC8174" format="default" sectionFormat="of" derivedConten
t="RFC8174"/> when, and only when, they appear in all capitals,
as shown here.</t>
</section> </section>
<section title="Semantics and Syntax" <section anchor="sec.semantics-and-syntax" numbered="true" toc="include" rem
anchor="sec.semantics-and-syntax"> oveInRFC="false" pn="section-3">
<section title="Signaling Model" anchor="sec.signaling-model"> <name slugifiedName="name-semantics-and-syntax">Semantics and Syntax</name
>
<t>JSEP does not specify a particular signaling model or state <section anchor="sec.signaling-model" numbered="true" toc="include" remove
InRFC="false" pn="section-3.1">
<name slugifiedName="name-signaling-model">Signaling Model</name>
<t indent="0" pn="section-3.1-1">JSEP does not specify a particular sign
aling model or state
machine, other than the generic need to exchange session machine, other than the generic need to exchange session
descriptions in the fashion described by descriptions in the fashion described by
<xref target="RFC3264"></xref> (offer/answer) in order for both <xref target="RFC3264" format="default" sectionFormat="of" derivedConten t="RFC3264"/> (offer/answer) in order for both
sides of the session to know how to conduct the session. JSEP sides of the session to know how to conduct the session. JSEP
provides mechanisms to create offers and answers, as well as to provides mechanisms to create offers and answers, as well as to
apply them to a session. However, the JSEP implementation is apply them to a session. However, the JSEP implementation is
totally decoupled from the actual mechanism by which these totally decoupled from the actual mechanism by which these
offers and answers are communicated to the remote side, offers and answers are communicated to the remote side,
including addressing, retransmission, forking, and glare including addressing, retransmission, forking, and glare
handling. These issues are left entirely up to the application; handling. These issues are left entirely up to the application;
the application has complete control over which offers and the application has complete control over which offers and
answers get handed to the implementation, and when.</t> answers get handed to the implementation, and when.</t>
<figure anchor="fig-sigModel" title="JSEP Signaling Model"> <figure anchor="fig-sigModel" align="left" suppress-title="false" pn="fi
<artwork> gure-1">
<![CDATA[ <name slugifiedName="name-jsep-signaling-model">JSEP Signaling Model</
+-----------+ +-----------+ name>
| Web App |<--- App-Specific Signaling -->| Web App | <artwork name="" type="ascii-art" align="left" alt="" pn="section-3.1-
+-----------+ +-----------+ 2.1">
^ ^ +-----------+ +-----------+
| SDP | SDP | Web App |&lt;--- App-Specific Signaling --&gt;| Web App |
V V +-----------+ +-----------+
+-----------+ +-----------+ ^ ^
| JSEP |<----------- Media ------------>| JSEP | | SDP | SDP
| Impl. | | Impl. | V V
+-----------+ +-----------+ +-----------+ +-----------+
]]> | JSEP |&lt;----------- Media ------------&gt;| JSEP |
</artwork> | Impl. | | Impl. |
+-----------+ +-----------+ </artwork>
</figure> </figure>
</section> </section>
<section title="Session Descriptions and State Machine" <section anchor="sec.session-descriptions-and-state-machine" numbered="tru
anchor="sec.session-descriptions-and-state-machine"> e" toc="include" removeInRFC="false" pn="section-3.2">
<name slugifiedName="name-session-descriptions-and-st">Session Descripti
<t>In order to establish the media plane, the JSEP ons and State Machine</name>
<t indent="0" pn="section-3.2-1">In order to establish the media plane,
the JSEP
implementation needs specific parameters to indicate what to implementation needs specific parameters to indicate what to
transmit to the remote side, as well as how to handle the media transmit to the remote side, as well as how to handle the media
that is received. These parameters are determined by the that is received. These parameters are determined by the
exchange of session descriptions in offers and answers, and exchange of session descriptions in offers and answers, and
there are certain details to this process that must be handled there are certain details to this process that must be handled
in the JSEP APIs.</t> in the JSEP APIs.</t>
<t indent="0" pn="section-3.2-2">Whether a session description applies t
<t>Whether a session description applies to the local side or o the local side or
the remote side affects the meaning of that description. For the remote side affects the meaning of that description. For
example, the list of codecs sent to a remote party indicates example, the list of codecs sent to a remote party indicates
what the local side is willing to receive, which, when what the local side is willing to receive, which, when
intersected with the set of codecs the remote side supports, intersected with the set of codecs the remote side supports,
specifies what the remote side should send. However, not all specifies what the remote side should send. However, not all
parameters follow this rule; some parameters are declarative parameters follow this rule; some parameters are declarative,
and the remote side MUST either accept them or reject them and the remote side must either accept them or reject them
altogether. An example of such a parameter is the DTLS altogether. An example of such a parameter is the TLS
fingerprints fingerprints <xref target="RFC8122" format="default" sectionFormat="of"
<xref target="RFC8122"></xref>, which are calculated based on derivedContent="RFC8122"/>
the local certificate(s) offered, and are not subject to as used in the context of DTLS <xref target="RFC6347" format="default" s
negotiation.</t> ectionFormat="of" derivedContent="RFC6347"/>;
these fingerprints are calculated based on
<t>In addition, various RFCs put different conditions on the the local certificate(s) offered and are not subject to
negotiation.
</t>
<t indent="0" pn="section-3.2-3">In addition, various RFCs put different
conditions on the
format of offers versus answers. For example, an offer may format of offers versus answers. For example, an offer may
propose an arbitrary number of m= sections (i.e., media propose an arbitrary number of "m=" sections (i.e., media
descriptions as described in descriptions as described in
<xref target="RFC4566" />, Section 5.14), but an answer must <xref target="RFC4566" sectionFormat="comma" section="5.14" format="defa ult" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.14" derivedConten t="RFC4566"/>), but an answer must
contain the exact same number as the offer.</t> contain the exact same number as the offer.</t>
<t indent="0" pn="section-3.2-4">Lastly, while the exact media parameter
<t>Lastly, while the exact media parameters are only known only s are known only
after an offer and an answer have been exchanged, the offerer after an offer and an answer have been exchanged, the offerer
may receive ICE checks, and possibly media (e.g., in the case may receive ICE checks, and possibly media (e.g., in the case
of a re-offer after a connection has been established) before of a re-offer after a connection has been established) before
it receives an answer. To properly process incoming media in it receives an answer. To properly process incoming media in
this case, the offerer's media handler must be aware of the this case, the offerer's media handler must be aware of the
details of the offer before the answer arrives.</t> details of the offer before the answer arrives.</t>
<t indent="0" pn="section-3.2-5">Therefore, in order to handle session d
<t>Therefore, in order to handle session descriptions properly, escriptions properly,
the JSEP implementation needs: the JSEP implementation needs:
<list style="numbers"> </t>
<ol spacing="normal" type="1" indent="adaptive" start="1" pn="section-3.
<t>To know if a session description pertains to the local or 2-6">
remote side.</t> <li pn="section-3.2-6.1" derivedCounter="1.">To know if a session desc
ription pertains to the local or
<t>To know if a session description is an offer or an remote side.</li>
answer.</t> <li pn="section-3.2-6.2" derivedCounter="2.">To know if a session desc
ription is an offer or an
<t>To allow the offer to be specified independently of the answer.</li>
answer.</t> <li pn="section-3.2-6.3" derivedCounter="3.">To allow the offer to be
</list>JSEP addresses this by adding both setLocalDescription specified independently of the
answer.</li>
</ol>
<t indent="0" pn="section-3.2-7">JSEP addresses this by adding both setL
ocalDescription
and setRemoteDescription methods and having session description and setRemoteDescription methods and having session description
objects contain a type field indicating the type of session objects contain a type field indicating the type of session
description being supplied. This satisfies the requirements description being supplied. This satisfies the requirements
listed above for both the offerer, who first calls listed above for both the offerer, who first calls
setLocalDescription(sdp [offer]) and then later setLocalDescription(sdp [offer]) and then later
setRemoteDescription(sdp [answer]), as well as for the setRemoteDescription(sdp [answer]), and the
answerer, who first calls setRemoteDescription(sdp [offer]) and answerer, who first calls setRemoteDescription(sdp [offer]) and
then later setLocalDescription(sdp [answer]).</t> then later setLocalDescription(sdp [answer]).</t>
<t indent="0" pn="section-3.2-8">During the offer/answer exchange, the o
<t>During the offer/answer exchange, the outstanding offer is utstanding offer is
considered to be "pending" at the offerer and the answerer, as considered to be "pending" at the offerer and the answerer, as
it may either be accepted or rejected. If this is a re-offer, it may be either accepted or rejected. If this is a re-offer,
each side will also have "current" local and remote each side will also have "current" local and remote
descriptions, which reflect the result of the last offer/answer descriptions, which reflect the result of the last offer/answer
exchange. Sections exchange. Sections
<xref target="sec.pendinglocaldescription" />, <xref target="sec.pendinglocaldescription" format="counter" sectionForma
<xref target="sec.pendingremotedescription" />, t="of" derivedContent="4.1.14"/>,
<xref target="sec.currentlocaldescription" />, and <xref target="sec.pendingremotedescription" format="counter" sectionForm
<xref target="sec.currentremotedescription" />, provide more at="of" derivedContent="4.1.16"/>,
<xref target="sec.currentlocaldescription" format="counter" sectionForma
t="of" derivedContent="4.1.13"/>, and
<xref target="sec.currentremotedescription" format="counter" sectionForm
at="of" derivedContent="4.1.15"/> provide more
detail on pending and current descriptions.</t> detail on pending and current descriptions.</t>
<t indent="0" pn="section-3.2-9">JSEP also allows for an answer to be tr
<t>JSEP also allows for an answer to be treated as provisional eated as provisional
by the application. Provisional answers provide a way for an by the application. Provisional answers provide a way for an
answerer to communicate initial session parameters back to the answerer to communicate initial session parameters back to the
offerer, in order to allow the session to begin, while allowing offerer, in order to allow the session to begin, while allowing
a final answer to be specified later. This concept of a final a final answer to be specified later. This concept of a final
answer is important to the offer/answer model; when such an answer is important to the offer/answer model; when such an
answer is received, any extra resources allocated by the caller answer is received, any extra resources allocated by the caller
can be released, now that the exact session configuration is can be released, now that the exact session configuration is
known. These "resources" can include things like extra ICE known. These "resources" can include things like extra ICE
components, TURN candidates, or video decoders. Provisional components, Traversal Using Relays around NAT (TURN) candidates, or vide o decoders. Provisional
answers, on the other hand, do no such deallocation; as a answers, on the other hand, do no such deallocation; as a
result, multiple dissimilar provisional answers, with their own result, multiple dissimilar provisional answers, with their own
codec choices, transport parameters, etc., can be received and codec choices, transport parameters, etc., can be received and
applied during call setup. Note that the final answer itself applied during call setup. Note that the final answer itself
may be different than any received provisional answers.</t> may be different than any received provisional answers.</t>
<t indent="0" pn="section-3.2-10">In
<t>In <xref target="RFC3264" format="default" sectionFormat="of" derivedConten
<xref target="RFC3264"></xref>, the constraint at the signaling t="RFC3264"/>, the constraint at the signaling
level is that only one offer can be outstanding for a given level is that only one offer can be outstanding for a given
session, but at the media stack level, a new offer can be session, but at the JSEP level, a new offer can be
generated at any point. For example, when using SIP for generated at any point. For example, when using SIP for
signaling, if one offer is sent, then cancelled using a SIP signaling, if one offer is sent and is then canceled using a SIP
CANCEL, another offer can be generated even though no answer CANCEL, another offer can be generated even though no answer
was received for the first offer. To support this, the JSEP was received for the first offer. To support this, the JSEP
media layer can provide an offer via the createOffer() method media layer can provide an offer via the createOffer method
whenever the JavaScript application needs one for the whenever the JavaScript application needs one for the
signaling. The answerer can send back zero or more provisional signaling. The answerer can send back zero or more provisional
answers, and finally end the offer-answer exchange by sending a answers and then finally end the offer/answer exchange by sending a
final answer. The state machine for this is as follows:</t> final answer. The state machine for this is as follows:</t>
<figure anchor="fig-state-machine" align="left" suppress-title="false" p
<t> n="figure-2">
<figure anchor="fig-state-machine" <name slugifiedName="name-jsep-state-machine">JSEP State Machine</name
title="JSEP State Machine"> >
<artwork> <artwork name="" type="ascii-art" align="left" alt="" pn="section-3.2-
<![CDATA[ 11.1">
setRemote(OFFER) setLocal(PRANSWER) setRemote(OFFER) setLocal(PRANSWER)
/-----\ /-----\ /-----\ /-----\
| | | | | | | |
v | v | v | v |
+---------------+ | +---------------+ | +---------------+ | +---------------+ |
| |----/ | |----/ | |----/ | |----/
| have- | setLocal(PRANSWER) | have- | | have- | setLocal(PRANSWER) | have- |
| remote-offer |------------------- >| local-pranswer| | remote-offer |------------------- &gt;| local-pranswer|
| | | | | | | |
| | | | | | | |
+---------------+ +---------------+ +---------------+ +---------------+
^ | | ^ | |
| | setLocal(ANSWER) | | | setLocal(ANSWER) |
setRemote(OFFER) | | setRemote(OFFER) | |
| V setLocal(ANSWER) | | V setLocal(ANSWER) |
+---------------+ | +---------------+ |
| | | | | |
| |<---------------------------+ | |&lt;---------------------------+
| stable | | stable |
| |<---------------------------+ | |&lt;---------------------------+
| | | | | |
+---------------+ setRemote(ANSWER) | +---------------+ setRemote(ANSWER) |
^ | | ^ | |
| | setLocal(OFFER) | | | setLocal(OFFER) |
setRemote(ANSWER) | | setRemote(ANSWER) | |
| V | | V |
+---------------+ +---------------+ +---------------+ +---------------+
| | | | | | | |
| have- | setRemote(PRANSWER) |have- | | have- | setRemote(PRANSWER) |have- |
| local-offer |------------------- >|remote-pranswer| | local-offer |------------------- &gt;|remote-pranswer|
| | | | | | | |
| |----\ | |----\ | |----\ | |----\
+---------------+ | +---------------+ | +---------------+ | +---------------+ |
^ | ^ | ^ | ^ |
| | | | | | | |
\-----/ \-----/ \-----/ \-----/
setLocal(OFFER) setRemote(PRANSWER) setLocal(OFFER) setRemote(PRANSWER) </artwork>
]]> </figure>
</artwork> <t indent="0" pn="section-3.2-12">Aside from these state transitions, th
</figure> ere is no other
</t>
<t>Aside from these state transitions there is no other
difference between the handling of provisional ("pranswer") and difference between the handling of provisional ("pranswer") and
final ("answer") answers.</t> final ("answer") answers.</t>
</section> </section>
<section title="Session Description Format" <section anchor="sec.session-description-forma" numbered="true" toc="inclu
anchor="sec.session-description-forma"> de" removeInRFC="false" pn="section-3.3">
<name slugifiedName="name-session-description-format">Session Descriptio
<t>JSEP's session descriptions use SDP syntax for their n Format</name>
<t indent="0" pn="section-3.3-1">JSEP's session descriptions use Session
Description Protocol (SDP) syntax for their
internal representation. While this format is not optimal for internal representation. While this format is not optimal for
manipulation from JavaScript, it is widely accepted, and manipulation from JavaScript, it is widely accepted and is
frequently updated with new features; any alternate encoding of frequently updated with new features; any alternate encoding of
session descriptions would have to keep pace with the changes session descriptions would have to keep pace with the changes
to SDP, at least until the time that this new encoding eclipsed to SDP, at least until the time that this new encoding eclipsed
SDP in popularity.</t> SDP in popularity.</t>
<t indent="0" pn="section-3.3-2">However, to provide for future flexibil
<t>However, to provide for future flexibility, the SDP syntax ity, the SDP syntax
is encapsulated within a SessionDescription object, which can is encapsulated within a SessionDescription object, which can
be constructed from SDP, and be serialized out to SDP. If be constructed from SDP and be serialized out to SDP. If
future specifications agree on a JSON format for session future specifications agree on a JSON format for session
descriptions, we could easily enable this object to generate descriptions, we could easily enable this object to generate
and consume that JSON.</t> and consume that JSON.</t>
<t indent="0" pn="section-3.3-3">As detailed below, most applications sh
<t>As detailed below, most applications should be able to treat ould be able to treat
the SessionDescriptions produced and consumed by these various the SessionDescriptions produced and consumed by these various
API calls as opaque blobs; that is, the application will not API calls as opaque blobs; that is, the application will not
need to read or change them.</t> need to read or change them.</t>
</section> </section>
<section title="Session Description Control" <section anchor="sec.session-description-ctrl" numbered="true" toc="includ
anchor="sec.session-description-ctrl"> e" removeInRFC="false" pn="section-3.4">
<name slugifiedName="name-session-description-control">Session Descripti
<t>In order to give the application control over various common on Control</name>
session parameters, JSEP provides control surfaces which tell <t indent="0" pn="section-3.4-1">In order to give the application contro
l over various common
session parameters, JSEP provides control surfaces that tell
the JSEP implementation how to generate session descriptions. the JSEP implementation how to generate session descriptions.
This avoids the need for JavaScript to modify session This avoids the need for JavaScript to modify session
descriptions in most cases.</t> descriptions in most cases.</t>
<t indent="0" pn="section-3.4-2">Changes to these objects result in chan
<t>Changes to these objects result in changes to the session ges to the session
descriptions generated by subsequent createOffer/Answer descriptions generated by subsequent createOffer/createAnswer
calls.</t> calls.</t>
<section title="RtpTransceivers" anchor="sec.rtptransceivers"> <section anchor="sec.rtptransceivers" numbered="true" toc="include" remo
veInRFC="false" pn="section-3.4.1">
<t>RtpTransceivers allow the application to control the RTP <name slugifiedName="name-rtptransceivers">RtpTransceivers</name>
media associated with one m= section. Each RtpTransceiver has <t indent="0" pn="section-3.4.1-1">RtpTransceivers allow the applicati
on to control the RTP
media associated with one "m=" section. Each RtpTransceiver has
an RtpSender and an RtpReceiver, which an application can use an RtpSender and an RtpReceiver, which an application can use
to control the sending and receiving of RTP media. The to control the sending and receiving of RTP media. The
application may also modify the RtpTransceiver directly, for application may also modify the RtpTransceiver directly, for
instance, by stopping it.</t> instance, by stopping it.</t>
<t indent="0" pn="section-3.4.1-2">RtpTransceivers generally have a 1:
<t>RtpTransceivers generally have a 1:1 mapping with m= 1 mapping with "m="
sections, although there may be more RtpTransceivers than m= sections, although there may be more RtpTransceivers than "m="
sections when RtpTransceivers are created but not yet sections when RtpTransceivers are created but not yet
associated with a m= section, or if RtpTransceivers have been associated with an "m=" section, or if RtpTransceivers have been
stopped and disassociated from m= sections. An RtpTransceiver stopped and disassociated from "m=" sections. An RtpTransceiver
is said to be associated with an m= section if its mid is said to be associated with an "m=" section if its
property is non-null; otherwise it is said to be media identification (mid) property is non-null; otherwise, it is said
disassociated. The associated m= section is determined using to be
a mapping between transceivers and m= section indices, formed disassociated. The associated "m=" section is determined using
a mapping between transceivers and "m=" section indices, formed
when creating an offer or applying a remote offer.</t> when creating an offer or applying a remote offer.</t>
<t indent="0" pn="section-3.4.1-3">An RtpTransceiver is never associat
<t>An RtpTransceiver is never associated with more than one ed with more than one
m= section, and once a session description is applied, a m= "m=" section, and once a session description is applied, an "m="
section is always associated with exactly one RtpTransceiver. section is always associated with exactly one RtpTransceiver.
However, in certain cases where a m= section has been However, in certain cases where an "m=" section has been
rejected, as discussed in rejected, as discussed in
<xref target="sec.subsequent-offers" /> below, that m= section <xref target="sec.subsequent-offers" format="default" sectionFormat="o f" derivedContent="Section 5.2.2"/> below, that "m=" section
will be "recycled" and associated with a new RtpTransceiver will be "recycled" and associated with a new RtpTransceiver
with a new mid value.</t> with a new MID value.</t>
<t indent="0" pn="section-3.4.1-4">RtpTransceivers can be created expl
<t>RtpTransceivers can be created explicitly by the icitly by the
application or implicitly by calling setRemoteDescription application or implicitly by calling setRemoteDescription
with an offer that adds new m= sections.</t> with an offer that adds new "m=" sections.</t>
</section> </section>
<section title="RtpSenders" anchor="sec.rtpsenders"> <section anchor="sec.rtpsenders" numbered="true" toc="include" removeInR
FC="false" pn="section-3.4.2">
<t>RtpSenders allow the application to control how RTP media <name slugifiedName="name-rtpsenders">RtpSenders</name>
<t indent="0" pn="section-3.4.2-1">RtpSenders allow the application to
control how RTP media
is sent. An RtpSender is conceptually responsible for the is sent. An RtpSender is conceptually responsible for the
outgoing RTP stream(s) described by an m= section. This outgoing RTP stream(s) described by an "m=" section. This
includes encoding the attached MediaStreamTrack, sending RTP includes encoding the attached MediaStreamTrack, sending RTP
media packets, and generating/processing RTCP for the media packets, and generating/processing the RTP Control Protocol (RTC P) for the
outgoing RTP streams(s).</t> outgoing RTP streams(s).</t>
</section> </section>
<section title="RtpReceivers" anchor="sec.rtpreceivers"> <section anchor="sec.rtpreceivers" numbered="true" toc="include" removeI
nRFC="false" pn="section-3.4.3">
<t>RtpReceivers allow the application to inspect how RTP <name slugifiedName="name-rtpreceivers">RtpReceivers</name>
<t indent="0" pn="section-3.4.3-1">RtpReceivers allow the application
to inspect how RTP
media is received. An RtpReceiver is conceptually responsible media is received. An RtpReceiver is conceptually responsible
for the incoming RTP stream(s) described by an m= section. for the incoming RTP stream(s) described by an "m=" section.
This includes processing received RTP media packets, decoding This includes processing received RTP media packets, decoding
the incoming stream(s) to produce a remote MediaStreamTrack, the incoming stream(s) to produce a remote MediaStreamTrack,
and generating/processing RTCP for the incoming RTP and generating/processing RTCP for the incoming RTP
stream(s).</t> stream(s).</t>
</section> </section>
</section> </section>
<section title="ICE" anchor="sec.ice"> <section anchor="sec.ice" numbered="true" toc="include" removeInRFC="false
<section title="ICE Gathering Overview" " pn="section-3.5">
anchor="sec.ice-gather-overview"> <name slugifiedName="name-ice">ICE</name>
<section anchor="sec.ice-gather-overview" numbered="true" toc="include"
<t>JSEP gathers ICE candidates as needed by the application. removeInRFC="false" pn="section-3.5.1">
<name slugifiedName="name-ice-gathering-overview">ICE Gathering Overvi
ew</name>
<t indent="0" pn="section-3.5.1-1">JSEP gathers ICE candidates as need
ed by the application.
Collection of ICE candidates is referred to as a gathering Collection of ICE candidates is referred to as a gathering
phase, and this is triggered either by the addition of a new phase, and this is triggered either by the addition of a new
or recycled m= section to the local session description, or or recycled "m=" section to the local session description or by
new ICE credentials in the description, indicating an ICE new ICE credentials in the description, indicating an ICE
restart. Use of new ICE credentials can be triggered restart. Use of new ICE credentials can be triggered
explicitly by the application, or implicitly by the JSEP explicitly by the application or implicitly by the JSEP
implementation in response to changes in the ICE implementation in response to changes in the ICE
configuration.</t> configuration.</t>
<t indent="0" pn="section-3.5.1-2">When the ICE configuration changes
<t>When the ICE configuration changes in a way that requires in a way that requires
a new gathering phase, a 'needs-ice-restart' bit is set. When a new gathering phase, a 'needs-ice-restart' bit is set. When
this bit is set, calls to the createOffer API will generate this bit is set, calls to the createOffer API will generate
new ICE credentials. This bit is cleared by a call to the new ICE credentials. This bit is cleared by a call to the
setLocalDescription API with new ICE credentials from either setLocalDescription API with new ICE credentials from either
an offer or an answer, i.e., from either a local- or an offer or an answer, i.e., from either a locally or
remote-initiated ICE restart.</t> remotely initiated ICE restart.</t>
<t indent="0" pn="section-3.5.1-3">When a new gathering phase starts,
<t>When a new gathering phase starts, the ICE agent will the ICE agent will
notify the application that gathering is occurring through an notify the application that gathering is occurring through a state
event. Then, when each new ICE candidate becomes available, change event. Then, when each new ICE candidate becomes available,
the ICE agent will supply it to the application via an the ICE agent will supply it to the application via an
additional event; these candidates will also automatically be onicecandidate event; these candidates will also automatically be
added to the current and/or pending local session added to the current and/or pending local session
description. Finally, when all candidates have been gathered, description. Finally, when all candidates have been gathered,
an event will be dispatched to signal that the gathering a final onicecandidate event will be dispatched to signal that the
process is complete.</t> gathering process is complete.</t>
<t indent="0" pn="section-3.5.1-4">Note that gathering phases only gat
<t>Note that gathering phases only gather the candidates her the candidates
needed by new/recycled/restarting m= sections; other m= needed by new/recycled/restarting "m=" sections; other "m="
sections continue to use their existing candidates. Also, if sections continue to use their existing candidates. Also, if
an m= section is bundled (either by a successful bundle an "m=" section is bundled (either by a successful bundle
negotiation or by being marked as bundle-only), then negotiation or by being marked as bundle-only), then
candidates will be gathered and exchanged for that m= section candidates will be gathered and exchanged for that "m=" section
if and only if its MID is a BUNDLE-tag, as described in if and only if its MID item is a BUNDLE-tag, as described in
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation" />.</t> <xref target="RFC8843" format="default" sectionFormat="of" derivedCont
ent="RFC8843"/>.</t>
</section> </section>
<section title="ICE Candidate Trickling" <section anchor="sec.ice-candidate-trickling" numbered="true" toc="inclu
anchor="sec.ice-candidate-trickling"> de" removeInRFC="false" pn="section-3.5.2">
<name slugifiedName="name-ice-candidate-trickling">ICE Candidate Trick
<t>Candidate trickling is a technique through which a caller ling</name>
<t indent="0" pn="section-3.5.2-1">Candidate trickling is a technique
through which a caller
may incrementally provide candidates to the callee after the may incrementally provide candidates to the callee after the
initial offer has been dispatched; the semantics of "Trickle initial offer has been dispatched; the semantics of "Trickle
ICE" are defined in ICE" are defined in
<xref target="I-D.ietf-ice-trickle"></xref>. This process <xref target="RFC8838" format="default" sectionFormat="of" derivedCont ent="RFC8838"/>. This process
allows the callee to begin acting upon the call and setting allows the callee to begin acting upon the call and setting
up the ICE (and perhaps DTLS) connections immediately, up the ICE (and perhaps DTLS) connections immediately,
without having to wait for the caller to gather all possible without having to wait for the caller to gather all possible
candidates. This results in faster media setup in cases where candidates. This results in faster media setup in cases where
gathering is not performed prior to initiating the call.</t> gathering is not performed prior to initiating the call.</t>
<t indent="0" pn="section-3.5.2-2">JSEP supports optional candidate tr
<t>JSEP supports optional candidate trickling by providing ickling by providing
APIs, as described above, that provide control and feedback APIs, as described above, that provide control and feedback
on the ICE candidate gathering process. Applications that on the ICE candidate gathering process. Applications that
support candidate trickling can send the initial offer support candidate trickling can send the initial offer
immediately and send individual candidates when they get the immediately and send individual candidates when they get
notified of a new candidate; applications that do not support notified of a new candidate; applications that do not support
this feature can simply wait for the indication that this feature can simply wait for the indication that
gathering is complete, and then create and send their offer, gathering is complete, and then create and send their offer,
with all the candidates, at this time.</t> with all the candidates, at that time.</t>
<t indent="0" pn="section-3.5.2-3">Upon receipt of trickled candidates
<t>Upon receipt of trickled candidates, the receiving , the receiving
application will supply them to its ICE agent. This triggers application will supply them to its ICE agent. This triggers
the ICE agent to start using the new remote candidates for the ICE agent to start using the new remote candidates for
connectivity checks.</t> connectivity checks.</t>
<section title="ICE Candidate Format" <section anchor="sec.ice-candidate-format" numbered="true" toc="includ
anchor="sec.ice-candidate-format"> e" removeInRFC="false" pn="section-3.5.2.1">
<name slugifiedName="name-ice-candidate-format">ICE Candidate Format
<t>In JSEP, ICE candidates are abstracted by an </name>
<t indent="0" pn="section-3.5.2.1-1">In JSEP, ICE candidates are abs
tracted by an
IceCandidate object, and as with session descriptions, SDP IceCandidate object, and as with session descriptions, SDP
syntax is used for the internal representation.</t> syntax is used for the internal representation.</t>
<t indent="0" pn="section-3.5.2.1-2">The candidate details are speci
<t>The candidate details are specified in an IceCandidate fied in an IceCandidate
field, using the same SDP syntax as the field, using the same SDP syntax as the
"candidate-attribute" field defined in "candidate-attribute" field defined in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, <xref target="RFC8839" sectionFormat="comma" section="5.1" format="d
Section 4.1. Note that this efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.1" derivedCont
ent="RFC8839"/>. Note that this
field does not contain an "a=" prefix, as indicated in the field does not contain an "a=" prefix, as indicated in the
following example:</t> following example:</t>
<figure> <sourcecode name="" type="sdp" markers="false" pn="section-3.5.2.1-3
<artwork> ">
<![CDATA[ candidate:1 1 UDP 1694498815 192.0.2.33 10000 typ host</sourcecode>
candidate:1 1 UDP 1694498815 192.0.2.33 10000 typ host <t indent="0" pn="section-3.5.2.1-4">The IceCandidate object contain
]]> s a field to indicate
</artwork> which ICE username fragment (ufrag) it is associated with, as define
</figure> d in
<xref target="RFC8839" sectionFormat="comma" section="5.4" format="d
<t>The IceCandidate object contains a field to indicate efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.4" derivedCont
which ICE ufrag it is associated with, as defined in ent="RFC8839"/>. This value is used
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />,
Section 4.4. This value is used
to determine which session description (and thereby which to determine which session description (and thereby which
gathering phase) this IceCandidate belongs to, which helps gathering phase) this IceCandidate belongs to, which helps
resolve ambiguities during ICE restarts. If this field is resolve ambiguities during ICE restarts. If this field is
absent in a received IceCandidate (perhaps when absent in a received IceCandidate (perhaps when
communicating with a non-JSEP endpoint), the most recently communicating with a non-JSEP endpoint), the most recently
received session description is assumed.</t> received session description is assumed.</t>
<t indent="0" pn="section-3.5.2.1-5">The IceCandidate object also co
<t>The IceCandidate object also contains fields to indicate ntains fields to indicate
which m= section it is associated with, which can be which "m=" section it is associated with, which can be
identified in one of two ways, either by a m= section identified in one of two ways: either by an "m=" section
index, or a MID. The m= section index is a zero-based index or by a MID. The "m=" section index is a zero-based
index, with index N referring to the N+1th m= section in index, with index N referring to the N+1th "m=" section in
the session description referenced by this IceCandidate. the session description referenced by this IceCandidate.
The MID is a "media stream identification" value, as The MID is a "media stream identification" value, as
defined in defined in
<xref target="RFC5888"></xref>, Section 4, which provides a <xref target="RFC5888" sectionFormat="comma" section="4" format="def
more robust way to identify the m= section in the session ault" derivedLink="https://rfc-editor.org/rfc/rfc5888#section-4" derivedContent=
"RFC5888"/>, which provides a
more robust way to identify the "m=" section in the session
description, using the MID of the associated RtpTransceiver description, using the MID of the associated RtpTransceiver
object (which may have been locally generated by the object (which may have been locally generated by the
answerer when interacting with a non-JSEP endpoint that answerer when interacting with a non-JSEP endpoint that
does not support the MID attribute, as discussed in does not support the MID attribute, as discussed in
<xref target="sec.applying-a-remote-desc" /> below). If the <xref target="sec.applying-a-remote-desc" format="default" sectionFo
MID field is present in a received IceCandidate, it MUST be rmat="of" derivedContent="Section 5.10"/> below). If the
used for identification; otherwise, the m= section index is MID field is present in a received IceCandidate, it <bcp14>MUST</bcp
14> be
used for identification; otherwise, the "m=" section index is
used instead.</t> used instead.</t>
<t indent="0" pn="section-3.5.2.1-6">Implementations <bcp14>MUST</bc
<t>When creating an IceCandidate object, JSEP p14>
implementations MUST populate each of the candidate, ufrag,
m= section index, and MID fields. Implementations MUST also
be prepared to receive objects with some fields missing, as be prepared to receive objects with some fields missing, as
mentioned above.</t> mentioned above.</t>
</section> </section>
</section> </section>
<section title="ICE Candidate Policy" <section anchor="sec.ice-candidate-policy" numbered="true" toc="include"
anchor="sec.ice-candidate-policy"> removeInRFC="false" pn="section-3.5.3">
<name slugifiedName="name-ice-candidate-policy">ICE Candidate Policy</
<t>Typically, when gathering ICE candidates, the JSEP name>
<t indent="0" pn="section-3.5.3-1">Typically, when gathering ICE candi
dates, the JSEP
implementation will gather all possible forms of initial implementation will gather all possible forms of initial
candidates - host, server reflexive, and relay. However, in candidates -- host, server-reflexive, and relay.
However, in
certain cases, applications may want to have more specific certain cases, applications may want to have more specific
control over the gathering process, due to privacy or related control over the gathering process, due to privacy or related
concerns. For example, one may want to only use relay concerns. For example, one may want to only use relay
candidates, to leak as little location information as candidates, to leak as little location information as
possible (keeping in mind that this choice comes with possible (keeping in mind that this choice comes with
corresponding operational costs). To accomplish this, JSEP corresponding operational costs). To accomplish this, JSEP
allows the application to restrict which ICE candidates are allows the application to restrict which ICE candidates are
used in a session. Note that this filtering is applied on top used in a session. Note that this filtering is applied on top
of any restrictions the implementation chooses to enforce of any restrictions the implementation chooses to enforce
regarding which IP addresses are permitted for the regarding which IP addresses are permitted for the
application, as discussed in application, as discussed in
<xref target="I-D.ietf-rtcweb-ip-handling" />.</t> <xref target="RFC8828" format="default" sectionFormat="of" derivedCont
ent="RFC8828"/>.</t>
<t>There may also be cases where the application wants to <t indent="0" pn="section-3.5.3-2">There may also be cases where the a
pplication wants to
change which types of candidates are used while the session change which types of candidates are used while the session
is active. A prime example is where a callee may initially is active. A prime example is where a callee may initially
want to use only relay candidates, to avoid leaking location want to use only relay candidates, to avoid leaking location
information to an arbitrary caller, but then change to use information to an arbitrary caller, but then change to use
all candidates (for lower operational cost) once the user has all candidates (for lower operational cost) once the user has
indicated they want to take the call. For this scenario, the indicated that they want to take the call. For this scenario, the
JSEP implementation MUST allow the candidate policy to be JSEP implementation <bcp14>MUST</bcp14> allow the candidate policy to
be
changed in mid-session, subject to the aforementioned changed in mid-session, subject to the aforementioned
interactions with local policy.</t> interactions with local policy.</t>
<t indent="0" pn="section-3.5.3-3">To administer the ICE candidate pol
<t>To administer the ICE candidate policy, the JSEP icy, the JSEP
implementation will determine the current setting at the implementation will determine the current setting at the
start of each gathering phase. Then, during the gathering start of each gathering phase. Then, during the gathering
phase, the implementation MUST NOT expose candidates phase, the implementation <bcp14>MUST NOT</bcp14> expose candidates
disallowed by the current policy to the application, use them disallowed by the current policy to the application, use them
as the source of connectivity checks, or indirectly expose as the source of connectivity checks, or indirectly expose
them via other fields, such as the raddr/rport attributes for them via other fields, such as the raddr/rport attributes for
other ICE candidates. Later, if a different policy is other ICE candidates. Later, if a different policy is
specified by the application, the application can apply it by specified by the application, the application can apply it by
kicking off a new gathering phase via an ICE restart.</t> kicking off a new gathering phase via an ICE restart.</t>
</section> </section>
<section title="ICE Candidate Pool" <section anchor="sec.ice-candidate-pool" numbered="true" toc="include" r
anchor="sec.ice-candidate-pool"> emoveInRFC="false" pn="section-3.5.4">
<name slugifiedName="name-ice-candidate-pool">ICE Candidate Pool</name
<t>JSEP applications typically inform the JSEP implementation >
<t indent="0" pn="section-3.5.4-1">JSEP applications typically inform
the JSEP implementation
to begin ICE gathering via the information supplied to to begin ICE gathering via the information supplied to
setLocalDescription, as the local description indicates the setLocalDescription, as the local description indicates the
number of ICE components which will be needed and for which number of ICE components that will be needed and for which
candidates must be gathered. However, to accelerate cases candidates must be gathered. However, to accelerate cases
where the application knows the number of ICE components to where the application knows the number of ICE components to
use ahead of time, it may ask the implementation to gather a use ahead of time, it may ask the implementation to gather a
pool of potential ICE candidates to help ensure rapid media pool of potential ICE candidates to help ensure rapid media
setup.</t> setup.</t>
<t indent="0" pn="section-3.5.4-2">When setLocalDescription is eventua
<t>When setLocalDescription is eventually called, and the lly called and the
JSEP implementation goes to gather the needed ICE candidates, JSEP implementation prepares to gather the needed ICE candidates,
it SHOULD start by checking if any candidates are available it <bcp14>SHOULD</bcp14> start by checking if any candidates are avail
in the pool. If there are candidates in the pool, they SHOULD able
in the pool. If there are candidates in the pool, they <bcp14>SHOULD</
bcp14>
be handed to the application immediately via the ICE be handed to the application immediately via the ICE
candidate event. If the pool becomes depleted, either because candidate event. If the pool becomes depleted, either because
a larger-than-expected number of ICE components is used, or a larger-than-expected number of ICE components are used or
because the pool has not had enough time to gather because the pool has not had enough time to gather
candidates, the remaining candidates are gathered as usual. candidates, the remaining candidates are gathered as usual.
This only occurs for the first offer/answer exchange, after This only occurs for the first offer/answer exchange, after
which the candidate pool is emptied and no longer used.</t> which the candidate pool is emptied and no longer used.</t>
<t indent="0" pn="section-3.5.4-3">One example of where this concept i
<t>One example of where this concept is useful is an s useful is an
application that expects an incoming call at some point in application that expects an incoming call at some point in
the future, and wants to minimize the time it takes to the future, and wants to minimize the time it takes to
establish connectivity, to avoid clipping of initial media. establish connectivity, to avoid clipping of initial media.
By pre-gathering candidates into the pool, it can exchange By pre-gathering candidates into the pool, it can exchange
and start sending connectivity checks from these candidates and start sending connectivity checks from these candidates
almost immediately upon receipt of a call. Note though that almost immediately upon receipt of a call. Note, though, that
by holding on to these pre-gathered candidates, which will be by holding on to these pre-gathered candidates, which will be
kept alive as long as they may be needed, the application kept alive as long as they may be needed, the application
will consume resources on the STUN/TURN servers it is will consume resources on the STUN/TURN servers it is
using.</t> using. ("STUN" stands for "Session Traversal Utilities for NAT".)</t>
</section> </section>
<section title="ICE Versions"> <section numbered="true" toc="include" removeInRFC="false" pn="section-3
<t>While this specification formally relies on <xref .5.5">
target="RFC8445"></xref>, at the time of its publication, the <name slugifiedName="name-ice-versions">ICE Versions</name>
<t indent="0" pn="section-3.5.5-1">While this specification formally r
elies on <xref target="RFC8445" format="default" sectionFormat="of" derivedConte
nt="RFC8445"/>, at the time of its publication, the
majority of WebRTC implementations support the version majority of WebRTC implementations support the version
of ICE described in <xref target="RFC5245"></xref>. The use of of ICE described in <xref target="RFC5245" format="default" sectionFor
the "ice2" attribute defined in <xref target="RFC8445"></xref> mat="of" derivedContent="RFC5245"/>. The "ice2" attribute defined in <xref targe
t="RFC8445" format="default" sectionFormat="of" derivedContent="RFC8445"/>
can be used to detect the version in use by a remote endpoint can be used to detect the version in use by a remote endpoint
and to provide a smooth transition from the older specification and to provide a smooth transition from the older specification
to the newer one. Implementations MUST be able to accept remote to the newer one. Implementations <bcp14>MUST</bcp14> be able to acce pt remote
descriptions that do not have the "ice2" attribute.</t> descriptions that do not have the "ice2" attribute.</t>
</section> </section>
</section> </section>
<section anchor="sec.imageattr" title="Video Size Negotiation"> <section anchor="sec.imageattr" numbered="true" toc="include" removeInRFC=
"false" pn="section-3.6">
<t>Video size negotiation is the process through which a <name slugifiedName="name-video-size-negotiation">Video Size Negotiation
</name>
<t indent="0" pn="section-3.6-1">Video size negotiation is the process t
hrough which a
receiver can use the "a=imageattr" SDP attribute receiver can use the "a=imageattr" SDP attribute
<xref target="RFC6236" /> to indicate what video frame sizes it <xref target="RFC6236" format="default" sectionFormat="of" derivedConten t="RFC6236"/> to indicate what video frame sizes it
is capable of receiving. A receiver may have hard limits on is capable of receiving. A receiver may have hard limits on
what its video decoder can process, or it may have some maximum what its video decoder can process, or it may have some maximum
set by policy. By specifying these limits in an "a=imageattr" set by policy. By specifying these limits in an "a=imageattr"
attribute, JSEP endpoints can attempt to ensure that the remote attribute, JSEP endpoints can attempt to ensure that the remote
sender transmits video at an acceptable resolution. However, sender transmits video at an acceptable resolution. However,
when communicating with a non-JSEP endpoint that does not when communicating with a non-JSEP endpoint that does not
understand this attribute, any signaled limits may be exceeded, understand this attribute, any signaled limits may be exceeded,
and the JSEP implementation MUST handle this gracefully, e.g., and the JSEP implementation <bcp14>MUST</bcp14> handle this gracefully, e.g.,
by discarding the video.</t> by discarding the video.</t>
<t indent="0" pn="section-3.6-2">Note that certain codecs support transm
<t>Note that certain codecs support transmission of samples ission of samples
with aspect ratios other than 1.0 (i.e., non-square pixels). with aspect ratios other than 1.0 (i.e., non-square pixels).
JSEP implementations will not transmit non-square pixels, but JSEP implementations will not transmit non-square pixels but
SHOULD receive and render such video with the correct aspect <bcp14>SHOULD</bcp14> receive and render such video with the correct asp
ect
ratio. However, sample aspect ratio has no impact on the size ratio. However, sample aspect ratio has no impact on the size
negotiation described below; all dimensions are measured in negotiation described below; all dimensions are measured in
pixels, whether square or not.</t> pixels, whether square or not.</t>
<section anchor="sec.creating-imageattr" <section anchor="sec.creating-imageattr" numbered="true" toc="include" r
title="Creating an imageattr Attribute"> emoveInRFC="false" pn="section-3.6.1">
<name slugifiedName="name-creating-an-imageattr-attri">Creating an ima
<t>The receiver will first intersect any known local limits geattr Attribute</name>
(e.g., hardware decoder capababilities, local policy) to <t indent="0" pn="section-3.6.1-1">The receiver will first combine any
known local limits
(e.g., hardware decoder capabilities or local policy) to
determine the absolute minimum and maximum sizes it can determine the absolute minimum and maximum sizes it can
receive. If there are no known local limits, the receive. If there are no known local limits, the
"a=imageattr" attribute SHOULD be omitted. If these local "a=imageattr" attribute <bcp14>SHOULD</bcp14> be omitted. If these loc al
limits preclude receiving any video, i.e., the degenerate limits preclude receiving any video, i.e., the degenerate
case of no permitted resolutions, the "a=imageattr" attribute case of no permitted resolutions, the "a=imageattr" attribute
MUST be omitted, and the m= section MUST be marked as <bcp14>MUST</bcp14> be omitted, and the "m=" section <bcp14>MUST</bcp1 4> be marked as
sendonly/inactive, as appropriate.</t> sendonly/inactive, as appropriate.</t>
<t indent="0" pn="section-3.6.1-2">Otherwise, an "a=imageattr" attribu
<t>Otherwise, an "a=imageattr" attribute is created with te is created with a
"recv" direction, and the resulting resolution space formed "recv" direction, and the resulting resolution space formed
from the aforementioned intersection is used to specify its from the aforementioned intersection is used to specify its
minimum and maximum x= and y= values.</t> minimum and maximum "x=" and "y=" values.</t>
<t indent="0" pn="section-3.6.1-3">The rules here express a single set
<t>The rules here express a single set of preferences, and of preferences, and
therefore, the "a=imageattr" q= value is not important. It therefore, the "a=imageattr" "q=" value is not important. It
SHOULD be set to 1.0.</t> <bcp14>SHOULD</bcp14> be set to "1.0".</t>
<t indent="0" pn="section-3.6.1-4">The "a=imageattr" field is payload
<t>The "a=imageattr" field is payload type specific. When all type specific. When all
video codecs supported have the same capabilities, use of a video codecs supported have the same capabilities, use of a
single attribute, with the wildcard payload type (*), is single attribute, with the wildcard payload type (*), is
RECOMMENDED. However, when the supported video codecs have <bcp14>RECOMMENDED</bcp14>. However, when the supported video codecs h
different limitations, specific "a=imageattr" attributes MUST ave
different limitations, specific "a=imageattr" attributes <bcp14>MUST</
bcp14>
be inserted for each payload type.</t> be inserted for each payload type.</t>
<t indent="0" pn="section-3.6.1-5">As an example, consider a system wi
<t>As an example, consider a system with a multiformat video th a multiformat video
decoder, which is capable of decoding any resolution from decoder, which is capable of decoding any resolution from
48x48 to 720p, In this case, the implementation would 48x48 to 720p. In this case, the implementation would
generate this attribute:</t> generate this attribute:</t>
<sourcecode type="sdp" markers="false" pn="section-3.6.1-6">
<t>a=imageattr:* recv [x=[48:1280],y=[48:720],q=1.0]</t> a=imageattr:* recv [x=[48:1280],y=[48:720],q=1.0]
</sourcecode>
<t>This declaration indicates that the receiver is capable of <t indent="0" pn="section-3.6.1-7">This declaration indicates that the
receiver is capable of
decoding any image resolution from 48x48 up to 1280x720 decoding any image resolution from 48x48 up to 1280x720
pixels.</t> pixels.</t>
</section> </section>
<section anchor="sec.interpreting-imageattr" <section anchor="sec.interpreting-imageattr" numbered="true" toc="includ
title="Interpreting imageattr Attributes"> e" removeInRFC="false" pn="section-3.6.2">
<name slugifiedName="name-interpreting-imageattr-attr">Interpreting im
<t> ageattr Attributes</name>
<xref target="RFC6236" /> defines "a=imageattr" to be an <t indent="0" pn="section-3.6.2-1">
<xref target="RFC6236" format="default" sectionFormat="of" derivedCont
ent="RFC6236"/> defines "a=imageattr" to be an
advisory field. This means that it does not absolutely advisory field. This means that it does not absolutely
constrain the video formats that the sender can use, but constrain the video formats that the sender can use but
gives an indication of the preferred values.</t> gives an indication of the preferred values.</t>
<t indent="0" pn="section-3.6.2-2">This specification prescribes behav
<t>This specification prescribes more specific behavior. When ior that is more specific. When
a MediaStreamTrack, which is producing video of a certain a MediaStreamTrack, which is producing video of a certain
resolution (the "track resolution"), is attached to a resolution (the "track resolution"), is attached to an
RtpSender, which is encoding the track video at the same or RtpSender, which is encoding the track video at the same or
lower resolution(s) (the "encoder resolutions"), and a remote lower resolution(s) (the "encoder resolutions"), and a remote
description is applied that references the sender and description is applied that references the sender and
contains valid "a=imageattr recv" attributes, it MUST follow contains valid "a=imageattr recv" attributes, it <bcp14>MUST</bcp14> f
the rules below to ensure the sender does not transmit a ollow
the rules below to ensure that the sender does not transmit a
resolution that would exceed the size criteria specified in resolution that would exceed the size criteria specified in
the attributes. These rules MUST be followed as long as the the attributes. These rules <bcp14>MUST</bcp14> be followed as long as the
attributes remain present in the remote description, attributes remain present in the remote description,
including cases in which the track changes its resolution, or including cases in which the track changes its resolution or
is replaced with a different track.</t> is replaced with a different track.</t>
<t indent="0" pn="section-3.6.2-3">Depending on how the RtpSender is c
<t>Depending on how the RtpSender is configured, it may be onfigured, it may be
producing a single encoding at a certain resolution, or, if producing a single encoding at a certain resolution or, if
simulcast simulcast
<xref target="sec.simulcast" /> has been negotiated, multiple (<xref target="sec.simulcast" format="default" sectionFormat="of" deri vedContent="Section 3.7"/>) has been negotiated, multiple
encodings, each at their own specific resolution. In encodings, each at their own specific resolution. In
addition, depending on the configuration, each encoding may addition, depending on the configuration, each encoding may
have the flexibility to reduce resolution when needed, or may have the flexibility to reduce resolution when needed or may
be locked to a specific output resolution.</t> be locked to a specific output resolution.</t>
<t indent="0" pn="section-3.6.2-4">For each encoding being produced by
<t>For each encoding being produced by the RtpSender, the set the RtpSender, the set
of "a=imageattr recv" attributes in the corresponding m= of "a=imageattr recv" attributes in the corresponding "m="
section of the remote description is processed to determine section of the remote description is processed to determine
what should be transmitted. Only attributes that reference what should be transmitted. Only attributes that reference
the media format selected for the encoding are considered; the media format selected for the encoding are considered;
each such attribute is evaluated individually, starting with each such attribute is evaluated individually, starting with
the attribute with the highest "q=" value. If multiple the attribute with the highest "q=" value. If multiple
attributes have the same "q=" value, they are evaluated in attributes have the same "q=" value, they are evaluated in
the order they appear in their containing m= section. Note the order they appear in their containing "m=" section. Note
that while JSEP endpoints will include at most one that while JSEP endpoints will include at most one
"a=imageattr recv" attribute per media format, JSEP endpoints "a=imageattr recv" attribute per media format, JSEP endpoints
may receive session descriptions from non-JSEP endpoints with may receive session descriptions from non-JSEP endpoints with
m= sections that contain multiple such attributes.</t> "m=" sections that contain multiple such attributes.</t>
<t indent="0" pn="section-3.6.2-5">For each "a=imageattr recv" attribu
<t>For each "a=imageattr recv" attribute, the following rules te, the following rules
are applied. If this processing is successful, the encoding are applied. If this processing is successful, the encoding
is transmitted accordingly, and no further attributes are is transmitted accordingly, and no further attributes are
considered for that encoding. Otherwise, the next attribute considered for that encoding. Otherwise, the next attribute
is evaluated, in the aforementioned order. If none of the is evaluated, in the aforementioned order. If none of the
supplied attributes can be processed successfully, the supplied attributes can be processed successfully, the
encoding MUST NOT be transmitted, and an error SHOULD be encoding <bcp14>MUST NOT</bcp14> be transmitted, and an error <bcp14>S HOULD</bcp14> be
raised to the application. raised to the application.
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>The limits from the attribute are compared to the -3.6.2-6">
<li pn="section-3.6.2-6.1">The limits from the attribute are compare
d to the
encoder resolution. Only the specific limits mentioned encoder resolution. Only the specific limits mentioned
below are considered; any other values, such as picture below are considered; any other values, such as picture
aspect ratio, MUST be ignored. When considering a aspect ratio, <bcp14>MUST</bcp14> be ignored. When considering a
MediaStreamTrack that is producing rotated video, the MediaStreamTrack that is producing rotated video, the
unrotated resolution MUST be used for the checks. This is unrotated resolution <bcp14>MUST</bcp14> be used for the checks. Thi s is
required regardless of whether the receiver supports required regardless of whether the receiver supports
performing receive-side rotation (e.g., through CVO performing receive-side rotation (e.g., through Coordination of
<xref target="TS26.114" />), as it significantly simplifies Video Orientation (CVO)
the matching logic.</t> <xref target="TS26.114" format="default" sectionFormat="of" derivedC
ontent="TS26.114"/>), as it significantly simplifies
<t>If the attribute includes a "sar=" (sample aspect ratio) the matching logic.</li>
value set to something other than "1.0", indicating the <li pn="section-3.6.2-6.2">If the attribute includes a "sar=" (sampl
e aspect ratio)
value set to something other than "1.0", indicating that the
receiver wants to receive non-square pixels, this cannot be receiver wants to receive non-square pixels, this cannot be
satisfied and the attribute MUST NOT be used.</t> satisfied and the attribute <bcp14>MUST NOT</bcp14> be used.</li>
<li pn="section-3.6.2-6.3">If the encoder resolution exceeds the max
<t>If the encoder resolution exceeds the maximum size imum size
permitted by the attribute, and the encoder is allowed to permitted by the attribute and the encoder is allowed to
adjust its resolution, the encoder SHOULD apply downscaling adjust its resolution, the encoder <bcp14>SHOULD</bcp14> apply downs
in order to satisfy the limits. Downscaling MUST NOT change caling
in order to satisfy the limits. Downscaling <bcp14>MUST NOT</bcp14>
change
the picture aspect ratio of the encoding, ignoring any the picture aspect ratio of the encoding, ignoring any
trivial differences due to rounding. For example, if the trivial differences due to rounding. For example, if the
encoder resolution is 1280x720, and the attribute specified encoder resolution is 1280x720 and the attribute specified
a maximum of 640x480, the expected output resolution would a maximum of 640x480, the expected output resolution would
be 640x360. If downscaling cannot be applied, the attribute be 640x360. If downscaling cannot be applied, the attribute
MUST NOT be used.</t> <bcp14>MUST NOT</bcp14> be used.</li>
<li pn="section-3.6.2-6.4">If the encoder resolution is less than th
<t>If the encoder resolution is less than the minimum size e minimum size
permitted by the attribute, the attribute MUST NOT be used; permitted by the attribute, the attribute <bcp14>MUST NOT</bcp14> be
the encoder MUST NOT apply upscaling. JSEP implementations used;
SHOULD avoid this situation by allowing receipt of the encoder <bcp14>MUST NOT</bcp14> apply upscaling. JSEP implementa
tions
<bcp14>SHOULD</bcp14> avoid this situation by allowing receipt of
arbitrarily small resolutions, perhaps via fallback to a arbitrarily small resolutions, perhaps via fallback to a
software decoder.</t> software decoder.</li>
<li pn="section-3.6.2-6.5">If the encoder resolution is within the m
<t>If the encoder resolution is within the maximum and aximum and
minimum sizes, no action is needed.</t> minimum sizes, no action is needed.</li>
</list></t> </ul>
</section> </section>
</section> </section>
<section title="Simulcast" anchor="sec.simulcast"> <section anchor="sec.simulcast" numbered="true" toc="include" removeInRFC=
"false" pn="section-3.7">
<t>JSEP supports simulcast transmission of a MediaStreamTrack, <name slugifiedName="name-simulcast">Simulcast</name>
<t indent="0" pn="section-3.7-1">JSEP supports simulcast transmission of
a MediaStreamTrack,
where multiple encodings of the source media can be transmitted where multiple encodings of the source media can be transmitted
within the context of a single m= section. The current JSEP API within the context of a single "m=" section. The current JSEP API
is designed to allow applications to send simulcasted media but is designed to allow applications to send simulcasted media but
only to receive a single encoding. This allows for multi-user only to receive a single encoding. This allows for multi-user
scenarios where each sending client sends multiple encodings to scenarios where each sending client sends multiple encodings to
a server, which then, for each receiving client, chooses the a server, which then, for each receiving client, chooses the
appropriate encoding to forward.</t> appropriate encoding to forward.</t>
<t indent="0" pn="section-3.7-2">Applications request support for simulc
<t>Applications request support for simulcast by configuring ast by configuring
multiple encodings on an RtpSender. Upon generation of an offer multiple encodings on an RtpSender. Upon generation of an offer
or answer, these encodings are indicated via SDP markings on or answer, these encodings are indicated via SDP markings on
the corresponding m= section, as described below. Receivers the corresponding "m=" section, as described below. Receivers
that understand simulcast and are willing to receive it will that understand simulcast and are willing to receive it will
also include SDP markings to indicate their support, and JSEP also include SDP markings to indicate their support, and JSEP
endpoints will use these markings to determine whether endpoints will use these markings to determine whether
simulcast is permitted for a given RtpSender. If simulcast simulcast is permitted for a given RtpSender. If simulcast
support is not negotiated, the RtpSender will only use the support is not negotiated, the RtpSender will only use the
first configured encoding.</t> first configured encoding.</t>
<t indent="0" pn="section-3.7-3">Note that the exact simulcast parameter
<t>Note that the exact simulcast parameters are up to the s are up to the
sending application. While the aforementioned SDP markings are sending application. While the aforementioned SDP markings are
provided to ensure the remote side can receive and demux provided to ensure that the remote side can receive and demux
multiple simulcast encodings, the specific resolutions and multiple simulcast encodings, the specific resolutions and
bitrates to be used for each encoding are purely a send-side bitrates to be used for each encoding are purely a send-side
decision in JSEP.</t> decision in JSEP.</t>
<t indent="0" pn="section-3.7-4">JSEP currently does not provide a mecha
<t>JSEP currently does not provide a mechanism to configure nism to configure
receipt of simulcast. This means that if simulcast is offered receipt of simulcast. This means that if simulcast is offered
by the remote endpoint, the answer generated by a JSEP endpoint by the remote endpoint, the answer generated by a JSEP endpoint
will not indicate support for receipt of simulcast, and as such will not indicate support for receipt of simulcast, and as such
the remote endpoint will only send a single encoding per m= the remote endpoint will only send a single encoding per "m="
section.</t> section.</t>
<t indent="0" pn="section-3.7-5">In addition, JSEP does not provide a me
<t>In addition, JSEP does not provide a mechanism to handle an chanism to handle an
incoming offer requesting simulcast from the JSEP endpoint. incoming offer requesting simulcast from the JSEP endpoint.
This means that setting up simulcast in the case where the JSEP This means that setting up simulcast in the case where the JSEP
endpoint receives the initial offer requires out-of-band endpoint receives the initial offer requires out-of-band
signaling or SDP inspection. However, in the case where the signaling or SDP inspection. However, in the case where the
JSEP endpoint sets up simulcast in its in initial offer, any JSEP endpoint sets up simulcast in its initial offer, any
established simulcast streams will continue to work upon established simulcast streams will continue to work upon
receipt of an incoming re-offer. Future versions of this receipt of an incoming re-offer. Future versions of this
specification may add additional APIs to handle the incoming specification may add additional APIs to handle the incoming
initial offer scenario.</t> initial offer scenario.</t>
<t indent="0" pn="section-3.7-6">When using JSEP to transmit multiple en
<t>When using JSEP to transmit multiple encodings from a codings from an
RtpSender, the techniques from RtpSender, the techniques from
<xref target="I-D.ietf-mmusic-sdp-simulcast" /> and <xref target="RFC8853" format="default" sectionFormat="of" derivedConten
<xref target="I-D.ietf-mmusic-rid" /> are used. Specifically, t="RFC8853"/> and
when multiple encodings have been configured for a RtpSender, <xref target="RFC8851" format="default" sectionFormat="of" derivedConten
the m= section for the RtpSender will include an "a=simulcast" t="RFC8851"/> are used. Specifically,
when multiple encodings have been configured for an RtpSender,
the "m=" section for the RtpSender will include an "a=simulcast"
attribute, as defined in attribute, as defined in
<xref target="I-D.ietf-mmusic-sdp-simulcast" />, Section 6.2, <xref target="RFC8853" sectionFormat="comma" section="5.1" format="defau lt" derivedLink="https://rfc-editor.org/rfc/rfc8853#section-5.1" derivedContent= "RFC8853"/>,
with a "send" simulcast stream description that lists each with a "send" simulcast stream description that lists each
desired encoding, and no "recv" simulcast stream description. desired encoding, and no "recv" simulcast stream description.
The m= section will also include an "a=rid" attribute for each The "m=" section will also include an "a=rid" attribute for each
encoding, as specified in encoding, as specified in
<xref target="I-D.ietf-mmusic-rid" />, Section 4; the use of <xref target="RFC8851" sectionFormat="comma" section="4" format="default
RID identifiers allows the individual encodings to be " derivedLink="https://rfc-editor.org/rfc/rfc8851#section-4" derivedContent="RFC
disambiguated even though they are all part of the same m= 8851"/>; the use of
Restriction Identifiers (RIDs, also called rid-ids or RtpStreamIds)
allows the individual encodings to be
disambiguated even though they are all part of the same "m="
section.</t> section.</t>
</section> </section>
<section title="Interactions With Forking" <section anchor="sec.interactions-with-forking" numbered="true" toc="inclu
anchor="sec.interactions-with-forking"> de" removeInRFC="false" pn="section-3.8">
<name slugifiedName="name-interactions-with-forking">Interactions with F
<t>Some call signaling systems allow various types of forking orking</name>
<t indent="0" pn="section-3.8-1">Some call signaling systems allow vario
us types of forking
where an SDP Offer may be provided to more than one device. For where an SDP Offer may be provided to more than one device. For
example, SIP example, SIP
<xref target="RFC3261"></xref> defines both a "Parallel Search" <xref target="RFC3261" format="default" sectionFormat="of" derivedConten
and "Sequential Search". Although these are primarily signaling t="RFC3261"/> defines both a "parallel search"
level issues that are outside the scope of JSEP, they do have and "sequential search". Although these are primarily signaling-level is
sues that are outside the scope of JSEP, they do have
some impact on the configuration of the media plane that is some impact on the configuration of the media plane that is
relevant. When forking happens at the signaling layer, the relevant. When forking happens at the signaling layer, the
JavaScript application responsible for the signaling needs to JavaScript application responsible for the signaling needs to
make the decisions about what media should be sent or received make the decisions about what media should be sent or received
at any point of time, as well as which remote endpoint it at any point in time, as well as which remote endpoint it
should communicate with; JSEP is used to make sure the media should communicate with; JSEP is used to make sure the media
engine can make the RTP and media perform as required by the engine can make the RTP and media perform as required by the
application. The basic operations that the applications can application. The basic operations that the applications can
have the media engine do are: have the media engine do are as follows:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section-3
<t>Start exchanging media with a given remote peer, but keep .8-2">
all the resources reserved in the offer.</t> <li pn="section-3.8-2.1">Start exchanging media with a given remote pe
er, but keep
<t>Start exchanging media with a given remote peer, and free all the resources reserved in the offer.</li>
any resources in the offer that are not being used.</t> <li pn="section-3.8-2.2">Start exchanging media with a given remote pe
</list></t> er, and free
<section title="Sequential Forking" any resources in the offer that are not being used.</li>
anchor="sec.sequential-forking"> </ul>
<section anchor="sec.sequential-forking" numbered="true" toc="include" r
<t>Sequential forking involves a call being dispatched to emoveInRFC="false" pn="section-3.8.1">
<name slugifiedName="name-sequential-forking">Sequential Forking</name
>
<t indent="0" pn="section-3.8.1-1">Sequential forking involves a call
being dispatched to
multiple remote callees, where each callee can accept the multiple remote callees, where each callee can accept the
call, but only one active session ever exists at a time; no call, but only one active session ever exists at a time; no
mixing of received media is performed.</t> mixing of received media is performed.</t>
<t indent="0" pn="section-3.8.1-2">JSEP handles sequential forking wel
<t>JSEP handles sequential forking well, allowing the l, allowing the
application to easily control the policy for selecting the application to easily control the policy for selecting the
desired remote endpoint. When an answer arrives from one of desired remote endpoint. When an answer arrives from one of
the callees, the application can choose to apply it either as the callees, the application can choose to apply it as either
a provisional answer, leaving open the possibility of using a (1) a provisional answer, leaving open the possibility of using a
different answer in the future, or apply it as a final different answer in the future or (2) a final
answer, ending the setup flow.</t> answer, ending the setup flow.</t>
<t indent="0" pn="section-3.8.1-3">In a "first-one-wins" situation, th
<t>In a "first-one-wins" situation, the first answer will be e first answer will be
applied as a final answer, and the application will reject applied as a final answer, and the application will reject
any subsequent answers. In SIP parlance, this would be ACK + any subsequent answers. In SIP parlance, this would be ACK +
BYE.</t> BYE.</t>
<t indent="0" pn="section-3.8.1-4">In a "last-one-wins" situation, all
<t>In a "last-one-wins" situation, all answers would be answers would be
applied as provisional answers, and any previous call leg applied as provisional answers, and any previous call leg
will be terminated. At some point, the application will end will be terminated. At some point, the application will end
the setup process, perhaps with a timer; at this point, the the setup process, perhaps with a timer; at this point, the
application could reapply the pending remote description as a application could reapply the pending remote description as a
final answer.</t> final answer.</t>
</section> </section>
<section title="Parallel Forking" <section anchor="sec.parallel-forking" numbered="true" toc="include" rem
anchor="sec.parallel-forking"> oveInRFC="false" pn="section-3.8.2">
<name slugifiedName="name-parallel-forking">Parallel Forking</name>
<t>Parallel forking involves a call being dispatched to <t indent="0" pn="section-3.8.2-1">Parallel forking involves a call be
ing dispatched to
multiple remote callees, where each callee can accept the multiple remote callees, where each callee can accept the
call, and multiple simultaneous active signaling sessions can call and multiple simultaneous active signaling sessions can
be established as a result. If multiple callees send media at be established as a result. If multiple callees send media at
the same time, the possibilities for handling this are the same time, the possibilities for handling this are
described in described in
<xref target="RFC3960"></xref>, Section 3.1. Most SIP devices <xref target="RFC3960" sectionFormat="comma" section="3.1" format="def ault" derivedLink="https://rfc-editor.org/rfc/rfc3960#section-3.1" derivedConten t="RFC3960"/>. Most SIP devices
today only support exchanging media with a single device at a today only support exchanging media with a single device at a
time, and do not try to mix multiple early media audio time and do not try to mix multiple early media audio
sources, as that could result in a confusing situation. For sources, as that could result in a confusing situation. For
example, consider having a European ringback tone mixed example, consider having a European ringback tone mixed
together with the North American ringback tone - the together with the North American ringback tone -- the
resulting sound would not be like either tone, and would resulting sound would not be like either tone and would
confuse the user. If the signaling application wishes to only confuse the user. If the signaling application wishes to only
exchange media with one of the remote endpoints at a time, exchange media with one of the remote endpoints at a time,
then from a media engine point of view, this is exactly like then from a media engine point of view, this is exactly like
the sequential forking case.</t> the sequential forking case.</t>
<t indent="0" pn="section-3.8.2-2">In the parallel forking case where
<t>In the parallel forking case where the JavaScript the JavaScript
application wishes to simultaneously exchange media with application wishes to simultaneously exchange media with
multiple peers, the flow is slightly more complex, but the multiple peers, the flow is slightly more complex, but the
JavaScript application can follow the strategy that JavaScript application can follow the strategy that
<xref target="RFC3960"></xref> describes using UPDATE. The <xref target="RFC3960" format="default" sectionFormat="of" derivedCont ent="RFC3960"/> describes, using UPDATE. The
UPDATE approach allows the signaling to set up a separate UPDATE approach allows the signaling to set up a separate
media flow for each peer that it wishes to exchange media media flow for each peer that it wishes to exchange media
with. In JSEP, this offer used in the UPDATE would be formed with. In JSEP, this offer used in the UPDATE would be formed
by simply creating a new PeerConnection (see by simply creating a new PeerConnection (see
<xref target="sec.peerconnection" />) and making sure that <xref target="sec.peerconnection" format="default" sectionFormat="of" derivedContent="Section 4.1"/>) and making sure that
the same local media streams have been added into this new the same local media streams have been added into this new
PeerConnection. Then the new PeerConnection object would PeerConnection. Then the new PeerConnection object would
produce a SDP offer that could be used by the signaling to produce an SDP offer that could be used by the signaling to
perform the UPDATE strategy discussed in perform the UPDATE strategy discussed in
<xref target="RFC3960"></xref>.</t> <xref target="RFC3960" format="default" sectionFormat="of" derivedCont
ent="RFC3960"/>.</t>
<t>As a result of sharing the media streams, the application <t indent="0" pn="section-3.8.2-3">As a result of sharing the media st
reams, the application
will end up with N parallel PeerConnection sessions, each will end up with N parallel PeerConnection sessions, each
with a local and remote description and their own local and with a local and remote description and their own local and
remote addresses. The media flow from these sessions can be remote addresses. The media flow from these sessions can be
managed using setDirection (see managed using setDirection (see
<xref target="sec.transceiver-set-direction" />), or the <xref target="sec.transceiver-set-direction" format="default" sectionF ormat="of" derivedContent="Section 4.2.3"/>), or the
application can choose to play out the media from all application can choose to play out the media from all
sessions mixed together. Of course, if the application wants sessions mixed together. Of course, if the application wants
to only keep a single session, it can simply terminate the to only keep a single session, it can simply terminate the
sessions that it no longer needs.</t> sessions that it no longer needs.</t>
</section> </section>
</section> </section>
</section> </section>
<section title="Interface" anchor="sec.interface"> <section anchor="sec.interface" numbered="true" toc="include" removeInRFC="f
alse" pn="section-4">
<t>This section details the basic operations that must be present <name slugifiedName="name-interface">Interface</name>
<t indent="0" pn="section-4-1">This section details the basic operations t
hat must be present
to implement JSEP functionality. The actual API exposed in the to implement JSEP functionality. The actual API exposed in the
W3C API may have somewhat different syntax, but should map easily W3C API may have somewhat different syntax but should map easily
to these concepts.</t> to these concepts.
<section title="PeerConnection" anchor="sec.peerconnection"> </t>
<section title="Constructor" anchor="sec.pc-constructor"> <section anchor="sec.peerconnection" numbered="true" toc="include" removeI
nRFC="false" pn="section-4.1">
<t>The PeerConnection constructor allows the application to <name slugifiedName="name-peerconnection">PeerConnection</name>
<section anchor="sec.pc-constructor" numbered="true" toc="include" remov
eInRFC="false" pn="section-4.1.1">
<name slugifiedName="name-constructor">Constructor</name>
<t indent="0" pn="section-4.1.1-1">The PeerConnection constructor allo
ws the application to
specify global parameters for the media session, such as the specify global parameters for the media session, such as the
STUN/TURN servers and credentials to use when gathering STUN/TURN servers and credentials to use when gathering
candidates, as well as the initial ICE candidate policy and candidates, as well as the initial ICE candidate policy and
pool size, and also the bundle policy to use.</t> pool size, and also the bundle policy to use.</t>
<t indent="0" pn="section-4.1.1-2">If an ICE candidate policy is speci
<t>If an ICE candidate policy is specified, it functions as fied, it functions as
described in described in
<xref target="sec.ice-candidate-policy" />, causing the JSEP <xref target="sec.ice-candidate-policy" format="default" sectionFormat ="of" derivedContent="Section 3.5.3"/>, causing the JSEP
implementation to only surface the permitted candidates implementation to only surface the permitted candidates
(including any implementation-internal filtering) to the (including any implementation-internal filtering) to the
application, and only use those candidates for connectivity application and only use those candidates for connectivity
checks. The set of available policies is as follows: checks. The set of available policies is as follows:
<list style="hanging"> </t>
<t hangText="all:">All candidates permitted by <dl newline="false" spacing="normal" indent="3" pn="section-4.1.1-3">
implementation policy will be gathered and used.</t> <dt pn="section-4.1.1-3.1">all:</dt>
<dd pn="section-4.1.1-3.2">All candidates permitted by
<t></t> implementation policy will be gathered and used.</dd>
<t hangText="relay:">All candidates except relay candidates <dt pn="section-4.1.1-3.3">relay:</dt>
<dd pn="section-4.1.1-3.4">All candidates except relay candidates
will be filtered out. This obfuscates the location will be filtered out. This obfuscates the location
information that might be ascertained by the remote peer information that might be ascertained by the remote peer
from the received candidates. Depending on how the from the received candidates. Depending on how the
application deploys and chooses relay servers, this could application deploys and chooses relay servers, this could
obfuscate location to a metro or possibly even global obfuscate location to a metro or possibly even global
level.</t> level.</dd>
</list></t> </dl>
<t indent="0" pn="section-4.1.1-4">The default ICE candidate policy <b
<t>The default ICE candidate policy MUST be set to "all" as cp14>MUST</bcp14> be set to "all", as
this is generally the desired policy, and also typically this is generally the desired policy and also typically
reduces use of application TURN server resources reduces the use of application TURN server resources
significantly.</t> significantly.</t>
<t indent="0" pn="section-4.1.1-5">If a size is specified for the ICE
<t>If a size is specified for the ICE candidate pool, this candidate pool, this
indicates the number of ICE components to pre-gather indicates the number of ICE components to pre-gather
candidates for. Because pre-gathering results in utilizing candidates for. Because pre‑gathering results in utilizing
STUN/TURN server resources for potentially long periods of STUN/TURN server resources for potentially long periods of
time, this must only occur upon application request, and time, this <bcp14>MUST</bcp14> only occur upon application request, an
therefore the default candidate pool size MUST be zero.</t> d
therefore the default candidate pool size <bcp14>MUST</bcp14> be zero.
<t>The application can specify its preferred policy regarding </t>
<t indent="0" pn="section-4.1.1-6">The application can specify its pre
ferred policy regarding
use of bundle, the multiplexing mechanism defined in use of bundle, the multiplexing mechanism defined in
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation"> <xref target="RFC8843" format="default" sectionFormat="of" derivedCont
</xref>. Regardless of policy, the application will always ent="RFC8843">
try to negotiate bundle onto a single transport, and will </xref>. Regardless of policy, the application will always
offer a single bundle group across all m= sections; use of try to negotiate bundle onto a single transport and will
offer a single bundle group across all "m=" sections; use of
this single transport is contingent upon the answerer this single transport is contingent upon the answerer
accepting bundle. However, by specifying a policy from the accepting bundle. However, by specifying a policy from the
list below, the application can control exactly how list below, the application can control exactly how
aggressively it will try to bundle media streams together, aggressively it will try to bundle media streams together,
which affects how it will interoperate with a which affects how it will interoperate with a
non-bundle-aware endpoint. When negotiating with a non-bundle-aware endpoint. When negotiating with a
non-bundle-aware endpoint, only the streams not marked as non-bundle-aware endpoint, only the streams not marked as
bundle-only streams will be established.</t> bundle-only streams will be established.</t>
<t indent="0" pn="section-4.1.1-7">The set of available policies is as
<t>The set of available policies is as follows: follows:
<list style="hanging"> </t>
<t hangText="balanced:">The first m= section of each type <dl newline="false" spacing="normal" indent="3" pn="section-4.1.1-8">
<dt pn="section-4.1.1-8.1">balanced:</dt>
<dd pn="section-4.1.1-8.2">The first "m=" section of each type
(audio, video, or application) will contain transport (audio, video, or application) will contain transport
parameters, which will allow an answerer to unbundle that parameters, which will allow an answerer to unbundle that
section. The second and any subsequent m= section of each section. The second and any subsequent "m=" sections of each
type will be marked bundle-only. The result is that if type will be marked bundle-only. The result is that if
there are N distinct media types, then candidates will be there are N distinct media types, then candidates will be
gathered for for N media streams. This policy balances gathered for N media streams. This policy balances
desire to multiplex with the need to ensure basic audio and desire to multiplex with the need to ensure that basic audio and
video can still be negotiated in legacy cases. When acting video can still be negotiated in legacy cases. When acting
as answerer, if there is no bundle group in the offer, the as answerer, if there is no bundle group in the offer, the
implementation will reject all but the first m= section of implementation will reject all but the first "m=" section of
each type.</t> each type.</dd>
<dt pn="section-4.1.1-8.3">max-compat:</dt>
<t></t> <dd pn="section-4.1.1-8.4">All "m=" sections will contain
<t hangText="max-compat:">All m= sections will contain
transport parameters; none will be marked as bundle-only. transport parameters; none will be marked as bundle-only.
This policy will allow all streams to be received by This policy will allow all streams to be received by
non-bundle-aware endpoints, but require separate candidates non-bundle-aware endpoints but will require separate candidates
to be gathered for each media stream.</t> to be gathered for each media stream.</dd>
<dt pn="section-4.1.1-8.5">max-bundle:</dt>
<t></t> <dd pn="section-4.1.1-8.6">Only the first "m=" section will
<t hangText="max-bundle:">Only the first m= section will
contain transport parameters; all streams other than the contain transport parameters; all streams other than the
first will be marked as bundle-only. This policy aims to first will be marked as bundle-only. This policy aims to
minimize candidate gathering and maximize multiplexing, at minimize candidate gathering and maximize multiplexing, at
the cost of less compatibility with legacy endpoints. When the cost of less compatibility with legacy endpoints. When
acting as answerer, the implementation will reject any m= acting as answerer, the implementation will reject any "m="
sections other than the first m= section, unless they are sections other than the first "m=" section, unless they are
in the same bundle group as that m= section.</t> in the same bundle group as that "m=" section.</dd>
</list></t> </dl>
<t indent="0" pn="section-4.1.1-9">As it provides the best trade-off b
<t>As it provides the best tradeoff between performance and etween performance and
compatibility with legacy endpoints, the default bundle compatibility with legacy endpoints, the default bundle
policy MUST be set to "balanced".</t> policy <bcp14>MUST</bcp14> be set to "balanced".</t>
<t indent="0" pn="section-4.1.1-10">The application can specify its pr
<t>The application can specify its preferred policy regarding eferred policy regarding
use of RTP/RTCP multiplexing use of RTP/RTCP multiplexing
<xref target="RFC5761"></xref> using one of the following <xref target="RFC5761" format="default" sectionFormat="of" derivedCont ent="RFC5761"/> using one of the following
policies: policies:
<list style="hanging"> </t>
<t hangText="negotiate:">The JSEP implementation will <dl newline="false" spacing="normal" indent="3" pn="section-4.1.1-11">
<dt pn="section-4.1.1-11.1">negotiate:</dt>
<dd pn="section-4.1.1-11.2">The JSEP implementation will
gather both RTP and RTCP candidates but also will offer gather both RTP and RTCP candidates but also will offer
"a=rtcp-mux", thus allowing for compatibility with either "a=rtcp-mux", thus allowing for compatibility with either
multiplexing or non-multiplexing endpoints.</t> multiplexing or non-multiplexing endpoints.</dd>
<t hangText="require:">The JSEP implementation will only <dt pn="section-4.1.1-11.3">require:</dt>
<dd pn="section-4.1.1-11.4">The JSEP implementation will only
gather RTP candidates and will insert an "a=rtcp-mux-only" gather RTP candidates and will insert an "a=rtcp-mux-only"
indication into any new m= sections in offers it generates. indication into any new "m=" sections in offers it generates.
This halves the number of candidates that the offerer needs This halves the number of candidates that the offerer needs
to gather. Applying a description with an m= section that to gather. Applying a description with an "m=" section that
does not contain an "a=rtcp-mux" attribute will cause an does not contain an "a=rtcp-mux" attribute will cause an
error to be returned.</t> error to be returned.</dd>
</list></t> </dl>
<t indent="0" pn="section-4.1.1-12">The default multiplexing policy <b
<t>The default multiplexing policy MUST be set to "require". cp14>MUST</bcp14> be set to "require".
Implementations MAY choose to reject attempts by the Implementations <bcp14>MAY</bcp14> choose to reject attempts by the
application to set the multiplexing policy to application to set the multiplexing policy to
"negotiate".</t> "negotiate".</t>
</section> </section>
<section title="addTrack" anchor="sec.addTrack"> <section anchor="sec.addTrack" numbered="true" toc="include" removeInRFC
="false" pn="section-4.1.2">
<t>The addTrack method adds a MediaStreamTrack to the <name slugifiedName="name-addtrack">addTrack</name>
<t indent="0" pn="section-4.1.2-1">The addTrack method adds a MediaStr
eamTrack to the
PeerConnection, using the MediaStream argument to associate PeerConnection, using the MediaStream argument to associate
the track with other tracks in the same MediaStream, so that the track with other tracks in the same MediaStream, so that
they can be added to the same "LS" group when creating an they can be added to the same "LS" (Lip Synchronization) group when cr eating an
offer or answer. Adding tracks to the same "LS" group offer or answer. Adding tracks to the same "LS" group
indicates that the playback of these tracks should be indicates that the playback of these tracks should be
synchronized for proper lip sync, as described in synchronized for proper lip sync, as described in
<xref target="RFC5888"></xref>, Section 7. addTrack attempts <xref target="RFC5888" sectionFormat="comma" section="7" format="defau
to minimize the number of transceivers as follows: If the lt" derivedLink="https://rfc-editor.org/rfc/rfc5888#section-7" derivedContent="R
PeerConnection is in the "have-remote-offer" state, the track FC5888"/>.  addTrack attempts
to minimize the number of transceivers as follows: if the
PeerConnection is in the "have‑remote-offer" state, the track
will be attached to the first compatible transceiver that was will be attached to the first compatible transceiver that was
created by the most recent call to setRemoteDescription() and created by the most recent call to setRemoteDescription and
does not have a local track. Otherwise, a new transceiver does not have a local track. Otherwise, a new transceiver
will be created, as described in will be created, as described in
<xref target="sec.addTransceiver" />.</t> <xref target="sec.addTransceiver" format="default" sectionFormat="of" derivedContent="Section 4.1.4"/>.</t>
</section> </section>
<section title="removeTrack" anchor="sec.removeTrack"> <section anchor="sec.removeTrack" numbered="true" toc="include" removeIn
RFC="false" pn="section-4.1.3">
<t>The removeTrack method removes a MediaStreamTrack from the <name slugifiedName="name-removetrack">removeTrack</name>
<t indent="0" pn="section-4.1.3-1">The removeTrack method removes a Me
diaStreamTrack from the
PeerConnection, using the RtpSender argument to indicate PeerConnection, using the RtpSender argument to indicate
which sender should have its track removed. The sender's which sender should have its track removed. The sender's
track is cleared, and the sender stops sending. Future calls track is cleared, and the sender stops sending. Future calls
to createOffer will mark the m= section associated with the to createOffer will mark the "m=" section associated with the
sender as recvonly (if transceiver.direction is sendrecv) or sender as recvonly (if transceiver.direction is sendrecv) or
as inactive (if transceiver.direction is sendonly).</t> as inactive (if transceiver.direction is sendonly).</t>
</section> </section>
<section title="addTransceiver" anchor="sec.addTransceiver"> <section anchor="sec.addTransceiver" numbered="true" toc="include" remov
eInRFC="false" pn="section-4.1.4">
<t>The addTransceiver method adds a new RtpTransceiver to the <name slugifiedName="name-addtransceiver">addTransceiver</name>
<t indent="0" pn="section-4.1.4-1">The addTransceiver method adds a ne
w RtpTransceiver to the
PeerConnection. If a MediaStreamTrack argument is provided, PeerConnection. If a MediaStreamTrack argument is provided,
then the transceiver will be configured with that media type then the transceiver will be configured with that media type
and the track will be attached to the transceiver. Otherwise, and the track will be attached to the transceiver. Otherwise,
the application MUST explicitly specify the type; this mode the application <bcp14>MUST</bcp14> explicitly specify the type; this mode
is useful for creating recvonly transceivers as well as for is useful for creating recvonly transceivers as well as for
creating transceivers to which a track can be attached at creating transceivers to which a track can be attached at
some later point.</t> some later point.</t>
<t indent="0" pn="section-4.1.4-2">At the time of creation, the applic
<t>At the time of creation, the application can also specify ation can also specify
a transceiver direction attribute, a set of MediaStreams a transceiver direction attribute, a set of MediaStreams
which the transceiver is associated with (allowing LS group that the transceiver is associated with (allowing "LS" group
assignments), and a set of encodings for the media (used for assignments), and a set of encodings for the media (used for
simulcast as described in simulcast as described in
<xref target="sec.simulcast" />).</t> <xref target="sec.simulcast" format="default" sectionFormat="of" deriv edContent="Section 3.7"/>).</t>
</section> </section>
<section title="createDataChannel" <section anchor="sec.onaddtrack" numbered="true" toc="include" removeInR
anchor="sec.createDataChannel"> FC="false" pn="section-4.1.5">
<name slugifiedName="name-onaddtrack-event">onaddtrack Event</name>
<t>The createDataChannel method creates a new data channel <t indent="0" pn="section-4.1.5-1">The onaddtrack event is dispatched
to the application when a new
remote track has been signaled as a result of a setRemoteDescription
call. The new track is supplied as a MediaStreamTrack object in the
event, along with the MediaStream(s) the track is part of.
</t>
</section>
<section anchor="sec.createDataChannel" numbered="true" toc="include" re
moveInRFC="false" pn="section-4.1.6">
<name slugifiedName="name-createdatachannel">createDataChannel</name>
<t indent="0" pn="section-4.1.6-1">The createDataChannel method create
s a new data channel
and attaches it to the PeerConnection. If no data channel and attaches it to the PeerConnection. If no data channel
currently exists for this PeerConnection, then a new currently exists for this PeerConnection, then a new
offer/answer exchange is required. All data channels on a offer/answer exchange is required. All data channels on a
given PeerConnection share the same SCTP/DTLS association and given PeerConnection share the same SCTP/DTLS association ("SCTP" stan
therefore the same m= section, so subsequent creation of data ds
for "Stream Control Transmission Protocol") and
therefore the same "m=" section, so subsequent creation of data
channels does not have any impact on the JSEP state.</t> channels does not have any impact on the JSEP state.</t>
<t indent="0" pn="section-4.1.6-2">The createDataChannel method also i
<t>The createDataChannel method also includes a number of ncludes a number of
arguments which are used by the PeerConnection (e.g., arguments that are used by the PeerConnection (e.g.,
maxPacketLifetime) but are not reflected in the SDP and do maxPacketLifetime) but are not reflected in the SDP and do
not affect the JSEP state.</t> not affect the JSEP state.</t>
</section> </section>
<section title="createOffer" anchor="sec.createoffer"> <section anchor="sec.ondatachannel" numbered="true" toc="include" remove
InRFC="false" pn="section-4.1.7">
<t>The createOffer method generates a blob of SDP that <name slugifiedName="name-ondatachannel-event">ondatachannel Event</na
contains a me>
<xref target="RFC3264"></xref> offer with the supported <t indent="0" pn="section-4.1.7-1">The ondatachannel event is dispatch
ed to the application when a
new data channel has been negotiated by the remote side, which can
occur at any time after the underlying SCTP/DTLS association has been
established. The new data channel object is supplied in the event.
</t>
</section>
<section anchor="sec.createoffer" numbered="true" toc="include" removeIn
RFC="false" pn="section-4.1.8">
<name slugifiedName="name-createoffer">createOffer</name>
<t indent="0" pn="section-4.1.8-1">The createOffer method generates a
blob of SDP that
contains an offer per <xref target="RFC3264" format="default" sectionF
ormat="of" derivedContent="RFC3264"/> with the supported
configurations for the session, including descriptions of the configurations for the session, including descriptions of the
media added to this PeerConnection, the codec/RTP/RTCP media added to this PeerConnection, the codec, RTP, and RTCP
options supported by this implementation, and any candidates options supported by this implementation, and any candidates
that have been gathered by the ICE agent. An options that have been gathered by the ICE agent. An options
parameter may be supplied to provide additional control over parameter may be supplied to provide additional control over
the generated offer. This options parameter allows an the generated offer. This options parameter allows an
application to trigger an ICE restart, for the purpose of application to trigger an ICE restart, for the purpose of
reestablishing connectivity.</t> reestablishing connectivity.</t>
<t indent="0" pn="section-4.1.8-2">In the initial offer, the generated
<t>In the initial offer, the generated SDP will contain all SDP will contain all
desired functionality for the session (functionality that is desired functionality for the session (functionality that is
supported but not desired by default may be omitted); for supported but not desired by default may be omitted); for
each SDP line, the generation of the SDP will follow the each SDP line, the generation of the SDP will follow the
process defined for generating an initial offer from the process defined for generating an initial offer from the
document that specifies the given SDP line. The exact specification that defines the given SDP line. The exact
handling of initial offer generation is detailed in handling of initial offer generation is detailed in
<xref target="sec.initial-offers" /> below.</t> <xref target="sec.initial-offers" format="default" sectionFormat="of"
derivedContent="Section 5.2.1"/> below.</t>
<t>In the event createOffer is called after the session is <t indent="0" pn="section-4.1.8-3">In the event createOffer is called
after the session is
established, createOffer will generate an offer to modify the established, createOffer will generate an offer to modify the
current session based on any changes that have been made to current session based on any changes that have been made to
the session, e.g., adding or stopping RtpTransceivers, or the session, e.g., adding or stopping RtpTransceivers, or
requesting an ICE restart. For each existing stream, the requesting an ICE restart. For each existing stream, the
generation of each SDP line must follow the process defined generation of each SDP line <bcp14>MUST</bcp14> follow the process def ined
for generating an updated offer from the RFC that specifies for generating an updated offer from the RFC that specifies
the given SDP line. For each new stream, the generation of the given SDP line. For each new stream, the generation of
the SDP must follow the process of generating an initial the SDP <bcp14>MUST</bcp14> follow the process of generating an initia l
offer, as mentioned above. If no changes have been made, or offer, as mentioned above. If no changes have been made, or
for SDP lines that are unaffected by the requested changes, for SDP lines that are unaffected by the requested changes,
the offer will only contain the parameters negotiated by the the offer will only contain the parameters negotiated by the
last offer-answer exchange. The exact handling of subsequent last offer/answer exchange. The exact handling of subsequent
offer generation is detailed in offer generation is detailed in
<xref target="sec.subsequent-offers" />. below.</t> <xref target="sec.subsequent-offers" format="default" sectionFormat="o
f" derivedContent="Section 5.2.2"/> below.</t>
<t>Session descriptions generated by createOffer must be <t indent="0" pn="section-4.1.8-4">Session descriptions generated by c
reateOffer <bcp14>MUST</bcp14> be
immediately usable by setLocalDescription; if a system has immediately usable by setLocalDescription; if a system has
limited resources (e.g. a finite number of decoders), limited resources (e.g., a finite number of decoders),
createOffer should return an offer that reflects the current createOffer <bcp14>SHOULD</bcp14> return an offer that reflects the cu
rrent
state of the system, so that setLocalDescription will succeed state of the system, so that setLocalDescription will succeed
when it attempts to acquire those resources.</t> when it attempts to acquire those resources.</t>
<t indent="0" pn="section-4.1.8-5">Calling this method may do things s
<t>Calling this method may do things such as generating new uch as generating new
ICE credentials, but does not change the PeerConnection ICE credentials, but it does not change the PeerConnection
state, trigger candidate gathering, or cause media to start state, trigger candidate gathering, or cause media to start
or stop flowing. Specifically, the offer is not applied, and or stop flowing. Specifically, the offer is not applied, and
does not become the pending local description, until does not become the pending local description, until
setLocalDescription is called.</t> setLocalDescription is called.</t>
</section> </section>
<section title="createAnswer" anchor="sec.createanswer"> <section anchor="sec.createanswer" numbered="true" toc="include" removeI
nRFC="false" pn="section-4.1.9">
<t>The createAnswer method generates a blob of SDP that <name slugifiedName="name-createanswer">createAnswer</name>
contains a <t indent="0" pn="section-4.1.9-1">The createAnswer method generates a
<xref target="RFC3264"></xref> SDP answer with the supported blob of SDP that
contains an SDP answer per <xref target="RFC3264" format="default" sec
tionFormat="of" derivedContent="RFC3264"/> with the supported
configuration for the session that is compatible with the configuration for the session that is compatible with the
parameters supplied in the most recent call to parameters supplied in the most recent call to
setRemoteDescription, which MUST have been called prior to setRemoteDescription; setRemoteDescription <bcp14>MUST</bcp14> have be en called prior to
calling createAnswer. Like createOffer, the returned blob calling createAnswer. Like createOffer, the returned blob
contains descriptions of the media added to this contains descriptions of the media added to this
PeerConnection, the codec/RTP/RTCP options negotiated for PeerConnection, the codec/RTP/RTCP options negotiated for
this session, and any candidates that have been gathered by this session, and any candidates that have been gathered by
the ICE agent. An options parameter may be supplied to the ICE agent. An options parameter may be supplied to
provide additional control over the generated answer.</t> provide additional control over the generated answer.</t>
<t indent="0" pn="section-4.1.9-2">As an answer, the generated SDP wil
<t>As an answer, the generated SDP will contain a specific l contain a specific
configuration that specifies how the media plane should be configuration that specifies how the media plane should be
established; for each SDP line, the generation of the SDP established; for each SDP line, the generation of the SDP
must follow the process defined for generating an answer from <bcp14>MUST</bcp14> follow the process defined for generating an answe
the document that specifies the given SDP line. The exact r from
the specification that defines the given SDP line. The exact
handling of answer generation is detailed in handling of answer generation is detailed in
<xref target="sec.generating-an-answer" />. below.</t> <xref target="sec.generating-an-answer" format="default" sectionFormat
="of" derivedContent="Section 5.3"/> below.</t>
<t>Session descriptions generated by createAnswer must be <t indent="0" pn="section-4.1.9-3">Session descriptions generated by c
reateAnswer <bcp14>MUST</bcp14> be
immediately usable by setLocalDescription; like createOffer, immediately usable by setLocalDescription; like createOffer,
the returned description should reflect the current state of the returned description <bcp14>SHOULD</bcp14> reflect the current sta te of
the system.</t> the system.</t>
<t indent="0" pn="section-4.1.9-4">Calling this method may do things s
<t>Calling this method may do things such as generating new uch as generating new
ICE credentials, but does not change the PeerConnection ICE credentials, but it does not change the PeerConnection
state, trigger candidate gathering, or or cause a media state state, trigger candidate gathering, or cause a media state
change. Specifically, the answer is not applied, and does not change. Specifically, the answer is not applied, and does not
become the current local description, until become the current local description, until
setLocalDescription is called.</t> setLocalDescription is called.</t>
</section> </section>
<section title="SessionDescriptionType" <section anchor="sec.sessiondescriptiontype" numbered="true" toc="includ
anchor="sec.sessiondescriptiontype"> e" removeInRFC="false" pn="section-4.1.10">
<name slugifiedName="name-sessiondescriptiontype">SessionDescriptionTy
<t>Session description objects (RTCSessionDescription) may be pe</name>
of type "offer", "pranswer", "answer" or "rollback". These <t indent="0" pn="section-4.1.10-1">Session description objects (RTCSe
ssionDescription) may be
of type "offer", "pranswer", "answer", or "rollback". These
types provide information as to how the description parameter types provide information as to how the description parameter
should be parsed, and how the media state should be should be parsed and how the media state should be
changed.</t> changed.</t>
<t indent="0" pn="section-4.1.10-2">"offer" indicates that a descripti
<t>"offer" indicates that a description should be parsed as on <bcp14>MUST</bcp14> be parsed as
an offer; said description may include many possible media an offer; said description may include many possible media
configurations. A description used as an "offer" may be configurations. A description used as an "offer" may be
applied anytime the PeerConnection is in a stable state, or applied any time the PeerConnection is in a "stable" state or
as an update to a previously supplied but unanswered applied as an update to a previously supplied but unanswered
"offer".</t> "offer".</t>
<t indent="0" pn="section-4.1.10-3">"pranswer" indicates that a descri
<t>"pranswer" indicates that a description should be parsed ption <bcp14>MUST</bcp14> be parsed
as an answer, but not a final answer, and so should not as an answer, but not a final answer, and so <bcp14>MUST NOT</bcp14>
result in the freeing of allocated resources. It may result result in the freeing of allocated resources. It may result
in the start of media transmission, if the answer does not in the start of media transmission, if the answer does not
specify an inactive media direction. A description used as a specify an inactive media direction. A description used as a
"pranswer" may be applied as a response to an "offer", or an "pranswer" may be applied as a response to an "offer" or as an
update to a previously sent "pranswer".</t> update to a previously sent "pranswer".</t>
<t indent="0" pn="section-4.1.10-4">"answer" indicates that a descript
<t>"answer" indicates that a description should be parsed as ion <bcp14>MUST</bcp14> be parsed as
an answer, the offer-answer exchange should be considered an answer, the offer/answer exchange <bcp14>MUST</bcp14> be considered
complete, and any resources (decoders, candidates) that are complete, and any resources (decoders, candidates) that are
no longer needed can be released. A description used as an no longer needed <bcp14>SHOULD</bcp14> be released. A description used
"answer" may be applied as a response to an "offer", or an as an
"answer" may be applied as a response to an "offer" or as an
update to a previously sent "pranswer".</t> update to a previously sent "pranswer".</t>
<t indent="0" pn="section-4.1.10-5">The only difference between a prov
<t>The only difference between a provisional and final answer isional and final answer
is that the final answer results in the freeing of any unused is that the final answer results in the freeing of any unused
resources that were allocated as a result of the offer. As resources that were allocated as a result of the offer. As
such, the application can use some discretion on whether an such, the application can use some discretion on whether an
answer should be applied as provisional or final, and can answer should be applied as provisional or final and can
change the type of the session description as needed. For change the type of the session description as needed. For
example, in a serial forking scenario, an application may example, in a serial forking scenario, an application may
receive multiple "final" answers, one from each remote receive multiple "final" answers, one from each remote
endpoint. The application could choose to accept the initial endpoint. The application could choose to accept the initial
answers as provisional answers, and only apply an answer as answers as provisional answers and only apply an answer as
final when it receives one that meets its criteria (e.g. a final when it receives one that meets its criteria (e.g., a
live user instead of voicemail).</t> live user instead of voicemail).</t>
<t indent="0" pn="section-4.1.10-6">"rollback" is a special session de
<t>"rollback" is a special session description type implying scription type indicating
that the state machine should be rolled back to the previous that the state machine <bcp14>MUST</bcp14> be rolled back to the previ
stable state, as described in ous
<xref target="sec.rollback" />. The contents MUST be "stable" state, as described in
<xref target="sec.rollback" format="default" sectionFormat="of" derive
dContent="Section 4.1.10.2"/>. The contents <bcp14>MUST</bcp14> be
empty.</t> empty.</t>
<section title="Use of Provisional Answers" <section anchor="sec.use-of-provisional-answer" numbered="true" toc="i
anchor="sec.use-of-provisional-answer"> nclude" removeInRFC="false" pn="section-4.1.10.1">
<name slugifiedName="name-use-of-provisional-answers">Use of Provisi
<t>Most applications will not need to create answers using onal Answers</name>
<t indent="0" pn="section-4.1.10.1-1">Most applications will not nee
d to create answers using
the "pranswer" type. While it is good practice to send an the "pranswer" type. While it is good practice to send an
immediate response to an offer, in order to warm up the immediate response to an offer, in order to warm up the
session transport and prevent media clipping, the preferred session transport and prevent media clipping, the preferred
handling for a JSEP application is to create and send a handling for a JSEP application is to create and send a
"sendonly" final answer with a null MediaStreamTrack "sendonly" final answer with a null MediaStreamTrack
immediately after receiving the offer, which will prevent immediately after receiving the offer, which will prevent
media from being sent by the caller, and allow media to be media from being sent by the caller and allow media to be
sent immediately upon answer by the callee. Later, when the sent immediately upon answer by the callee. Later, when the
callee actually accepts the call, the application can plug callee actually accepts the call, the application can plug
in the real MediaStreamTrack and create a new "sendrecv" in the real MediaStreamTrack and create a new "sendrecv"
offer to update the previous offer/answer pair and start offer to update the previous offer/answer pair and start
bidirectional media flow. While this could also be done bidirectional media flow. While this could also be done
with a "sendonly" pranswer, followed by a "sendrecv" with a "sendonly" pranswer followed by a "sendrecv"
answer, the initial pranswer leaves the offer-answer answer, the initial pranswer leaves the offer/answer
exchange open, which means that the caller cannot send an exchange open, which means that the caller cannot send an
updated offer during this time.</t> updated offer during this time. </t>
<t indent="0" pn="section-4.1.10.1-2">As an example, consider a typi
<t>As an example, consider a typical JSEP application that cal JSEP application that
wants to set up audio and video as quickly as possible. wants to set up audio and video as quickly as possible.
When the callee receives an offer with audio and video When the callee receives an offer with audio and video
MediaStreamTracks, it will send an immediate answer MediaStreamTracks, it will send an immediate answer
accepting these tracks as sendonly (meaning that the caller accepting these tracks as sendonly (meaning that the caller
will not send the callee any media yet, and because the will not send the callee any media yet, and because the
callee has not yet added its own MediaStreamTracks, the callee has not yet added its own MediaStreamTracks, the
callee will not send any media either). It will then ask callee will not send any media either). It will then ask
the user to accept the call and acquire the needed local the user to accept the call and acquire the needed local
tracks. Upon acceptance by the user, the application will tracks. Upon acceptance by the user, the application will
plug in the tracks it has acquired, which, because ICE and plug in the tracks it has acquired, which, because ICE handshaking
DTLS handshaking have likely completed by this point, can and DTLS handshaking have likely completed by this point, can
start transmitting immediately. The application will also start transmitting immediately. The application will also
send a new offer to the remote side indicating call send a new offer to the remote side indicating call
acceptance and moving the audio and video to be two-way acceptance and moving the audio and video to be two-way
media. A detailed example flow along these lines is shown media. A detailed example flow along these lines is shown
in in
<xref target="sec.warmup-example"></xref>.</t> <xref target="sec.warmup-example" format="default" sectionFormat="of
" derivedContent="Section 7.3"/>.</t>
<t>Of course, some applications may not be able to perform <t indent="0" pn="section-4.1.10.1-3">Of course, some applications m
this double offer-answer exchange, particularly ones that ay not be able to perform
this double offer/answer exchange, particularly ones that
are attempting to gateway to legacy signaling protocols. In are attempting to gateway to legacy signaling protocols. In
these cases, pranswer can still provide the application these cases, pranswer can still provide the application
with a mechanism to warm up the transport.</t> with a mechanism to warm up the transport.</t>
</section> </section>
<section title="Rollback" anchor="sec.rollback"> <section anchor="sec.rollback" numbered="true" toc="include" removeInR
FC="false" pn="section-4.1.10.2">
<t>In certain situations it may be desirable to "undo" a <name slugifiedName="name-rollback">Rollback</name>
<t indent="0" pn="section-4.1.10.2-1">In certain situations, it may
be desirable to "undo" a
change made to setLocalDescription or setRemoteDescription. change made to setLocalDescription or setRemoteDescription.
Consider a case where a call is ongoing, and one side wants Consider a case where a call is ongoing and one side wants
to change some of the session parameters; that side to change some of the session parameters; that side
generates an updated offer and then calls generates an updated offer and then calls
setLocalDescription. However, the remote side, either setLocalDescription. However, the remote side, either
before or after setRemoteDescription, decides it does not before or after setRemoteDescription, decides it does not
want to accept the new parameters, and sends a reject want to accept the new parameters and sends a reject
message back to the offerer. Now, the offerer, and possibly message back to the offerer. Now, the offerer, and possibly
the answerer as well, need to return to a stable state and the answerer as well, needs to return to a "stable" state and
the previous local/remote description. To support this, we the previous local/remote description. To support this, we
introduce the concept of "rollback", which discards any introduce the concept of "rollback", which discards any
proposed changes to the session, returning the state proposed changes to the session, returning the state
machine to the stable state. A rollback is performed by machine to the "stable" state. A rollback is performed by
supplying a session description of type "rollback" with supplying a session description of type "rollback" with
empty contents to either setLocalDescription or empty contents to either setLocalDescription or
setRemoteDescription.</t> setRemoteDescription.</t>
</section> </section>
</section> </section>
<section title="setLocalDescription" <section anchor="sec.setlocaldescription" numbered="true" toc="include"
anchor="sec.setlocaldescription"> removeInRFC="false" pn="section-4.1.11">
<name slugifiedName="name-setlocaldescription">setLocalDescription</na
<t>The setLocalDescription method instructs the me>
<t indent="0" pn="section-4.1.11-1">The setLocalDescription method ins
tructs the
PeerConnection to apply the supplied session description as PeerConnection to apply the supplied session description as
its local configuration. The type field indicates whether the its local configuration. The type field indicates whether the
description should be processed as an offer, provisional description should be processed as an offer, provisional
answer, final answer, or rollback; offers and answers are answer, final answer, or rollback; offers and answers are
checked differently, using the various rules that exist for checked differently, using the various rules that exist for
each SDP line.</t> each SDP line.</t>
<t indent="0" pn="section-4.1.11-2">This API changes the local media s
<t>This API changes the local media state; among other tate; among other
things, it sets up local resources for receiving and decoding things, it sets up local resources for receiving and decoding
media. In order to successfully handle scenarios where the media. In order to successfully handle scenarios where the
application wants to offer to change from one media format to application wants to offer to change from one media format to
a different, incompatible format, the PeerConnection must be a different, incompatible format, the PeerConnection <bcp14>MUST</bcp1 4> be
able to simultaneously support use of both the current and able to simultaneously support use of both the current and
pending local descriptions (e.g., support the codecs that pending local descriptions (e.g., support the codecs that
exist in either description). This dual processing begins exist in either description). This dual processing begins
when the PeerConnection enters the "have-local-offer" state, when the PeerConnection enters the "have-local-offer" state,
and continues until setRemoteDescription is called with and it continues until setRemoteDescription is called with
either a final answer, at which point the PeerConnection can either (1) a final answer, at which point the PeerConnection can
fully adopt the pending local description, or a rollback, fully adopt the pending local description or (2) a rollback,
which results in a revert to the current local which results in a revert to the current local
description.</t> description.</t>
<t indent="0" pn="section-4.1.11-3">This API indirectly controls the c
<t>This API indirectly controls the candidate gathering andidate gathering
process. When a local description is supplied, and the number process. When a local description is supplied and the number
of transports currently in use does not match the number of of transports currently in use does not match the number of
transports needed by the local description, the transports needed by the local description, the
PeerConnection will create transports as needed and begin PeerConnection will create transports as needed and begin
gathering candidates for each transport, using ones from the gathering candidates for each transport, using ones from the
candidate pool if available.</t> candidate pool if available.</t>
<t indent="0" pn="section-4.1.11-4">If (1) setRemoteDescription was pr
<t>If setRemoteDescription was previously called with an eviously called with an
offer, and setLocalDescription is called with an answer offer, (2) setLocalDescription is called with an answer
(provisional or final), and the media directions are (provisional or final), (3) the media directions are
compatible, and media is available to send, this will result compatible, and (4) media is available to send, this will result
in the starting of media transmission.</t> in the starting of media transmission.
</t>
</section> </section>
<section title="setRemoteDescription" <section anchor="sec.setremotedescription" numbered="true" toc="include"
anchor="sec.setremotedescription"> removeInRFC="false" pn="section-4.1.12">
<name slugifiedName="name-setremotedescription">setRemoteDescription</
<t>The setRemoteDescription method instructs the name>
<t indent="0" pn="section-4.1.12-1">The setRemoteDescription method in
structs the
PeerConnection to apply the supplied session description as PeerConnection to apply the supplied session description as
the desired remote configuration. As in setLocalDescription, the desired remote configuration. As in setLocalDescription,
the type field of the description indicates how it should be the type field of the description indicates how it should be
processed.</t> processed.</t>
<t indent="0" pn="section-4.1.12-2">This API changes the local media s
<t>This API changes the local media state; among other tate; among other
things, it sets up local resources for sending and encoding things, it sets up local resources for sending and encoding
media.</t> media. </t>
<t indent="0" pn="section-4.1.12-3">If (1) setLocalDescription was pre
<t>If setLocalDescription was previously called with an viously called with an
offer, and setRemoteDescription is called with an answer offer, (2) setRemoteDescription is called with an answer
(provisional or final), and the media directions are (provisional or final), (3) the media directions are
compatible, and media is available to send, this will result compatible, and (4) media is available to send, this will result
in the starting of media transmission.</t> in the starting of media transmission.</t>
</section> </section>
<section title="currentLocalDescription" <section anchor="sec.currentlocaldescription" numbered="true" toc="inclu
anchor="sec.currentlocaldescription"> de" removeInRFC="false" pn="section-4.1.13">
<name slugifiedName="name-currentlocaldescription">currentLocalDescrip
<t>The currentLocalDescription method returns the current tion</name>
negotiated local description - i.e., the local description <t indent="0" pn="section-4.1.13-1">The currentLocalDescription method
from the last successful offer/answer exchange - in addition returns the current
negotiated local description -- i.e., the local description
from the last successful offer/answer exchange -- in addition
to any local candidates that have been generated by the ICE to any local candidates that have been generated by the ICE
agent since the local description was set.</t> agent since the local description was set.</t>
<t indent="0" pn="section-4.1.13-2">A null object will be returned if
<t>A null object will be returned if an offer/answer exchange an offer/answer exchange
has not yet been completed.</t> has not yet been completed.</t>
</section> </section>
<section title="pendingLocalDescription" <section anchor="sec.pendinglocaldescription" numbered="true" toc="inclu
anchor="sec.pendinglocaldescription"> de" removeInRFC="false" pn="section-4.1.14">
<name slugifiedName="name-pendinglocaldescription">pendingLocalDescrip
<t>The pendingLocalDescription method returns a copy of the tion</name>
local description currently in negotiation - i.e., a local <t indent="0" pn="section-4.1.14-1">The pendingLocalDescription method
offer set without any corresponding remote answer - in returns a copy of the
local description currently in negotiation -- i.e., a local
offer set without any corresponding remote answer -- in
addition to any local candidates that have been generated by addition to any local candidates that have been generated by
the ICE agent since the local description was set.</t> the ICE agent since the local description was set.</t>
<t indent="0" pn="section-4.1.14-2">A null object will be returned if
<t>A null object will be returned if the state of the the state of the
PeerConnection is "stable" or "have-remote-offer".</t> PeerConnection is "stable" or "have-remote-offer".</t>
</section> </section>
<section title="currentRemoteDescription" <section anchor="sec.currentremotedescription" numbered="true" toc="incl
anchor="sec.currentremotedescription"> ude" removeInRFC="false" pn="section-4.1.15">
<name slugifiedName="name-currentremotedescription">currentRemoteDescr
<t>The currentRemoteDescription method returns a copy of the iption</name>
current negotiated remote description - i.e., the remote <t indent="0" pn="section-4.1.15-1">The currentRemoteDescription metho
description from the last successful offer/answer exchange - d returns a copy of the
current negotiated remote description -- i.e., the remote
description from the last successful offer/answer exchange --
in addition to any remote candidates that have been supplied in addition to any remote candidates that have been supplied
via processIceMessage since the remote description was via processIceMessage since the remote description was
set.</t> set.</t>
<t indent="0" pn="section-4.1.15-2">A null object will be returned if
<t>A null object will be returned if an offer/answer exchange an offer/answer exchange
has not yet been completed.</t> has not yet been completed.</t>
</section> </section>
<section title="pendingRemoteDescription" <section anchor="sec.pendingremotedescription" numbered="true" toc="incl
anchor="sec.pendingremotedescription"> ude" removeInRFC="false" pn="section-4.1.16">
<name slugifiedName="name-pendingremotedescription">pendingRemoteDescr
<t>The pendingRemoteDescription method returns a copy of the iption</name>
remote description currently in negotiation - i.e., a remote <t indent="0" pn="section-4.1.16-1">The pendingRemoteDescription metho
offer set without any corresponding local answer - in d returns a copy of the
remote description currently in negotiation -- i.e., a remote
offer set without any corresponding local answer -- in
addition to any remote candidates that have been supplied via addition to any remote candidates that have been supplied via
processIceMessage since the remote description was set.</t> processIceMessage since the remote description was set.</t>
<t indent="0" pn="section-4.1.16-2">A null object will be returned if
<t>A null object will be returned if the state of the the state of the
PeerConnection is "stable" or "have-local-offer".</t> PeerConnection is "stable" or "have-local-offer".</t>
</section> </section>
<section title="canTrickleIceCandidates" <section anchor="sec.cantrickle" numbered="true" toc="include" removeInR
anchor="sec.cantrickle"> FC="false" pn="section-4.1.17">
<name slugifiedName="name-cantrickleicecandidates">canTrickleIceCandid
<t>The canTrickleIceCandidates property indicates whether the ates</name>
<t indent="0" pn="section-4.1.17-1">The canTrickleIceCandidates proper
ty indicates whether the
remote side supports receiving trickled candidates. There are remote side supports receiving trickled candidates. There are
three potential values: three potential values:
<list style="hanging"> </t>
<t hangText="null:">No SDP has been received from the other <dl newline="false" spacing="normal" indent="3" pn="section-4.1.17-2">
<dt pn="section-4.1.17-2.1">null:</dt>
<dd pn="section-4.1.17-2.2">No SDP has been received from the other
side, so it is not known if it can handle trickle. This is side, so it is not known if it can handle trickle. This is
the initial value before setRemoteDescription() is the initial value before setRemoteDescription is
called.</t> called.</dd>
<t hangText="true:">SDP has been received from the other <dt pn="section-4.1.17-2.3">true:</dt>
side indicating that it can support trickle.</t> <dd pn="section-4.1.17-2.4">SDP has been received from the other
<t hangText="false:">SDP has been received from the other side indicating that it can support trickle.</dd>
side indicating that it cannot support trickle.</t> <dt pn="section-4.1.17-2.5">false:</dt>
</list></t> <dd pn="section-4.1.17-2.6">SDP has been received from the other
side indicating that it cannot support trickle.</dd>
<t>As described in </dl>
<xref target="sec.ice-candidate-trickling" />, JSEP <t indent="0" pn="section-4.1.17-3">As described in
<xref target="sec.ice-candidate-trickling" format="default" sectionFor
mat="of" derivedContent="Section 3.5.2"/>, JSEP
implementations always provide candidates to the application implementations always provide candidates to the application
individually, consistent with what is needed for Trickle ICE. individually, consistent with what is needed for Trickle ICE.
However, applications can use the canTrickleIceCandidates However, applications can use the canTrickleIceCandidates
property to determine whether their peer can actually do property to determine whether their peer can actually do
Trickle ICE, i.e., whether it is safe to send an initial Trickle ICE, i.e., whether it is safe to send an initial
offer or answer followed later by candidates as they are offer or answer followed later by candidates as they are
gathered. As "true" is the only value that definitively gathered. As "true" is the only value that definitively
indicates remote Trickle ICE support, an application which indicates remote Trickle ICE support, an application that
compares canTrickleIceCandidates against "true" will by compares canTrickleIceCandidates against "true" will by
default attempt Half Trickle on initial offers and Full default attempt Half Trickle on initial offers and Full
Trickle on subsequent interactions with a Trickle Trickle on subsequent interactions with a Trickle
ICE-compatible agent.</t> ICE-compatible agent.</t>
</section> </section>
<section title="setConfiguration" <section anchor="sec.setconfiguration" numbered="true" toc="include" rem
anchor="sec.setconfiguration"> oveInRFC="false" pn="section-4.1.18">
<name slugifiedName="name-setconfiguration">setConfiguration</name>
<t>The setConfiguration method allows the global <t indent="0" pn="section-4.1.18-1">The setConfiguration method allows
the global
configuration of the PeerConnection, which was initially set configuration of the PeerConnection, which was initially set
by constructor parameters, to be changed during the session. by constructor parameters, to be changed during the session.
The effects of this method call depend on when it is invoked, The effects of calling this method depend on when it is invoked,
and differ depending on which specific parameters are and they will differ, depending on which specific parameters are
changed:</t> changed: </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t> -4.1.18-2">
<list style="symbols"> <li pn="section-4.1.18-2.1">Any changes to the STUN/TURN servers to
use affect the
<t>Any changes to the STUN/TURN servers to use affect the
next gathering phase. If an ICE gathering phase has next gathering phase. If an ICE gathering phase has
already started or completed, the 'needs-ice-restart' bit already started or completed, the 'needs-ice-restart' bit
mentioned in mentioned in
<xref target="sec.ice-gather-overview" /> will be set. <xref target="sec.ice-gather-overview" format="default" sectionFor mat="of" derivedContent="Section 3.5.1"/> will be set.
This will cause the next call to createOffer to generate This will cause the next call to createOffer to generate
new ICE credentials, for the purpose of forcing an ICE new ICE credentials, for the purpose of forcing an ICE
restart and kicking off a new gathering phase, in which restart and kicking off a new gathering phase, in which
the new servers will be used. If the ICE candidate pool the new servers will be used. If the ICE candidate pool
has a nonzero size, and a local description has not yet has a nonzero size and a local description has not yet
been applied, any existing candidates will be discarded, been applied, any existing candidates will be discarded,
and new candidates will be gathered from the new and new candidates will be gathered from the new
servers.</t> servers.</li>
<li pn="section-4.1.18-2.2">Any change to the ICE candidate policy a
<t>Any change to the ICE candidate policy affects the ffects the
next gathering phase. If an ICE gathering phase has next gathering phase. If an ICE gathering phase has
already started or completed, the 'needs-ice-restart' bit already started or completed, the 'needs-ice-restart' bit
will be set. Either way, changes to the policy have no will be set. Either way, changes to the policy have no
effect on the candidate pool, because pooled candidates effect on the candidate pool, because pooled candidates
are not made available to the application until a are not made available to the application until a
gathering phase occurs, and so any necessary filtering gathering phase occurs, and so any necessary filtering
can still be done on any pooled candidates.</t> can still be done on any pooled candidates.</li>
<li pn="section-4.1.18-2.3">The ICE candidate pool size <bcp14>MUST
<t>The ICE candidate pool size MUST NOT be changed after NOT</bcp14> be changed after
applying a local description. If a local description has applying a local description. If a local description has
not yet been applied, any changes to the ICE candidate not yet been applied, any changes to the ICE candidate
pool size take effect immediately; if increased, pool size take effect immediately; if increased,
additional candidates are pre-gathered; if decreased, the additional candidates are pre-gathered; if decreased, the
now-superfluous candidates are discarded.</t> now-superfluous candidates are discarded.</li>
<li pn="section-4.1.18-2.4">The bundle and RTCP-multiplexing policie
<t>The bundle and RTCP-multiplexing policies MUST NOT be s <bcp14>MUST NOT</bcp14> be
changed after the construction of the PeerConnection.</t> changed after the construction of the PeerConnection.</li>
</list> </ul>
</t> <t indent="0" pn="section-4.1.18-3">Calling this method may result in
a change to the state of the ICE
<t>This call may result in a change to the state of the ICE agent.</t>
Agent.</t>
</section> </section>
<section title="addIceCandidate" anchor="sec.addicecandidate"> <section anchor="sec.addicecandidate" numbered="true" toc="include" remo
veInRFC="false" pn="section-4.1.19">
<t>The addIceCandidate method provides an update to the ICE <name slugifiedName="name-addicecandidate">addIceCandidate</name>
<t indent="0" pn="section-4.1.19-1">The addIceCandidate method provide
s an update to the ICE
agent via an IceCandidate object agent via an IceCandidate object
<xref target="sec.ice-candidate-format" />. If the (<xref target="sec.ice-candidate-format" format="default" sectionForma
IceCandidate's candidate field is filled in, the IceCandidate t="of" derivedContent="Section 3.5.2.1"/>). If the
IceCandidate's candidate field is non-null, the IceCandidate
is treated as a new remote ICE candidate, which will be added is treated as a new remote ICE candidate, which will be added
to the current and/or pending remote description according to to the current and/or pending remote description according to
the rules defined for Trickle ICE. Otherwise, the the rules defined for Trickle ICE. Otherwise, the
IceCandidate is treated as an end-of-candidates indication, IceCandidate is treated as an end-of-candidates indication,
as defined in as defined in
<xref target="I-D.ietf-ice-trickle" />.</t> <xref target="RFC8838" sectionFormat="comma" section="14" format="defa
ult" derivedLink="https://rfc-editor.org/rfc/rfc8838#section-14" derivedContent=
<t>In either case, the m= section index, MID, and ufrag "RFC8838"/>.</t>
<t indent="0" pn="section-4.1.19-2">In either case, the "m=" section i
ndex, MID, and ufrag
fields from the supplied IceCandidate are used to determine fields from the supplied IceCandidate are used to determine
which m= section and ICE candidate generation the which "m=" section and ICE candidate generation the
IceCandidate belongs to, as described in IceCandidate belongs to, as described in
<xref target="sec.ice-candidate-format" /> above. In the case <xref target="sec.ice-candidate-format" format="default" sectionFormat
of an end-of-candidates indication, the absence of both the ="of" derivedContent="Section 3.5.2.1"/> above. In the case
m= section index and MID fields is interpreted to mean that of an end-of-candidates indication, null values for the
the indication applies to all m= sections in the specified "m=" section index and MID fields are interpreted to mean that
ICE candidate generation. However, if both fields are absent the indication applies to all "m=" sections in the specified
for a new remote candidate, this MUST be treated as an ICE candidate generation. However, if both fields are null
for a new remote candidate, this <bcp14>MUST</bcp14> be treated as an
invalid condition, as specified below.</t> invalid condition, as specified below.</t>
<t indent="0" pn="section-4.1.19-3">If any IceCandidate fields contain
<t>If any IceCandidate fields contain invalid values, or an invalid values or an
error occurs during the processing of the IceCandidate error occurs during the processing of the IceCandidate
object, the supplied IceCandidate MUST be ignored and an object, the supplied IceCandidate <bcp14>MUST</bcp14> be ignored and a
error MUST be returned.</t> n
error <bcp14>MUST</bcp14> be returned.</t>
<t>Otherwise, the new remote candidate or end-of-candidates <t indent="0" pn="section-4.1.19-4">Otherwise, the new remote candidat
e or end-of-candidates
indication is supplied to the ICE agent. In the case of a new indication is supplied to the ICE agent. In the case of a new
remote candidate, connectivity checks will be sent to the new remote candidate, connectivity checks will be sent to the new
candidate.</t> candidate, assuming setLocalDescription has already been
called to initialize the ICE gathering process.</t>
</section>
<section anchor="sec.onicecandidate" numbered="true" toc="include" remov
eInRFC="false" pn="section-4.1.20">
<name slugifiedName="name-onicecandidate-event">onicecandidate Event</
name>
<t indent="0" pn="section-4.1.20-1">The onicecandidate event is dispat
ched to the application in two
situations: (1) when the ICE agent has discovered a new allowed local
ICE candidate during ICE gathering, as outlined in
<xref target="sec.ice-gather-overview" format="default" sectionFormat=
"of" derivedContent="Section 3.5.1"/> and
subject to the restrictions discussed in
<xref target="sec.ice-candidate-policy" format="default" sectionFormat
="of" derivedContent="Section 3.5.3"/>, or
(2) when an ICE gathering phase completes. The event contains a single
IceCandidate object, as defined in
<xref target="sec.ice-candidate-format" format="default" sectionFormat
="of" derivedContent="Section 3.5.2.1"/>.</t>
<t indent="0" pn="section-4.1.20-2">In the first case, the newly disco
vered candidate is reflected
in the IceCandidate object, and all of its fields <bcp14>MUST</bcp14>
be non-null.
This candidate will also be added to the current and/or pending local
description according to the rules defined for Trickle ICE.</t>
<t indent="0" pn="section-4.1.20-3">In the second case, the event's Ic
eCandidate object
<bcp14>MUST</bcp14> have its candidate field set to null to indicate
that the current gathering phase is complete, i.e., there will be no
further onicecandidate events in this phase. However, the
IceCandidate's ufrag field <bcp14>MUST</bcp14> be specified to
indicate which ICE candidate generation is ending. The IceCandidate's
"m=" section index and MID fields <bcp14>MAY</bcp14> be specified to i
ndicate that
the event applies to a specific "m=" section, or set to null to
indicate it applies to all "m=" sections in the current ICE candidate
generation. This event can be used by the application to generate an
end-of-candidates indication, as defined in
<xref target="RFC8838" sectionFormat="comma" section="13" format="defa
ult" derivedLink="https://rfc-editor.org/rfc/rfc8838#section-13" derivedContent=
"RFC8838"/>.</t>
</section> </section>
</section> </section>
<section title="RtpTransceiver" anchor="sec.transceiver"> <section anchor="sec.transceiver" numbered="true" toc="include" removeInRF
<section title="stop" anchor="sec.transceiver-stop"> C="false" pn="section-4.2">
<name slugifiedName="name-rtptransceiver">RtpTransceiver</name>
<t>The stop method stops an RtpTransceiver. This will cause <section anchor="sec.transceiver-stop" numbered="true" toc="include" rem
oveInRFC="false" pn="section-4.2.1">
<name slugifiedName="name-stop">stop</name>
<t indent="0" pn="section-4.2.1-1">The stop method stops an RtpTransce
iver. This will cause
future calls to createOffer to generate a zero port for the future calls to createOffer to generate a zero port for the
associated m= section. See below for more details.</t> associated "m=" section. See below for more details.</t>
</section> </section>
<section title="stopped" anchor="sec.transceiver-stopped"> <section anchor="sec.transceiver-stopped" numbered="true" toc="include"
removeInRFC="false" pn="section-4.2.2">
<t>The stopped property indicates whether the transceiver has <name slugifiedName="name-stopped">stopped</name>
been stopped, either by a call to stopTransceiver or by <t indent="0" pn="section-4.2.2-1">The stopped property indicates whet
applying an answer that rejects the associated m= section. In her the transceiver has
either of these cases, it is set to "true", and otherwise been stopped, either by a call to stop or by
applying an answer that rejects the associated "m=" section. In
either of these cases, it is set to "true" and otherwise
will be set to "false".</t> will be set to "false".</t>
<t indent="0" pn="section-4.2.2-2">A stopped RtpTransceiver does not s
<t>A stopped RtpTransceiver does not send any outgoing RTP or end any outgoing RTP or
RTCP or process any incoming RTP or RTCP. It cannot be RTCP or process any incoming RTP or RTCP. It cannot be
restarted.</t> restarted.</t>
</section> </section>
<section title="setDirection" <section anchor="sec.transceiver-set-direction" numbered="true" toc="inc
anchor="sec.transceiver-set-direction"> lude" removeInRFC="false" pn="section-4.2.3">
<name slugifiedName="name-setdirection">setDirection</name>
<t>The setDirection method sets the direction of a <t indent="0" pn="section-4.2.3-1">The setDirection method sets the di
rection of a
transceiver, which affects the direction property of the transceiver, which affects the direction property of the
associated m= section on future calls to createOffer and associated "m=" section on future calls to createOffer and
createAnswer. The permitted values for direction are createAnswer. The permitted values for direction are
"recvonly", "sendrecv", "sendonly", and "inactive", mirroring "recvonly", "sendrecv", "sendonly", and "inactive", mirroring
the identically-named directional attributes defined in the identically named direction attributes defined in
<xref target="RFC4566"></xref>, Section 6.</t> <xref target="RFC4566" sectionFormat="comma" section="6" format="defau
lt" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedContent="R
<t>When creating offers, the transceiver direction is FC4566"/>.</t>
<t indent="0" pn="section-4.2.3-2">When creating offers, the transceiv
er direction is
directly reflected in the output, even for re-offers. When directly reflected in the output, even for re-offers. When
creating answers, the transceiver direction is intersected creating answers, the transceiver direction is intersected
with the offered direction, as explained in with the offered direction, as explained in
<xref target="sec.generating-an-answer" /> below.</t> <xref target="sec.generating-an-answer" format="default" sectionFormat
="of" derivedContent="Section 5.3"/> below.</t>
<t>Note that while setDirection sets the direction property <t indent="0" pn="section-4.2.3-3">Note that while setDirection sets t
of the transceiver immediately ( he direction property
<xref target="sec.transceiver-direction" />), this property of the transceiver immediately (<xref target="sec.transceiver-directio
n" format="default" sectionFormat="of" derivedContent="Section 4.2.4"/>), this p
roperty
does not immediately affect whether the transceiver's does not immediately affect whether the transceiver's
RtpSender will send or its RtpReceiver will receive. The RtpSender will send or its RtpReceiver will receive. The
direction in effect is represented by the currentDirection direction in effect is represented by the currentDirection
property, which is only updated when an answer is property, which is only updated when an answer is
applied.</t> applied.</t>
</section> </section>
<section title="direction" anchor="sec.transceiver-direction"> <section anchor="sec.transceiver-direction" numbered="true" toc="include
" removeInRFC="false" pn="section-4.2.4">
<t>The direction property indicates the last value passed <name slugifiedName="name-direction">direction</name>
<t indent="0" pn="section-4.2.4-1">The direction property indicates th
e last value passed
into setDirection. If setDirection has never been called, it into setDirection. If setDirection has never been called, it
is set to the direction the transceiver was initialized is set to the direction the transceiver was initialized
with.</t> with.</t>
</section> </section>
<section title="currentDirection" <section anchor="sec.transceiver-current-direction" numbered="true" toc=
anchor="sec.transceiver-current-direction"> "include" removeInRFC="false" pn="section-4.2.5">
<name slugifiedName="name-currentdirection">currentDirection</name>
<t>The currentDirection property indicates the last <t indent="0" pn="section-4.2.5-1">The currentDirection property indic
negotiated direction for the transceiver's associated m= ates the last
negotiated direction for the transceiver's associated "m="
section. More specifically, it indicates the section. More specifically, it indicates the
<xref target="RFC3264"></xref> directional attribute of the direction attribute <xref target="RFC3264" format="default" sectionFor
associated m= section in the last applied answer (including mat="of" derivedContent="RFC3264"/> of the
associated "m=" section in the last applied answer (including
provisional answers), with "send" and "recv" directions provisional answers), with "send" and "recv" directions
reversed if it was a remote answer. For example, if the reversed if it was a remote answer. For example, if the
directional attribute for the associated m= section in a direction attribute for the associated "m=" section in a
remote answer is "recvonly", currentDirection is set to remote answer is "recvonly", currentDirection is set to
"sendonly".</t> "sendonly".</t>
<t indent="0" pn="section-4.2.5-2">If an answer that references this t
<t>If an answer that references this transceiver has not yet ransceiver has not yet
been applied, or if the transceiver is stopped, been applied or if the transceiver is stopped,
currentDirection is set to null.</t> currentDirection is set to "null".</t>
</section> </section>
<section title="setCodecPreferences" <section anchor="sec.transceiver-set-codec-preferences" numbered="true"
anchor="sec.transceiver-set-codec-preferences"> toc="include" removeInRFC="false" pn="section-4.2.6">
<name slugifiedName="name-setcodecpreferences">setCodecPreferences</na
<t>The setCodecPreferences method sets the codec preferences me>
<t indent="0" pn="section-4.2.6-1">The setCodecPreferences method sets
the codec preferences
of a transceiver, which in turn affect the presence and order of a transceiver, which in turn affect the presence and order
of codecs of the associated m= section on future calls to of codecs of the associated "m=" section on future calls to
createOffer and createAnswer. Note that setCodecPreferences createOffer and createAnswer. Note that setCodecPreferences
does not directly affect which codec the implementation does not directly affect which codec the implementation
decides to send. It only affects which codecs the decides to send. It only affects which codecs the
implementation indicates that it prefers to receive, via the implementation indicates that it prefers to receive, via the
offer or answer. Even when a codec is excluded by offer or answer. Even when a codec is excluded by
setCodecPreferences, it still may be used to send until the setCodecPreferences, it still may be used to send until the
next offer/answer exchange discards it.</t> next offer/answer exchange discards it.</t>
<t indent="0" pn="section-4.2.6-2">The codec preferences of an RtpTran
<t>The codec preferences of an RtpTransceiver can cause sceiver can cause
codecs to be excluded by subsequent calls to createOffer and codecs to be excluded by subsequent calls to createOffer and
createAnswer, in which case the corresponding media formats createAnswer, in which case the corresponding media formats
in the associated m= section will be excluded. The codec in the associated "m=" section will be excluded. The codec
preferences cannot add media formats that would otherwise not preferences cannot add media formats that would otherwise not
be present.</t> be present.</t>
<t indent="0" pn="section-4.2.6-3">The codec preferences of an RtpTran
<t>The codec preferences of an RtpTransceiver can also sceiver can also
determine the order of codecs in subsequent calls to determine the order of codecs in subsequent calls to
createOffer and createAnswer, in which case the order of the createOffer and createAnswer, in which case the order of the
media formats in the associated m= section will follow the media formats in the associated "m=" section will follow the
specified preferences.</t> specified preferences.</t>
</section> </section>
</section> </section>
</section> </section>
<section title="SDP Interaction Procedures" <section anchor="sec.sdp-interaction-procedure" numbered="true" toc="include
anchor="sec.sdp-interaction-procedure"> " removeInRFC="false" pn="section-5">
<name slugifiedName="name-sdp-interaction-procedures">SDP Interaction Proc
<t>This section describes the specific procedures to be followed edures</name>
<t indent="0" pn="section-5-1">This section describes the specific procedu
res to be followed
when creating and parsing SDP objects.</t> when creating and parsing SDP objects.</t>
<section title="Requirements Overview" <section anchor="sec.requirements-overview" numbered="true" toc="include"
anchor="sec.requirements-overview"> removeInRFC="false" pn="section-5.1">
<name slugifiedName="name-requirements-overview">Requirements Overview</
<t>JSEP implementations must comply with the specifications name>
<t indent="0" pn="section-5.1-1">JSEP implementations <bcp14>MUST</bcp14
> comply with the specifications
listed below that govern the creation and processing of offers listed below that govern the creation and processing of offers
and answers.</t> and answers.</t>
<section title="Usage Requirements" <section anchor="sec.usage-requirements" numbered="true" toc="include" r
anchor="sec.usage-requirements"> emoveInRFC="false" pn="section-5.1.1">
<name slugifiedName="name-usage-requirements">Usage Requirements</name
<t>All session descriptions handled by JSEP implementations, >
both local and remote, MUST indicate support for the <t indent="0" pn="section-5.1.1-1">All session descriptions handled by
JSEP implementations,
both local and remote, <bcp14>MUST</bcp14> indicate support for the
following specifications. If any of these are absent, this following specifications. If any of these are absent, this
omission MUST be treated as an error. omission <bcp14>MUST</bcp14> be treated as an error.
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>ICE, as specified in -5.1.1-2">
<xref target="RFC8445"></xref>, MUST be used. Note that the <li pn="section-5.1.1-2.1">ICE, as specified in
remote endpoint may use a Lite implementation; <xref target="RFC8445" format="default" sectionFormat="of" derivedCo
implementations MUST properly handle remote endpoints which ntent="RFC8445"/>, <bcp14>MUST</bcp14> be used. Note that the
do ICE-Lite.</t> remote endpoint may use a lite implementation;
implementations <bcp14>MUST</bcp14> properly handle remote endpoints
<t>DTLS that
<xref target="RFC6347" /> or DTLS-SRTP use ICE-lite. The remote endpoint may also use
<xref target="RFC5763"></xref>, MUST be used, as an older version of ICE; implementations <bcp14>MUST</bcp14> properly handle rem
ote endpoints that use ICE
as specified in <xref target="RFC5245" format="default" sectionFormat="of" deriv
edContent="RFC5245"/>.</li>
<li pn="section-5.1.1-2.2">DTLS
<xref target="RFC6347" format="default" sectionFormat="of" derivedCo
ntent="RFC6347"/> or DTLS-SRTP
<xref target="RFC5763" format="default" sectionFormat="of" derivedCo
ntent="RFC5763"/> <bcp14>MUST</bcp14> be used, as
appropriate for the media type, as specified in appropriate for the media type, as specified in
<xref target="I-D.ietf-rtcweb-security-arch" /></t> <xref target="RFC8827" format="default" sectionFormat="of" derivedCo
</list></t> ntent="RFC8827"/>.</li>
</ul>
<t>The SDES SRTP keying mechanism from <t indent="0" pn="section-5.1.1-3">The SDP security descriptions mecha
<xref target="RFC4568" /> MUST NOT be used, as discussed in nism for SRTP keying
<xref target="I-D.ietf-rtcweb-security-arch" />.</t> <xref target="RFC4568" format="default" sectionFormat="of" derivedCont
ent="RFC4568"/> <bcp14>MUST NOT</bcp14> be used, as discussed in
<xref target="RFC8827" format="default" sectionFormat="of" derivedCont
ent="RFC8827"/>.</t>
</section> </section>
<section title="Profile Names and Interoperability" <section anchor="sec.profile-names" numbered="true" toc="include" remove
anchor="sec.profile-names"> InRFC="false" pn="section-5.1.2">
<name slugifiedName="name-profile-names-and-interoper">Profile Names a
<t>For media m= sections, JSEP implementations MUST support nd Interoperability</name>
<t indent="0" pn="section-5.1.2-1">For media "m=" sections, JSEP imple
mentations <bcp14>MUST</bcp14> support
the "UDP/TLS/RTP/SAVPF" profile specified in the "UDP/TLS/RTP/SAVPF" profile specified in
<xref target="RFC5764"></xref> as well as the "TCP/DTLS/RTP/SAVPF" <xref target="RFC5764" format="default" sectionFormat="of" derivedCont
profile specified in <xref target="RFC7850"></xref>, and MUST indicate ent="RFC5764"/> as well as the "TCP/DTLS/RTP/SAVPF"
one of these profiles for each media m= line they produce in an offer. profile specified in <xref target="RFC7850" format="default" sectionFo
For data m= sections, implementations MUST support the rmat="of" derivedContent="RFC7850"/> and <bcp14>MUST</bcp14> indicate
"UDP/DTLS/SCTP" profile as well as the "TCP/DTLS/SCTP" profile, and one of these profiles for each media "m=" line they produce in an offe
MUST indicate one of these profiles for each data m= line they produce r.
For data "m=" sections, implementations <bcp14>MUST</bcp14> support th
e
"UDP/DTLS/SCTP" profile as well as the "TCP/DTLS/SCTP" profile and
<bcp14>MUST</bcp14> indicate one of these profiles for each data "m="
line they produce
in an offer. The exact profile to use is determined by the protocol in an offer. The exact profile to use is determined by the protocol
associated with the current default or selected ICE candidate, as associated with the current default or selected ICE candidate, as
described in described in
<xref target="I-D.ietf-mmusic-ice-sip-sdp"></xref>, Section 3.2.1.2. <xref target="RFC8839" sectionFormat="comma" section="4.2.1.2" format=
</t> "default" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-4.2.1.2" deriv
edContent="RFC8839"/>.</t>
<t>Unfortunately, in an attempt at compatibility, some <t indent="0" pn="section-5.1.2-2">Unfortunately, in an attempt at com
patibility, some
endpoints generate other profile strings even when they mean endpoints generate other profile strings even when they mean
to support one of these profiles. For instance, an endpoint to support one of these profiles. For instance, an endpoint
might generate "RTP/AVP" but supply "a=fingerprint" and might generate "RTP/AVP" but supply "a=fingerprint" and
"a=rtcp-fb" attributes, indicating its willingness to support "a=rtcp-fb" attributes, indicating its willingness to support
"UDP/TLS/RTP/SAVPF" or "TCP/DTLS/RTP/SAVPF". In order to "UDP/TLS/RTP/SAVPF" or "TCP/DTLS/RTP/SAVPF". In order to
simplify compatibility with such endpoints, JSEP simplify compatibility with such endpoints, JSEP
implementations MUST follow the following rules when implementations <bcp14>MUST</bcp14> follow the following rules when
processing the media m= sections in a received offer:</t> processing the media "m=" sections in a received offer:</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t> -5.1.2-3">
<list style="symbols"> <li pn="section-5.1.2-3.1">
<t indent="0" pn="section-5.1.2-3.1.1">Any profile in the offer ma
<t>Any profile in the offer matching one of the following tching one of the following
MUST be accepted: <bcp14>MUST</bcp14> be accepted:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="sec
<t>"RTP/AVP" (Defined in tion-5.1.2-3.1.2">
<xref target="RFC4566"></xref>, Section 8.2.2)</t> <li pn="section-5.1.2-3.1.2.1">"RTP/AVP" (defined in
<xref target="RFC4566" sectionFormat="comma" section="8.2.2" for
<t>"RTP/AVPF" (Defined in mat="default" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-8.2.2" der
<xref target="RFC4585"></xref>, Section 9)</t> ivedContent="RFC4566"/>)</li>
<li pn="section-5.1.2-3.1.2.2">"RTP/AVPF" (defined in
<t>"RTP/SAVP" (Defined in <xref target="RFC4585" sectionFormat="comma" section="9" format=
<xref target="RFC3711"></xref>, Section 12)</t> "default" derivedLink="https://rfc-editor.org/rfc/rfc4585#section-9" derivedCont
ent="RFC4585"/>)</li>
<t>"RTP/SAVPF" (Defined in <li pn="section-5.1.2-3.1.2.3">"RTP/SAVP" (defined in
<xref target="RFC5124"></xref>, Section 6)</t> <xref target="RFC3711" sectionFormat="comma" section="12" format
="default" derivedLink="https://rfc-editor.org/rfc/rfc3711#section-12" derivedCo
<t>"TCP/DTLS/RTP/SAVP" (Defined in ntent="RFC3711"/>)</li>
<xref target="RFC7850"></xref>, Section 3.4)</t> <li pn="section-5.1.2-3.1.2.4">"RTP/SAVPF" (defined in
<xref target="RFC5124" sectionFormat="comma" section="6" format=
<t>"TCP/DTLS/RTP/SAVPF" (Defined in "default" derivedLink="https://rfc-editor.org/rfc/rfc5124#section-6" derivedCont
<xref target="RFC7850"></xref>, Section 3.5)</t> ent="RFC5124"/>)</li>
<li pn="section-5.1.2-3.1.2.5">"TCP/DTLS/RTP/SAVP" (defined in
<t>"UDP/TLS/RTP/SAVP" (Defined in <xref target="RFC7850" sectionFormat="comma" section="3.4" forma
<xref target="RFC5764"></xref>, Section 9)</t> t="default" derivedLink="https://rfc-editor.org/rfc/rfc7850#section-3.4" derived
Content="RFC7850"/>)</li>
<t>"UDP/TLS/RTP/SAVPF" (Defined in <li pn="section-5.1.2-3.1.2.6">"TCP/DTLS/RTP/SAVPF" (defined in
<xref target="RFC5764"></xref>, Section 9)</t> <xref target="RFC7850" sectionFormat="comma" section="3.5" forma
</list></t> t="default" derivedLink="https://rfc-editor.org/rfc/rfc7850#section-3.5" derived
Content="RFC7850"/>)</li>
<t>The profile in any "m=" line in any generated answer <li pn="section-5.1.2-3.1.2.7">"UDP/TLS/RTP/SAVP" (defined in
MUST exactly match the profile provided in the offer.</t> <xref target="RFC5764" sectionFormat="comma" section="9" format=
"default" derivedLink="https://rfc-editor.org/rfc/rfc5764#section-9" derivedCont
<t>Because DTLS-SRTP is REQUIRED, the choice of SAVP or ent="RFC5764"/>)</li>
<li pn="section-5.1.2-3.1.2.8">"UDP/TLS/RTP/SAVPF" (defined in
<xref target="RFC5764" sectionFormat="comma" section="9" format=
"default" derivedLink="https://rfc-editor.org/rfc/rfc5764#section-9" derivedCont
ent="RFC5764"/>)</li>
</ul>
</li>
<li pn="section-5.1.2-3.2">The profile in any "m=" line in any gener
ated answer
<bcp14>MUST</bcp14> exactly match the profile provided in the offe
r.</li>
<li pn="section-5.1.2-3.3">Because DTLS-SRTP is <bcp14>REQUIRED</bcp
14>, the choice of SAVP or
AVP has no effect; support for DTLS-SRTP is determined by AVP has no effect; support for DTLS-SRTP is determined by
the presence of one or more "a=fingerprint" attribute. the presence of one or more "a=fingerprint" attributes.
Note that lack of an "a=fingerprint" attribute will lead Note that lack of an "a=fingerprint" attribute will lead
to negotiation failure.</t> to negotiation failure.</li>
<li pn="section-5.1.2-3.4">The use of AVPF or AVP simply controls th
<t>The use of AVPF or AVP simply controls the timing e timing
rules used for RTCP feedback. If AVPF is provided, or an rules used for RTCP feedback. If AVPF is provided or an
"a=rtcp-fb" attribute is present, assume AVPF timing, "a=rtcp-fb" attribute is present, assume AVPF timing,
i.e., a default value of "trr-int=0". Otherwise, assume i.e., a default value of "trr-int=0". Otherwise, assume
that AVPF is being used in an AVP compatible mode and use that AVPF is being used in an AVP-compatible mode and use
a value of "trr-int=4000".</t> a value of "trr-int=4000".</li>
<li pn="section-5.1.2-3.5">For data "m=" sections, implementations <
<t>For data m= sections, implementations MUST support bcp14>MUST</bcp14> support
receiving the "UDP/DTLS/SCTP", "TCP/DTLS/SCTP", or receiving the "UDP/DTLS/SCTP", "TCP/DTLS/SCTP", or
"DTLS/SCTP" (for backwards compatibility) profiles.</t> "DTLS/SCTP" (for backwards compatibility) profiles.</li>
</list> </ul>
</t> <t indent="0" pn="section-5.1.2-4">Note that re-offers by JSEP impleme
ntations <bcp14>MUST</bcp14> use the
<t>Note that re-offers by JSEP implementations MUST use the
correct profile strings even if the initial offer/answer correct profile strings even if the initial offer/answer
exchange used an (incorrect) older profile string. This exchange used an (incorrect) older profile string. This
simplifies JSEP behavior, with minimal downside, as any simplifies JSEP behavior, with minimal downside, as any
remote endpoint that fails to handle such a re-offer will remote endpoint that fails to handle such a re-offer will
also fail to handle a JSEP endpoint's initial offer.</t> also fail to handle a JSEP endpoint's initial offer.</t>
</section> </section>
</section> </section>
<section anchor="sec-create-offer" title="Constructing an Offer"> <section anchor="sec-create-offer" numbered="true" toc="include" removeInR
FC="false" pn="section-5.2">
<t>When createOffer is called, a new SDP description must be <name slugifiedName="name-constructing-an-offer">Constructing an Offer</
name>
<t indent="0" pn="section-5.2-1">When createOffer is called, a new SDP d
escription <bcp14>MUST</bcp14> be
created that includes the functionality specified in created that includes the functionality specified in
<xref target="I-D.ietf-rtcweb-rtp-usage"></xref>. The exact <xref target="RFC8834" format="default" sectionFormat="of" derivedConten t="RFC8834"/>. The exact
details of this process are explained below.</t> details of this process are explained below.</t>
<section title="Initial Offers" anchor="sec.initial-offers"> <section anchor="sec.initial-offers" numbered="true" toc="include" remov
eInRFC="false" pn="section-5.2.1">
<t>When createOffer is called for the first time, the result <name slugifiedName="name-initial-offers">Initial Offers</name>
<t indent="0" pn="section-5.2.1-1">When createOffer is called for the
first time, the result
is known as the initial offer.</t> is known as the initial offer.</t>
<t indent="0" pn="section-5.2.1-2">The first step in generating an ini
<t>The first step in generating an initial offer is to tial offer is to
generate session-level attributes, as specified in generate session-level attributes, as specified in
<xref target="RFC4566"></xref>, Section 5. Specifically: <xref target="RFC4566" sectionFormat="comma" section="5" format="defau
<list style="symbols"> lt" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5" derivedContent="R
FC4566"/>. Specifically:
<t>The first SDP line MUST be "v=0", as specified in </t>
<xref target="RFC4566"></xref>, Section 5.1</t> <ul spacing="normal" bare="false" empty="false" indent="3" pn="section
-5.2.1-3">
<t>The second SDP line MUST be an "o=" line, as specified <li pn="section-5.2.1-3.1">The first SDP line <bcp14>MUST</bcp14> be
"v=0" as defined in
<xref target="RFC4566" sectionFormat="comma" section="5.1" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.1" derivedCont
ent="RFC4566"/>.</li>
<li pn="section-5.2.1-3.2">The second SDP line <bcp14>MUST</bcp14> b
e an "o=" line as defined
in in
<xref target="RFC4566"></xref>, Section 5.2. The value of <xref target="RFC4566" sectionFormat="comma" section="5.2" format="d
the &lt;username&gt; field SHOULD be "-". The sess-id MUST efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.2" derivedCont
ent="RFC4566"/>.
The value of
the &lt;username&gt; field <bcp14>SHOULD</bcp14> be "-". The &lt;ses
s-id&gt; <bcp14>MUST</bcp14>
be representable by a 64-bit signed integer, and the be representable by a 64-bit signed integer, and the
value MUST be less than (2**63)-1. It is RECOMMENDED that the value <bcp14>MUST</bcp14> be less than
sess-id be constructed by generating a 64-bit quantity with 2<sup>63</sup>-1.
It is <bcp14>RECOMMENDED</bcp14> that the
&lt;sess-id&gt; be constructed by generating a 64-bit quantity with
the highest bit set to zero and the remaining 63 the highest bit set to zero and the remaining 63
bits being cryptographically random. The value of the bits being cryptographically random. The value of the
&lt;nettype&gt; &lt;addrtype&gt; &lt;unicast-address&gt; &lt;nettype&gt; &lt;addrtype&gt; &lt;unicast-address&gt;
tuple SHOULD be set to a non-meaningful address, such as IN tuple <bcp14>SHOULD</bcp14> be set to a non-meaningful address, such as IN
IP4 0.0.0.0, to prevent leaking a local IP address in this IP4 0.0.0.0, to prevent leaking a local IP address in this
field; this problem is discussed in field; this problem is discussed in
<xref target="I-D.ietf-rtcweb-ip-handling" />. As mentioned in <xref target="RFC8828" format="default" sectionFormat="of" derivedCo
<xref target="RFC4566"></xref>, the entire o= line needs to ntent="RFC8828"/>. As mentioned in
<xref target="RFC4566" format="default" sectionFormat="of" derivedCo
ntent="RFC4566"/>, the entire "o=" line needs to
be unique, but selecting a random number for be unique, but selecting a random number for
&lt;sess-id&gt; is sufficient to accomplish this.</t> &lt;sess-id&gt; is sufficient to accomplish this.</li>
<li pn="section-5.2.1-3.3">The third SDP line <bcp14>MUST</bcp14> be
<t>The third SDP line MUST be a "s=" line, as specified in a "s=" line as defined in
<xref target="RFC4566"></xref>, Section 5.3; to match the <xref target="RFC4566" sectionFormat="comma" section="5.3" format="d
"o=" line, a single dash SHOULD be used as the session efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.3" derivedCont
name, e.g. "s=-". Note that this differs from the advice in ent="RFC4566"/>; to match the
"o=" line, a single dash <bcp14>SHOULD</bcp14> be used as the sessio
n
name, e.g., "s=-". Note that this differs from the advice in
<xref target="RFC4566" /> which proposes a single space, but <xref target="RFC4566" format="default" sectionFormat="of" derivedCo ntent="RFC4566"/>, which proposes a single space, but
as both "o=" and "s=" are meaningless in JSEP, having the as both "o=" and "s=" are meaningless in JSEP, having the
same meaningless value seems clearer.</t> same meaningless value seems clearer.</li>
<li pn="section-5.2.1-3.4">Session Information ("i="), URI ("u="), E
<t>Session Information ("i="), URI ("u="), Email Address mail Address
("e="), Phone Number ("p="), Repeat Times ("r="), and Time ("e="), Phone Number ("p="), Repeat Times ("r="), and Time
Zones ("z=") lines are not useful in this context and Zones ("z=") lines are not useful in this context and
SHOULD NOT be included.</t> <bcp14>SHOULD NOT</bcp14> be included.</li>
<li pn="section-5.2.1-3.5">Encryption Keys ("k=") lines do not provi
<t>Encryption Keys ("k=") lines do not provide sufficient de sufficient
security and MUST NOT be included.</t> security and <bcp14>MUST NOT</bcp14> be included.</li>
<li pn="section-5.2.1-3.6">A "t=" line <bcp14>MUST</bcp14> be added,
<t>A "t=" line MUST be added, as specified in as specified in
<xref target="RFC4566"></xref>, Section 5.9; both <xref target="RFC4566" sectionFormat="comma" section="5.9" format="d
&lt;start-time&gt; and &lt;stop-time&gt; SHOULD be set to efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.9" derivedCont
zero, e.g. "t=0 0".</t> ent="RFC4566"/>; both
&lt;start-time&gt; and &lt;stop-time&gt; <bcp14>SHOULD</bcp14> be se
<t>An "a=ice-options" line with the "trickle" and "ice2" t to
options MUST be added, as specified in <xref zero, e.g., "t=0 0".</li>
target="I-D.ietf-ice-trickle"></xref>, Section 3 and <li pn="section-5.2.1-3.7">An "a=ice-options" line with the "trickle
<xref target="RFC8445"></xref>, Section 10.</t> " and "ice2"
options <bcp14>MUST</bcp14> be added, as specified in <xref target="
<t>If WebRTC identity is being used, an "a=identity" line RFC8840" sectionFormat="comma" section="4.1.1" format="default" derivedLink="htt
as described in ps://rfc-editor.org/rfc/rfc8840#section-4.1.1" derivedContent="RFC8840"/> and
<xref target="I-D.ietf-rtcweb-security-arch" />, Section <xref target="RFC8445" sectionFormat="comma" section="10" format="de
5.</t> fault" derivedLink="https://rfc-editor.org/rfc/rfc8445#section-10" derivedConten
</list></t> t="RFC8445"/>.
</li>
<t>The next step is to generate m= sections, as specified in <li pn="section-5.2.1-3.8">If WebRTC identity is being used, an "a=i
<xref target="RFC4566" />, Section 5.14. An m= section is dentity" line
<bcp14>MUST</bcp14> be added, as described in
<xref target="RFC8827" sectionFormat="comma" section="5" format="def
ault" derivedLink="https://rfc-editor.org/rfc/rfc8827#section-5" derivedContent=
"RFC8827"/>.</li>
</ul>
<t indent="0" pn="section-5.2.1-4">The next step is to generate "m=" s
ections, as specified in
<xref target="RFC4566" sectionFormat="comma" section="5.14" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.14" derivedCont
ent="RFC4566"/>. An "m=" section is
generated for each RtpTransceiver that has been added to the generated for each RtpTransceiver that has been added to the
PeerConnection, excluding any stopped RtpTransceivers; this PeerConnection, excluding any stopped RtpTransceivers; this
is done in the order the RtpTransceivers were added to the is done in the order the RtpTransceivers were added to the
PeerConnection. If there are no such RtpTransceivers, no m= PeerConnection. If there are no such RtpTransceivers, no "m="
sections are generated; more can be added later, as discussed sections are generated; more can be added later, as discussed
in in
<xref target="RFC3264" />, Section 5.</t> <xref target="RFC3264" sectionFormat="comma" section="5" format="defau
lt" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-5" derivedContent="R
<t>For each m= section generated for an RtpTransceiver, FC3264"/>.</t>
<t indent="0" pn="section-5.2.1-5">For each "m=" section generated for
an RtpTransceiver,
establish a mapping between the transceiver and the index of establish a mapping between the transceiver and the index of
the generated m= section.</t> the generated "m=" section.</t>
<t indent="0" pn="section-5.2.1-6">Each "m=" section, provided it is n
<t>Each m= section, provided it is not marked as bundle-only, ot marked as bundle-only,
MUST generate a unique set of ICE credentials and gather its <bcp14>MUST</bcp14> contain a unique set of ICE credentials and
own unique set of ICE candidates. Bundle-only m= sections a unique set of ICE candidates. Bundle-only "m=" sections
MUST NOT contain any ICE credentials and MUST NOT gather any <bcp14>MUST NOT</bcp14> contain any ICE credentials and <bcp14>MUST NO
T</bcp14> gather any
candidates.</t> candidates.</t>
<t indent="0" pn="section-5.2.1-7">For DTLS, all "m=" sections <bcp14>
<t>For DTLS, all m= sections MUST use all the certificate(s) MUST</bcp14> use any and all certificates
that have been specified for the PeerConnection; as a result, that have been specified for the PeerConnection; as a result,
they MUST all have the same they <bcp14>MUST</bcp14> all have the same fingerprint value or values
<xref target="RFC8122"></xref> fingerprint value(s), or these <xref target="RFC8122" format="default" sectionFormat="of" derivedCont
value(s) MUST be session-level attributes.</t> ent="RFC8122"/>, or these
values <bcp14>MUST</bcp14> be session-level attributes.</t>
<t>Each m= section should be generated as specified in <t indent="0" pn="section-5.2.1-8">Each "m=" section <bcp14>MUST</bcp1
<xref target="RFC4566"></xref>, Section 5.14. For the m= line 4> be generated as specified in
itself, the following rules MUST be followed: <xref target="RFC4566" sectionFormat="comma" section="5.14" format="de
<list style="symbols"> fault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.14" derivedCont
ent="RFC4566"/>. For the "m=" line
<t>If the m= section is marked as bundle-only, then the itself, the following rules <bcp14>MUST</bcp14> be followed:
port value MUST be set to 0. Otherwise, the port value is </t>
set to the port of the default ICE candidate for this m= <ul spacing="normal" bare="false" empty="false" indent="3" pn="section
-5.2.1-9">
<li pn="section-5.2.1-9.1">If the "m=" section is marked as bundle-o
nly, then the
&lt;port&gt; value <bcp14>MUST</bcp14> be set to zero. Otherwise, th
e &lt;port&gt; value is
set to the port of the default ICE candidate for this "m="
section, but given that no candidates are available yet, section, but given that no candidates are available yet,
the "dummy" port value of 9 (Discard) MUST be used, as the default port value of 9 (Discard) <bcp14>MUST</bcp14> be used, a s
indicated in indicated in
<xref target="I-D.ietf-ice-trickle"></xref>, Section <xref target="RFC8840" sectionFormat="comma" section="4.1.1" format=
5.1.</t> "default" derivedLink="https://rfc-editor.org/rfc/rfc8840#section-4.1.1" derived
Content="RFC8840"/>.</li>
<t>To properly indicate use of DTLS, the &lt;proto&gt; <li pn="section-5.2.1-9.2">To properly indicate use of DTLS, the &lt
field MUST be set to "UDP/TLS/RTP/SAVPF", as specified in ;proto&gt;
<xref target="RFC5764" />, Section 8.</t> field <bcp14>MUST</bcp14> be set to "UDP/TLS/RTP/SAVPF", as specifie
d in
<t>If codec preferences have been set for the associated <xref target="RFC5764" sectionFormat="comma" section="8" format="def
transceiver, media formats MUST be generated in the ault" derivedLink="https://rfc-editor.org/rfc/rfc5764#section-8" derivedContent=
corresponding order, and MUST exclude any codecs not "RFC5764"/>.</li>
present in the codec preferences.</t> <li pn="section-5.2.1-9.3">If codec preferences have been set for th
e associated
<t>Unless excluded by the above restrictions, the media transceiver, media formats <bcp14>MUST</bcp14> be generated in the
formats MUST include the mandatory audio/video codecs as corresponding order and <bcp14>MUST</bcp14> exclude any codecs not
present in the codec preferences.</li>
<li pn="section-5.2.1-9.4">Unless excluded by the above restrictions
, the media
formats <bcp14>MUST</bcp14> include the mandatory audio/video codecs
as
specified in specified in
<xref target="RFC7874"></xref>, Section 3, and <xref target="RFC7874" sectionFormat="comma" section="3" format="def
<xref target="RFC7742"></xref>, Section 5.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc7874#section-3" derivedContent=
</list></t> "RFC7874"/> and
<xref target="RFC7742" sectionFormat="comma" section="5" format="def
<t>The m= line MUST be followed immediately by a "c=" line, ault" derivedLink="https://rfc-editor.org/rfc/rfc7742#section-5" derivedContent=
"RFC7742"/>.</li>
</ul>
<t indent="0" pn="section-5.2.1-10">The "m=" line <bcp14>MUST</bcp14>
be followed immediately by a "c=" line,
as specified in as specified in
<xref target="RFC4566"></xref>, Section 5.7. Again, as no <xref target="RFC4566" sectionFormat="comma" section="5.7" format="def
candidates are available yet, the "c=" line must contain the ault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.7" derivedConten
"dummy" value "IN IP4 0.0.0.0", as defined in t="RFC4566"/>. Again, as no
<xref target="I-D.ietf-ice-trickle"></xref>, Section 5.1.</t> candidates are available yet, the "c=" line <bcp14>MUST</bcp14> contai
n the
<t> default value "IN IP4 0.0.0.0", as defined in
<xref target="I-D.ietf-mmusic-sdp-mux-attributes" /> groups <xref target="RFC8840" sectionFormat="comma" section="4.1.1" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc8840#section-4.1.1" derivedCo
ntent="RFC8840"/>.</t>
<t indent="0" pn="section-5.2.1-11">
<xref target="RFC8859" format="default" sectionFormat="of" derivedCont
ent="RFC8859"/> groups
SDP attributes into different categories. To avoid SDP attributes into different categories. To avoid
unnecessary duplication when bundling, attributes of category unnecessary duplication when bundling, attributes of category
IDENTICAL or TRANSPORT MUST NOT be repeated in bundled m= IDENTICAL or TRANSPORT <bcp14>MUST NOT</bcp14> be repeated in bundled "m="
sections, repeating the guidance from sections, repeating the guidance from
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation" />, <xref target="RFC8843" sectionFormat="comma" section="7.1.3" format="d
Section 8.1. This includes m= sections for which bundling has efault" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-7.1.3" derivedCo
been negotiated and is still desired, as well as m= sections ntent="RFC8843"/>.
This includes "m=" sections for which bundling has
been negotiated and is still desired, as well as "m=" sections
marked as bundle-only.</t> marked as bundle-only.</t>
<t indent="0" pn="section-5.2.1-12">The following attributes, which ar
<t>The following attributes, which are of a category other e of a category other
than IDENTICAL or TRANSPORT, MUST be included in each m= than IDENTICAL or TRANSPORT, <bcp14>MUST</bcp14> be included in each "
m="
section:</t> section:</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t> -5.2.1-13">
<list style="symbols"> <li pn="section-5.2.1-13.1">An "a=mid" line, as specified in
<xref target="RFC5888" sectionFormat="comma" section="4" format="d
<t>An "a=mid" line, as specified in efault" derivedLink="https://rfc-editor.org/rfc/rfc5888#section-4" derivedConten
<xref target="RFC5888"></xref>, Section 4. All MID values t="RFC5888"/>. All MID values
MUST be generated in a fashion that does not leak user <bcp14>MUST</bcp14> be generated in a fashion that does not leak u
ser
information, e.g., randomly or using a per-PeerConnection information, e.g., randomly or using a per-PeerConnection
counter, and SHOULD be 3 bytes or less, to allow them to counter, and <bcp14>SHOULD</bcp14> be 3 bytes or less, to allow th em to
efficiently fit into the RTP header extension defined in efficiently fit into the RTP header extension defined in
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation"> <xref target="RFC8843" sectionFormat="comma" section="15.2" format
</xref>, Section 14. Note that this does not set the ="default" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-15.2" derived
Content="RFC8843"/>.
Note that this does not set the
RtpTransceiver mid property, as that only occurs when the RtpTransceiver mid property, as that only occurs when the
description is applied. The generated MID value can be description is applied. The generated MID value can be
considered a "proposed" MID at this point.</t> considered a "proposed" MID at this point.</li>
<li pn="section-5.2.1-13.2">A direction attribute that is the same a
<t>A direction attribute which is the same as that of the s that of the
associated transceiver.</t> associated transceiver.</li>
<li pn="section-5.2.1-13.3">For each media format on the "m=" line,
<t>For each media format on the m= line, "a=rtpmap" and "a=rtpmap" and "a=fmtp" lines, as specified in
"a=fmtp" lines, as specified in <xref target="RFC4566" sectionFormat="comma" section="6" format="d
<xref target="RFC4566"></xref>, Section 6, and efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedConten
<xref target="RFC3264"></xref>, Section 5.1.</t> t="RFC4566"/> and
<xref target="RFC3264" sectionFormat="comma" section="5.1" format=
<t>For each primary codec where RTP retransmission should "default" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-5.1" derivedCo
ntent="RFC3264"/>.</li>
<li pn="section-5.2.1-13.4">For each primary codec where RTP retrans
mission should
be used, a corresponding "a=rtpmap" line indicating "rtx" be used, a corresponding "a=rtpmap" line indicating "rtx"
with the clock rate of the primary codec and an "a=fmtp" with the clock rate of the primary codec and an "a=fmtp"
line that references the payload type of the primary line that references the payload type of the primary
codec, as specified in codec, as specified in
<xref target="RFC4588"></xref>, Section 8.1.</t> <xref target="RFC4588" sectionFormat="comma" section="8.1" format=
"default" derivedLink="https://rfc-editor.org/rfc/rfc4588#section-8.1" derivedCo
<t>For each supported FEC mechanism, "a=rtpmap" and ntent="RFC4588"/>.</li>
<li pn="section-5.2.1-13.5">For each supported Forward Error Correct
ion (FEC) mechanism, "a=rtpmap" and
"a=fmtp" lines, as specified in "a=fmtp" lines, as specified in
<xref target="RFC4566"></xref>, Section 6. The FEC <xref target="RFC4566" sectionFormat="comma" section="6" format="d
mechanisms that MUST be supported are specified in efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedConten
<xref target="I-D.ietf-rtcweb-fec"></xref>, Section 6, t="RFC4566"/>. The FEC
mechanisms that <bcp14>MUST</bcp14> be supported are specified in
<xref target="RFC8854" sectionFormat="comma" section="7" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc8854#section-7" derivedConten
t="RFC8854"/>,
and specific usage for each media type is outlined in and specific usage for each media type is outlined in
Sections 4 and 5.</t> Sections <xref target="sec.interface" format="counter" sectionForm
at="of" derivedContent="4"/> and <xref target="sec.sdp-interaction-procedure" fo
<t>If this m= section is for media with configurable rmat="counter" sectionFormat="of" derivedContent="5"/>.</li>
<li pn="section-5.2.1-13.6">If this "m=" section is for media with c
onfigurable
durations of media per packet, e.g., audio, an durations of media per packet, e.g., audio, an
"a=maxptime" line, indicating the maximum amount of "a=maxptime" line, indicating the maximum amount of
media, specified in milliseconds, that can be media, specified in milliseconds, that can be
encapsulated in each packet, as specified in encapsulated in each packet, as specified in
<xref target="RFC4566"></xref>, Section 6. This value is <xref target="RFC4566" sectionFormat="comma" section="6" format="d efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedConten t="RFC4566"/>. This value is
set to the smallest of the maximum duration values across set to the smallest of the maximum duration values across
all the codecs included in the m= section.</t> all the codecs included in the "m=" section.</li>
<li pn="section-5.2.1-13.7">If this "m=" section is for video media
<t>If this m= section is for video media, and there are and there are
known limitations on the size of images which can be known limitations on the size of images that can be
decoded, an "a=imageattr" line, as specified in decoded, an "a=imageattr" line, as specified in
<xref target="sec.imageattr"></xref>.</t> <xref target="sec.imageattr" format="default" sectionFormat="of" d
erivedContent="Section 3.6"/>.</li>
<t>For each supported RTP header extension, an "a=extmap" <li pn="section-5.2.1-13.8">For each supported RTP header extension,
an "a=extmap"
line, as specified in line, as specified in
<xref target="RFC5285"></xref>, Section 5. The list of <xref target="RFC5285" sectionFormat="comma" section="5" format="d
header extensions that SHOULD/MUST be supported is efault" derivedLink="https://rfc-editor.org/rfc/rfc5285#section-5" derivedConten
t="RFC5285"/>.
The list of
header extensions that <bcp14>SHOULD</bcp14>/<bcp14>MUST</bcp14> b
e supported is
specified in specified in
<xref target="I-D.ietf-rtcweb-rtp-usage"></xref>, Section <xref target="RFC8834" sectionFormat="comma" section="5.2" format=
5.2. Any header extensions that require encryption MUST "default" derivedLink="https://rfc-editor.org/rfc/rfc8834#section-5.2" derivedCo
ntent="RFC8834"/>. Any header extensions that require encryption <bcp14>MUST</bc
p14>
be specified as indicated in be specified as indicated in
<xref target="RFC6904"></xref>, Section 4.</t> <xref target="RFC6904" sectionFormat="comma" section="4" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc6904#section-4" derivedConten
<t>For each supported RTCP feedback mechanism, an t="RFC6904"/>.</li>
<li pn="section-5.2.1-13.9">For each supported RTCP feedback mechani
sm, an
"a=rtcp-fb" line, as specified in "a=rtcp-fb" line, as specified in
<xref target="RFC4585"></xref>, Section 4.2. The list of <xref target="RFC4585" sectionFormat="comma" section="4.2" format=
RTCP feedback mechanisms that SHOULD/MUST be supported is "default" derivedLink="https://rfc-editor.org/rfc/rfc4585#section-4.2" derivedCo
ntent="RFC4585"/>. The list of
RTCP feedback mechanisms that <bcp14>SHOULD</bcp14>/<bcp14>MUST</b
cp14> be supported is
specified in specified in
<xref target="I-D.ietf-rtcweb-rtp-usage"></xref>, Section <xref target="RFC8834" sectionFormat="comma" section="5.1" format=
5.1.</t> "default" derivedLink="https://rfc-editor.org/rfc/rfc8834#section-5.1" derivedCo
ntent="RFC8834"/>.</li>
<t>If the RtpTransceiver has a sendrecv or sendonly <li pn="section-5.2.1-13.10">
<t indent="0" pn="section-5.2.1-13.10.1">If the RtpTransceiver has
a sendrecv or sendonly
direction: direction:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="sec
<t>For each MediaStream that was associated with the tion-5.2.1-13.10.2">
<li pn="section-5.2.1-13.10.2.1">For each MediaStream that was a
ssociated with the
transceiver when it was created via addTrack or transceiver when it was created via addTrack or
addTransceiver, an "a=msid" line, as specified in addTransceiver, an "a=msid" line, as specified in
<xref target="I-D.ietf-mmusic-msid"></xref>, Section 2, <xref target="RFC8830" sectionFormat="comma" section="2" format=
but omitting the "appdata" field.</t> "default" derivedLink="https://rfc-editor.org/rfc/rfc8830#section-2" derivedCont
</list></t> ent="RFC8830"/>,
but omitting the "appdata" field.</li>
<t>If the RtpTransceiver has a sendrecv or sendonly </ul>
direction, and the application has specified RID values </li>
<li pn="section-5.2.1-13.11">If the RtpTransceiver has a sendrecv or
sendonly
direction, and the application has specified a rid-id for an encod
ing,
or has specified more than one encoding in the or has specified more than one encoding in the
RtpSenders's parameters, an "a=rid" line for each RtpSenders's parameters, an "a=rid" line for each
encoding specified. The "a=rid" line is specified in encoding specified. The "a=rid" line is specified in
<xref target="I-D.ietf-mmusic-rid"></xref>, and its <xref target="RFC8851" format="default" sectionFormat="of" derived
direction MUST be "send". If the application has chosen a Content="RFC8851"/>, and its
RID value, it MUST be used as the rid-identifier; direction <bcp14>MUST</bcp14> be "send". If the application has ch
otherwise a RID value MUST be generated by the osen a
implementation. RID values MUST be generated in a fashion rid-id, it <bcp14>MUST</bcp14> be used;
otherwise, a rid-id <bcp14>MUST</bcp14> be generated by the
implementation. rid-ids <bcp14>MUST</bcp14> be generated in a fash
ion
that does not leak user information, e.g., randomly or that does not leak user information, e.g., randomly or
using a per-PeerConnection counter, and SHOULD be 3 bytes using a per-PeerConnection counter (see guidance at the end
of <xref target="RFC8852" sectionFormat="comma" section="3.3" form
at="default" derivedLink="https://rfc-editor.org/rfc/rfc8852#section-3.3" derive
dContent="RFC8852"/>), and <bcp14>SHOULD</bcp14> be 3 bytes
or less, to allow them to efficiently fit into the RTP or less, to allow them to efficiently fit into the RTP
header extension defined in header extensions defined in
<xref target="I-D.ietf-avtext-rid"></xref>, Section 3. If <xref target="RFC8852" sectionFormat="comma" section="3.3" format=
no encodings have been specified, or only one encoding is "default" derivedLink="https://rfc-editor.org/rfc/rfc8852#section-3.3" derivedCo
specified but without a RID value, then no "a=rid" lines ntent="RFC8852"/>.
are generated.</t> If no encodings have been specified, or only one encoding is
specified but without a rid-id, then no "a=rid" lines
<t>If the RtpTransceiver has a sendrecv or sendonly are generated.</li>
<li pn="section-5.2.1-13.12">If the RtpTransceiver has a sendrecv or
sendonly
direction and more than one "a=rid" line has been direction and more than one "a=rid" line has been
generated, an "a=simulcast" line, with direction "send", generated, an "a=simulcast" line, with direction "send",
as defined in as defined in
<xref target="I-D.ietf-mmusic-sdp-simulcast"></xref>, <xref target="RFC8853" sectionFormat="comma" section="5.1" format=
Section 6.2. The list of RIDs MUST include all of the RID "default" derivedLink="https://rfc-editor.org/rfc/rfc8853#section-5.1" derivedCo
identifiers used in the "a=rid" lines for this m= ntent="RFC8853"/>. The associated set of rid-ids <bcp14>MUST</bcp14>
section.</t> include all of the rid-ids used in the "a=rid" lines for this "m="
section.</li>
<t>If the bundle policy for this PeerConnection is set to <li pn="section-5.2.1-13.13">If (1) the bundle policy for this PeerC
"max-bundle", and this is not the first m= section, or onnection is set to
the bundle policy is set to "balanced", and this is not "max-bundle" and this is not the first "m=" section or (2)
the first m= section for this media type, an the bundle policy is set to "balanced" and this is not
"a=bundle-only" line.</t> the first "m=" section for this media type, an
</list> "a=bundle-only" line.</li>
</t> </ul>
<t indent="0" pn="section-5.2.1-14">The following attributes, which ar
<t>The following attributes, which are of category IDENTICAL e of category IDENTICAL
or TRANSPORT, MUST appear only in "m=" sections which either or TRANSPORT, <bcp14>MUST</bcp14> appear only in "m=" sections that ei
have a unique address or which are associated with the ther
bundle-tag. (In initial offers, this means those "m=" have a unique address or are associated with the
sections which do not contain an "a=bundle-only" BUNDLE-tag. (In initial offers, this means those "m="
sections that do not contain an "a=bundle-only"
attribute.)</t> attribute.)</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t> -5.2.1-15">
<list style="symbols"> <li pn="section-5.2.1-15.1">"a=ice-ufrag" and "a=ice-pwd" lines, as
specified in
<t>"a=ice-ufrag" and "a=ice-pwd" lines, as specified in <xref target="RFC8839" sectionFormat="comma" section="5.4" format=
<xref target="I-D.ietf-mmusic-ice-sip-sdp"></xref>, "default" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.4" derivedCo
Section 4.4.</t> ntent="RFC8839"/>.</li>
<li pn="section-5.2.1-15.2">For each desired digest algorithm, one o
<t>For each desired digest algorithm, one or more r more
"a=fingerprint" lines for each of the endpoint's "a=fingerprint" lines for each of the endpoint's
certificates, as specified in certificates, as specified in
<xref target="RFC8122"></xref>, Section 5.</t> <xref target="RFC8122" sectionFormat="comma" section="5" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc8122#section-5" derivedConten
<t>An "a=setup" line, as specified in t="RFC8122"/>.</li>
<xref target="RFC4145"></xref>, Section 4, and clarified <li pn="section-5.2.1-15.3">An "a=setup" line, as specified in
<xref target="RFC4145" sectionFormat="comma" section="4" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc4145#section-4" derivedConten
t="RFC4145"/> and clarified
for use in DTLS-SRTP scenarios in for use in DTLS-SRTP scenarios in
<xref target="RFC5763"></xref>, Section 5. The role value <xref target="RFC5763" sectionFormat="comma" section="5" format="d
in the offer MUST be "actpass".</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc5763#section-5" derivedConten
t="RFC5763"/>. The role value
<t>An "a=tls-id" line, as specified in in the offer <bcp14>MUST</bcp14> be "actpass".</li>
<xref target="I-D.ietf-mmusic-dtls-sdp" />, Section <li pn="section-5.2.1-15.4">An "a=tls-id" line, as specified in
5.2.</t> <xref target="RFC8842" sectionFormat="comma" section="5.2" format=
"default" derivedLink="https://rfc-editor.org/rfc/rfc8842#section-5.2" derivedCo
<t>An "a=rtcp" line, as specified in ntent="RFC8842"/>.</li>
<xref target="RFC3605"></xref>, Section 2.1, containing <li pn="section-5.2.1-15.5">An "a=rtcp" line, as specified in
the dummy value "9 IN IP4 0.0.0.0", because no candidates <xref target="RFC3605" sectionFormat="comma" section="2.1" format=
have yet been gathered.</t> "default" derivedLink="https://rfc-editor.org/rfc/rfc3605#section-2.1" derivedCo
ntent="RFC3605"/>, containing
<t>An "a=rtcp-mux" line, as specified in the default value "9 IN IP4 0.0.0.0", because no candidates
<xref target="RFC5761"></xref>, Section 5.1.3.</t> have yet been gathered.</li>
<li pn="section-5.2.1-15.6">An "a=rtcp-mux" line, as specified in
<t>If the RTP/RTCP multiplexing policy is "require", an <xref target="RFC5761" sectionFormat="comma" section="5.1.3" forma
t="default" derivedLink="https://rfc-editor.org/rfc/rfc5761#section-5.1.3" deriv
edContent="RFC5761"/>.</li>
<li pn="section-5.2.1-15.7">If the RTP/RTCP multiplexing policy is "
require", an
"a=rtcp-mux-only" line, as specified in "a=rtcp-mux-only" line, as specified in
<xref target="I-D.ietf-mmusic-mux-exclusive" />, Section <xref target="RFC8858" sectionFormat="comma" section="4" format="d
4.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8858#section-4" derivedConten
t="RFC8858"/>.</li>
<t>An "a=rtcp-rsize" line, as specified in <li pn="section-5.2.1-15.8">An "a=rtcp-rsize" line, as specified in
<xref target="RFC5506"></xref>, Section 5.</t> <xref target="RFC5506" sectionFormat="comma" section="5" format="d
</list> efault" derivedLink="https://rfc-editor.org/rfc/rfc5506#section-5" derivedConten
</t> t="RFC5506"/>.</li>
</ul>
<t>Lastly, if a data channel has been created, a m= section <t indent="0" pn="section-5.2.1-16">Lastly, if a data channel has been
MUST be generated for data. The &lt;media&gt; field MUST be created, an "m=" section
set to "application" and the &lt;proto&gt; field MUST be set <bcp14>MUST</bcp14> be generated for data. The &lt;media&gt; field <bc
p14>MUST</bcp14> be
set to "application", and the &lt;proto&gt; field <bcp14>MUST</bcp14>
be set
to "UDP/DTLS/SCTP" to "UDP/DTLS/SCTP"
<xref target="I-D.ietf-mmusic-sctp-sdp"></xref>. The "fmt" <xref target="RFC8841" format="default" sectionFormat="of" derivedCont
value MUST be set to "webrtc-datachannel" as specified in ent="RFC8841"/>. The &lt;fmt&gt;
<xref target="I-D.ietf-mmusic-sctp-sdp"></xref>, Section value <bcp14>MUST</bcp14> be set to "webrtc-datachannel" as specified
4.1.</t> in
<xref target="RFC8841" sectionFormat="comma" section="4.2.2" format="d
<t>Within the data m= section, an "a=mid" line MUST be efault" derivedLink="https://rfc-editor.org/rfc/rfc8841#section-4.2.2" derivedCo
ntent="RFC8841"/>.
</t>
<t indent="0" pn="section-5.2.1-17">Within the data "m=" section, an "
a=mid" line <bcp14>MUST</bcp14> be
generated and included as described above, along with an generated and included as described above, along with an
"a=sctp-port" line referencing the SCTP port number, as "a=sctp-port" line referencing the SCTP port number, as
defined in defined in
<xref target="I-D.ietf-mmusic-sctp-sdp"></xref>, Section 5.1, <xref target="RFC8841" sectionFormat="comma" section="5.1" format="def ault" derivedLink="https://rfc-editor.org/rfc/rfc8841#section-5.1" derivedConten t="RFC8841"/>;
and, if appropriate, an "a=max-message-size" line, as defined and, if appropriate, an "a=max-message-size" line, as defined
in in
<xref target="I-D.ietf-mmusic-sctp-sdp"></xref>, Section <xref target="RFC8841" sectionFormat="comma" section="6.1" format="def
6.1.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc8841#section-6.1" derivedConten
t="RFC8841"/>.</t>
<t>As discussed above, the following attributes of category <t indent="0" pn="section-5.2.1-18">As discussed above, the following
IDENTICAL or TRANSPORT are included only if the data m= attributes of category
IDENTICAL or TRANSPORT are included only if the data "m="
section either has a unique address or is associated with the section either has a unique address or is associated with the
bundle-tag (e.g., if it is the only m= section): BUNDLE-tag (e.g., if it is the only "m=" section):
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>"a=ice-ufrag"</t> -5.2.1-19">
<li pn="section-5.2.1-19.1">"a=ice-ufrag"</li>
<t>"a=ice-pwd"</t> <li pn="section-5.2.1-19.2">"a=ice-pwd"</li>
<li pn="section-5.2.1-19.3">"a=fingerprint"</li>
<t>"a=fingerprint"</t> <li pn="section-5.2.1-19.4">"a=setup"</li>
<li pn="section-5.2.1-19.5">"a=tls-id"</li>
<t>"a=setup"</t> </ul>
<t indent="0" pn="section-5.2.1-20">Once all "m=" sections have been g
<t>"a=tls-id"</t> enerated, a session-level
</list></t> "a=group" attribute <bcp14>MUST</bcp14> be added as specified in
<xref target="RFC5888" format="default" sectionFormat="of" derivedCont
<t>Once all m= sections have been generated, a session-level ent="RFC5888"/>. This attribute <bcp14>MUST</bcp14> have
"a=group" attribute MUST be added as specified in semantics "BUNDLE" and <bcp14>MUST</bcp14> include the mid identifiers
<xref target="RFC5888"></xref>. This attribute MUST have of
semantics "BUNDLE", and MUST include the mid identifiers of each "m=" section. The effect of this is that the JSEP
each m= section. The effect of this is that the JSEP implementation offers all "m=" sections as one bundle group.
implementation offers all m= sections as one bundle group. However, whether the "m=" sections are bundle-only or not
However, whether the m= sections are bundle-only or not
depends on the bundle policy.</t> depends on the bundle policy.</t>
<t indent="0" pn="section-5.2.1-21">The next step is to generate sessi
<t>The next step is to generate session-level lip sync groups on-level lip sync groups
as defined in as defined in
<xref target="RFC5888" />, Section 7. For each MediaStream <xref target="RFC5888" sectionFormat="comma" section="7" format="defau lt" derivedLink="https://rfc-editor.org/rfc/rfc5888#section-7" derivedContent="R FC5888"/>. For each MediaStream
referenced by more than one RtpTransceiver (by passing those referenced by more than one RtpTransceiver (by passing those
MediaStreams as arguments to the addTrack and addTransceiver MediaStreams as arguments to the addTrack and addTransceiver
methods), a group of type "LS" MUST be added that contains methods), a group of type "LS" <bcp14>MUST</bcp14> be added that conta
the mid values for each RtpTransceiver.</t> ins
the MID values for each RtpTransceiver.</t>
<t>Attributes which SDP permits to either be at the session <t indent="0" pn="section-5.2.1-22">Attributes that SDP permits to be
level or the media level SHOULD generally be at the media at either the session
level or the media level <bcp14>SHOULD</bcp14> generally be at the med
ia
level even if they are identical. This assists development level even if they are identical. This assists development
and debugging by making it easier to understand individual and debugging by making it easier to understand individual
media sections, especially if one of a set of initially media sections, especially if one of a set of initially
identical attributes is subsequently changed. However, identical attributes is subsequently changed. However,
implementations MAY choose to aggregate attributes at the implementations <bcp14>MAY</bcp14> choose to aggregate attributes at t
session level and JSEP implementations MUST be prepared to he
session level, and JSEP implementations <bcp14>MUST</bcp14> be prepare
d to
receive attributes in either location.</t> receive attributes in either location.</t>
<t indent="0" pn="section-5.2.1-23">Attributes other than the ones spe
<t>Attributes other than the ones specified above MAY be cified above <bcp14>MAY</bcp14> be
included, except for the following attributes which are included, except for the following attributes, which are
specifically incompatible with the requirements of specifically incompatible with the requirements of
<xref target="I-D.ietf-rtcweb-rtp-usage"></xref>, and MUST <xref target="RFC8834" format="default" sectionFormat="of" derivedCont
NOT be included: ent="RFC8834"/> and <bcp14>MUST NOT</bcp14> be included:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>"a=crypto"</t> -5.2.1-24">
<li pn="section-5.2.1-24.1">"a=crypto"</li>
<t>"a=key-mgmt"</t> <li pn="section-5.2.1-24.2">"a=key-mgmt"</li>
<li pn="section-5.2.1-24.3">"a=ice-lite"</li>
<t>"a=ice-lite"</t> </ul>
</list></t> <t indent="0" pn="section-5.2.1-25">Note that when bundle is used, any
additional attributes
<t>Note that when bundle is used, any additional attributes that are added <bcp14>MUST</bcp14> follow the advice in
that are added MUST follow the advice in <xref target="RFC8859" format="default" sectionFormat="of" derivedCont
<xref target="I-D.ietf-mmusic-sdp-mux-attributes"></xref> on ent="RFC8859"/> on
how those attributes interact with bundle.</t> how those attributes interact with bundle.</t>
<t indent="0" pn="section-5.2.1-26">Note that these requirements are i
<t>Note that these requirements are in some cases stricter n some cases stricter
than those of SDP. Implementations MUST be prepared to accept than those of SDP. Implementations <bcp14>MUST</bcp14> be prepared to
accept
compliant SDP even if it would not conform to the compliant SDP even if it would not conform to the
requirements for generating SDP in this specification.</t> requirements for generating SDP in this specification.</t>
</section> </section>
<section title="Subsequent Offers" <section anchor="sec.subsequent-offers" numbered="true" toc="include" re
anchor="sec.subsequent-offers"> moveInRFC="false" pn="section-5.2.2">
<name slugifiedName="name-subsequent-offers">Subsequent Offers</name>
<t>When createOffer is called a second (or later) time, or is <t indent="0" pn="section-5.2.2-1">When createOffer is called a second
(or later) time or is
called after a local description has already been installed, called after a local description has already been installed,
the processing is somewhat different than for an initial the processing is somewhat different than for an initial
offer.</t> offer.</t>
<t indent="0" pn="section-5.2.2-2">If the previous offer was not appli
<t>If the previous offer was not applied using ed using
setLocalDescription, meaning the PeerConnection is still in setLocalDescription, meaning the PeerConnection is still in
the "stable" state, the steps for generating an initial offer the "stable" state, the steps for generating an initial offer
should be followed, subject to the following restriction: <bcp14>MUST</bcp14> be followed, subject to the following restriction:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>The fields of the "o=" line MUST stay the same except -5.2.2-3">
for the &lt;session-version&gt; field, which MUST increment <li pn="section-5.2.2-3.1">The fields of the "o=" line <bcp14>MUST</
bcp14> stay the same except
for the &lt;session-version&gt; field, which <bcp14>MUST</bcp14> inc
rement
by one on each call to createOffer if the offer might by one on each call to createOffer if the offer might
differ from the output of the previous call to createOffer; differ from the output of the previous call to createOffer;
implementations MAY opt to increment implementations <bcp14>MAY</bcp14> opt to increment
&lt;session-version&gt; on every call. The value of the &lt;session-version&gt; on every call. The value of the
generated &lt;session-version&gt; is independent of the generated &lt;session-version&gt; is independent of the
&lt;session-version&gt; of the current local description; &lt;session-version&gt; of the current local description;
in particular, in the case where the current version is N, in particular, in the case where the current version is N,
an offer is created and applied with version N+1, and then an offer is created and applied with version N+1, and then
that offer is rolled back so that the current version is that offer is rolled back so that the current version is
again N, the next generated offer will still have version again N, the next generated offer will still have version
N+2.</t> N+2.</li>
</list></t> </ul>
<t indent="0" pn="section-5.2.2-4">Note that if the application create
<t>Note that if the application creates an offer by reading s an offer by reading
currentLocalDescription instead of calling createOffer, the currentLocalDescription instead of calling createOffer, the
returned SDP may be different than when setLocalDescription returned SDP may be different than when setLocalDescription
was originally called, due to the addition of gathered ICE was originally called, due to the addition of gathered ICE
candidates, but the &lt;session-version&gt; will not have candidates, but the &lt;session-version&gt; will not have
changed. There are no known scenarios in which this causes changed. There are no known scenarios in which this causes
problems, but if this is a concern, the solution is simply to problems, but if this is a concern, the solution is simply to
use createOffer to ensure a unique use createOffer to ensure a unique
&lt;session-version&gt;.</t> &lt;session-version&gt;.</t>
<t indent="0" pn="section-5.2.2-5">If the previous offer was applied u
<t>If the previous offer was applied using sing
setLocalDescription, but a corresponding answer from the setLocalDescription, but a corresponding answer from the
remote side has not yet been applied, meaning the remote side has not yet been applied, meaning the
PeerConnection is still in the "have-local-offer" state, an PeerConnection is still in the "have-local-offer" state, an
offer is generated by following the steps in the "stable" offer is generated by following the steps in the "stable"
state above, along with these exceptions: state above, along with these exceptions:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>The "s=" and "t=" lines MUST stay the same.</t> -5.2.2-6">
<li pn="section-5.2.2-6.1">The "s=" and "t=" lines <bcp14>MUST</bcp1
<t>If any RtpTransceiver has been added, and there exists 4> stay the same.</li>
an m= section with a zero port in the current local <li pn="section-5.2.2-6.2">If any RtpTransceiver has been added and
description or the current remote description, that m= there exists
section MUST be recycled by generating an m= section for an "m=" section with a zero port in the current local
the added RtpTransceiver as if the m= section were being description or the current remote description, that "m="
section <bcp14>MUST</bcp14> be recycled by generating an "m=" sectio
n for
the added RtpTransceiver as if the "m=" section were being
added to the session description (including a new MID added to the session description (including a new MID
value), and placing it at the same index as the m= section value) and placing it at the same index as the "m=" section
with a zero port.</t> with a zero port.</li>
<li pn="section-5.2.2-6.3">If an RtpTransceiver is stopped and is no
<t>If an RtpTransceiver is stopped and is not associated t associated
with an m= section, an m= section MUST NOT be generated for with an "m=" section, an "m=" section <bcp14>MUST NOT</bcp14> be gen
it. This prevents adding back RtpTransceivers whose m= erated for
it. This prevents adding back RtpTransceivers whose "m="
sections were recycled and used for a new RtpTransceiver in sections were recycled and used for a new RtpTransceiver in
a previous offer/ answer exchange, as described above.</t> a previous offer/ answer exchange, as described above.</li>
<li pn="section-5.2.2-6.4">If an RtpTransceiver has been stopped and
<t>If an RtpTransceiver has been stopped and is associated is associated
with an m= section, and the m= section is not being with an "m=" section, and the "m=" section is not being
recycled as described above, an m= section MUST be recycled as described above, an "m=" section <bcp14>MUST</bcp14> be
generated for it with the port set to zero and all "a=msid" generated for it with the port set to zero and all "a=msid"
lines removed.</t> lines removed.</li>
<li pn="section-5.2.2-6.5">For RtpTransceivers that are not stopped,
<t>For RtpTransceivers that are not stopped, the "a=msid" the "a=msid"
line(s) MUST stay the same if they are present in the line or lines <bcp14>MUST</bcp14> stay the same if they are present
in the
current description, regardless of changes to the current description, regardless of changes to the
transceiver's direction or track. If no "a=msid" line is transceiver's direction or track. If no "a=msid" line is
present in the current description, "a=msid" line(s) MUST present in the current description, "a=msid" line(s) <bcp14>MUST</bc p14>
be generated according to the same rules as for an initial be generated according to the same rules as for an initial
offer.</t> offer.</li>
<li pn="section-5.2.2-6.6">Each "m=" and "c=" line <bcp14>MUST</bcp1
<t>Each "m=" and c=" line MUST be filled in with the port, 4> be filled in with the port,
relevant RTP profile, and address of the default candidate for the relevant RTP profile, and address of the default candidate for the
m= section, as described in "m=" section, as described in
<xref target="I-D.ietf-mmusic-ice-sip-sdp"></xref>, <xref target="RFC8839" sectionFormat="comma" section="4.2.1.2" forma
Section 3.2.1.2, and clarified in t="default" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-4.2.1.2" der
<xref target="sec.profile-names"/>. ivedContent="RFC8839"/> and clarified in
If no RTP candidates have yet been gathered, dummy <xref target="sec.profile-names" format="default" sectionFormat="of"
values MUST still be used, as described above.</t> derivedContent="Section 5.1.2"/>.
If no RTP candidates have yet been gathered, default
<t>Each "a=mid" line MUST stay the same.</t> values <bcp14>MUST</bcp14> still be used, as described above.</li>
<li pn="section-5.2.2-6.7">Each "a=mid" line <bcp14>MUST</bcp14> sta
<t>Each "a=ice-ufrag" and "a=ice-pwd" line MUST stay the y the same.</li>
same, unless the ICE configuration has changed (either <li pn="section-5.2.2-6.8">Each "a=ice-ufrag" and "a=ice-pwd" line <
changes to the supported STUN/TURN servers, or the ICE bcp14>MUST</bcp14> stay the
candidate policy), or the "IceRestart" option ( same, unless the ICE configuration has changed (e.g., changes to
<xref target="sec.icerestart" /> was specified. If the m= either the supported STUN/TURN servers or the ICE
section is bundled into another m= section, it still MUST candidate policy) or the IceRestart option
NOT contain any ICE credentials.</t> (<xref target="sec.icerestart" format="default" sectionFormat="of" d
erivedContent="Section 5.2.3.1"/>) was specified.
<t>If the m= section is not bundled into another m= If the "m="
section, its "a=rtcp" attribute line MUST be filled in with section is bundled into another "m=" section, it still <bcp14>MUST N
OT</bcp14> contain any ICE credentials.</li>
<li pn="section-5.2.2-6.9">If the "m=" section is not bundled into a
nother "m="
section, its "a=rtcp" attribute line <bcp14>MUST</bcp14> be filled i
n with
the port and address of the default RTCP candidate, as the port and address of the default RTCP candidate, as
indicated in indicated in
<xref target="RFC5761"></xref>, Section 5.1.3. If no RTCP <xref target="RFC5761" sectionFormat="comma" section="5.1.3" format=
candidates have yet been gathered, dummy values MUST be "default" derivedLink="https://rfc-editor.org/rfc/rfc5761#section-5.1.3" derived
used, as described in the initial offer section above.</t> Content="RFC5761"/>. If no RTCP
candidates have yet been gathered, default values <bcp14>MUST</bcp14
<t>If the m= section is not bundled into another m= > be
used, as described in <xref target="sec.initial-offers" format="defa
ult" sectionFormat="of" derivedContent="Section 5.2.1"/> above.</li>
<li pn="section-5.2.2-6.10">If the "m=" section is not bundled into
another "m="
section, for each candidate that has been gathered during section, for each candidate that has been gathered during
the most recent gathering phase (see the most recent gathering phase (see
<xref target="sec.ice-gather-overview"></xref>), an <xref target="sec.ice-gather-overview" format="default" sectionForma
"a=candidate" line MUST be added, as defined in t="of" derivedContent="Section 3.5.1"/>), an
<xref target="I-D.ietf-mmusic-ice-sip-sdp"></xref>, Section 4.1. "a=candidate" line <bcp14>MUST</bcp14> be added, as defined in
<xref target="RFC8839" sectionFormat="comma" section="5.1" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.1" derivedCont
ent="RFC8839"/>.
If candidate gathering for the section has completed, an If candidate gathering for the section has completed, an
"a=end-of-candidates" attribute MUST be added, as described "a=end-of-candidates" attribute <bcp14>MUST</bcp14> be added, as des cribed
in in
<xref target="I-D.ietf-ice-trickle"></xref>, Section 9.3. <xref target="RFC8840" sectionFormat="comma" section="8.2" format="d
If the m= section is bundled into another m= section, both efault" derivedLink="https://rfc-editor.org/rfc/rfc8840#section-8.2" derivedCont
"a=candidate" and "a=end-of-candidates" MUST be ent="RFC8840"/>.
omitted.</t> If the "m=" section is bundled into another "m=" section, both
"a=candidate" and "a=end-of-candidates" <bcp14>MUST</bcp14> be
<t>For RtpTransceivers that are still present, the "a=rid" omitted.
lines MUST stay the same.</t> </li>
<li pn="section-5.2.2-6.11">For RtpTransceivers that are still prese
<t>For RtpTransceivers that are still present, any nt, the "a=rid"
"a=simulcast" line MUST stay the same.</t> lines <bcp14>MUST</bcp14> stay the same.</li>
</list></t> <li pn="section-5.2.2-6.12">For RtpTransceivers that are still prese
nt, any
<t>If the previous offer was applied using "a=simulcast" line <bcp14>MUST</bcp14> stay the same.</li>
</ul>
<t indent="0" pn="section-5.2.2-7">If the previous offer was applied u
sing
setLocalDescription, and a corresponding answer from the setLocalDescription, and a corresponding answer from the
remote side has been applied using setRemoteDescription, remote side has been applied using setRemoteDescription,
meaning the PeerConnection is in the "have-remote-pranswer" meaning the PeerConnection is in the "have-remote-pranswer"
or "stable" states, an offer is generated based on the state or the "stable" state, an offer is generated based on the
negotiated session descriptions by following the steps negotiated session descriptions by following the steps
mentioned for the "have-local-offer" state above.</t> mentioned for the "have-local-offer" state above.</t>
<t indent="0" pn="section-5.2.2-8">In addition, for each existing, non
<t>In addition, for each existing, non-recycled, non-rejected -recycled, non-rejected
m= section in the new offer, the following adjustments are "m=" section in the new offer, the following adjustments are
made based on the contents of the corresponding m= section in made based on the contents of the corresponding "m=" section in
the current local or remote description, as appropriate: the current local or remote description, as appropriate:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>The m= line and corresponding "a=rtpmap" and "a=fmtp" -5.2.2-9">
lines MUST only include media formats which have not been <li pn="section-5.2.2-9.1">The "m=" line and corresponding "a=rtpmap
" and "a=fmtp"
lines <bcp14>MUST</bcp14> only include media formats that have not b
een
excluded by the codec preferences of the associated excluded by the codec preferences of the associated
transceiver, and MUST include all currently available transceiver and also <bcp14>MUST</bcp14> include all currently avail able
formats. Media formats that were previously offered but are formats. Media formats that were previously offered but are
no longer available (e.g., a shared hardware codec) MAY be no longer available (e.g., a shared hardware codec) <bcp14>MAY</bcp1
excluded.</t> 4> be
excluded.</li>
<t>Unless codec preferences have been set for the <li pn="section-5.2.2-9.2">Unless codec preferences have been set fo
associated transceiver, the media formats on the m= line r the
MUST be generated in the same order as in the most recent associated transceiver, the media formats on the "m=" line
<bcp14>MUST</bcp14> be generated in the same order as in the most re
cent
answer. Any media formats that were not present in the most answer. Any media formats that were not present in the most
recent answer MUST be added after all existing formats.</t> recent answer <bcp14>MUST</bcp14> be added after all existing format
s.</li>
<t>The RTP header extensions MUST only include those that <li pn="section-5.2.2-9.3">The RTP header extensions <bcp14>MUST</bc
are present in the most recent answer.</t> p14> only include those that
are present in the most recent answer.</li>
<t>The RTCP feedback mechanisms MUST only include those <li pn="section-5.2.2-9.4">The RTCP feedback mechanisms <bcp14>MUST<
/bcp14> only include those
that are present in the most recent answer, except for the that are present in the most recent answer, except for the
case of format-specific mechanisms that are referencing a case of format-specific mechanisms that are referencing a
newly-added media format.</t> newly added media format.</li>
<li pn="section-5.2.2-9.5">The "a=rtcp" line <bcp14>MUST NOT</bcp14>
<t>The "a=rtcp" line MUST NOT be added if the most recent be added if the most recent
answer included an "a=rtcp-mux" line.</t> answer included an "a=rtcp-mux" line.</li>
<li pn="section-5.2.2-9.6">The "a=rtcp-mux" line <bcp14>MUST</bcp14>
<t>The "a=rtcp-mux" line MUST be the same as that in the be the same as that in the
most recent answer.</t> most recent answer.</li>
<li pn="section-5.2.2-9.7">The "a=rtcp-mux-only" line <bcp14>MUST NO
<t>The "a=rtcp-mux-only" line MUST NOT be added.</t> T</bcp14> be added.</li>
<li pn="section-5.2.2-9.8">The "a=rtcp-rsize" line <bcp14>MUST NOT</
<t>The "a=rtcp-rsize" line MUST NOT be added unless present bcp14> be added unless present
in the most recent answer.</t> in the most recent answer.</li>
<li pn="section-5.2.2-9.9">An "a=bundle-only" line, as defined in
<t>An "a=bundle-only" line MUST NOT be added, as indicated <xref target="RFC8843" sectionFormat="comma" section="6" format="def
in ault" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-6" derivedContent=
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation" />, "RFC8843"/>,
Section 6. Instead, JSEP implementations MUST simply omit <bcp14>MUST NOT</bcp14> be added.
Instead, JSEP implementations <bcp14>MUST</bcp14> simply omit
parameters in the IDENTICAL and TRANSPORT categories for parameters in the IDENTICAL and TRANSPORT categories for
bundled m= sections, as described in bundled "m=" sections, as described in
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation" />, <xref target="RFC8843" sectionFormat="comma" section="7.1.3" format=
Section 8.1.</t> "default" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-7.1.3" derived
Content="RFC8843"/>.</li>
<t>Note that if media m= sections are bundled into a data <li pn="section-5.2.2-9.10">Note that if media "m=" sections are bun
m= section, then certain TRANSPORT and IDENTICAL attributes dled into a data
may appear in the data m= section even if they would "m=" section, then certain TRANSPORT and IDENTICAL attributes
otherwise only be appropriate for a media m= section (e.g., may appear in the data "m=" section even if they would
otherwise only be appropriate for a media "m=" section (e.g.,
"a=rtcp-mux"). This cannot happen in initial offers because "a=rtcp-mux"). This cannot happen in initial offers because
in the initial offer JSEP implementations always list media in the initial offer JSEP implementations always list media
m= sections (if any) before the data m= section (if any), "m=" sections (if any) before the data "m=" section (if any),
and at least one of those media m= sections will not have and at least one of those media "m=" sections will not have
the "a=bundle-only" attribute. Therefore, in initial the "a=bundle-only" attribute. Therefore, in initial
offers, any "a=bundle-only" m= sections will be bundled offers, any "a=bundle-only" "m=" sections will be bundled
into a preceding non-bundle-only media m= section.</t> into a preceding non-bundle-only media "m=" section.</li>
</list></t> </ul>
<t indent="0" pn="section-5.2.2-10">The "a=group:BUNDLE" attribute <bc
<t>The "a=group:BUNDLE" attribute MUST include the MID p14>MUST</bcp14> include the MID
identifiers specified in the bundle group in the most recent identifiers specified in the bundle group in the most recent
answer, minus any m= sections that have been marked as answer, minus any "m=" sections that have been marked as
rejected, plus any newly added or re-enabled m= sections. In rejected, plus any newly added or re-enabled "m=" sections. In
other words, the bundle attribute must contain all m= other words, the bundle attribute <bcp14>MUST</bcp14> contain all "m="
sections that were previously bundled, as long as they are sections that were previously bundled, as long as they are
still alive, as well as any new m= sections.</t> still alive, as well as any new "m=" sections.</t>
<t indent="0" pn="section-5.2.2-11">"a=group:LS" attributes are genera
<t>"a=group:LS" attributes are generated in the same way as ted in the same way as
for initial offers, with the additional stipulation that any for initial offers, with the additional stipulation that any
lip sync groups that were present in the most recent answer lip sync groups that were present in the most recent answer
MUST continue to exist and MUST contain any previously <bcp14>MUST</bcp14> continue to exist and <bcp14>MUST</bcp14> contain
existing MID identifiers, as long as the identified m= any previously
existing MID identifiers, as long as the identified "m="
sections still exist and are not rejected, and the group sections still exist and are not rejected, and the group
still contains at least two MID identifiers. This ensures still contains at least two MID identifiers. This ensures
that any synchronized "recvonly" m= sections continue to be that any synchronized "recvonly" "m=" sections continue to be
synchronized in the new offer.</t> synchronized in the new offer.</t>
</section> </section>
<section title="Options Handling" <section anchor="sec.options-handling1" numbered="true" toc="include" re
anchor="sec.options-handling1"> moveInRFC="false" pn="section-5.2.3">
<name slugifiedName="name-options-handling">Options Handling</name>
<t>The createOffer method takes as a parameter an <t indent="0" pn="section-5.2.3-1">The createOffer method takes as a p
arameter an
RTCOfferOptions object. Special processing is performed when RTCOfferOptions object. Special processing is performed when
generating a SDP description if the following options are generating an SDP description if the following options are
present.</t> present.</t>
<section title="IceRestart" anchor="sec.icerestart"> <section anchor="sec.icerestart" numbered="true" toc="include" removeI
nRFC="false" pn="section-5.2.3.1">
<t>If the "IceRestart" option is specified, with a value of <name slugifiedName="name-icerestart">IceRestart</name>
"true", the offer MUST indicate an ICE restart by <t indent="0" pn="section-5.2.3.1-1">If the IceRestart option is spe
cified, with a value of
"true", the offer <bcp14>MUST</bcp14> indicate an ICE restart by
generating new ICE ufrag and pwd attributes, as specified generating new ICE ufrag and pwd attributes, as specified
in in
<xref target="I-D.ietf-mmusic-ice-sip-sdp"></xref>, <xref target="RFC8839" sectionFormat="comma" section="4.4.3.1.1" for
Section 3.4.1.1.1. If this mat="default" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-4.4.3.1.1"
derivedContent="RFC8839"/>. If this
option is specified on an initial offer, it has no effect option is specified on an initial offer, it has no effect
(since a new ICE ufrag and pwd are already generated). (since a new ICE ufrag and pwd are already generated).
Similarly, if the ICE configuration has changed, this Similarly, if the ICE configuration has changed, this
option has no effect, since new ufrag and pwd attributes option has no effect, since new ufrag and pwd attributes
will be generated automatically. This option is primarily will be generated automatically. This option is primarily
useful for reestablishing connectivity in cases where useful for reestablishing connectivity in cases where
failures are detected by the application.</t> failures are detected by the application.</t>
</section> </section>
<section title="VoiceActivityDetection" <section anchor="sec.voiceactivitydetection1" numbered="true" toc="inc
anchor="sec.voiceactivitydetection1"> lude" removeInRFC="false" pn="section-5.2.3.2">
<name slugifiedName="name-voiceactivitydetection">VoiceActivityDetec
<t>Silence suppression, also known as discontinuous tion</name>
<t indent="0" pn="section-5.2.3.2-1">Silence suppression, also known
as discontinuous
transmission ("DTX"), can reduce the bandwidth used for transmission ("DTX"), can reduce the bandwidth used for
audio by switching to a special encoding when voice audio by switching to a special encoding when voice
activity is not detected, at the cost of some fidelity.</t> activity is not detected, at the cost of some fidelity.</t>
<t indent="0" pn="section-5.2.3.2-2">If the "VoiceActivityDetection"
<t>If the "VoiceActivityDetection" option is specified, option is specified,
with a value of "true", the offer MUST indicate support for with a value of "true", the offer <bcp14>MUST</bcp14> indicate suppo
rt for
silence suppression in the audio it receives by including silence suppression in the audio it receives by including
comfort noise ("CN") codecs for each offered audio codec, comfort noise ("CN") codecs for each offered audio codec,
as specified in as specified in
<xref target="RFC3389"></xref>, Section 5.1, except for <xref target="RFC3389" sectionFormat="comma" section="5.1" format="d efault" derivedLink="https://rfc-editor.org/rfc/rfc3389#section-5.1" derivedCont ent="RFC3389"/>, except for
codecs that have their own internal silence suppression codecs that have their own internal silence suppression
support. For codecs that have their own internal silence support. For codecs that have their own internal silence
suppression support, the appropriate fmtp parameters for suppression support, the appropriate fmtp parameters for
that codec MUST be specified to indicate that silence that codec <bcp14>MUST</bcp14> be specified to indicate that silence
suppression for received audio is desired. For example, suppression for received audio is desired. For example,
when using the Opus codec when using the Opus codec
<xref target="RFC6716" />, the "usedtx=1" parameter, <xref target="RFC6716" format="default" sectionFormat="of" derivedCo ntent="RFC6716"/>, the "usedtx=1" parameter,
specified in specified in
<xref target="RFC7587" />, would be used in the offer.</t> <xref target="RFC7587" format="default" sectionFormat="of" derivedCo
ntent="RFC7587"/>, would be used in the offer.</t>
<t>If the "VoiceActivityDetection" option is specified, <t indent="0" pn="section-5.2.3.2-3">If the "VoiceActivityDetection"
with a value of "false", the JSEP implementation MUST NOT option is specified,
with a value of "false", the JSEP implementation <bcp14>MUST NOT</bc
p14>
emit "CN" codecs. For codecs that have their own internal emit "CN" codecs. For codecs that have their own internal
silence suppression support, the appropriate fmtp silence suppression support, the appropriate fmtp
parameters for that codec MUST be specified to indicate parameters for that codec <bcp14>MUST</bcp14> be specified to indica te
that silence suppression for received audio is not desired. that silence suppression for received audio is not desired.
For example, when using the Opus codec, the "usedtx=0" For example, when using the Opus codec, the "usedtx=0"
parameter would be specified in the offer. In addition, the parameter would be specified in the offer. In addition, the
implementation MUST NOT use silence suppression for media implementation <bcp14>MUST NOT</bcp14> use silence suppression for m edia
it generates, regardless of whether the "CN" codecs or it generates, regardless of whether the "CN" codecs or
related fmtp parameters appear in the peer's description. related fmtp parameters appear in the peer's description.
The impact of these rules is that silence suppression in The impact of these rules is that silence suppression in
JSEP depends on mutual agreement of both sides, which JSEP depends on mutual agreement of both sides, which
ensures consistent handling regardless of which codec is ensures consistent handling regardless of which codec is
used.</t> used.</t>
<t indent="0" pn="section-5.2.3.2-4">The "VoiceActivityDetection" op
<t>The "VoiceActivityDetection" option does not have any tion does not have any
impact on the setting of the "vad" value in the signaling impact on the setting of the "vad" value in the signaling
of the client to mixer audio level header extension of the client-to-mixer audio level header extension
described in described in
<xref target="RFC6464"></xref>, Section 4.</t> <xref target="RFC6464" sectionFormat="comma" section="4" format="def ault" derivedLink="https://rfc-editor.org/rfc/rfc6464#section-4" derivedContent= "RFC6464"/>.</t>
</section> </section>
</section> </section>
</section> </section>
<section title="Generating an Answer" <section anchor="sec.generating-an-answer" numbered="true" toc="include" r
anchor="sec.generating-an-answer"> emoveInRFC="false" pn="section-5.3">
<name slugifiedName="name-generating-an-answer">Generating an Answer</na
<t>When createAnswer is called, a new SDP description must be me>
<t indent="0" pn="section-5.3-1">When createAnswer is called, a new SDP
description <bcp14>MUST</bcp14> be
created that is compatible with the supplied remote description created that is compatible with the supplied remote description
as well as the requirements specified in as well as the requirements specified in
<xref target="I-D.ietf-rtcweb-rtp-usage"></xref>. The exact <xref target="RFC8834" format="default" sectionFormat="of" derivedConten t="RFC8834"/>. The exact
details of this process are explained below.</t> details of this process are explained below.</t>
<section title="Initial Answers" anchor="sec.initial-answers"> <section anchor="sec.initial-answers" numbered="true" toc="include" remo
veInRFC="false" pn="section-5.3.1">
<t>When createAnswer is called for the first time after a <name slugifiedName="name-initial-answers">Initial Answers</name>
<t indent="0" pn="section-5.3.1-1">When createAnswer is called for the
first time after a
remote description has been provided, the result is known as remote description has been provided, the result is known as
the initial answer. If no remote description has been the initial answer. If no remote description has been
installed, an answer cannot be generated, and an error MUST installed, an answer cannot be generated, and an error <bcp14>MUST</bc p14>
be returned.</t> be returned.</t>
<t indent="0" pn="section-5.3.1-2">Note that the remote description SD
<t>Note that the remote description SDP may not have been P may not have been
created by a JSEP endpoint and may not conform to all the created by a JSEP endpoint and may not conform to all the
requirements listed in requirements listed in
<xref target="sec-create-offer"></xref>. For many cases, this <xref target="sec-create-offer" format="default" sectionFormat="of" de rivedContent="Section 5.2"/>. For many cases, this
is not a problem. However, if any mandatory SDP attributes is not a problem. However, if any mandatory SDP attributes
are missing, or functionality listed as mandatory-to-use are missing or functionality listed as mandatory-to-use
above is not present, this MUST be treated as an error, and above is not present, this <bcp14>MUST</bcp14> be treated as an error
MUST cause the affected m= sections to be marked as and
<bcp14>MUST</bcp14> cause the affected "m=" sections to be marked as
rejected.</t> rejected.</t>
<t indent="0" pn="section-5.3.1-3">The first step in generating an ini
<t>The first step in generating an initial answer is to tial answer is to
generate session-level attributes. The process here is generate session-level attributes. The process here is
identical to that indicated in the initial offers section identical to that indicated in <xref target="sec.initial-offers" forma
above, except that the "a=ice-options" line, with the t="default" sectionFormat="of" derivedContent="Section 5.2.1"/> above, except th
at the "a=ice-options" line, with the
"trickle" option as specified in "trickle" option as specified in
<xref target="I-D.ietf-ice-trickle"></xref>, Section 3, <xref target="RFC8840" sectionFormat="comma" section="4.1.3" format="d efault" derivedLink="https://rfc-editor.org/rfc/rfc8840#section-4.1.3" derivedCo ntent="RFC8840"/>
and the "ice2" option as specified in and the "ice2" option as specified in
<xref target="RFC8445"></xref>, Section 10, is <xref target="RFC8445" sectionFormat="comma" section="10" format="defa ult" derivedLink="https://rfc-editor.org/rfc/rfc8445#section-10" derivedContent= "RFC8445"/>, is
only included if such an option was present in the offer.</t> only included if such an option was present in the offer.</t>
<t indent="0" pn="section-5.3.1-4">The next step is to generate sessio
<t>The next step is to generate session-level lip sync n-level lip sync
groups, as defined in groups, as defined in
<xref target="RFC5888" />, Section 7. For each group of type <xref target="RFC5888" sectionFormat="comma" section="7" format="defau lt" derivedLink="https://rfc-editor.org/rfc/rfc5888#section-7" derivedContent="R FC5888"/>. For each group of type
"LS" present in the offer, select the local RtpTransceivers "LS" present in the offer, select the local RtpTransceivers
that are referenced by the MID values in the specified group, that are referenced by the MID values in the specified group,
and determine which of them either reference a common local and determine which of them either reference a common local
MediaStream (specified in the calls to MediaStream (specified in the calls to
addTrack/addTransceiver used to create them), or have no addTrack/addTransceiver used to create them) or have no
MediaStream to reference because they were not created by MediaStream to reference because they were not created by
addTrack/addTransceiver. If at least two such RtpTransceivers addTrack/addTransceiver. If at least two such RtpTransceivers
exist, a group of type "LS" with the mid values of these exist, a group of type "LS" with the MID values of these
RtpTransceivers MUST be added. Otherwise the offered "LS" RtpTransceivers <bcp14>MUST</bcp14> be added. Otherwise, the offered "
group MUST be ignored and no corresponding group generated in LS"
group <bcp14>MUST</bcp14> be ignored and no corresponding group genera
ted in
the answer.</t> the answer.</t>
<t indent="0" pn="section-5.3.1-5">As a simple example, consider the f
<t>As a simple example, consider the following offer of a ollowing offer of a
single audio and single video track contained in the same single audio and single video track contained in the same
MediaStream. SDP lines not relevant to this example have been MediaStream. SDP lines not relevant to this example have been
removed for clarity. As explained in removed for clarity. As explained in
<xref target="sec-create-offer" />, a group of type "LS" has <xref target="sec-create-offer" format="default" sectionFormat="of" de rivedContent="Section 5.2"/>, a group of type "LS" has
been added that references each track's RtpTransceiver.</t> been added that references each track's RtpTransceiver.</t>
<sourcecode name="" type="sdp" markers="false" pn="section-5.3.1-6">
<t>
<figure>
<artwork>
<![CDATA[
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 10000 UDP/TLS/RTP/SAVPF 0 m=audio 10000 UDP/TLS/RTP/SAVPF 0
a=mid:a1 a=mid:a1
a=msid:ms1 a=msid:ms1
m=video 10001 UDP/TLS/RTP/SAVPF 96 m=video 10001 UDP/TLS/RTP/SAVPF 96
a=mid:v1 a=mid:v1
a=msid:ms1 a=msid:ms1</sourcecode>
]]> <t indent="0" pn="section-5.3.1-7">If the answerer uses a single Media
</artwork> Stream when it adds its
</figure>
</t>
<t>If the answerer uses a single MediaStream when it adds its
tracks, both of its transceivers will reference this stream, tracks, both of its transceivers will reference this stream,
and so the subsequent answer will contain a "LS" group and so the subsequent answer will contain a "LS" group
identical to that in the offer, as shown below:</t> identical to that in the offer, as shown below:</t>
<sourcecode name="" type="sdp" markers="false" pn="section-5.3.1-8">
<t>
<figure>
<artwork>
<![CDATA[
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 20000 UDP/TLS/RTP/SAVPF 0 m=audio 20000 UDP/TLS/RTP/SAVPF 0
a=mid:a1 a=mid:a1
a=msid:ms2 a=msid:ms2
m=video 20001 UDP/TLS/RTP/SAVPF 96 m=video 20001 UDP/TLS/RTP/SAVPF 96
a=mid:v1 a=mid:v1
a=msid:ms2 a=msid:ms2</sourcecode>
]]> <t indent="0" pn="section-5.3.1-9">However, if the answerer groups its
</artwork> tracks into separate
</figure>
</t>
<t>However, if the answerer groups its tracks into separate
MediaStreams, its transceivers will reference different MediaStreams, its transceivers will reference different
streams, and so the subsequent answer will not contain a "LS" streams, and so the subsequent answer will not contain a "LS"
group.</t> group.</t>
<sourcecode name="" type="sdp" markers="false" pn="section-5.3.1-10">
<t>
<figure>
<artwork>
<![CDATA[
m=audio 20000 UDP/TLS/RTP/SAVPF 0 m=audio 20000 UDP/TLS/RTP/SAVPF 0
a=mid:a1 a=mid:a1
a=msid:ms2a a=msid:ms2a
m=video 20001 UDP/TLS/RTP/SAVPF 96 m=video 20001 UDP/TLS/RTP/SAVPF 96
a=mid:v1 a=mid:v1
a=msid:ms2b a=msid:ms2b</sourcecode>
]]> <t indent="0" pn="section-5.3.1-11">Finally, if the answerer does not
</artwork> add any tracks, its
</figure>
</t>
<t>Finally, if the answerer does not add any tracks, its
transceivers will not reference any MediaStreams, causing the transceivers will not reference any MediaStreams, causing the
preferences of the offerer to be maintained, and so the preferences of the offerer to be maintained, and so the
subsequent answer will contain an identical "LS" group.</t> subsequent answer will contain an identical "LS" group.</t>
<sourcecode name="" type="sdp" markers="false" pn="section-5.3.1-12">
<t>
<figure>
<artwork>
<![CDATA[
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 20000 UDP/TLS/RTP/SAVPF 0 m=audio 20000 UDP/TLS/RTP/SAVPF 0
a=mid:a1 a=mid:a1
a=recvonly a=recvonly
m=video 20001 UDP/TLS/RTP/SAVPF 96 m=video 20001 UDP/TLS/RTP/SAVPF 96
a=mid:v1 a=mid:v1
a=recvonly a=recvonly</sourcecode>
]]> <t indent="0" pn="section-5.3.1-13">The example in <xref target="sec.d
</artwork> etailed-example" format="default" sectionFormat="of" derivedContent="Section 7.2
</figure> "/> shows a more involved case of "LS" group
</t>
<t>The
<xref target="sec.detailed-example" /> example later in this
document shows a more involved case of "LS" group
generation.</t> generation.</t>
<t indent="0" pn="section-5.3.1-14">The next step is to generate an "m
<t>The next step is to generate m= sections for each m= =" section for each "m="
section that is present in the remote offer, as specified in section that is present in the remote offer, as specified in
<xref target="RFC3264"></xref>, Section 6. For the purposes <xref target="RFC3264" sectionFormat="comma" section="6" format="defau lt" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-6" derivedContent="R FC3264"/>. For the purposes
of this discussion, any session-level attributes in the offer of this discussion, any session-level attributes in the offer
that are also valid as media-level attributes are considered that are also valid as media-level attributes are considered
to be present in each m= section. Each offered m= section to be present in each "m=" section. Each offered "m=" section
will have an associated RtpTransceiver, as described in will have an associated RtpTransceiver, as described in
<xref target="sec.applying-a-remote-desc" />. If there are <xref target="sec.applying-a-remote-desc" format="default" sectionForm
more RtpTransceivers than there are m= sections, the at="of" derivedContent="Section 5.10"/>. If there are
more RtpTransceivers than there are "m=" sections, the
unmatched RtpTransceivers will need to be associated in a unmatched RtpTransceivers will need to be associated in a
subsequent offer.</t> subsequent offer.</t>
<t indent="0" pn="section-5.3.1-15">For each offered "m=" section, if
<t>For each offered m= section, if any of the following any of the following
conditions are true, the corresponding m= section in the conditions are true, the corresponding "m=" section in the
answer MUST be marked as rejected by setting the port in the answer <bcp14>MUST</bcp14> be marked as rejected by setting the &lt;po
m= line to zero, as indicated in rt&gt; in the
<xref target="RFC3264"></xref>, Section 6, and further "m=" line to zero, as indicated in
processing for this m= section can be skipped: <xref target="RFC3264" sectionFormat="comma" section="6" format="defau
<list style="symbols"> lt" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-6" derivedContent="R
FC3264"/>, and further
<t>The associated RtpTransceiver has been stopped.</t> processing for this "m=" section can be skipped:
</t>
<t>None of the offered media formats are supported and, if <ul spacing="normal" bare="false" empty="false" indent="3" pn="section
applicable, allowed by codec preferences.</t> -5.3.1-16">
<li pn="section-5.3.1-16.1">The associated RtpTransceiver has been s
<t>The bundle policy is "max-bundle", and this is not the topped.</li>
first m= section or in the same bundle group as the first <li pn="section-5.3.1-16.2">There is no offered media format that is
m= section.</t> both supported
and, if applicable, allowed by codec preferences.</li>
<t>The bundle policy is "balanced", and this is not the <li pn="section-5.3.1-16.3">The bundle policy is "max-bundle", and t
first m= section for this media type or in the same bundle his is not the
group as the first m= section for this media type.</t> first "m=" section or in the same bundle group as the first
"m=" section.</li>
<t>This m= section is in a bundle group, and the group's <li pn="section-5.3.1-16.4">The bundle policy is "balanced", and thi
offerer tagged m= section is being rejected due to one of s is not the
the above reasons. This requires all m= sections in the first "m=" section for this media type or in the same bundle
group as the first "m=" section for this media type.</li>
<li pn="section-5.3.1-16.5">This "m=" section is in a bundle group,
and the group's
offerer tagged "m=" section is being rejected due to one of
the above reasons. This requires all "m=" sections in the
bundle group to be rejected, as specified in bundle group to be rejected, as specified in
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation" />, <xref target="RFC8843" sectionFormat="comma" section="7.3.3" format=
Section 7.3.3.</t> "default" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-7.3.3" derived
</list></t> Content="RFC8843"/>.</li>
</ul>
<t>Otherwise, each m= section in the answer should then be <t indent="0" pn="section-5.3.1-17">Otherwise, each "m=" section in th
e answer <bcp14>MUST</bcp14> then be
generated as specified in generated as specified in
<xref target="RFC3264"></xref>, Section 6.1. For the m= line <xref target="RFC3264" sectionFormat="comma" section="6.1" format="def
itself, the following rules must be followed: ault" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-6.1" derivedConten
<list style="symbols"> t="RFC3264"/>. For the "m=" line
itself, the following rules <bcp14>MUST</bcp14> be followed:</t>
<t>The port value would normally be set to the port of the <ul spacing="normal" bare="false" empty="false" indent="3" pn="section
default ICE candidate for this m= section, but given that -5.3.1-18">
no candidates are available yet, the "dummy" port value of <li pn="section-5.3.1-18.1">The &lt;port&gt; value would normally be
9 (Discard) MUST be used, as indicated in set to the port of the
<xref target="I-D.ietf-ice-trickle"></xref>, Section default ICE candidate for this "m=" section, but given that
5.1.</t> no candidates are available yet, the default &lt;port&gt; value of
9 (Discard) <bcp14>MUST</bcp14> be used, as indicated in
<t>The &lt;proto&gt; field MUST be set to exactly match the <xref target="RFC8840" sectionFormat="comma" section="4.1.1" format=
&lt;proto&gt; field for the corresponding m= line in the "default" derivedLink="https://rfc-editor.org/rfc/rfc8840#section-4.1.1" derived
offer.</t> Content="RFC8840"/>.</li>
<li pn="section-5.3.1-18.2">The &lt;proto&gt; field <bcp14>MUST</bcp
<t>If codec preferences have been set for the associated 14> be set to exactly match the
transceiver, media formats MUST be generated in the &lt;proto&gt; field for the corresponding "m=" line in the
offer.</li>
<li pn="section-5.3.1-18.3">If codec preferences have been set for t
he associated
transceiver, media formats <bcp14>MUST</bcp14> be generated in the
corresponding order, regardless of what was offered, and corresponding order, regardless of what was offered, and
MUST exclude any codecs not present in the codec <bcp14>MUST</bcp14> exclude any codecs not present in the codec
preferences.</t> preferences.</li>
<li pn="section-5.3.1-18.4">Otherwise, the media formats on the "m="
<t>Otherwise, the media formats on the m= line MUST be line <bcp14>MUST</bcp14> be
generated in the same order as those offered in the current generated in the same order as those offered in the current
remote description, excluding any currently unsupported remote description, excluding any currently unsupported
formats. Any currently available media formats that are not formats. Any currently available media formats that are not
present in the current remote description MUST be added present in the current remote description <bcp14>MUST</bcp14> be add
after all existing formats.</t> ed
after all existing formats.</li>
<t>In either case, the media formats in the answer MUST <li pn="section-5.3.1-18.5">In either case, the media formats in the
include at least one format that is present in the offer, answer <bcp14>MUST</bcp14>
but MAY include formats that are locally supported but not include at least one format that is present in the offer
but <bcp14>MAY</bcp14> include formats that are locally supported bu
t not
present in the offer, as mentioned in present in the offer, as mentioned in
<xref target="RFC3264" />, Section 6.1. If no common format <xref target="RFC3264" sectionFormat="comma" section="6.1" format="d
exists, the m= section is rejected as described above.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-6.1" derivedCont
</list></t> ent="RFC3264"/>. If no common format
exists, the "m=" section is rejected as described above.</li>
<t>The m= line MUST be followed immediately by a "c=" line, </ul>
<t indent="0" pn="section-5.3.1-19">The "m=" line <bcp14>MUST</bcp14>
be followed immediately by a "c=" line,
as specified in as specified in
<xref target="RFC4566"></xref>, Section 5.7. Again, as no <xref target="RFC4566" sectionFormat="comma" section="5.7" format="def
candidates are available yet, the "c=" line must contain the ault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.7" derivedConten
"dummy" value "IN IP4 0.0.0.0", as defined in t="RFC4566"/>. Again, as no
<xref target="I-D.ietf-ice-trickle"></xref>, Section 5.1.</t> candidates are available yet, the "c=" line <bcp14>MUST</bcp14> contai
n the
<t>If the offer supports bundle, all m= sections to be default value "IN IP4 0.0.0.0", as defined in
bundled must use the same ICE credentials and candidates; all <xref target="RFC8840" sectionFormat="comma" section="4.1.3" format="d
m= sections not being bundled must use unique ICE credentials efault" derivedLink="https://rfc-editor.org/rfc/rfc8840#section-4.1.3" derivedCo
and candidates. Each m= section MUST contain the following ntent="RFC8840"/>.</t>
<t indent="0" pn="section-5.3.1-20">If the offer supports bundle, all
"m=" sections to be
bundled <bcp14>MUST</bcp14> use the same ICE credentials and candidate
s; all
"m=" sections not being bundled <bcp14>MUST</bcp14> use unique ICE cre
dentials
and candidates. Each "m=" section <bcp14>MUST</bcp14> contain the foll
owing
attributes (which are of attribute types other than IDENTICAL attributes (which are of attribute types other than IDENTICAL
and TRANSPORT): or TRANSPORT):
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>If and only if present in the offer, an "a=mid" line, as -5.3.1-21">
<li pn="section-5.3.1-21.1">If and only if present in the offer, an
"a=mid" line, as
specified in specified in
<xref target="RFC5888"></xref>, Section 9.1. The "mid" <xref target="RFC5888" sectionFormat="comma" section="9.1" format="d
value MUST match that specified in the offer.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc5888#section-9.1" derivedCont
ent="RFC5888"/>. The MID
<t>A direction attribute, determined by applying the rules value <bcp14>MUST</bcp14> match that specified in the offer.</li>
<li pn="section-5.3.1-21.2">A direction attribute, determined by app
lying the rules
regarding the offered direction specified in regarding the offered direction specified in
<xref target="RFC3264" />, Section 6.1, and then <xref target="RFC3264" sectionFormat="comma" section="6.1" format="d efault" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-6.1" derivedCont ent="RFC3264"/>, and then
intersecting with the direction of the associated intersecting with the direction of the associated
RtpTransceiver. For example, in the case where an m= RtpTransceiver. For example, in the case where an "m="
section is offered as "sendonly", and the local transceiver section is offered as "sendonly" and the local transceiver
is set to "sendrecv", the result in the answer is a is set to "sendrecv", the result in the answer is a
"recvonly" direction.</t> "recvonly" direction.</li>
<li pn="section-5.3.1-21.3">For each media format on the "m=" line,
<t>For each media format on the m= line, "a=rtpmap" and "a=rtpmap" and "a=fmtp" lines, as specified in
"a=fmtp" lines, as specified in <xref target="RFC4566" sectionFormat="comma" section="6" format="def
<xref target="RFC4566"></xref>, Section 6, and ault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedContent=
<xref target="RFC3264"></xref>, Section 6.1.</t> "RFC4566"/> and
<xref target="RFC3264" sectionFormat="comma" section="6.1" format="d
<t>If "rtx" is present in the offer, for each primary codec efault" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-6.1" derivedCont
ent="RFC3264"/>.</li>
<li pn="section-5.3.1-21.4">If "rtx" is present in the offer, for ea
ch primary codec
where RTP retransmission should be used, a corresponding where RTP retransmission should be used, a corresponding
"a=rtpmap" line indicating "rtx" with the clock rate of the "a=rtpmap" line indicating "rtx" with the clock rate of the
primary codec and an "a=fmtp" line that references the primary codec and an "a=fmtp" line that references the
payload type of the primary codec, as specified in payload type of the primary codec, as specified in
<xref target="RFC4588"></xref>, Section 8.1.</t> <xref target="RFC4588" sectionFormat="comma" section="8.1" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc4588#section-8.1" derivedCont
<t>For each supported FEC mechanism, "a=rtpmap" and ent="RFC4588"/>.</li>
<li pn="section-5.3.1-21.5">For each supported FEC mechanism, "a=rtp
map" and
"a=fmtp" lines, as specified in "a=fmtp" lines, as specified in
<xref target="RFC4566"></xref>, Section 6. The FEC <xref target="RFC4566" sectionFormat="comma" section="6" format="def
mechanisms that MUST be supported are specified in ault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedContent=
<xref target="I-D.ietf-rtcweb-fec"></xref>, Section 6, and "RFC4566"/>. The FEC
mechanisms that <bcp14>MUST</bcp14> be supported are specified in
<xref target="RFC8854" sectionFormat="comma" section="7" format="def
ault" derivedLink="https://rfc-editor.org/rfc/rfc8854#section-7" derivedContent=
"RFC8854"/>, and
specific usage for each media type is outlined in Sections specific usage for each media type is outlined in Sections
4 and 5.</t> <xref target="sec.interface" format="counter" sectionFormat="of" der
ivedContent="4"/> and <xref target="sec.sdp-interaction-procedure" format="count
<t>If this m= section is for media with configurable er" sectionFormat="of" derivedContent="5"/>.</li>
<li pn="section-5.3.1-21.6">If this "m=" section is for media with c
onfigurable
durations of media per packet, e.g., audio, an "a=maxptime" durations of media per packet, e.g., audio, an "a=maxptime"
line, as described in line, as described in
<xref target="sec-create-offer" />.</t> <xref target="sec-create-offer" format="default" sectionFormat="of"
derivedContent="Section 5.2"/>.</li>
<t>If this m= section is for video media, and there are <li pn="section-5.3.1-21.7">If this "m=" section is for video media
known limitations on the size of images which can be and there are
known limitations on the size of images that can be
decoded, an "a=imageattr" line, as specified in decoded, an "a=imageattr" line, as specified in
<xref target="sec.imageattr"></xref>.</t> <xref target="sec.imageattr" format="default" sectionFormat="of" der
ivedContent="Section 3.6"/>.</li>
<t>For each supported RTP header extension that is present <li pn="section-5.3.1-21.8">For each supported RTP header extension
that is present
in the offer, an "a=extmap" line, as specified in in the offer, an "a=extmap" line, as specified in
<xref target="RFC5285"></xref>, Section 5. The list of <xref target="RFC5285" sectionFormat="comma" section="5" format="def
header extensions that SHOULD/MUST be supported is ault" derivedLink="https://rfc-editor.org/rfc/rfc5285#section-5" derivedContent=
"RFC5285"/>. The list of
header extensions that <bcp14>SHOULD</bcp14>/<bcp14>MUST</bcp14> be
supported is
specified in specified in
<xref target="I-D.ietf-rtcweb-rtp-usage"></xref>, Section <xref target="RFC8834" sectionFormat="comma" section="5.2" format="d
5.2. Any header extensions that require encryption MUST be efault" derivedLink="https://rfc-editor.org/rfc/rfc8834#section-5.2" derivedCont
ent="RFC8834"/>. Any header extensions that require encryption <bcp14>MUST</bcp1
4> be
specified as indicated in specified as indicated in
<xref target="RFC6904"></xref>, Section 4.</t> <xref target="RFC6904" sectionFormat="comma" section="4" format="def
ault" derivedLink="https://rfc-editor.org/rfc/rfc6904#section-4" derivedContent=
<t>For each supported RTCP feedback mechanism that is "RFC6904"/>.</li>
<li pn="section-5.3.1-21.9">For each supported RTCP feedback mechani
sm that is
present in the offer, an "a=rtcp-fb" line, as specified in present in the offer, an "a=rtcp-fb" line, as specified in
<xref target="RFC4585"></xref>, Section 4.2. The list of <xref target="RFC4585" sectionFormat="comma" section="4.2" format="d
RTCP feedback mechanisms that SHOULD/MUST be supported is efault" derivedLink="https://rfc-editor.org/rfc/rfc4585#section-4.2" derivedCont
ent="RFC4585"/>. The list of
RTCP feedback mechanisms that <bcp14>SHOULD</bcp14>/<bcp14>MUST</bcp
14> be supported is
specified in specified in
<xref target="I-D.ietf-rtcweb-rtp-usage"></xref>, Section <xref target="RFC8834" sectionFormat="comma" section="5.1" format="d
5.1.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8834#section-5.1" derivedCont
ent="RFC8834"/>.</li>
<t>If the RtpTransceiver has a sendrecv or sendonly <li pn="section-5.3.1-21.10">
<t indent="0" pn="section-5.3.1-21.10.1">If the RtpTransceiver has
a sendrecv or sendonly
direction: direction:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="sec
<t>For each MediaStream that was associated with the tion-5.3.1-21.10.2">
<li pn="section-5.3.1-21.10.2.1">For each MediaStream that was a
ssociated with the
transceiver when it was created via addTrack or transceiver when it was created via addTrack or
addTransceiver, an "a=msid" line, as specified in addTransceiver, an "a=msid" line, as specified in
<xref target="I-D.ietf-mmusic-msid"></xref>, Section 2, <xref target="RFC8830" sectionFormat="comma" section="2" format="d
but omitting the "appdata" field.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8830#section-2" derivedConten
</list></t> t="RFC8830"/>,
</list></t> but omitting the "appdata" field.</li>
</ul>
<t>Each m= section which is not bundled into another m= </li>
section, MUST contain the following attributes (which are of </ul>
<t indent="0" pn="section-5.3.1-22">Each "m=" section that is not bund
led into another "m="
section <bcp14>MUST</bcp14> contain the following attributes (which ar
e of
category IDENTICAL or TRANSPORT):</t> category IDENTICAL or TRANSPORT):</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t> -5.3.1-23">
<list style="symbols"> <li pn="section-5.3.1-23.1">"a=ice-ufrag" and "a=ice-pwd" lines, as
specified in
<t>"a=ice-ufrag" and "a=ice-pwd" lines, as specified in <xref target="RFC8839" sectionFormat="comma" section="5.4" format=
<xref target="I-D.ietf-mmusic-ice-sip-sdp"></xref>, "default" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.4" derivedCo
Section 4.4.</t> ntent="RFC8839"/>.</li>
<li pn="section-5.3.1-23.2">For each desired digest algorithm, one o
<t>For each desired digest algorithm, one or more r more
"a=fingerprint" lines for each of the endpoint's "a=fingerprint" lines for each of the endpoint's
certificates, as specified in certificates, as specified in
<xref target="RFC8122"></xref>, Section 5.</t> <xref target="RFC8122" sectionFormat="comma" section="5" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc8122#section-5" derivedConten
<t>An "a=setup" line, as specified in t="RFC8122"/>.</li>
<xref target="RFC4145"></xref>, Section 4, and clarified <li pn="section-5.3.1-23.3">An "a=setup" line, as specified in
<xref target="RFC4145" sectionFormat="comma" section="4" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc4145#section-4" derivedConten
t="RFC4145"/> and clarified
for use in DTLS-SRTP scenarios in for use in DTLS-SRTP scenarios in
<xref target="RFC5763"></xref>, Section 5. The role value <xref target="RFC5763" sectionFormat="comma" section="5" format="d
in the answer MUST be "active" or "passive". When the efault" derivedLink="https://rfc-editor.org/rfc/rfc5763#section-5" derivedConten
t="RFC5763"/>. The role value
in the answer <bcp14>MUST</bcp14> be "active" or "passive". When t
he
offer contains the "actpass" value, as will always be the offer contains the "actpass" value, as will always be the
case with JSEP endpoints, the answerer SHOULD use the case with JSEP endpoints, the answerer <bcp14>SHOULD</bcp14> use t
"active" role. Offers from non-JSEP endpoints MAY send he
other values for "a=setup", in which case the answer MUST "active" role. Offers from non-JSEP endpoints <bcp14>MAY</bcp14> s
use a value consistent with the value in the offer.</t> end
other values for "a=setup", in which case the answer <bcp14>MUST</
<t>An "a=tls-id" line, as specified in bcp14>
<xref target="I-D.ietf-mmusic-dtls-sdp" />, Section use a value consistent with the value in the offer.</li>
5.3.</t> <li pn="section-5.3.1-23.4">An "a=tls-id" line, as specified in
<xref target="RFC8842" sectionFormat="comma" section="5.3" format=
<t>If present in the offer, an "a=rtcp-mux" line, as "default" derivedLink="https://rfc-editor.org/rfc/rfc8842#section-5.3" derivedCo
ntent="RFC8842"/>.</li>
<li pn="section-5.3.1-23.5">If present in the offer, an "a=rtcp-mux"
line, as
specified in specified in
<xref target="RFC5761"></xref>, Section 5.1.3. Otherwise, <xref target="RFC5761" sectionFormat="comma" section="5.1.3" forma t="default" derivedLink="https://rfc-editor.org/rfc/rfc5761#section-5.1.3" deriv edContent="RFC5761"/>. Otherwise,
an "a=rtcp" line, as specified in an "a=rtcp" line, as specified in
<xref target="RFC3605"></xref>, Section 2.1, containing <xref target="RFC3605" sectionFormat="comma" section="2.1" format=
the dummy value "9 IN IP4 0.0.0.0" (because no candidates "default" derivedLink="https://rfc-editor.org/rfc/rfc3605#section-2.1" derivedCo
have yet been gathered).</t> ntent="RFC3605"/>, containing
the default value "9 IN IP4 0.0.0.0" (because no candidates
<t>If present in the offer, an "a=rtcp-rsize" line, as have yet been gathered).</li>
<li pn="section-5.3.1-23.6">If present in the offer, an "a=rtcp-rsiz
e" line, as
specified in specified in
<xref target="RFC5506"></xref>, Section 5.</t> <xref target="RFC5506" sectionFormat="comma" section="5" format="d
</list> efault" derivedLink="https://rfc-editor.org/rfc/rfc5506#section-5" derivedConten
</t> t="RFC5506"/>.</li>
</ul>
<t>If a data channel m= section has been offered, a m= <t indent="0" pn="section-5.3.1-24">If a data channel "m=" section has
section MUST also be generated for data. The &lt;media&gt; been offered, an "m="
field MUST be set to "application" and the &lt;proto&gt; and section <bcp14>MUST</bcp14> also be generated for data. The &lt;media&
&lt;fmt&gt; fields MUST be set to exactly match the fields in gt;
field <bcp14>MUST</bcp14> be set to "application", and the &lt;proto&g
t; and
&lt;fmt&gt; fields <bcp14>MUST</bcp14> be set to exactly match the fie
lds in
the offer.</t> the offer.</t>
<t indent="0" pn="section-5.3.1-25">Within the data "m=" section, an "
<t>Within the data m= section, an "a=mid" line MUST be a=mid" line <bcp14>MUST</bcp14> be
generated and included as described above, along with an generated and included as described above, along with an
"a=sctp-port" line referencing the SCTP port number, as "a=sctp-port" line referencing the SCTP port number, as
defined in defined in
<xref target="I-D.ietf-mmusic-sctp-sdp"></xref>, Section 5.1, <xref target="RFC8841" sectionFormat="comma" section="5.1" format="def ault" derivedLink="https://rfc-editor.org/rfc/rfc8841#section-5.1" derivedConten t="RFC8841"/>;
and, if appropriate, an "a=max-message-size" line, as defined and, if appropriate, an "a=max-message-size" line, as defined
in in
<xref target="I-D.ietf-mmusic-sctp-sdp"></xref>, Section <xref target="RFC8841" sectionFormat="comma" section="6.1" format="def
6.1.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc8841#section-6.1" derivedConten
t="RFC8841"/>.</t>
<t>As discussed above, the following attributes of category <t indent="0" pn="section-5.3.1-26">As discussed above, the following
IDENTICAL or TRANSPORT are included only if the data m= attributes of category
section is not bundled into another m= section: IDENTICAL or TRANSPORT are included only if the data "m="
<list style="symbols"> section is not bundled into another "m=" section:
</t>
<t>"a=ice-ufrag"</t> <ul spacing="normal" bare="false" empty="false" indent="3" pn="section
-5.3.1-27">
<t>"a=ice-pwd"</t> <li pn="section-5.3.1-27.1">"a=ice-ufrag"</li>
<li pn="section-5.3.1-27.2">"a=ice-pwd"</li>
<t>"a=fingerprint"</t> <li pn="section-5.3.1-27.3">"a=fingerprint"</li>
<li pn="section-5.3.1-27.4">"a=setup"</li>
<t>"a=setup"</t> <li pn="section-5.3.1-27.5">"a=tls-id"</li>
</ul>
<t>"a=tls-id"</t> <t indent="0" pn="section-5.3.1-28">Note that if media "m=" sections a
</list></t> re bundled into a data "m="
<t>Note that if media m= sections are bundled into a data m=
section, then certain TRANSPORT and IDENTICAL attributes may section, then certain TRANSPORT and IDENTICAL attributes may
also appear in the data m= section even if they would also appear in the data "m=" section even if they would
otherwise only be appropriate for a media m= section (e.g., otherwise only be appropriate for a media "m=" section (e.g.,
"a=rtcp-mux").</t> "a=rtcp-mux").</t>
<t indent="0" pn="section-5.3.1-29">If "a=group" attributes with seman
<t>If "a=group" attributes with semantics of "BUNDLE" are tics of "BUNDLE" are
offered, corresponding session-level "a=group" attributes offered, corresponding session-level "a=group" attributes
MUST be added as specified in <bcp14>MUST</bcp14> be added as specified in
<xref target="RFC5888"></xref>. These attributes MUST have <xref target="RFC5888" format="default" sectionFormat="of" derivedCont
semantics "BUNDLE", and MUST include the all mid identifiers ent="RFC5888"/>. These attributes <bcp14>MUST</bcp14> have
semantics "BUNDLE" and <bcp14>MUST</bcp14> include all mid identifiers
from the offered bundle groups that have not been rejected. from the offered bundle groups that have not been rejected.
Note that regardless of the presence of "a=bundle-only" in Note that regardless of the presence of "a=bundle-only" in
the offer, no m= sections in the answer should have an the offer, all "m=" sections in the answer <bcp14>MUST NOT</bcp14> hav e an
"a=bundle-only" line.</t> "a=bundle-only" line.</t>
<t indent="0" pn="section-5.3.1-30">Attributes that are common between
<t>Attributes that are common between all m= sections MAY be all "m=" sections <bcp14>MAY</bcp14> be
moved to session-level, if explicitly defined to be valid at moved to the session level if explicitly defined to be valid at
session-level.</t> the session level.</t>
<t indent="0" pn="section-5.3.1-31">The attributes prohibited in the c
<t>The attributes prohibited in the creation of offers are reation of offers are
also prohibited in the creation of answers.</t> also prohibited in the creation of answers.</t>
</section> </section>
<section title="Subsequent Answers" <section anchor="sec.subsequent-answers" numbered="true" toc="include" r
anchor="sec.subsequent-answers"> emoveInRFC="false" pn="section-5.3.2">
<name slugifiedName="name-subsequent-answers">Subsequent Answers</name
<t>When createAnswer is called a second (or later) time, or >
<t indent="0" pn="section-5.3.2-1">When createAnswer is called a secon
d (or later) time or
is called after a local description has already been is called after a local description has already been
installed, the processing is somewhat different than for an installed, the processing is somewhat different than for an
initial answer.</t> initial answer.</t>
<t indent="0" pn="section-5.3.2-2">If the previous answer was not appl
<t>If the previous answer was not applied using ied using
setLocalDescription, meaning the PeerConnection is still in setLocalDescription, meaning the PeerConnection is still in
the "have-remote-offer" state, the steps for generating an the "have-remote-offer" state, the steps for generating an
initial answer should be followed, subject to the following initial answer <bcp14>MUST</bcp14> be followed, subject to the followi ng
restriction: restriction:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>The fields of the "o=" line MUST stay the same except -5.3.2-3">
for the &lt;session-version&gt; field, which MUST increment <li pn="section-5.3.2-3.1">The fields of the "o=" line <bcp14>MUST</
bcp14> stay the same except
for the &lt;session-version&gt; field, which <bcp14>MUST</bcp14> inc
rement
if the session description changes in any way from the if the session description changes in any way from the
previously generated answer.</t> previously generated answer.</li>
</list></t> </ul>
<t indent="0" pn="section-5.3.2-4">If any session description was prev
<t>If any session description was previously supplied to iously supplied to
setLocalDescription, an answer is generated by following the setLocalDescription, an answer is generated by following the
steps in the "have-remote-offer" state above, along with steps in the "have-remote-offer" state above, along with
these exceptions: these exceptions:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>The "s=" and "t=" lines MUST stay the same.</t> -5.3.2-5">
<li pn="section-5.3.2-5.1">The "s=" and "t=" lines <bcp14>MUST</bcp1
<t>Each "m=" and c=" line MUST be filled in with the port 4> stay the same.</li>
and address of the default candidate for the m= section, as <li pn="section-5.3.2-5.2">Each "m=" and "c=" line <bcp14>MUST</bcp1
4> be filled in with the port
and address of the default candidate for the "m=" section, as
described in described in
<xref target="I-D.ietf-mmusic-ice-sip-sdp"></xref>, <xref target="RFC8839" sectionFormat="comma" section="4.2.1.2" forma
Section 3.2.1.2. Note that in certain cases, the m= line protocol t="default" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-4.2.1.2" der
may not match that of the default candidate, because the m= line ivedContent="RFC8839"/>. Note that in certain cases, the "m=" line protocol
protocol value MUST match what was supplied in the offer, as may not match that of the default candidate, because the "m=" line
described above.</t> protocol value <bcp14>MUST</bcp14> match what was supplied in the of
fer, as
<t>Each "a=ice-ufrag" and "a=ice-pwd" line MUST stay the described above.</li>
same, unless the m= section is restarting, in which case <li pn="section-5.3.2-5.3">Each "a=ice-ufrag" and "a=ice-pwd" line <
new ICE credentials must be created as specified in bcp14>MUST</bcp14> stay the
<xref target="I-D.ietf-mmusic-ice-sip-sdp"></xref>, same, unless the "m=" section is restarting, in which case
Section 3.4.1.1.1. If the m= new ICE credentials <bcp14>MUST</bcp14> be created as specified in
section is bundled into another m= section, it still MUST <xref target="RFC8839" sectionFormat="comma" section="4.4.1.1.1" for
NOT contain any ICE credentials.</t> mat="default" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-4.4.1.1.1"
derivedContent="RFC8839"/>. If the "m="
<t>Each "a=tls-id" line MUST stay the same unless the section is bundled into another "m=" section, it still <bcp14>MUST N
OT</bcp14> contain any ICE credentials.</li>
<li pn="section-5.3.2-5.4">Each "a=tls-id" line <bcp14>MUST</bcp14>
stay the same, unless the
offerer's "a=tls-id" line changed, in which case a new offerer's "a=tls-id" line changed, in which case a new
"a=tls-id" value MUST be created, as described in tls-id value <bcp14>MUST</bcp14> be created, as described in
<xref target="I-D.ietf-mmusic-dtls-sdp" />, Section <xref target="RFC8842" sectionFormat="comma" section="5.2" format="d
5.2.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8842#section-5.2" derivedCont
ent="RFC8842"/>.</li>
<t>Each "a=setup" line MUST use an "active" or "passive" <li pn="section-5.3.2-5.5">Each "a=setup" line <bcp14>MUST</bcp14> u
se an "active" or "passive"
role value consistent with the existing DTLS association, role value consistent with the existing DTLS association,
if the association is being continued by the offerer.</t> if the association is being continued by the offerer.</li>
<li pn="section-5.3.2-5.6">RTCP multiplexing <bcp14>MUST</bcp14> be
<t>RTCP multiplexing must be used, and an "a=rtcp-mux" line used, and an "a=rtcp-mux" line
inserted if and only if the m= section previously used RTCP inserted if and only if the "m=" section previously used RTCP
multiplexing.</t> multiplexing.</li>
<li pn="section-5.3.2-5.7">If the "m=" section is not bundled into a
<t>If the m= section is not bundled into another m= section nother "m=" section
and RTCP multiplexing is not active, an "a=rtcp" attribute and RTCP multiplexing is not active, an "a=rtcp" attribute
line MUST be filled in with the port and address of the line <bcp14>MUST</bcp14> be filled in with the port and address of t he
default RTCP candidate. If no RTCP candidates have yet been default RTCP candidate. If no RTCP candidates have yet been
gathered, dummy values MUST be used, as described in the gathered, default values <bcp14>MUST</bcp14> be used, as described i
initial answer section above.</t> n
<xref target="sec.initial-answers" format="default" sectionFormat="o
<t>If the m= section is not bundled into another m= f" derivedContent="Section 5.3.1"/> above.</li>
<li pn="section-5.3.2-5.8">If the "m=" section is not bundled into a
nother "m="
section, for each candidate that has been gathered during section, for each candidate that has been gathered during
the most recent gathering phase (see the most recent gathering phase (see
<xref target="sec.ice-gather-overview"></xref>), an <xref target="sec.ice-gather-overview" format="default" sectionForma
"a=candidate" line MUST be added, as defined in t="of" derivedContent="Section 3.5.1"/>), an
<xref target="I-D.ietf-mmusic-ice-sip-sdp"></xref>, "a=candidate" line <bcp14>MUST</bcp14> be added, as defined in
Section 4.1. <xref target="RFC8839" sectionFormat="comma" section="5.1" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.1" derivedCont
ent="RFC8839"/>.
If candidate gathering for the section has completed, an If candidate gathering for the section has completed, an
"a=end-of-candidates" attribute MUST be added, as described "a=end-of-candidates" attribute <bcp14>MUST</bcp14> be added, as des cribed
in in
<xref target="I-D.ietf-ice-trickle"></xref>, Section 9.3. <xref target="RFC8840" sectionFormat="comma" section="8.2" format="d
If the m= section is bundled into another m= section, both efault" derivedLink="https://rfc-editor.org/rfc/rfc8840#section-8.2" derivedCont
"a=candidate" and "a=end-of-candidates" MUST be ent="RFC8840"/>.
omitted.</t> If the "m=" section is bundled into another "m=" section, both
"a=candidate" and "a=end-of-candidates" <bcp14>MUST</bcp14> be
<t>For RtpTransceivers that are not stopped, the "a=msid" omitted.
line(s) MUST stay the same, regardless of changes to the </li>
<li pn="section-5.3.2-5.9">For RtpTransceivers that are not stopped,
the "a=msid"
line(s) <bcp14>MUST</bcp14> stay the same, regardless of changes to
the
transceiver's direction or track. If no "a=msid" line is transceiver's direction or track. If no "a=msid" line is
present in the current description, "a=msid" line(s) MUST present in the current description, "a=msid" line(s) <bcp14>MUST</bc p14>
be generated according to the same rules as for an initial be generated according to the same rules as for an initial
answer.</t> answer.</li>
</list></t> </ul>
</section> </section>
<section title="Options Handling" <section anchor="sec.options-handling2" numbered="true" toc="include" re
anchor="sec.options-handling2"> moveInRFC="false" pn="section-5.3.3">
<name slugifiedName="name-options-handling-2">Options Handling</name>
<t>The createAnswer method takes as a parameter an <t indent="0" pn="section-5.3.3-1">The createAnswer method takes as a
parameter an
RTCAnswerOptions object. The set of parameters for RTCAnswerOptions object. The set of parameters for
RTCAnswerOptions is different than those supported in RTCAnswerOptions is different than those supported in
RTCOfferOptions; the IceRestart option is unnecessary, as ICE RTCOfferOptions; the IceRestart option is unnecessary, as ICE
credentials will automatically be changed for all m= sections credentials will automatically be changed for all "m=" sections
where the offerer chose to perform ICE restart.</t> where the offerer chose to perform ICE restart.</t>
<t indent="0" pn="section-5.3.3-2">The following options are supported
<t>The following options are supported in in
RTCAnswerOptions.</t> RTCAnswerOptions.</t>
<section title="VoiceActivityDetection" <section anchor="sec.voiceactivitydetection2" numbered="true" toc="inc
anchor="sec.voiceactivitydetection2"> lude" removeInRFC="false" pn="section-5.3.3.1">
<name slugifiedName="name-voiceactivitydetection-2">VoiceActivityDet
<t>Silence suppression in the answer is handled as ection</name>
<t indent="0" pn="section-5.3.3.1-1">Silence suppression in the answ
er is handled as
described in described in
<xref target="sec.voiceactivitydetection1"></xref>, with <xref target="sec.voiceactivitydetection1" format="default" sectionF ormat="of" derivedContent="Section 5.2.3.2"/>, with
one exception: if support for silence suppression was not one exception: if support for silence suppression was not
indicated in the offer, the VoiceActivityDetection indicated in the offer, the VoiceActivityDetection
parameter has no effect, and the answer should be generated parameter has no effect, and the answer <bcp14>MUST</bcp14> be gener
as if VoiceActivityDetection was set to false. This is done ated
as if VoiceActivityDetection was set to "false". This is done
on a per-codec basis (e.g., if the offerer somehow offered on a per-codec basis (e.g., if the offerer somehow offered
support for CN but set "usedtx=0" for Opus, setting support for CN but set "usedtx=0" for Opus, setting
VoiceActivityDetection to true would result in an answer VoiceActivityDetection to "true" would result in an answer
with CN codecs and "usedtx=0"). The impact of this rule is with CN codecs and "usedtx=0"). The impact of this rule is
that an answerer will not try to use silence suppression that an answerer will not try to use silence suppression
with any endpoint that does not offer it, making silence with any endpoint that does not offer it, making silence
suppression support bilateral even with non-JSEP suppression support bilateral even with non-JSEP
endpoints.</t> endpoints.</t>
</section> </section>
</section> </section>
</section> </section>
<section title="Modifying an Offer or Answer" <section anchor="sec.modifying-sdp" numbered="true" toc="include" removeIn
anchor="sec.modifying-sdp"> RFC="false" pn="section-5.4">
<name slugifiedName="name-modifying-an-offer-or-answe">Modifying an Offe
<t>The SDP returned from createOffer or createAnswer MUST NOT r or Answer</name>
<t indent="0" pn="section-5.4-1">The SDP returned from createOffer or cr
eateAnswer <bcp14>MUST NOT</bcp14>
be changed before passing it to setLocalDescription. If precise be changed before passing it to setLocalDescription. If precise
control over the SDP is needed, the aforementioned control over the SDP is needed, the aforementioned
createOffer/createAnswer options or RtpTransceiver APIs MUST be createOffer/createAnswer options or RtpTransceiver APIs <bcp14>MUST</bcp 14> be
used.</t> used.</t>
<t indent="0" pn="section-5.4-2">After calling setLocalDescription with
<t>After calling setLocalDescription with an offer or answer, an offer or answer,
the application MAY modify the SDP to reduce its capabilities the application <bcp14>MAY</bcp14> modify the SDP to reduce its capabili
ties
before sending it to the far side, as long as it follows the before sending it to the far side, as long as it follows the
rules above that define a valid JSEP offer or answer. Likewise, rules above that define a valid JSEP offer or answer. Likewise,
an application that has received an offer or answer from a peer an application that has received an offer or answer from a peer
MAY modify the received SDP, subject to the same constraints, <bcp14>MAY</bcp14> modify the received SDP, subject to the same constrai nts,
before calling setRemoteDescription.</t> before calling setRemoteDescription.</t>
<t indent="0" pn="section-5.4-3">As always, the application is solely re
<t>As always, the application is solely responsible for what it sponsible for what it
sends to the other party, and all incoming SDP will be sends to the other party, and all incoming SDP will be
processed by the JSEP implementation to the extent of its processed by the JSEP implementation to the extent of its
capabilities. It is an error to assume that all SDP is capabilities. It is an error to assume that all SDP is
well-formed; however, one should be able to assume that any well formed; however, one should be able to assume that any
implementation of this specification will be able to process, implementation of this specification will be able to process,
as a remote offer or answer, unmodified SDP coming from any as a remote offer or answer, unmodified SDP coming from any
other implementation of this specification.</t> other implementation of this specification.</t>
</section> </section>
<section title="Processing a Local Description" <section anchor="sec.processing-a-local-desc" numbered="true" toc="include
anchor="sec.processing-a-local-desc"> " removeInRFC="false" pn="section-5.5">
<name slugifiedName="name-processing-a-local-descript">Processing a Loca
<t>When a SessionDescription is supplied to l Description</name>
setLocalDescription, the following steps MUST be performed: <t indent="0" pn="section-5.5-1">When a SessionDescription is supplied t
<list style="symbols"> o
setLocalDescription, the following steps <bcp14>MUST</bcp14> be performe
<t>If the description is of type "rollback", follow the d:
</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section-5
.5-2">
<li pn="section-5.5-2.1">If the description is of type "rollback", fol
low the
processing defined in processing defined in
<xref target="sec.processing-a-rollback" /> and skip the <xref target="sec.processing-a-rollback" format="default" sectionForma
processing described in the rest of this section.</t> t="of" derivedContent="Section 5.7"/> and skip the
processing described in the rest of this section.</li>
<t>Otherwise, the type of the SessionDescription is checked <li pn="section-5.5-2.2">
<t indent="0" pn="section-5.5-2.2.1">Otherwise, the type of the Sess
ionDescription is checked
against the current state of the PeerConnection: against the current state of the PeerConnection:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="secti
<t>If the type is "offer", the PeerConnection state MUST be on-5.5-2.2.2">
either "stable" or "have-local-offer".</t> <li pn="section-5.5-2.2.2.1">If the type is "offer", the PeerConne
ction state <bcp14>MUST</bcp14> be
<t>If the type is "pranswer" or "answer", the either "stable" or "have-local-offer".</li>
PeerConnection state MUST be either "have-remote-offer" or <li pn="section-5.5-2.2.2.2">If the type is "pranswer" or "answer"
"have-local-pranswer".</t> , the
</list></t> PeerConnection state <bcp14>MUST</bcp14> be either "have-remote-offe
r" or
<t>If the type is not correct for the current state, "have-local-pranswer".</li>
processing MUST stop and an error MUST be returned.</t> </ul>
</li>
<t>The SessionDescription is then checked to ensure that its <li pn="section-5.5-2.3">If the type is not correct for the current st
ate,
processing <bcp14>MUST</bcp14> stop and an error <bcp14>MUST</bcp14> b
e returned.</li>
<li pn="section-5.5-2.4">The SessionDescription is then checked to ens
ure that its
contents are identical to those generated in the last call to contents are identical to those generated in the last call to
createOffer/createAnswer, and thus have not been altered, as createOffer/createAnswer, and thus have not been altered, as
discussed in discussed in
<xref target="sec.modifying-sdp" />; otherwise, processing <xref target="sec.modifying-sdp" format="default" sectionFormat="of" d
MUST stop and an error MUST be returned.</t> erivedContent="Section 5.4"/>; otherwise, processing
<bcp14>MUST</bcp14> stop and an error <bcp14>MUST</bcp14> be returned.
<t>Next, the SessionDescription is parsed into a data </li>
<li pn="section-5.5-2.5">Next, the SessionDescription is parsed into a
data
structure, as described in structure, as described in
<xref target="sec.parsing-a-desc" /> below.</t> <xref target="sec.parsing-a-desc" format="default" sectionFormat="of"
derivedContent="Section 5.8"/> below.</li>
<t>Finally, the parsed SessionDescription is applied as <li pn="section-5.5-2.6">Finally, the parsed SessionDescription is app
lied as
described in described in
<xref target="sec.applying-a-local-desc" /> below.</t> <xref target="sec.applying-a-local-desc" format="default" sectionForma
</list></t> t="of" derivedContent="Section 5.9"/> below.</li>
</ul>
</section> </section>
<section title="Processing a Remote Description" <section anchor="sec.processing-a-remote-desc" numbered="true" toc="includ
anchor="sec.processing-a-remote-desc"> e" removeInRFC="false" pn="section-5.6">
<name slugifiedName="name-processing-a-remote-descrip">Processing a Remo
<t>When a SessionDescription is supplied to te Description</name>
setRemoteDescription, the following steps MUST be performed: <t indent="0" pn="section-5.6-1">When a SessionDescription is supplied t
<list style="symbols"> o
setRemoteDescription, the following steps <bcp14>MUST</bcp14> be perform
<t>If the description is of type "rollback", follow the ed:
</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section-5
.6-2">
<li pn="section-5.6-2.1">If the description is of type "rollback", fol
low the
processing defined in processing defined in
<xref target="sec.processing-a-rollback" /> and skip the <xref target="sec.processing-a-rollback" format="default" sectionForma
processing described in the rest of this section.</t> t="of" derivedContent="Section 5.7"/> and skip the
processing described in the rest of this section.</li>
<t>Otherwise, the type of the SessionDescription is checked <li pn="section-5.6-2.2">
<t indent="0" pn="section-5.6-2.2.1">Otherwise, the type of the Sess
ionDescription is checked
against the current state of the PeerConnection: against the current state of the PeerConnection:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="secti
<t>If the type is "offer", the PeerConnection state MUST be on-5.6-2.2.2">
either "stable" or "have-remote-offer".</t> <li pn="section-5.6-2.2.2.1">If the type is "offer", the PeerConne
ction state <bcp14>MUST</bcp14> be
<t>If the type is "pranswer" or "answer", the either "stable" or "have-remote-offer".</li>
PeerConnection state MUST be either "have-local-offer" or <li pn="section-5.6-2.2.2.2">If the type is "pranswer" or "answer"
"have-remote-pranswer".</t> , the
</list></t> PeerConnection state <bcp14>MUST</bcp14> be either "have-local-offer
" or
<t>If the type is not correct for the current state, "have-remote-pranswer".</li>
processing MUST stop and an error MUST be returned.</t> </ul>
</li>
<t>Next, the SessionDescription is parsed into a data <li pn="section-5.6-2.3">If the type is not correct for the current st
ate,
processing <bcp14>MUST</bcp14> stop and an error <bcp14>MUST</bcp14> b
e returned.</li>
<li pn="section-5.6-2.4">Next, the SessionDescription is parsed into a
data
structure, as described in structure, as described in
<xref target="sec.parsing-a-desc" /> below. If parsing fails <xref target="sec.parsing-a-desc" format="default" sectionFormat="of"
for any reason, processing MUST stop and an error MUST be derivedContent="Section 5.8"/> below. If parsing fails
returned.</t> for any reason, processing <bcp14>MUST</bcp14> stop and an error <bcp1
4>MUST</bcp14> be
<t>Finally, the parsed SessionDescription is applied as returned.</li>
<li pn="section-5.6-2.5">Finally, the parsed SessionDescription is app
lied as
described in described in
<xref target="sec.applying-a-remote-desc" /> below.</t> <xref target="sec.applying-a-remote-desc" format="default" sectionForm
</list></t> at="of" derivedContent="Section 5.10"/> below.</li>
</ul>
</section> </section>
<section title="Processing a Rollback" <section anchor="sec.processing-a-rollback" numbered="true" toc="include"
anchor="sec.processing-a-rollback"> removeInRFC="false" pn="section-5.7">
<name slugifiedName="name-processing-a-rollback">Processing a Rollback</
<t>A rollback may be performed if the PeerConnection is in any name>
<t indent="0" pn="section-5.7-1">A rollback may be performed if the Peer
Connection is in any
state except for "stable". This means that both offers and state except for "stable". This means that both offers and
provisional answers can be rolled back. Rollback can only be provisional answers can be rolled back. Rollback can only be
used to cancel proposed changes; there is no support for used to cancel proposed changes; there is no support for
rolling back from a stable state to a previous stable state. If rolling back from a "stable" state to a previous "stable" state. If
a rollback is attempted in the "stable" state, processing MUST a rollback is attempted in the "stable" state, processing <bcp14>MUST</b
stop and an error MUST be returned. Note that this implies that cp14>
once the answerer has performed setLocalDescription with his stop and an error <bcp14>MUST</bcp14> be returned. Note that this implie
s that
once the answerer has performed setLocalDescription with its
answer, this cannot be rolled back.</t> answer, this cannot be rolled back.</t>
<t indent="0" pn="section-5.7-2">The effect of rollback <bcp14>MUST</bcp
<t>The effect of rollback MUST be the same regardless of 14> be the same regardless of
whether setLocalDescription or setRemoteDescription is whether setLocalDescription or setRemoteDescription is
called.</t> called.</t>
<t indent="0" pn="section-5.7-3">In order to process rollback, a JSEP im
<t>In order to process rollback, a JSEP implementation abandons plementation abandons
the current offer/answer transaction, sets the signaling state the current offer/answer transaction, sets the signaling state
to "stable", and sets the pending local and/or remote to "stable", and sets the pending local and/or remote
description (see description (see Sections
<xref target="sec.pendinglocaldescription" /> and <xref target="sec.pendinglocaldescription" format="counter" sectionForma
<xref target="sec.pendingremotedescription" />) to null. Any t="of" derivedContent="4.1.14"/> and
<xref target="sec.pendingremotedescription" format="counter" sectionForm
at="of" derivedContent="4.1.16"/>) to "null". Any
resources or candidates that were allocated by the abandoned resources or candidates that were allocated by the abandoned
local description are discarded; any media that is received is local description are discarded; any media that is received is
processed according to the previous local and remote processed according to the previous local and remote
descriptions.</t> descriptions.</t>
<t indent="0" pn="section-5.7-4">A rollback disassociates any RtpTransce
<t>A rollback disassociates any RtpTransceivers that were ivers that were
associated with m= sections by the application of the associated with "m=" sections by the application of the
rolled-back session description (see rolled-back session description (see Sections
<xref target="sec.applying-a-remote-desc" /> and <xref target="sec.applying-a-remote-desc" format="counter" sectionFormat
<xref target="sec.applying-a-local-desc" />). This means that ="of" derivedContent="5.10"/> and
<xref target="sec.applying-a-local-desc" format="counter" sectionFormat=
"of" derivedContent="5.9"/>).
This means that
some RtpTransceivers that were previously associated will no some RtpTransceivers that were previously associated will no
longer be associated with any m= section; in such cases, the longer be associated with any "m=" section; in such cases, the
value of the RtpTransceiver's mid property MUST be set to null, value of the RtpTransceiver's mid property <bcp14>MUST</bcp14> be set to
and the mapping between the transceiver and its m= section "null",
index MUST be discarded. RtpTransceivers that were created by and the mapping between the transceiver and its "m=" section
applying a remote offer that was subsequently rolled back MUST index <bcp14>MUST</bcp14> be discarded. RtpTransceivers that were create
be stopped and removed from the PeerConnection. However, a d by
RtpTransceiver MUST NOT be removed if a track was attached to applying a remote offer that was subsequently rolled back <bcp14>MUST</b
cp14>
be stopped and removed from the PeerConnection. However, an
RtpTransceiver <bcp14>MUST NOT</bcp14> be removed if a track was attache
d to
the RtpTransceiver via the addTrack method. This is so that an the RtpTransceiver via the addTrack method. This is so that an
application may call addTrack, then call setRemoteDescription application may call addTrack, then call setRemoteDescription
with an offer, then roll back that offer, then call createOffer with an offer, then roll back that offer, then call createOffer
and have a m= section for the added track appear in the and have an "m=" section for the added track appear in the
generated offer.</t> generated offer.</t>
</section> </section>
<section title="Parsing a Session Description" <section anchor="sec.parsing-a-desc" numbered="true" toc="include" removeI
anchor="sec.parsing-a-desc"> nRFC="false" pn="section-5.8">
<name slugifiedName="name-parsing-a-session-descripti">Parsing a Session
<t>The SDP contained in the session description object consists Description</name>
<t indent="0" pn="section-5.8-1">The SDP contained in the session descri
ption object consists
of a sequence of text lines, each containing a key-value of a sequence of text lines, each containing a key-value
expression, as described in expression, as described in
<xref target="RFC4566" />, Section 5. The SDP is read, <xref target="RFC4566" sectionFormat="comma" section="5" format="default
line-by-line, and converted to a data structure that contains " derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5" derivedContent="RFC
4566"/>. The SDP is read,
line by line, and converted to a data structure that contains
the deserialized information. However, SDP allows many types of the deserialized information. However, SDP allows many types of
lines, not all of which are relevant to JSEP applications. For lines, not all of which are relevant to JSEP applications. For
each line, the implementation will first ensure it is each line, the implementation will first ensure that it is
syntactically correct according to its defining ABNF, check syntactically correct according to its defining ABNF, check
that it conforms to that it conforms to the semantics used in
<xref target="RFC4566" /> and <xref target="RFC4566" format="default" sectionFormat="of" derivedConten
<xref target="RFC3264" /> semantics, and then either parse and t="RFC4566"/> and
<xref target="RFC3264" format="default" sectionFormat="of" derivedConten
t="RFC3264"/>, and then either parse and
store or discard the provided value, as described below.</t> store or discard the provided value, as described below.</t>
<t indent="0" pn="section-5.8-2">If any line is not well formed or canno
<t>If any line is not well-formed, or cannot be parsed as t be parsed as
described, the parser MUST stop with an error and reject the described, the parser <bcp14>MUST</bcp14> stop with an error and reject
the
session description, even if the value is to be discarded. This session description, even if the value is to be discarded. This
ensures that implementations do not accidentally misinterpret ensures that implementations do not accidentally misinterpret
ambiguous SDP.</t> ambiguous SDP.</t>
<section title="Session-Level Parsing" <section anchor="sec.session-level-parse" numbered="true" toc="include"
anchor="sec.session-level-parse"> removeInRFC="false" pn="section-5.8.1">
<name slugifiedName="name-session-level-parsing">Session-Level Parsing
<t>First, the session-level lines are checked and parsed. </name>
These lines MUST occur in a specific order, and with a <t indent="0" pn="section-5.8.1-1">First, the session-level lines are
checked and parsed.
These lines <bcp14>MUST</bcp14> occur in a specific order, and with a
specific syntax, as defined in specific syntax, as defined in
<xref target="RFC4566" />, Section 5. Note that while the <xref target="RFC4566" sectionFormat="comma" section="5" format="defau
specific line types (e.g. "v=", "c=") MUST occur in the lt" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5" derivedContent="R
FC4566"/>. Note that while the
specific line types (e.g., "v=", "c=") <bcp14>MUST</bcp14> occur in th
e
defined order, lines of the same type (typically "a=") can defined order, lines of the same type (typically "a=") can
occur in any order.</t> occur in any order.</t>
<t indent="0" pn="section-5.8.1-2">The following non-attribute lines a
<t>The following non-attribute lines are not meaningful in re not meaningful in
the JSEP context and MAY be discarded once they have been the JSEP context and <bcp14>MAY</bcp14> be discarded once they have be
en
checked. checked.
<list> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>The "c=" line MUST be checked for syntax but its value -5.8.1-3">
<li pn="section-5.8.1-3.1">The "c=" line <bcp14>MUST</bcp14> be chec
ked for syntax, but its value
is only used for ICE mismatch detection, as defined in is only used for ICE mismatch detection, as defined in
<xref target="RFC8445" />, Section 5.4. Note that JSEP <xref target="RFC8445" sectionFormat="comma" section="5.4" format="d efault" derivedLink="https://rfc-editor.org/rfc/rfc8445#section-5.4" derivedCont ent="RFC8445"/>. Note that JSEP
implementations should never encounter this condition implementations should never encounter this condition
because ICE is required for WebRTC.</t> because ICE is required for WebRTC.</li>
<li pn="section-5.8.1-3.2">The "i=", "u=", "e=", "p=", "t=", "r=", "
<t>The "i=", "u=", "e=", "p=", "t=", "r=", "z=", and "k=" z=", and "k="
lines are not used by this specification; they MUST be lines <bcp14>MUST</bcp14> be
checked for syntax but their values are not used.</t> checked for syntax, but their values are not otherwise used. </li>
</list></t> </ul>
<t indent="0" pn="section-5.8.1-4">The remaining non-attribute lines a
<t>The remaining non-attribute lines are processed as re processed as
follows: follows:
<list> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>The "v=" line MUST have a version of 0, as specified in -5.8.1-5">
<xref target="RFC4566" />, Section 5.1.</t> <li pn="section-5.8.1-5.1">The "v=" line <bcp14>MUST</bcp14> have a
version of 0, as specified in
<t>The "o=" line MUST be parsed as specified in <xref target="RFC4566" sectionFormat="comma" section="5.1" format="d
<xref target="RFC4566" />, Section 5.2.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.1" derivedCont
ent="RFC4566"/>.</li>
<t>The "b=" line, if present, MUST be parsed as specified <li pn="section-5.8.1-5.2">The "o=" line <bcp14>MUST</bcp14> be pars
ed as specified in
<xref target="RFC4566" sectionFormat="comma" section="5.2" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.2" derivedCont
ent="RFC4566"/>.</li>
<li pn="section-5.8.1-5.3">The "b=" line, if present, <bcp14>MUST</b
cp14> be parsed as specified
in in
<xref target="RFC4566" />, Section 5.8, and the bwtype and <xref target="RFC4566" sectionFormat="comma" section="5.8" format="d
bandwidth values stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.8" derivedCont
</list></t> ent="RFC4566"/>, and the bwtype and
bandwidth values stored.</li>
<t>Finally, the attribute lines are processed. Specific </ul>
processing MUST be applied for the following session-level <t indent="0" pn="section-5.8.1-6">Finally, the attribute lines are pr
ocessed. Specific
processing <bcp14>MUST</bcp14> be applied for the following session-le
vel
attribute ("a=") lines: attribute ("a=") lines:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>Any "a=group" lines are parsed as specified in -5.8.1-7">
<xref target="RFC5888" />, Section 5, and the group's <li pn="section-5.8.1-7.1">Any "a=group" lines are parsed as specifi
semantics and mids are stored.</t> ed in
<xref target="RFC5888" sectionFormat="comma" section="5" format="def
<t>If present, a single "a=ice-lite" line is parsed as ault" derivedLink="https://rfc-editor.org/rfc/rfc5888#section-5" derivedContent=
specified in "RFC5888"/>, and the group's
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, semantics and mids are stored.</li>
Section 4.3, and a value <li pn="section-5.8.1-7.2">If present, a single "a=ice-lite" line is
indicating the presence of ice-lite is stored.</t> parsed as
<t>If present, a single "a=ice-ufrag" line is parsed as
specified in specified in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, <xref target="RFC8839" sectionFormat="comma" section="5.3" format="d
Section 4.4, and the ufrag value is stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.3" derivedCont
ent="RFC8839"/>, and a value
<t>If present, a single "a=ice-pwd" line is parsed as indicating the presence of ice-lite is stored.</li>
<li pn="section-5.8.1-7.3">If present, a single "a=ice-ufrag" line i
s parsed as
specified in specified in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, <xref target="RFC8839" sectionFormat="comma" section="5.4" format="d
Section 4.4, and the password value is stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.4" derivedCont
ent="RFC8839"/>, and the ufrag value is stored.</li>
<t>If present, a single "a=ice-options" line is parsed as <li pn="section-5.8.1-7.4">If present, a single "a=ice-pwd" line is
parsed as
specified in specified in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, <xref target="RFC8839" sectionFormat="comma" section="5.4" format="d
Section 4.6, and the set of specified options is stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.4" derivedCont
ent="RFC8839"/>, and the password value is stored.</li>
<t>Any "a=fingerprint" lines are parsed as specified in <li pn="section-5.8.1-7.5">If present, a single "a=ice-options" line
<xref target="RFC8122" />, Section 5, and the set of is parsed as
fingerprint and algorithm values is stored.</t>
<t>If present, a single "a=setup" line is parsed as
specified in specified in
<xref target="RFC4145" />, Section 4, and the setup value <xref target="RFC8839" sectionFormat="comma" section="5.6" format="d
is stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.6" derivedCont
ent="RFC8839"/>, and the set of specified options is stored.</li>
<t>If present, a single "a=tls-id" line is parsed as <li pn="section-5.8.1-7.6">Any "a=fingerprint" lines are parsed as s
pecified in
<xref target="RFC8122" sectionFormat="comma" section="5" format="def
ault" derivedLink="https://rfc-editor.org/rfc/rfc8122#section-5" derivedContent=
"RFC8122"/>, and the set of
fingerprint and algorithm values is stored.</li>
<li pn="section-5.8.1-7.7">If present, a single "a=setup" line is pa
rsed as
specified in specified in
<xref target="I-D.ietf-mmusic-dtls-sdp" /> Section 5, and <xref target="RFC4145" sectionFormat="comma" section="4" format="def
the tls-id value is stored.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc4145#section-4" derivedContent=
"RFC4145"/>, and the setup value
<t>Any "a=identity" lines are parsed and the identity is stored.</li>
values stored for subsequent verification, as specified <li pn="section-5.8.1-7.8">If present, a single "a=tls-id" line is p
<xref target="I-D.ietf-rtcweb-security-arch" />, Section arsed as
5.</t> specified in <xref target="RFC8842" sectionFormat="comma" section="5
" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8842#section-5" de
<t>Any "a=extmap" lines are parsed as specified in rivedContent="RFC8842"/>, and
<xref target="RFC5285" />, Section 5, and their values are the attribute value is stored.</li>
stored.</t> <li pn="section-5.8.1-7.9">Any "a=identity" lines are parsed and the
</list></t> identity
values stored for subsequent verification, as specified in
<t>Other attributes that are not relevant to JSEP may also be <xref target="RFC8827" sectionFormat="comma" section="5" format="def
present, and implementations SHOULD process any that they ault" derivedLink="https://rfc-editor.org/rfc/rfc8827#section-5" derivedContent=
"RFC8827"/>.</li>
<li pn="section-5.8.1-7.10">Any "a=extmap" lines are parsed as speci
fied in
<xref target="RFC5285" sectionFormat="comma" section="5" format="def
ault" derivedLink="https://rfc-editor.org/rfc/rfc5285#section-5" derivedContent=
"RFC5285"/>, and their values are
stored.</li>
</ul>
<t indent="0" pn="section-5.8.1-8">Other attributes that are not relev
ant to JSEP may also be
present, and implementations <bcp14>SHOULD</bcp14> process any that th
ey
recognize. As required by recognize. As required by
<xref target="RFC4566"></xref>, Section 5.13, unknown <xref target="RFC4566" sectionFormat="comma" section="5.13" format="de
attribute lines MUST be ignored.</t> fault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.13" derivedCont
ent="RFC4566"/>, unknown
<t>Once all the session-level lines have been parsed, attribute lines <bcp14>MUST</bcp14> be ignored.</t>
processing continues with the lines in m= sections.</t> <t indent="0" pn="section-5.8.1-9">Once all the session-level lines ha
ve been parsed,
processing continues with the lines in "m=" sections.</t>
</section> </section>
<section title="Media Section Parsing" <section anchor="sec.media-level-parse" numbered="true" toc="include" re
anchor="sec.media-level-parse"> moveInRFC="false" pn="section-5.8.2">
<name slugifiedName="name-media-section-parsing">Media Section Parsing
<t>Like the session-level lines, the media section lines MUST </name>
<t indent="0" pn="section-5.8.2-1">Like the session-level lines, the m
edia section lines <bcp14>MUST</bcp14>
occur in the specific order and with the specific syntax occur in the specific order and with the specific syntax
defined in defined in
<xref target="RFC4566" />, Section 5.</t> <xref target="RFC4566" sectionFormat="comma" section="5" format="defau
lt" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5" derivedContent="R
<t>The "m=" line itself MUST be parsed as described in FC4566"/>.</t>
<xref target="RFC4566" />, Section 5.14, and the media, port, <t indent="0" pn="section-5.8.2-2">The "m=" line itself <bcp14>MUST</b
proto, and fmt values stored.</t> cp14> be parsed as described in
<xref target="RFC4566" sectionFormat="comma" section="5.14" format="de
<t>Following the "m=" line, specific processing MUST be fault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.14" derivedCont
ent="RFC4566"/>, and the &lt;media&gt;, &lt;port&gt;,
&lt;proto&gt;, and &lt;fmt&gt; values stored.</t>
<t indent="0" pn="section-5.8.2-3">Following the "m=" line, specific p
rocessing <bcp14>MUST</bcp14> be
applied for the following non-attribute lines: applied for the following non-attribute lines:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>As with the "c=" line at the session level, the "c=" -5.8.2-4">
line MUST be parsed according to <li pn="section-5.8.2-4.1">As with the "c=" line at the session leve
<xref target="RFC4566" />, Section 5.7, but its value is l, the "c="
not used.</t> line <bcp14>MUST</bcp14> be parsed according to
<xref target="RFC4566" sectionFormat="comma" section="5.7" format="d
<t>The "b=" line, if present, MUST be parsed as specified efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.7" derivedCont
ent="RFC4566"/>, but its value is
not used.</li>
<li pn="section-5.8.2-4.2">The "b=" line, if present, <bcp14>MUST</b
cp14> be parsed as specified
in in
<xref target="RFC4566" />, Section 5.8, and the bwtype and <xref target="RFC4566" sectionFormat="comma" section="5.8" format="d
bandwidth values stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.8" derivedCont
</list></t> ent="RFC4566"/>, and the bwtype and
bandwidth values stored.</li>
<t>Specific processing MUST also be applied for the following </ul>
<t indent="0" pn="section-5.8.2-5">Specific processing <bcp14>MUST</bc
p14> also be applied for the following
attribute lines: attribute lines:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>If present, a single "a=ice-ufrag" line is parsed as -5.8.2-6">
<li pn="section-5.8.2-6.1">If present, a single "a=ice-ufrag" line i
s parsed as
specified in specified in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, <xref target="RFC8839" sectionFormat="comma" section="5.4" format="d
Section 4.4, and the ufrag value is stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.4" derivedCont
ent="RFC8839"/>, and the ufrag value is stored.</li>
<t>If present, a single "a=ice-pwd" line is parsed as <li pn="section-5.8.2-6.2">If present, a single "a=ice-pwd" line is
parsed as
specified in specified in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, <xref target="RFC8839" sectionFormat="comma" section="5.4" format="d
Section 4.4, and the password value is stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.4" derivedCont
ent="RFC8839"/>, and the password value is stored.</li>
<t>If present, a single "a=ice-options" line is parsed as <li pn="section-5.8.2-6.3">If present, a single "a=ice-options" line
is parsed as
specified in specified in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, Section 4.6, <xref target="RFC8839" sectionFormat="comma" section="5.6" format="d
and the set of specified options is stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.6" derivedCont
ent="RFC8839"/>,
<t>Any "a=candidate" attributes MUST be parsed as specified and the set of specified options is stored.</li>
<li pn="section-5.8.2-6.4">Any "a=candidate" attributes <bcp14>MUST<
/bcp14> be parsed as specified
in in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, <xref target="RFC8839" sectionFormat="comma" section="5.1" format="d
Section 4.1, and their values stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.1" derivedCont
ent="RFC8839"/>, and their values stored.</li>
<t>Any "a=remote-candidates" attributes MUST be parsed as <li pn="section-5.8.2-6.5">Any "a=remote-candidates" attributes <bcp
14>MUST</bcp14> be parsed as
specified in specified in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, <xref target="RFC8839" sectionFormat="comma" section="5.2" format="d
Section 4.2, but their values are ignored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.2" derivedCont
ent="RFC8839"/>, but their values are ignored.</li>
<t>If present, a single "a=end-of-candidates" attribute <li pn="section-5.8.2-6.6">If present, a single "a=end-of-candidates
MUST be parsed as specified in " attribute
<xref target="I-D.ietf-ice-trickle" />, Section 8.2, and <bcp14>MUST</bcp14> be parsed as specified in
its presence or absence flagged and stored.</t> <xref target="RFC8840" sectionFormat="comma" section="8.1" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc8840#section-8.1" derivedCont
<t>Any "a=fingerprint" lines are parsed as specified in ent="RFC8840"/>, and
<xref target="RFC8122" />, Section 5, and the set of its presence or absence flagged and stored.</li>
fingerprint and algorithm values is stored.</t> <li pn="section-5.8.2-6.7">Any "a=fingerprint" lines are parsed as s
</list></t> pecified in
<xref target="RFC8122" sectionFormat="comma" section="5" format="def
<t>If the "m=" proto value indicates use of RTP, as described ault" derivedLink="https://rfc-editor.org/rfc/rfc8122#section-5" derivedContent=
"RFC8122"/>, and the set of
fingerprint and algorithm values is stored.</li>
</ul>
<t indent="0" pn="section-5.8.2-7">If the "m=" &lt;proto&gt; value ind
icates use of RTP, as described
in in
<xref target="sec.profile-names" /> above, the following <xref target="sec.profile-names" format="default" sectionFormat="of" d
attribute lines MUST be processed: erivedContent="Section 5.1.2"/> above, the following
<list style="symbols"> attribute lines <bcp14>MUST</bcp14> be processed:
</t>
<t>The "m=" fmt value MUST be parsed as specified in <ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<xref target="RFC4566" />, Section 5.14, and the individual -5.8.2-8">
values stored.</t> <li pn="section-5.8.2-8.1">The "m=" &lt;fmt&gt; value <bcp14>MUST</b
cp14> be parsed as specified in
<t>Any "a=rtpmap" or "a=fmtp" lines MUST be parsed as <xref target="RFC4566" sectionFormat="comma" section="5.14" format="
default" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.14" derivedCo
ntent="RFC4566"/>, and the individual
values stored.</li>
<li pn="section-5.8.2-8.2">Any "a=rtpmap" or "a=fmtp" lines <bcp14>M
UST</bcp14> be parsed as
specified in specified in
<xref target="RFC4566" />, Section 6, and their values <xref target="RFC4566" sectionFormat="comma" section="6" format="def
stored.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedContent=
"RFC4566"/>, and their values
<t>If present, a single "a=ptime" line MUST be parsed as stored.</li>
<li pn="section-5.8.2-8.3">If present, a single "a=ptime" line <bcp1
4>MUST</bcp14> be parsed as
described in described in
<xref target="RFC4566" />, Section 6, and its value <xref target="RFC4566" sectionFormat="comma" section="6" format="def
stored.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedContent=
"RFC4566"/>, and its value
<t>If present, a single "a=maxptime" line MUST be parsed as stored.</li>
<li pn="section-5.8.2-8.4">If present, a single "a=maxptime" line <b
cp14>MUST</bcp14> be parsed as
described in described in
<xref target="RFC4566" />, Section 6, and its value <xref target="RFC4566" sectionFormat="comma" section="6" format="def
stored.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedContent=
"RFC4566"/>, and its value
<t>If present, a single direction attribute line (e.g. stored.</li>
"a=sendrecv") MUST be parsed as described in <li pn="section-5.8.2-8.5">If present, a single direction attribute
<xref target="RFC4566" />, Section 6, and its value line (e.g.,
stored.</t> "a=sendrecv") <bcp14>MUST</bcp14> be parsed as described in
<xref target="RFC4566" sectionFormat="comma" section="6" format="def
<t>Any "a=ssrc" attributes MUST be parsed as specified in ault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedContent=
<xref target="RFC5576" />, Section 4.1, and their values "RFC4566"/>, and its value
stored.</t> stored.</li>
<li pn="section-5.8.2-8.6">Any "a=ssrc" attributes <bcp14>MUST</bcp1
<t>Any "a=extmap" attributes MUST be parsed as specified in 4> be parsed as specified in
<xref target="RFC5576" sectionFormat="comma" section="4.1" format="d
<xref target="RFC5285" />, Section 5, and their values efault" derivedLink="https://rfc-editor.org/rfc/rfc5576#section-4.1" derivedCont
stored.</t> ent="RFC5576"/>, and their values
stored.</li>
<li pn="section-5.8.2-8.7">Any "a=extmap" attributes <bcp14>MUST</bc
p14> be parsed as specified in
<t>Any "a=rtcp-fb" attributes MUST be parsed as specified <xref target="RFC5285" sectionFormat="comma" section="5" format="def
ault" derivedLink="https://rfc-editor.org/rfc/rfc5285#section-5" derivedContent=
"RFC5285"/>, and their values
stored.</li>
<li pn="section-5.8.2-8.8">Any "a=rtcp-fb" attributes <bcp14>MUST</b
cp14> be parsed as specified
in in
<xref target="RFC4585" />, Section 4.2., and their values <xref target="RFC4585" sectionFormat="comma" section="4.2" format="d
stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc4585#section-4.2" derivedCont
ent="RFC4585"/>, and their values
<t>If present, a single "a=rtcp-mux" attribute MUST be stored.</li>
<li pn="section-5.8.2-8.9">If present, a single "a=rtcp-mux" attribu
te <bcp14>MUST</bcp14> be
parsed as specified in parsed as specified in
<xref target="RFC5761"></xref>, Section 5.1.3, and its <xref target="RFC5761" sectionFormat="comma" section="5.1.3" format=
presence or absence flagged and stored.</t> "default" derivedLink="https://rfc-editor.org/rfc/rfc5761#section-5.1.3" derived
Content="RFC5761"/>, and its
<t>If present, a single "a=rtcp-mux-only" attribute MUST be presence or absence flagged and stored.</li>
<li pn="section-5.8.2-8.10">If present, a single "a=rtcp-mux-only" a
ttribute <bcp14>MUST</bcp14> be
parsed as specified in parsed as specified in
<xref target="I-D.ietf-mmusic-mux-exclusive" />, Section 3, <xref target="RFC8858" sectionFormat="comma" section="3" format="def
and its presence or absence flagged and stored.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc8858#section-3" derivedContent=
"RFC8858"/>,
<t>If present, a single "a=rtcp-rsize" attribute MUST be and its presence or absence flagged and stored.</li>
<li pn="section-5.8.2-8.11">If present, a single "a=rtcp-rsize" attr
ibute <bcp14>MUST</bcp14> be
parsed as specified in parsed as specified in
<xref target="RFC5506" />, Section 5, and its presence or <xref target="RFC5506" sectionFormat="comma" section="5" format="def
absence flagged and stored.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc5506#section-5" derivedContent=
"RFC5506"/>, and its presence or
<t>If present, a single "a=rtcp" attribute MUST be parsed absence flagged and stored.</li>
<li pn="section-5.8.2-8.12">If present, a single "a=rtcp" attribute
<bcp14>MUST</bcp14> be parsed
as specified in as specified in
<xref target="RFC3605" />, Section 2.1, but its value is <xref target="RFC3605" sectionFormat="comma" section="2.1" format="d efault" derivedLink="https://rfc-editor.org/rfc/rfc3605#section-2.1" derivedCont ent="RFC3605"/>, but its value is
ignored, as this information is superfluous when using ignored, as this information is superfluous when using
ICE.</t> ICE.</li>
<li pn="section-5.8.2-8.13">If present, "a=msid" attributes <bcp14>M
<t>If present, "a=msid" attributes MUST be parsed as UST</bcp14> be parsed as
specified in specified in
<xref target="I-D.ietf-mmusic-msid" />, Section 3.2, and <xref target="RFC8830" sectionFormat="comma" section="3.2" format="d efault" derivedLink="https://rfc-editor.org/rfc/rfc8830#section-3.2" derivedCont ent="RFC8830"/>, and
their values stored, ignoring any "appdata" field. If no "a=msid" their values stored, ignoring any "appdata" field. If no "a=msid"
attributes are present, a random msid-id value is generated for a attributes are present, a random msid-id value is generated for a
"default" MediaStream for the session, if not already present, and "default" MediaStream for the session, if not already present, and
this value is stored.</t> this value is stored.</li>
<li pn="section-5.8.2-8.14">Any "a=imageattr" attributes <bcp14>MUST
<t>Any "a=imageattr" attributes MUST be parsed as specified </bcp14> be parsed as specified
in in
<xref target="RFC6236" />, Section 3, and their values <xref target="RFC6236" sectionFormat="comma" section="3" format="def
stored.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc6236#section-3" derivedContent=
"RFC6236"/>, and their values
<t>Any "a=rid" lines MUST be parsed as specified in stored.</li>
<xref target="I-D.ietf-mmusic-rid"></xref>, Section 10, and <li pn="section-5.8.2-8.15">Any "a=rid" lines <bcp14>MUST</bcp14> be
their values stored.</t> parsed as specified in
<xref target="RFC8851" sectionFormat="comma" section="10" format="de
<t>If present, a single "a=simulcast" line MUST be parsed fault" derivedLink="https://rfc-editor.org/rfc/rfc8851#section-10" derivedConten
t="RFC8851"/>, and
their values stored.</li>
<li pn="section-5.8.2-8.16">If present, a single "a=simulcast" line
<bcp14>MUST</bcp14> be parsed
as specified in as specified in
<xref target="I-D.ietf-mmusic-sdp-simulcast"></xref>, and <xref target="RFC8853" format="default" sectionFormat="of" derivedCo
its values stored.</t> ntent="RFC8853"/>, and
</list></t> its values stored.</li>
</ul>
<t>Otherwise, if the "m=" proto value indicates use of SCTP, <t indent="0" pn="section-5.8.2-9">Otherwise, if the "m=" &lt;proto&gt
the following attribute lines MUST be processed: ; value indicates use of SCTP,
<list style="symbols"> the following attribute lines <bcp14>MUST</bcp14> be processed:
</t>
<t>The "m=" fmt value MUST be parsed as specified in <ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<xref target="I-D.ietf-mmusic-sctp-sdp" />, Section 4.3, -5.8.2-10">
and the application protocol value stored.</t> <li pn="section-5.8.2-10.1">The "m=" &lt;fmt&gt; value <bcp14>MUST<
/bcp14> be parsed as specified in
<t>An "a=sctp-port" attribute MUST be present, and it MUST <xref target="RFC8841" sectionFormat="comma" section="4.3" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc8841#section-4.3" derivedCont
ent="RFC8841"/>,
and the application protocol value stored.</li>
<li pn="section-5.8.2-10.2">An "a=sctp-port" attribute <bcp14>MUST</
bcp14> be present, and it <bcp14>MUST</bcp14>
be parsed as specified in be parsed as specified in
<xref target="I-D.ietf-mmusic-sctp-sdp" />, Section 5.2, <xref target="RFC8841" sectionFormat="comma" section="5.2" format="d
and the value stored.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc8841#section-5.2" derivedCont
ent="RFC8841"/>,
<t>If present, a single "a=max-message-size" attribute MUST and the value stored.</li>
<li pn="section-5.8.2-10.3">If present, a single "a=max-message-size
" attribute <bcp14>MUST</bcp14>
be parsed as specified in be parsed as specified in
<xref target="I-D.ietf-mmusic-sctp-sdp" />, Section 6, and <xref target="RFC8841" sectionFormat="comma" section="6" format="def
the value stored. Otherwise, use the specified default.</t> ault" derivedLink="https://rfc-editor.org/rfc/rfc8841#section-6" derivedContent=
</list></t> "RFC8841"/>, and
the value stored. Otherwise, use the specified default.</li>
<t>Other attributes that are not relevant to JSEP may also be </ul>
present, and implementations SHOULD process any that they <t indent="0" pn="section-5.8.2-11">Other attributes that are not rele
vant to JSEP may also be
present, and implementations <bcp14>SHOULD</bcp14> process any that th
ey
recognize. As required by recognize. As required by
<xref target="RFC4566"></xref>, Section 5.13, unknown <xref target="RFC4566" sectionFormat="comma" section="5.13" format="de
attribute lines MUST be ignored.</t> fault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.13" derivedCont
ent="RFC4566"/>, unknown
attribute lines <bcp14>MUST</bcp14> be ignored.</t>
</section> </section>
<section title="Semantics Verification"> <section numbered="true" toc="include" removeInRFC="false" pn="section-5
.8.3">
<t>Assuming parsing completes successfully, the parsed <name slugifiedName="name-semantics-verification">Semantics Verificati
on</name>
<t indent="0" pn="section-5.8.3-1">Assuming that parsing completes suc
cessfully, the parsed
description is then evaluated to ensure internal consistency description is then evaluated to ensure internal consistency
as well as proper support for mandatory features. as well as proper support for mandatory features.
Specifically, the following checks are performed: Specifically, the following checks are performed:
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section
<t>For each m= section, valid values for each of the -5.8.3-2">
<li pn="section-5.8.3-2.1">
<t indent="0" pn="section-5.8.3-2.1.1">For each "m=" section, vali
d values for each of the
mandatory-to-use features enumerated in mandatory-to-use features enumerated in
<xref target="sec.usage-requirements" /> MUST be present. <xref target="sec.usage-requirements" format="default" sectionFormat
These values MAY either be present at the media level, or ="of" derivedContent="Section 5.1.1"/> <bcp14>MUST</bcp14> be present.
These values <bcp14>MAY</bcp14> be either present at the media level
or
inherited from the session level. inherited from the session level.
<list style="symbols"> </t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="sec
<t>ICE ufrag and password values, which MUST comply with tion-5.8.3-2.1.2">
<li pn="section-5.8.3-2.1.2.1">ICE ufrag and password values, wh
ich <bcp14>MUST</bcp14> comply with
the size limits specified in the size limits specified in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, Section 4.4.</t> <xref target="RFC8839" sectionFormat="comma" section="5.4" format=
"default" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.4" derivedCo
<t>tls-id value, which MUST be set according to ntent="RFC8839"/>.</li>
<xref target="I-D.ietf-mmusic-dtls-sdp" />, Section 5. If <li pn="section-5.8.3-2.1.2.2">A tls-id value, which <bcp14>MUST
this is a re-offer or a response to a re-offer and the </bcp14> be set according to
tls-id value is different from that presently in use, the <xref target="RFC8842" sectionFormat="comma" section="5" format="d
DTLS connection is not being continued and the remote efault" derivedLink="https://rfc-editor.org/rfc/rfc8842#section-5" derivedConten
description MUST be part of an ICE restart, together with t="RFC8842"/>. If
new ufrag and password values.</t> this is a re-offer or a response to a re-offer and the
tls-id value is different from that presently in use, the
<t>DTLS setup value, which MUST be set according to the DTLS connection is not being continued and the remote
rules specified in description <bcp14>MUST</bcp14> be part of an ICE restart, togethe
<xref target="RFC5763" />, Section 5 and MUST be r with
consistent with the selected role of the current DTLS new ufrag and password values.</li>
connection, if one exists and is being continued.</t> <li pn="section-5.8.3-2.1.2.3">A DTLS setup value, which <bcp14>
MUST</bcp14> be set according to the
<t>DTLS fingerprint values, where at least one rules specified in
fingerprint MUST be present.</t> <xref target="RFC5763" sectionFormat="comma" section="5" format="d
</list></t> efault" derivedLink="https://rfc-editor.org/rfc/rfc5763#section-5" derivedConten
t="RFC5763"/> and <bcp14>MUST</bcp14> be
<t>All RID values referenced in an "a=simulcast" line MUST consistent with the selected role of the current DTLS
exist as "a=rid" lines.</t> connection, if one exists and is being continued.</li>
<li pn="section-5.8.3-2.1.2.4">DTLS fingerprint values, where at
<t>Each m= section is also checked to ensure prohibited least one
features are not used.</t> fingerprint <bcp14>MUST</bcp14> be present.</li>
</ul>
<t>If the RTP/RTCP multiplexing policy is "require", each </li>
m= section MUST contain an "a=rtcp-mux" attribute. If an m= <li pn="section-5.8.3-2.2">All rid-ids referenced in an "a=simulcast
section contains an "a=rtcp-mux-only" attribute, that " line <bcp14>MUST</bcp14>
section MUST also contain an "a=rtcp-mux" attribute.</t> exist as "a=rid" lines.</li>
<li pn="section-5.8.3-2.3">Each "m=" section is also checked to ensu
<t>If an m= section was present in the previous answer, the re that prohibited
state of RTP/RTCP multiplexing MUST match what was features are not used.</li>
previously negotiated.</t> <li pn="section-5.8.3-2.4">If the RTP/RTCP multiplexing policy is "r
</list></t> equire", each
"m=" section <bcp14>MUST</bcp14> contain an "a=rtcp-mux" attribute.
<t>If this session description is of type "pranswer" or If an "m="
"answer", the following additional checks are applied: section contains an "a=rtcp-mux-only" attribute, that
<list style="symbols"> section <bcp14>MUST</bcp14> also contain an "a=rtcp-mux" attribute.<
/li>
<t>The session description must follow the rules defined in <li pn="section-5.8.3-2.5">If an "m=" section was present in the pre
vious answer, the
<xref target="RFC3264" />, Section 6, including the state of RTP/RTCP multiplexing <bcp14>MUST</bcp14> match what was
requirement that the number of m= sections MUST exactly previously negotiated.</li>
match the number of m= sections in the associated </ul>
offer.</t> <t indent="0" pn="section-5.8.3-3">If this session description is of t
ype "pranswer" or
<t>For each m= section, the media type and protocol values "answer", the following additional checks are applied:
MUST exactly match the media type and protocol values in </t>
the corresponding m= section in the associated offer.</t> <ul spacing="normal" bare="false" empty="false" indent="3" pn="section
</list></t> -5.8.3-4">
<li pn="section-5.8.3-4.1">The session description <bcp14>MUST</bcp1
<t>If any of the preceding checks failed, processing MUST 4> follow the rules defined in
stop and an error MUST be returned.</t> <xref target="RFC3264" sectionFormat="comma" section="6" format="def
ault" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-6" derivedContent=
"RFC3264"/>, including the
requirement that the number of "m=" sections <bcp14>MUST</bcp14> exa
ctly
match the number of "m=" sections in the associated
offer.</li>
<li pn="section-5.8.3-4.2">For each "m=" section, the media type and
protocol values
<bcp14>MUST</bcp14> exactly match the media type and protocol values
in
the corresponding "m=" section in the associated offer.</li>
</ul>
<t indent="0" pn="section-5.8.3-5">If any of the preceding checks fail
ed, processing <bcp14>MUST</bcp14>
stop and an error <bcp14>MUST</bcp14> be returned.</t>
</section> </section>
</section> </section>
<section title="Applying a Local Description" <section anchor="sec.applying-a-local-desc" numbered="true" toc="include"
anchor="sec.applying-a-local-desc"> removeInRFC="false" pn="section-5.9">
<name slugifiedName="name-applying-a-local-descriptio">Applying a Local
<t>The following steps are performed at the media engine level Description</name>
to apply a local description. If an error is returned, the <t indent="0" pn="section-5.9-1">The following steps are performed at th
session MUST be restored to the state it was in before e media engine level
performing these steps.</t> to apply a local description. If an error is returned, the
session <bcp14>MUST</bcp14> be restored to the state it was in before
<t>First, m= sections are processed. For each m= section, the performing these steps.</t>
following steps MUST be performed; if any parameters are out of <t indent="0" pn="section-5.9-2">First, "m=" sections are processed. For
bounds, or cannot be applied, processing MUST stop and an error each "m=" section, the
MUST be returned. following steps <bcp14>MUST</bcp14> be performed; if any parameters are
<list style="symbols"> out of
bounds or cannot be applied, processing <bcp14>MUST</bcp14> stop and an
<t>If this m= section is new, begin gathering candidates for error
it, as defined in <bcp14>MUST</bcp14> be returned.
<xref target="RFC8445" />, Section 5.1.1, unless it is </t>
definitively being bundled (either this is an offer and the <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-5
m= section is marked bundle-only, or it is an answer and the .9-3">
m= section is bundled into into another m= section.)</t> <li pn="section-5.9-3.1">If this "m=" section is new, begin gathering
candidates for
<t>Or, if the ICE ufrag and password values have changed, it, as defined in
trigger the ICE agent to start an ICE restart as described in <xref target="RFC8445" sectionFormat="comma" section="5.1.1" format="d
<xref target="RFC8445" />, Section 9, and begin efault" derivedLink="https://rfc-editor.org/rfc/rfc8445#section-5.1.1" derivedCo
gathering new candidates for the m= section. If this ntent="RFC8445"/>, unless it is
description is an answer, also start checks on that media definitively being bundled (either (1) this is an offer and the
section.</t> "m=" section is marked bundle-only or (2) it is an answer and the
"m=" section is bundled into another "m=" section).</li>
<t>If the m= section proto value indicates use of RTP: <li pn="section-5.9-3.2">Or, if the ICE ufrag and password values have
<list style="symbols"> changed,
trigger the ICE agent to start an ICE restart as described in
<t>If there is no RtpTransceiver associated with this m= <xref target="RFC8445" sectionFormat="comma" section="9" format="defau
section, find one and associate it with this m= section lt" derivedLink="https://rfc-editor.org/rfc/rfc8445#section-9" derivedContent="R
according to the following steps. Note that this situation FC8445"/>, and begin
will only occur when applying an offer. gathering new candidates for the "m=" section. If this
<list style="symbols"> description is an answer, also start checks on that media
section.</li>
<t>Find the RtpTransceiver that corresponds to this m= <li pn="section-5.9-3.3">
section, using the mapping between transceivers and m= <t indent="0" pn="section-5.9-3.3.1">If the "m=" section &lt;proto&g
section indices established when creating the offer.</t> t; value indicates use of RTP:
</t>
<t>Set the value of this RtpTransceiver's mid property to <ul spacing="normal" bare="false" empty="false" indent="3" pn="secti
the MID of the m= section.</t> on-5.9-3.3.2">
</list></t> <li pn="section-5.9-3.3.2.1">
<t indent="0" pn="section-5.9-3.3.2.1.1">If there is no RtpTrans
<t>If RTCP mux is indicated, prepare to demux RTP and RTCP ceiver associated with this "m="
from the RTP ICE component, as specified in section, find one and associate it with this "m=" section
<xref target="RFC5761" />, Section 5.1.3.</t> according to the following steps. Note that this situation
will only occur when applying an offer.
<t>For each specified RTP header extension, establish a </t>
mapping between the extension ID and URI, as described in <ul spacing="normal" bare="false" empty="false" indent="3" pn="s
<xref target="RFC5285" />, Section 6.</t> ection-5.9-3.3.2.1.2">
<li pn="section-5.9-3.3.2.1.2.1">Find the RtpTransceiver that
<t>If the MID header extension is supported, prepare to corresponds to this "m="
demux RTP streams intended for this m= section based on the section, using the mapping between transceivers and "m="
MID header extension, as described in section indices established when creating the offer.</li>
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation" />, <li pn="section-5.9-3.3.2.1.2.2">Set the value of this RtpTran
Section 15.</t> sceiver's mid property to
the MID of the "m=" section.</li>
<t>For each specified media format, establish a mapping </ul>
between the payload type and the actual media format, as </li>
described in <li pn="section-5.9-3.3.2.2">If RTCP mux is indicated, prepare to
<xref target="RFC3264" />, Section 6.1. In addition, demux RTP and RTCP
prepare to demux RTP streams intended for this m= section from the RTP ICE component, as specified in
based on the media formats supported by this m= section, as <xref target="RFC5761" sectionFormat="comma" section="5.1.3" format=
described in "default" derivedLink="https://rfc-editor.org/rfc/rfc5761#section-5.1.3" derived
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation" />, Content="RFC5761"/>.</li>
Section 10.2.</t> <li pn="section-5.9-3.3.2.3">For each specified RTP header extensi
on, establish a
<t>For each specified "rtx" media format, establish a mapping between the extension ID and URI, as described in
mapping between the RTX payload type and its associated <xref target="RFC5285" sectionFormat="comma" section="6" format="def
primary payload type, as described in ault" derivedLink="https://rfc-editor.org/rfc/rfc5285#section-6" derivedContent=
<xref target="RFC4588" />, Sections 8.6 and 8.7.</t> "RFC5285"/>.</li>
<li pn="section-5.9-3.3.2.4">If the MID header extension is suppor
<t>If the directional attribute is of type "sendrecv" or ted, prepare to
"recvonly", enable receipt and decoding of media.</t> demux RTP streams intended for this "m=" section based on the
</list></t> MID header extension, as described in
</list></t> <xref target="RFC8843" sectionFormat="comma" section="15" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-15" derivedConten
t="RFC8843"/>.</li>
<li pn="section-5.9-3.3.2.5">For each specified media format, esta
blish a mapping
between the payload type and the actual media format, as
described in
<xref target="RFC3264" sectionFormat="comma" section="6.1" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-6.1" derivedCont
ent="RFC3264"/>. In addition,
prepare to demux RTP streams intended for this "m=" section
based on the media formats supported by this "m=" section, as
described in
<xref target="RFC8843" sectionFormat="comma" section="9.2" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-9.2" derivedCont
ent="RFC8843"/>.
</li>
<li pn="section-5.9-3.3.2.6">For each specified "rtx" media format
, establish a
mapping between the RTX payload type and its associated
primary payload type, as described in
Sections <xref target="RFC4588" section="8.6" sectionFormat="bare" f
ormat="default" derivedLink="https://rfc-editor.org/rfc/rfc4588#section-8.6" der
ivedContent="RFC4588"/> and <xref target="RFC4588" section="8.7" sectionFormat="
bare" format="default" derivedLink="https://rfc-editor.org/rfc/rfc4588#section-8
.7" derivedContent="RFC4588"/> of <xref target="RFC4588" format="default" sectio
nFormat="of" derivedContent="RFC4588"/>.
<t>Finally, if this description is of type "pranswer" or </li>
"answer", follow the processing defined in <li pn="section-5.9-3.3.2.7">If the direction attribute is of type
<xref target="sec.applying-an-answer" /> below.</t> "sendrecv" or
"recvonly", enable receipt and decoding of media.</li>
</ul>
</li>
</ul>
<t indent="0" pn="section-5.9-4">Finally, if this description is of type
"pranswer" or
"answer", follow the processing defined in
<xref target="sec.applying-an-answer" format="default" sectionFormat="of
" derivedContent="Section 5.11"/> below.</t>
</section> </section>
<section title="Applying a Remote Description" <section anchor="sec.applying-a-remote-desc" numbered="true" toc="include"
anchor="sec.applying-a-remote-desc"> removeInRFC="false" pn="section-5.10">
<name slugifiedName="name-applying-a-remote-descripti">Applying a Remote
<t>The following steps are performed to apply a remote Description</name>
description. If an error is returned, the session MUST be <t indent="0" pn="section-5.10-1">The following steps are performed to a
restored to the state it was in before performing these pply a remote
steps.</t> description. If an error is returned, the session <bcp14>MUST</bcp14> be
restored to the state it was in before performing these
<t>If the answer contains any "a=ice-options" attributes where steps.</t>
"trickle" is listed as an attribute, update the PeerConnection <t indent="0" pn="section-5.10-2">If the answer contains any "a=ice-opti
canTrickle property to be true. Otherwise, set this property to ons" attributes where
false.</t> "trickle" is listed as an attribute, update the PeerConnection
canTrickleIceCandidates property to be "true". Otherwise, set this prope
<t>The following steps MUST be performed for attributes at the rty to
session level; if any parameters are out of bounds, or cannot "false".</t>
be applied, processing MUST stop and an error MUST be returned. <t indent="0" pn="section-5.10-3">The following steps <bcp14>MUST</bcp14
> be performed for attributes at the
<list style="symbols"> session level; if any parameters are out of bounds or cannot
be applied, processing <bcp14>MUST</bcp14> stop and an error <bcp14>MUST
<t>For any specified "CT" bandwidth value, set this as the </bcp14> be returned.
limit for the maximum total bitrate for all m= sections, as
specified in
<xref target="RFC4566"></xref>, Section 5.8. Within this
overall limit, the implementation can dynamically decide how
to best allocate the available bandwidth between m= sections,
respecting any specific limits that have been specified for
individual m= sections.</t>
<t>For any specified "RR" or "RS" bandwidth values, handle as
specified in
<xref target="RFC3556"></xref>, Section 2.</t>
<t>Any "AS" bandwidth value MUST be ignored, as the meaning
of this construct at the session level is not well
defined.</t>
</list></t>
<t>For each m= section, the following steps MUST be performed;
if any parameters are out of bounds, or cannot be applied,
processing MUST stop and an error MUST be returned.
<list style="symbols">
<t>If the ICE ufrag or password changed from the previous
remote description:
<list style="symbols">
<t>If the description is of type "offer", the
implementation MUST note that an ICE restart is needed, as
described in
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />,
Section 3.4.1.1.1</t>
<t>If the description is of type "answer" or "pranswer",
then check to see if the current local description is an
ICE restart, and if not, generate an error. If the
PeerConnection state is "have-remote-pranswer", and the ICE
ufrag or password changed from the previous provisional
answer, then signal the ICE agent to discard any previous
ICE check list state for the m= section. Finally, signal
the ICE agent to begin checks.</t>
</list></t>
<t>If the current local description indicates an ICE restart,
and either the ICE ufrag or password has not changed from the
previous remote description, as prescribed by
<xref target="RFC8445" />, Section 9, generate an
error.</t>
<t>Configure the ICE components associated with this media
section to use the supplied ICE remote ufrag and password for
their connectivity checks.</t>
<t>Pair any supplied ICE candidates with any gathered local
candidates, as described in
<xref target="RFC8445" />, Section 6.1.2, and start
connectivity checks with the appropriate credentials.</t>
<t>If an "a=end-of-candidates" attribute is present, process
the end-of-candidates indication as described in
<xref target="I-D.ietf-ice-trickle" />, Section 11.</t>
<t>If the m= section proto value indicates use of RTP:
<list style="symbols">
<t>If the m= section is being recycled (see
<xref target="sec.subsequent-offers"></xref>), dissociate
the currently associated RtpTransceiver by setting its mid
property to null, and discard the mapping between the
transceiver and its m= section index.</t>
<t>If the m= section is not associated with any
RtpTransceiver (possibly because it was dissociated in the
previous step), either find an RtpTransceiver or create one
according to the following steps:
<list style="symbols">
<t>If the m= section is sendrecv or recvonly, and there
are RtpTransceivers of the same type that were added to
the PeerConnection by addTrack and are not associated
with any m= section and are not stopped, find the first
(according to the canonical order described in
<xref target="sec.initial-offers" />) such
RtpTransceiver.</t>
<t>If no RtpTransceiver was found in the previous step,
create one with a recvonly direction.</t>
<t>Associate the found or created RtpTransceiver with the
m= section by setting the value of the RtpTransceiver's
mid property to the MID of the m= section, and establish
a mapping between the transceiver and the index of the m=
section. If the m= section does not include a MID (i.e.,
the remote endpoint does not support the MID extension),
generate a value for the RtpTransceiver mid property,
following the guidance for "a=mid" mentioned in
<xref target="sec.initial-offers" />.</t>
</list></t>
<t>For each specified media format that is also supported
by the local implementation, establish a mapping between
the specified payload type and the media format, as
described in
<xref target="RFC3264" />, Section 6.1. Specifically, this
means that the implementation records the payload type to
be used in outgoing RTP packets when sending each specified
media format, as well as the relative preference for each
format that is indicated in their ordering. If any
indicated media format is not supported by the local
implementation, it MUST be ignored.</t>
<t>For each specified "rtx" media format, establish a
mapping between the RTX payload type and its associated
primary payload type, as described in
<xref target="RFC4588" />, Section 4. If any referenced
primary payload types are not present, this MUST result in
an error. Note that RTX payload types may refer to primary
payload types which are not supported by the local media
implementation, in which case, the RTX payload type MUST
also be ignored.</t>
<t>For each specified fmtp parameter that is supported by
the local implementation, enable them on the associated
media formats.</t>
<t>For each specified SSRC that is signaled in the m=
section, prepare to demux RTP streams intended for this m=
section using that SSRC, as described in
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation" />,
Section 10.2.</t>
<t>For each specified RTP header extension that is also
supported by the local implementation, establish a mapping
between the extension ID and URI, as described in
<xref target="RFC5285" />, Section 5. Specifically, this
means that the implementation records the extension ID to
be used in outgoing RTP packets when sending each specified
header extension. If any indicated RTP header extension is
not supported by the local implementation, it MUST be
ignored.</t>
<t>For each specified RTCP feedback mechanism that is
supported by the local implementation, enable them on the
associated media formats.</t>
<t>For any specified "TIAS" bandwidth value, set this value
as a constraint on the maximum RTP bitrate to be used when
sending media, as specified in
<xref target="RFC3890"></xref>. If a "TIAS" value is not
present, but an "AS" value is specified, generate a "TIAS"
value using this formula:
<list style="format">
<t>TIAS = AS * 1000 * 0.95 - (50 * 40 * 8)</t>
</list>The 50 is based on 50 packets per second, the 40 is
based on an estimate of total header size, the 1000 changes
the unit from kbps to bps (as required by TIAS), and the
0.95 is to allocate 5% to RTCP. "TIAS" is used in
preference to "AS" because it provides more accurate
control of bandwidth.</t>
<t>For any "RR" or "RS" bandwidth values, handle as
specified in
<xref target="RFC3556"></xref>, Section 2.</t>
<t>Any specified "CT" bandwidth value MUST be ignored, as
the meaning of this construct at the media level is not
well defined.</t>
<t>If the m= section is of type audio:
<list style="symbols">
<t>For each specified "CN" media format, configure
silence suppression for all supported media formats with
the same clockrate, as described in
<xref target="RFC3389" />, Section 5, except for formats
that have their own internal silence suppression
mechanisms. Silence suppression for such formats (e.g.,
Opus) is controlled via fmtp parameters, as discussed in
<xref target="sec.voiceactivitydetection1" />.</t>
<t>For each specified "telephone-event" media format,
enable DTMF transmission for all supported media formats
with the same clockrate, as described in
<xref target="RFC4733" />, Section 2.5.1.2. If there are
any supported media formats that do not have a
corresponding telephone-event format, disable DTMF
transmission for those formats.</t>
<t>For any specified "ptime" value, configure the
available media formats to use the specified packet size
when sending. If the specified size is not supported for
a media format, use the next closest value instead.</t>
</list></t>
</list></t>
</list></t>
<t>Finally, if this description is of type "pranswer" or </t>
"answer", follow the processing defined in <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-5
<xref target="sec.applying-an-answer" /> below.</t> .10-4">
<li pn="section-5.10-4.1">For any specified "CT" bandwidth value, set
this value as the
limit for the maximum total bitrate for all "m=" sections, as
specified in
<xref target="RFC4566" sectionFormat="comma" section="5.8" format="def
ault" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-5.8" derivedConten
t="RFC4566"/>. Within this
overall limit, the implementation can dynamically decide how
to best allocate the available bandwidth between "m=" sections,
respecting any specific limits that have been specified for
individual "m=" sections.</li>
<li pn="section-5.10-4.2">For any specified "RR" or "RS" bandwidth val
ues, handle as
specified in
<xref target="RFC3556" sectionFormat="comma" section="2" format="defau
lt" derivedLink="https://rfc-editor.org/rfc/rfc3556#section-2" derivedContent="R
FC3556"/>.</li>
<li pn="section-5.10-4.3">Any "AS" bandwidth value (<xref target="RFC4
566" sectionFormat="comma" section="5.8" format="default" derivedLink="https://r
fc-editor.org/rfc/rfc4566#section-5.8" derivedContent="RFC4566"/>)
<bcp14>MUST</bcp14> be ignored, as the meaning
of this construct at the session level is not well
defined. </li>
</ul>
<t indent="0" pn="section-5.10-5">For each "m=" section, the following s
teps <bcp14>MUST</bcp14> be performed;
if any parameters are out of bounds or cannot be applied,
processing <bcp14>MUST</bcp14> stop and an error <bcp14>MUST</bcp14> be
returned.
</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="section-5
.10-6">
<li pn="section-5.10-6.1">
<t indent="0" pn="section-5.10-6.1.1">If the ICE ufrag or password c
hanged from the previous
remote description:
</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="secti
on-5.10-6.1.2">
<li pn="section-5.10-6.1.2.1">If the description is of type "offer
", the
implementation <bcp14>MUST</bcp14> note that an ICE restart is neede
d, as
described in
<xref target="RFC8839" sectionFormat="comma" section="4.4.1.1.1" for
mat="default" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-4.4.1.1.1"
derivedContent="RFC8839"/>.</li>
<li pn="section-5.10-6.1.2.2">If the description is of type "answe
r" or "pranswer",
then check to see if the current local description is an
ICE restart, and if not, generate an error. If the
PeerConnection state is "have-remote-pranswer" and the ICE
ufrag or password changed from the previous provisional
answer, then signal the ICE agent to discard any previous
ICE checklist state for the "m=" section. Finally, signal
the ICE agent to begin checks.
</li>
</ul>
</li>
<li pn="section-5.10-6.2">If the current local description indicates a
n ICE restart
but neither the ICE ufrag nor the password has changed from the
previous remote description (as prescribed by
<xref target="RFC8445" sectionFormat="comma" section="9" format="defau
lt" derivedLink="https://rfc-editor.org/rfc/rfc8445#section-9" derivedContent="R
FC8445"/>), generate an
error.</li>
<li pn="section-5.10-6.3">Configure the ICE components associated with
this media
section to use the supplied ICE remote ufrag and password for
their connectivity checks.</li>
<li pn="section-5.10-6.4">Pair any supplied ICE candidates with any ga
thered local
candidates, as described in
<xref target="RFC8445" sectionFormat="comma" section="6.1.2" format="d
efault" derivedLink="https://rfc-editor.org/rfc/rfc8445#section-6.1.2" derivedCo
ntent="RFC8445"/>, and start
connectivity checks with the appropriate credentials.</li>
<li pn="section-5.10-6.5">If an "a=end-of-candidates" attribute is pre
sent, process
the end-of-candidates indication as described in
<xref target="RFC8838" sectionFormat="comma" section="14" format="defa
ult" derivedLink="https://rfc-editor.org/rfc/rfc8838#section-14" derivedContent=
"RFC8838"/>.</li>
<li pn="section-5.10-6.6">
<t indent="0" pn="section-5.10-6.6.1">If the "m=" section &lt;proto&
gt; value indicates use of RTP:
</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="secti
on-5.10-6.6.2">
<li pn="section-5.10-6.6.2.1">If the "m=" section is being recycle
d (see
<xref target="sec.subsequent-offers" format="default" sectionFormat
="of" derivedContent="Section 5.2.2"/>), disassociate
the currently associated RtpTransceiver by setting its mid
property to "null", and discard the mapping between the
transceiver and its "m=" section index.</li>
<li pn="section-5.10-6.6.2.2">
<t indent="0" pn="section-5.10-6.6.2.2.1">If the "m=" section is
not associated with any
RtpTransceiver (possibly because it was disassociated in the
previous step), either find an RtpTransceiver or create one
according to the following steps:
</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="s
ection-5.10-6.6.2.2.2">
<li pn="section-5.10-6.6.2.2.2.1">If the "m=" section is sendr
ecv or recvonly, and there
are RtpTransceivers of the same type that were added to
the PeerConnection by addTrack and are not associated
with any "m=" section and are not stopped, find the first
(according to the canonical order described in
<xref target="sec.initial-offers" format="default" sectionFormat=
"of" derivedContent="Section 5.2.1"/>) such
RtpTransceiver.</li>
<li pn="section-5.10-6.6.2.2.2.2">If no RtpTransceiver was fou
nd in the previous step,
create one with a recvonly direction.</li>
<li pn="section-5.10-6.6.2.2.2.3">Associate the found or creat
ed RtpTransceiver with the
"m=" section by setting the value of the RtpTransceiver's
mid property to the MID of the "m=" section, and establish
a mapping between the transceiver and the index of the "m="
section. If the "m=" section does not include a MID (i.e.,
the remote endpoint does not support the MID extension),
generate a value for the RtpTransceiver mid property,
following the guidance for "a=mid" mentioned in
<xref target="sec.initial-offers" format="default" sectionFormat=
"of" derivedContent="Section 5.2.1"/>.</li>
</ul>
</li>
<li pn="section-5.10-6.6.2.3">For each specified media format that
is also supported
by the local implementation, establish a mapping between
the specified payload type and the media format, as
described in
<xref target="RFC3264" sectionFormat="comma" section="6.1" format="
default" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-6.1" derivedCon
tent="RFC3264"/>. Specifically, this
means that the implementation records the payload type to
be used in outgoing RTP packets when sending each specified
media format, as well as the relative preference for each
format that is indicated in their ordering. If any
indicated media format is not supported by the local
implementation, it <bcp14>MUST</bcp14> be ignored.</li>
<li pn="section-5.10-6.6.2.4">For each specified "rtx" media forma
t, establish a
mapping between the RTX payload type and its associated
primary payload type, as described in
<xref target="RFC4588" sectionFormat="comma" section="4" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc4588#section-4" derivedContent
="RFC4588"/>. If any referenced
primary payload types are not present, this <bcp14>MUST</bcp14> res
ult in
an error. Note that RTX payload types may refer to primary
payload types that are not supported by the local media
implementation, in which case the RTX payload type <bcp14>MUST</bcp
14>
also be ignored.</li>
<li pn="section-5.10-6.6.2.5">For each specified fmtp parameter th
at is supported by
the local implementation, enable them on the associated
media formats.</li>
<li pn="section-5.10-6.6.2.6">For each specified Synchronization S
ource (SSRC) that is signaled in the "m="
section, prepare to demux RTP streams intended for this "m="
section using that SSRC, as described in
<xref target="RFC8843" sectionFormat="comma" section="9.2" format="
default" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-9.2" derivedCon
tent="RFC8843"/>.</li>
<li pn="section-5.10-6.6.2.7">For each specified RTP header extens
ion that is also
supported by the local implementation, establish a mapping
between the extension ID and URI, as described in
<xref target="RFC5285" sectionFormat="comma" section="5" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc5285#section-5" derivedContent
="RFC5285"/>. Specifically, this
means that the implementation records the extension ID to
be used in outgoing RTP packets when sending each specified
header extension. If any indicated RTP header extension is
not supported by the local implementation, it <bcp14>MUST</bcp14> b
e
ignored.</li>
<li pn="section-5.10-6.6.2.8">For each specified RTCP feedback mec
hanism that is
supported by the local implementation, enable them on the
associated media formats.</li>
<li pn="section-5.10-6.6.2.9">
<t indent="0" pn="section-5.10-6.6.2.9.1">For any specified "TIA
S" ("Transport
Independent Application Specific Maximum") bandwidth value, set this value
as a constraint on the maximum RTP bitrate to be used when
sending media, as specified in
<xref target="RFC3890" format="default" sectionFormat="of" derivedC
ontent="RFC3890"/>. If a "TIAS" value is not
present but an "AS" value is specified, generate a "TIAS"
value using this formula:
</t>
<artwork align="left" pn="section-5.10-6.6.2.9.2">
TIAS = AS * 1000 * 0.95 - (50 * 40 * 8)
</artwork>
<t indent="0" pn="section-5.10-6.6.2.9.3">
The 1000 changes the unit from kbps to bps (as required
by TIAS), and the 0.95 is to allocate 5% to RTCP.
An estimate of header overhead is then subtracted out, in which
the 50 is based on 50 packets per second, the 40 is based on
typical header size (in bytes), and the 8 converts bytes to bits.
Note that "TIAS" is preferred over
"AS" because it provides more accurate
control of bandwidth.</t>
</li>
<li pn="section-5.10-6.6.2.10">For any "RR" or "RS" bandwidth valu
es, handle as
specified in
<xref target="RFC3556" sectionFormat="comma" section="2" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc3556#section-2" derivedContent
="RFC3556"/>.</li>
<li pn="section-5.10-6.6.2.11">Any specified "CT" bandwidth value
<bcp14>MUST</bcp14> be ignored, as
the meaning of this construct at the media level is not
well defined.</li>
<li pn="section-5.10-6.6.2.12">
<t indent="0" pn="section-5.10-6.6.2.12.1">If the "m=" section i
s of type "audio":
</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="s
ection-5.10-6.6.2.12.2">
<li pn="section-5.10-6.6.2.12.2.1">For each specified "CN" med
ia format, configure
silence suppression for all supported media formats with
the same clock rate, as described in
<xref target="RFC3389" sectionFormat="comma" section="5" format="
default" derivedLink="https://rfc-editor.org/rfc/rfc3389#section-5" derivedConte
nt="RFC3389"/>, except for formats
that have their own internal silence suppression
mechanisms. Silence suppression for such formats (e.g.,
Opus) is controlled via fmtp parameters, as discussed in
<xref target="sec.voiceactivitydetection1" format="default" secti
onFormat="of" derivedContent="Section 5.2.3.2"/>.</li>
<li pn="section-5.10-6.6.2.12.2.2">For each specified "telepho
ne-event" media format,
enable dual-tone multifrequency (DTMF) transmission for all suppo
rted media formats
with the same clock rate, as described in
<xref target="RFC4733" sectionFormat="comma" section="2.5.1.2" fo
rmat="default" derivedLink="https://rfc-editor.org/rfc/rfc4733#section-2.5.1.2"
derivedContent="RFC4733"/>. If there are
any supported media formats that do not have a
corresponding telephone-event format, disable DTMF
transmission for those formats.</li>
<li pn="section-5.10-6.6.2.12.2.3">For any specified "ptime" v
alue, configure the
available media formats to use the specified packet size
when sending. If the specified size is not supported for
a media format, use the next closest value instead.</li>
</ul>
</li>
</ul>
</li>
</ul>
<t indent="0" pn="section-5.10-7">Finally, if this description is of typ
e "pranswer" or
"answer", follow the processing defined in
<xref target="sec.applying-an-answer" format="default" sectionFormat="o
f" derivedContent="Section 5.11"/> below.</t>
</section> </section>
<section title="Applying an Answer" <section anchor="sec.applying-an-answer" numbered="true" toc="include" rem
anchor="sec.applying-an-answer"> oveInRFC="false" pn="section-5.11">
<name slugifiedName="name-applying-an-answer">Applying an Answer</name>
<t>In addition to the steps mentioned above for processing a <t indent="0" pn="section-5.11-1">In addition to the steps mentioned abo
local or remote description, the following steps are performed ve for processing a
when processing a description of type "pranswer" or local or remote description, the following steps are performed
"answer".</t> when processing a description of type "pranswer" or
"answer".</t>
<t>For each m= section, the following steps MUST be performed: <t indent="0" pn="section-5.11-2">For each "m=" section, the following s
<list style="symbols"> teps <bcp14>MUST</bcp14> be performed:
</t>
<t>If the m= section has been rejected (i.e. port is set to <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-5
zero in the answer), stop any reception or transmission of .11-3">
media for this section, and, unless a non-rejected m= section <li pn="section-5.11-3.1">If the "m=" section has been rejected (i.e.,
is bundled with this m= section, discard any associated ICE the &lt;port&gt; value is set to
components, as described in zero in the answer), stop any reception or transmission of
<xref target="I-D.ietf-mmusic-ice-sip-sdp" />, Section 3.4.3.1.</t> media for this section, and, unless a non-rejected "m=" section
is bundled with this "m=" section, discard any associated ICE
<t>If the remote DTLS fingerprint has been changed or the components, as described in
tls-id has changed, tear down the DTLS connection. This <xref target="RFC8839" sectionFormat="comma" section="4.4.3.1" format
includes the case when the PeerConnection state is ="default" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-4.4.3.1" deri
"have-remote-pranswer". If a DTLS connection needs to be torn vedContent="RFC8839"/>.</li>
down but the answer does not indicate an ICE restart or, in <li pn="section-5.11-3.2">If the remote DTLS fingerprint has been chan
the case of "have-remote-pranswer", new ICE credentials, an ged or the
error MUST be generated. If an ICE restart is performed value of the "a=tls-id" attribute has changed, tear down the DTLS co
without a change in tls-id or fingerprint, then the same DTLS nnection. This
connection is continued over the new ICE channel. Note that includes the case when the PeerConnection state is
although JSEP requires that answerers change the tls-id value "have-remote-pranswer". If a DTLS connection needs to be torn
if and only if the offerer does, non-JSEP answerers are down but the answer does not indicate an ICE restart or, in
permitted to change the tls-id as long as the offer contained the case of "have-remote-pranswer", new ICE credentials, an
an ICE restart. Thus, JSEP implementations which process DTLS error <bcp14>MUST</bcp14> be generated. If an ICE restart is perform
data prior to receiving an answer MUST be prepared to receive ed
either a ClientHello or data from the previous DTLS without a change in the tls-id value or fingerprint, then the same D
connection.</t> TLS
connection is continued over the new ICE channel. Note that
<t>If no valid DTLS connection exists, prepare to start a although JSEP requires that answerers change the tls-id value
DTLS connection, using the specified roles and fingerprints, if and only if the offerer does, non-JSEP answerers are
on any underlying ICE components, once they are active.</t> permitted to change the tls-id value as long as the offer contained
an ICE restart. Thus, JSEP implementations that process DTLS
<t>If the m= section proto value indicates use of RTP: data prior to receiving an answer <bcp14>MUST</bcp14> be prepared to
<list style="symbols"> receive
either a ClientHello or data from the previous DTLS
<t>If the m= section references RTCP feedback mechanisms connection.</li>
that were not present in the corresponding m= section in <li pn="section-5.11-3.3">If no valid DTLS connection exists, prepare
the offer, this indicates a negotiation problem and MUST to start a
result in an error. However, new media formats and new RTP DTLS connection, using the specified roles and fingerprints,
header extension values are permitted in the answer, as on any underlying ICE components, once they are active.</li>
described in <li pn="section-5.11-3.4">
<xref target="RFC3264" />, Section 7, and <t indent="0" pn="section-5.11-3.4.1">If the "m=" section &lt;proto&
<xref target="RFC5285" />, Section 6.</t> gt; value indicates use of RTP:
</t>
<t>If the m= section has RTCP mux enabled, discard the RTCP <ul spacing="normal" bare="false" empty="false" indent="3" pn="secti
ICE component, if one exists, and begin or continue muxing on-5.11-3.4.2">
RTCP over the RTP ICE component, as specified in <li pn="section-5.11-3.4.2.1">If the "m=" section references RTCP
<xref target="RFC5761" />, Section 5.1.3. Otherwise, feedback mechanisms
prepare to transmit RTCP over the RTCP ICE component; if no that were not present in the corresponding "m=" section in
RTCP ICE component exists, because RTCP mux was previously the offer, this indicates a negotiation problem and <bcp14>MUST</b
enabled, this MUST result in an error.</t> cp14>
result in an error. However, new media formats and new RTP
<t>If the m= section has reduced-size RTCP enabled, header extension values are permitted in the answer, as
configure the RTCP transmission for this m= section to use described in
reduced-size RTCP, as specified in <xref target="RFC3264" sectionFormat="comma" section="7" format="d
<xref target="RFC5506" />.</t> efault" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-7" derivedConten
t="RFC3264"/> and
<t>If the directional attribute in the answer indicates <xref target="RFC5285" sectionFormat="comma" section="6" format="d
that the JSEP implementation should be sending media efault" derivedLink="https://rfc-editor.org/rfc/rfc5285#section-6" derivedConten
("sendonly" for local answers, "recvonly" for remote t="RFC5285"/>.</li>
answers, or "sendrecv" for either type of answer), choose <li pn="section-5.11-3.4.2.2">If the "m=" section has RTCP mux ena
the media format to send as the most preferred media format bled, discard the RTCP
from the remote description that is also locally supported, ICE component, if one exists, and begin or continue muxing
as discussed in RTCP over the RTP ICE component, as specified in
<xref target="RFC3264" />, Sections 6.1 and 7, and start <xref target="RFC5761" sectionFormat="comma" section="5.1.3" forma
transmitting RTP media using that format once the t="default" derivedLink="https://rfc-editor.org/rfc/rfc5761#section-5.1.3" deriv
underlying transport layers have been established. If an edContent="RFC5761"/>. Otherwise,
SSRC has not already been chosen for this outgoing RTP prepare to transmit RTCP over the RTCP ICE component; if no
stream, choose a random one. If media is already being RTCP ICE component exists because RTCP mux was previously
transmitted, the same SSRC SHOULD be used unless the enabled, this <bcp14>MUST</bcp14> result in an error.</li>
clockrate of the new codec is different, in which case a <li pn="section-5.11-3.4.2.3">If the "m=" section has Reduced-Size
new SSRC MUST be chosen, as specified in RTCP enabled,
<xref target="RFC7160" />, Section 3.1.</t> configure the RTCP transmission for this "m=" section to use
Reduced-Size RTCP, as specified in
<t>The payload type mapping from the remote description is <xref target="RFC5506" format="default" sectionFormat="of" derived
used to determine payload types for the outgoing RTP Content="RFC5506"/>.</li>
streams, including the payload type for the send media <li pn="section-5.11-3.4.2.4">If the direction attribute in the an
format chosen above. Any RTP header extensions that were swer indicates
negotiated should be included in the outgoing RTP streams, that the JSEP implementation should be sending media
using the extension mapping from the remote description; if ("sendonly" for local answers, "recvonly" for remote
the RID header extension has been negotiated, and RID answers, or "sendrecv" for either type of answer), choose
values are specified, include the RID header extension in the media format to send as the most preferred media format
the outgoing RTP streams, as indicated in from the remote description that is also locally supported,
<xref target="I-D.ietf-mmusic-rid"></xref>, Section 4.</t> as discussed in Sections <xref target="RFC3264" section="6.1" sect
ionFormat="bare" format="default" derivedLink="https://rfc-editor.org/rfc/rfc326
<t>If the m= section is of type audio, and silence 4#section-6.1" derivedContent="RFC3264"/> and <xref target="RFC3264" section="7"
suppression was configured for the send media format as a sectionFormat="bare" format="default" derivedLink="https://rfc-editor.org/rfc/r
result of processing the remote description, and is also fc3264#section-7" derivedContent="RFC3264"/> of <xref target="RFC3264" format="d
enabled for that format in the local description, use efault" sectionFormat="of" derivedContent="RFC3264"/>, and start
silence suppression for outgoing media, in accordance with transmitting RTP media using that format once the
the guidance in underlying transport layers have been established. If an
<xref target="sec.voiceactivitydetection1" />. If these SSRC has not already been chosen for this outgoing RTP
conditions are not met, silence suppression MUST NOT be stream, choose a unique random one. If media is already being
used for outgoing media.</t> transmitted, the same SSRC <bcp14>SHOULD</bcp14> be used unless th
e
<t>If simulcast has been negotiated, send the number of clock rate of the new codec is different, in which case a
Source RTP Streams as specified in new SSRC <bcp14>MUST</bcp14> be chosen, as specified in
<xref target="I-D.ietf-mmusic-sdp-simulcast"></xref>, <xref target="RFC7160" sectionFormat="comma" section="4.1" format=
Section 6.2.2.</t> "default" derivedLink="https://rfc-editor.org/rfc/rfc7160#section-4.1" derivedCo
ntent="RFC7160"/>.</li>
<t>If the send media format chosen above has a <li pn="section-5.11-3.4.2.5">The payload type mapping from the re
corresponding "rtx" media format, or a FEC mechanism has mote description is
been negotiated, establish a Redundancy RTP Stream with a used to determine payload types for the outgoing RTP
random SSRC for each Source RTP Stream, and start or streams, including the payload type for the send media
continue transmitting RTX/FEC packets as needed.</t> format chosen above. Any RTP header extensions that were
negotiated should be included in the outgoing RTP streams,
<t>If the send media format chosen above has a using the extension mapping from the remote description. If the MI
corresponding "red" media format of the same clockrate, D
allow redundant encoding using the specified format for header extension has been negotiated, include it in the outgoing RTP
resiliency purposes, as discussed in streams, as indicated in
<xref target="I-D.ietf-rtcweb-fec" />, Section 3.2. Note <xref target="RFC8843" sectionFormat="comma" section="15" format="defau
that unlike RTX or FEC media formats, the "red" format is lt" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-15" derivedContent="
transmitted on the Source RTP Stream, not the Redundancy RFC8843"/>.
RTP Stream.</t> If the RtpStreamId or RepairedRtpStreamId header extensions have b
een
<t>Enable the RTCP feedback mechanisms referenced in the negotiated and rid-ids have been established, include these header
media section for all Source RTP Streams using the extensions in the outgoing RTP streams, as indicated in
specified media formats. Specifically, begin or continue <xref target="RFC8851" sectionFormat="comma" section="4" format="d
sending the requested feedback types and reacting to efault" derivedLink="https://rfc-editor.org/rfc/rfc8851#section-4" derivedConten
received feedback, as specified in t="RFC8851"/>.</li>
<xref target="RFC4585" />, Section 4.2. When sending RTCP <li pn="section-5.11-3.4.2.6">If the "m=" section is of type "audi
feedback, follow the rules and recommendations from o", and silence
<xref target="RFC8108"></xref> Section 5.4.1, to select suppression was (1) configured for the send media format as a
which SSRC to use.</t> result of processing the remote description and (2) also
enabled for that format in the local description, use
<t>If the directional attribute in the answer indicates silence suppression for outgoing media, in accordance with
that the JSEP implementation should not be sending media the guidance in
("recvonly" for local answers, "sendonly" for remote <xref target="sec.voiceactivitydetection1" format="default" sectio
answers, or "inactive" for either type of answer) stop nFormat="of" derivedContent="Section 5.2.3.2"/>.
transmitting all RTP media, but continue sending RTCP, as If these
described in conditions are not met, silence suppression <bcp14>MUST NOT</bcp14
<xref target="RFC3264" />, Section 5.1.</t> > be
</list></t> used for outgoing media.</li>
<li pn="section-5.11-3.4.2.7">If simulcast has been negotiated, se
<t>If the m= section proto value indicates use of SCTP: nd the appropriate number of
<list style="symbols"> Source RTP Streams as specified in
<xref target="RFC8853" sectionFormat="comma" section="5.3.3" forma
<t>If an SCTP association exists, and the remote SCTP port t="default" derivedLink="https://rfc-editor.org/rfc/rfc8853#section-5.3.3" deriv
has changed, discard the existing SCTP association. This edContent="RFC8853"/>.</li>
includes the case when the PeerConnection state is <li pn="section-5.11-3.4.2.8">If the send media format chosen abov
"have-remote-pranswer".</t> e has a
corresponding "rtx" media format or a FEC mechanism has
<t>If no valid SCTP association exists, prepare to initiate been negotiated, establish a redundancy RTP stream with a
a SCTP association over the associated ICE component and unique random SSRC for each Source RTP Stream, and start or
DTLS connection, using the local SCTP port value from the continue transmitting RTX/FEC packets as needed.</li>
local description, and the remote SCTP port value from the <li pn="section-5.11-3.4.2.9">If the send media format chosen abov
remote description, as described in e has a
<xref target="I-D.ietf-mmusic-sctp-sdp" />, Section corresponding "red" media format of the same clock rate,
10.2.</t> allow redundant encoding using the specified format for
</list></t> resiliency purposes, as discussed in
</list></t> <xref target="RFC8854" sectionFormat="comma" section="3.2" format=
"default" derivedLink="https://rfc-editor.org/rfc/rfc8854#section-3.2" derivedCo
<t>If the answer contains valid bundle groups, discard any ICE ntent="RFC8854"/>. Note
components for the m= sections that will be bundled onto the that unlike RTX or FEC media formats, the "red" format is
primary ICE components in each bundle, and begin muxing these transmitted on the Source RTP Stream, not the redundancy
m= sections accordingly, as described in RTP stream.</li>
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation" />, <li pn="section-5.11-3.4.2.10">Enable the RTCP feedback mechanisms
Section 8.2.</t> referenced in the
media section for all Source RTP Streams using the
<t>If the description is of type "answer", and there are still specified media formats. Specifically, begin or continue
remaining candidates in the ICE candidate pool, discard sending the requested feedback types and reacting to
them.</t> received feedback, as specified in
<xref target="RFC4585" sectionFormat="comma" section="4.2" format=
"default" derivedLink="https://rfc-editor.org/rfc/rfc4585#section-4.2" derivedCo
ntent="RFC4585"/>. When sending RTCP
feedback, follow the rules and recommendations from
<xref target="RFC8108" sectionFormat="comma" section="5.4.1" format="default"
derivedLink="https://rfc-editor.org/rfc/rfc8108#section-5.4.1" derivedContent="
RFC8108"/> to select
which SSRC to use.</li>
<li pn="section-5.11-3.4.2.11">If the direction attribute in the a
nswer indicates
that the JSEP implementation should not be sending media
("recvonly" for local answers, "sendonly" for remote
answers, or "inactive" for either type of answer), stop
transmitting all RTP media, but continue sending RTCP, as
described in
<xref target="RFC3264" sectionFormat="comma" section="5.1" format=
"default" derivedLink="https://rfc-editor.org/rfc/rfc3264#section-5.1" derivedCo
ntent="RFC3264"/>.</li>
</ul>
</li>
<li pn="section-5.11-3.5">
<t indent="0" pn="section-5.11-3.5.1">If the "m=" section &lt;proto&
gt; value indicates use of SCTP:
</t>
<ul spacing="normal" bare="false" empty="false" indent="3" pn="secti
on-5.11-3.5.2">
<li pn="section-5.11-3.5.2.1">If an SCTP association exists and th
e remote SCTP port
has changed, discard the existing SCTP association. This
includes the case when the PeerConnection state is
"have-remote-pranswer".</li>
<li pn="section-5.11-3.5.2.2">If no valid SCTP association exists,
prepare to initiate
an SCTP association over the associated ICE component and
DTLS connection, using the local SCTP port value from the
local description and the remote SCTP port value from the
remote description, as described in
<xref target="RFC8841" sectionFormat="comma" section="10.2" format
="default" derivedLink="https://rfc-editor.org/rfc/rfc8841#section-10.2" derived
Content="RFC8841"/>.</li>
</ul>
</li>
</ul>
<t indent="0" pn="section-5.11-4">If the answer contains valid bundle gr
oups, discard any ICE
components for the "m=" sections that will be bundled onto the
primary ICE components in each bundle, and begin muxing these
"m=" sections accordingly, as described in
<xref target="RFC8843" sectionFormat="comma" section="7.4" format="def
ault" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-7.4" derivedConten
t="RFC8843"/>.</t>
<t indent="0" pn="section-5.11-5">If the description is of type "answer"
and there are still
remaining candidates in the ICE candidate pool, discard
them.</t>
</section> </section>
</section> </section>
<section title="Processing RTP/RTCP" anchor="sec.rtp.demux"> <section anchor="sec.rtp.demux" numbered="true" toc="include" removeInRFC="f
alse" pn="section-6">
<t>When bundling, associating incoming RTP/RTCP with the proper <name slugifiedName="name-processing-rtp-rtcp">Processing RTP/RTCP</name>
m= section is defined in <t indent="0" pn="section-6-1">When bundling, associating incoming RTP/RTC
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation" />, Section P with the proper
10.2. When not bundling, the proper m= section is clear from the "m=" section is defined in
ICE component over which the RTP/RTCP is received.</t> <xref target="RFC8843" sectionFormat="comma" section="9.2" format="defau
lt" derivedLink="https://rfc-editor.org/rfc/rfc8843#section-9.2" derivedContent=
<t>Once the proper m= section(s) are known, RTP/RTCP is delivered "RFC8843"/>. When not bundling, the proper "m=" section is clear from the
to the RtpTransceiver(s) associated with the m= section(s) and ICE component over which the RTP/RTCP is received.</t>
further processing of the RTP/RTCP is done at the RtpTransceiver <t indent="0" pn="section-6-2">Once the proper "m=" section or sections ar
level. This includes using RID e known, RTP/RTCP is delivered
<xref target="I-D.ietf-mmusic-rid" /> to distinguish between to the RtpTransceiver(s) associated with the "m=" section(s) and
multiple Encoded Streams, as well as determine which Source RTP further processing of the RTP/RTCP is done at the RtpTransceiver
stream should be repaired by a given Redundancy RTP stream.</t> level. This includes using the RID mechanism
<xref target="RFC8851" format="default" sectionFormat="of" derivedConten
t="RFC8851"/> and its associated RtpStreamId and
RepairedRtpStreamId identifiers to distinguish between
multiple encoded streams and determine which Source RTP
stream should be repaired by a given redundancy RTP stream.</t>
</section> </section>
<section title="Examples" anchor="sec.examples"> <section anchor="sec.examples" numbered="true" toc="include" removeInRFC="fa
lse" pn="section-7">
<t>Note that this example section shows several SDP fragments. To <name slugifiedName="name-examples">Examples</name>
format in 72 columns, some of the lines in SDP have been split <t indent="0" pn="section-7-1">Note that this example section shows severa
into multiple lines, where leading whitespace indicates that a l SDP fragments. To
line is a continuation of the previous line. In addition, some accommodate RFC line-length restrictions, some of the SDP lines have bee
blank lines have been added to improve readability but are not n split
valid in SDP.</t> into multiple lines, where leading whitespace indicates that a
line is a continuation of the previous line. In addition, some
<t>More examples of SDP for WebRTC call flows, including examples blank lines have been added to improve readability but are not
with IPv6 addresses, can be found in valid in SDP.</t>
<xref target="I-D.ietf-rtcweb-sdp"></xref>.</t> <t indent="0" pn="section-7-2">More examples of SDP for WebRTC call flows,
<section title="Simple Example" anchor="sec.simple-examples"> including examples
with IPv6 addresses, can be found in
<t>This section shows a very simple example that sets up a <xref target="I-D.ietf-rtcweb-sdp" format="default" sectionFormat="of" d
minimal audio / video call between two JSEP endpoints without erivedContent="SDP4WebRTC"/>.</t>
using trickle ICE. The example in the following section <section anchor="sec.simple-examples" numbered="true" toc="include" remove
provides a more detailed example of what could happen in a JSEP InRFC="false" pn="section-7.1">
session.</t> <name slugifiedName="name-simple-example">Simple Example</name>
<t indent="0" pn="section-7.1-1">This section shows a very simple exampl
<t>The code flow below shows Alice's endpoint initiating the e that sets up a
session to Bob's endpoint. The messages from the JavaScript minimal audio/video call between two JSEP endpoints without
application in Alice's browser to the JavaScript in Bob's using Trickle ICE. The example in the following section
browser, abbreviated as AliceJS and BobJS respectively, are provides a more detailed example of what could happen in a JSEP
assumed to flow over some signaling protocol via a web server. session.</t>
The JavaScript on both Alice's side and Bob's side waits for <t indent="0" pn="section-7.1-2">The code flow below shows Alice's endpo
all candidates before sending the offer or answer, so the int initiating the
offers and answers are complete; trickle ICE is not used. The session to Bob's endpoint. The messages from the JavaScript
user agents (JSEP implementations) in Alice and Bob's browsers, application in Alice's browser to the JavaScript in Bob's
abbreviated as AliceUA and BobUA respectively, are using the browser, abbreviated as "AliceJS" and "BobJS", respectively, are
default bundle policy of "balanced", and the default RTCP mux assumed to flow over some signaling protocol via a web server.
policy of "require".</t> The JavaScript on both Alice's side and Bob's side waits for
all candidates before sending the offer or answer, so the
<t> offers and answers are complete; Trickle ICE is not used. The
<figure> user agents (JSEP implementations) in Alice's and Bob's browsers,
<artwork> abbreviated as "AliceUA" and "BobUA", respectively, are both using the
<![CDATA[ default bundle policy of "balanced" and the default RTCP mux
policy of "require".</t>
<artwork name="" type="ascii-art" align="left" alt="" pn="section-7.1-3"
>
// set up local media state // set up local media state
AliceJS->AliceUA: create new PeerConnection AliceJS-&gt;AliceUA: create new PeerConnection
AliceJS->AliceUA: addTrack with two tracks: audio and video AliceJS-&gt;AliceUA: addTrack with two tracks: audio and video
AliceJS->AliceUA: createOffer to get offer AliceJS-&gt;AliceUA: createOffer to get offer
AliceJS->AliceUA: setLocalDescription with offer AliceJS-&gt;AliceUA: setLocalDescription with offer
AliceUA->AliceJS: multiple onicecandidate events with candidates AliceUA-&gt;AliceJS: multiple onicecandidate events with candidates
// wait for ICE gathering to complete // wait for ICE gathering to complete
AliceUA->AliceJS: onicecandidate event with null candidate AliceUA-&gt;AliceJS: onicecandidate event with null candidate
AliceJS->AliceUA: get |offer-A1| from pendingLocalDescription AliceJS-&gt;AliceUA: get |offer-A1| from pendingLocalDescription
// |offer-A1| is sent over signaling protocol to Bob // |offer-A1| is sent over signaling protocol to Bob
AliceJS->WebServer: signaling with |offer-A1| AliceJS-&gt;WebServer: signaling with |offer-A1|
WebServer->BobJS: signaling with |offer-A1| WebServer-&gt;BobJS: signaling with |offer-A1|
// |offer-A1| arrives at Bob // |offer-A1| arrives at Bob
BobJS->BobUA: create a PeerConnection BobJS-&gt;BobUA: create a PeerConnection
BobJS->BobUA: setRemoteDescription with |offer-A1| BobJS-&gt;BobUA: setRemoteDescription with |offer-A1|
BobUA->BobJS: ontrack events for audio and video tracks BobUA-&gt;BobJS: ontrack events for audio and video tracks
// Bob accepts call // Bob accepts call
BobJS->BobUA: addTrack with local tracks BobJS-&gt;BobUA: addTrack with local tracks
BobJS->BobUA: createAnswer BobJS-&gt;BobUA: createAnswer
BobJS->BobUA: setLocalDescription with answer BobJS-&gt;BobUA: setLocalDescription with answer
BobUA->BobJS: multiple onicecandidate events with candidates BobUA-&gt;BobJS: multiple onicecandidate events with candidates
// wait for ICE gathering to complete // wait for ICE gathering to complete
BobUA->BobJS: onicecandidate event with null candidate BobUA-&gt;BobJS: onicecandidate event with null candidate
BobJS->BobUA: get |answer-A1| from currentLocalDescription BobJS-&gt;BobUA: get |answer-A1| from currentLocalDescription
// |answer-A1| is sent over signaling protocol to Alice // |answer-A1| is sent over signaling protocol
BobJS->WebServer: signaling with |answer-A1| // to Alice
WebServer->AliceJS: signaling with |answer-A1| BobJS-&gt;WebServer: signaling with |answer-A1|
WebServer-&gt;AliceJS: signaling with |answer-A1|
// |answer-A1| arrives at Alice // |answer-A1| arrives at Alice
AliceJS->AliceUA: setRemoteDescription with |answer-A1| AliceJS-&gt;AliceUA: setRemoteDescription with |answer-A1|
AliceUA->AliceJS: ontrack events for audio and video tracks AliceUA-&gt;AliceJS: ontrack events for audio and video tracks
// media flows // media flows
BobUA->AliceUA: media sent from Bob to Alice BobUA-&gt;AliceUA: media sent from Bob to Alice
AliceUA->BobUA: media sent from Alice to Bob AliceUA-&gt;BobUA: media sent from Alice to Bob </artwork>
]]> <t indent="0" pn="section-7.1-4">The SDP for |offer-A1| looks like:</t>
</artwork> <sourcecode name="offer-A1" type="sdp" markers="false" pn="section-7.1-5
</figure> ">
</t>
<t>The SDP for |offer-A1| looks like:</t>
<t>
<figure>
<artwork alt="offer-A1">
<![CDATA[
v=0 v=0
o=- 4962303333179871722 1 IN IP4 0.0.0.0 o=- 4962303333179871722 1 IN IP4 0.0.0.0
s=- s=-
t=0 0 t=0 0
a=ice-options:trickle ice2 a=ice-options:trickle ice2
a=group:BUNDLE a1 v1 a=group:BUNDLE a1 v1
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 10100 UDP/TLS/RTP/SAVPF 96 0 8 97 98 m=audio 10100 UDP/TLS/RTP/SAVPF 96 0 8 97 98
c=IN IP4 203.0.113.100 c=IN IP4 203.0.113.100
skipping to change at line 4260 skipping to change at line 4180
m=video 10102 UDP/TLS/RTP/SAVPF 100 101 102 103 m=video 10102 UDP/TLS/RTP/SAVPF 100 101 102 103
c=IN IP4 203.0.113.100 c=IN IP4 203.0.113.100
a=mid:v1 a=mid:v1
a=sendrecv a=sendrecv
a=rtpmap:100 VP8/90000 a=rtpmap:100 VP8/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=fmtp:101 packetization-mode=1;profile-level-id=42e01f a=fmtp:101 packetization-mode=1;profile-level-id=42e01f
a=rtpmap:102 rtx/90000 a=rtpmap:102 rtx/90000
a=fmtp:102 apt=100 a=fmtp:102 apt=100
=rtpmap:103 rtx/90000 a=rtpmap:103 rtx/90000
a=fmtp:103 apt=101 a=fmtp:103 apt=101
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=rtcp-fb:100 ccm fir a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli a=rtcp-fb:100 nack pli
a=msid:47017fee-b6c1-4162-929c-a25110252400 a=msid:47017fee-b6c1-4162-929c-a25110252400
a=ice-ufrag:BGKk a=ice-ufrag:BGKk
a=ice-pwd:mqyWsAjvtKwTGnvhPztQ9mIf a=ice-pwd:mqyWsAjvtKwTGnvhPztQ9mIf
a=fingerprint:sha-256 a=fingerprint:sha-256
19:E2:1C:3B:4B:9F:81:E6:B8:5C:F4:A5:A8:D8:73:04: 19:E2:1C:3B:4B:9F:81:E6:B8:5C:F4:A5:A8:D8:73:04:
BB:05:2F:70:9F:04:A9:0E:05:E9:26:33:E8:70:88:A2 BB:05:2F:70:9F:04:A9:0E:05:E9:26:33:E8:70:88:A2
a=setup:actpass a=setup:actpass
a=tls-id:91bbf309c0990a6bec11e38ba2933cee a=tls-id:91bbf309c0990a6bec11e38ba2933cee
a=rtcp:10103 IN IP4 203.0.113.100 a=rtcp:10103 IN IP4 203.0.113.100
a=rtcp-mux a=rtcp-mux
a=rtcp-rsize a=rtcp-rsize
a=candidate:1 1 udp 2113929471 203.0.113.100 10102 typ host a=candidate:1 1 udp 2113929471 203.0.113.100 10102 typ host
a=candidate:1 2 udp 2113929470 203.0.113.100 10103 typ host a=candidate:1 2 udp 2113929470 203.0.113.100 10103 typ host
a=end-of-candidates a=end-of-candidates</sourcecode>
]]> <t indent="0" pn="section-7.1-6">The SDP for |answer-A1| looks like:</t>
</artwork> <sourcecode name="answer-A1" type="sdp" markers="false" pn="section-7.1-
</figure> 7">
</t>
<t>The SDP for |answer-A1| looks like:</t>
<t>
<figure>
<artwork alt="answer-A1">
<![CDATA[
v=0 v=0
o=- 6729291447651054566 1 IN IP4 0.0.0.0 o=- 6729291447651054566 1 IN IP4 0.0.0.0
s=- s=-
t=0 0 t=0 0
a=ice-options:trickle ice2 a=ice-options:trickle ice2
a=group:BUNDLE a1 v1 a=group:BUNDLE a1 v1
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 10200 UDP/TLS/RTP/SAVPF 96 0 8 97 98 m=audio 10200 UDP/TLS/RTP/SAVPF 96 0 8 97 98
c=IN IP4 203.0.113.200 c=IN IP4 203.0.113.200
skipping to change at line 4336 skipping to change at line 4247
m=video 10200 UDP/TLS/RTP/SAVPF 100 101 102 103 m=video 10200 UDP/TLS/RTP/SAVPF 100 101 102 103
c=IN IP4 203.0.113.200 c=IN IP4 203.0.113.200
a=mid:v1 a=mid:v1
a=sendrecv a=sendrecv
a=rtpmap:100 VP8/90000 a=rtpmap:100 VP8/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=fmtp:101 packetization-mode=1;profile-level-id=42e01f a=fmtp:101 packetization-mode=1;profile-level-id=42e01f
a=rtpmap:102 rtx/90000 a=rtpmap:102 rtx/90000
a=fmtp:102 apt=100 a=fmtp:102 apt=100
=rtpmap:103 rtx/90000 a=rtpmap:103 rtx/90000
a=fmtp:103 apt=101 a=fmtp:103 apt=101
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=rtcp-fb:100 ccm fir a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli a=rtcp-fb:100 nack pli
a=msid:61317484-2ed4-49d7-9eb7-1414322a7aae a=msid:61317484-2ed4-49d7-9eb7-1414322a7aae</sourcecode>
]]>
</artwork>
</figure>
</t>
</section> </section>
<section title="Detailed Example" anchor="sec.detailed-example"> <section anchor="sec.detailed-example" numbered="true" toc="include" remov
eInRFC="false" pn="section-7.2">
<t>This section shows a more involved example of a session <name slugifiedName="name-detailed-example">Detailed Example</name>
between two JSEP endpoints. Trickle ICE is used in full trickle <t indent="0" pn="section-7.2-1">This section shows a more involved exam
mode, with a bundle policy of "max-bundle", an RTCP mux policy ple of a session
of "require", and a single TURN server. Initially, both Alice between two JSEP endpoints. Trickle ICE is used in full trickle
and Bob establish an audio channel and a data channel. Later, mode, with a bundle policy of "max-bundle", an RTCP mux policy
Bob adds two video flows, one for his video feed, and one for of "require", and a single TURN server. Initially, both Alice
screensharing, both supporting FEC, and with the video feed and Bob establish an audio channel and a data channel. Later,
configured for simulcast. Alice accepts these video flows, but Bob adds two video flows -- one for his video feed and one for
does not add video flows of her own, so they are handled as screen sharing, both supporting FEC -- with the video feed
recvonly. Alice also specifies a maximum video decoder configured for simulcast. Alice accepts these video flows but
resolution.</t> does not add video flows of her own, so they are handled as
recvonly. Alice also specifies a maximum video decoder
<t> resolution.</t>
<figure> <artwork name="" type="ascii-art" align="left" alt="" pn="section-7.2-2"
<artwork> >
<![CDATA[
// set up local media state // set up local media state
AliceJS->AliceUA: create new PeerConnection AliceJS-&gt;AliceUA: create new PeerConnection
AliceJS->AliceUA: addTrack with an audio track AliceJS-&gt;AliceUA: addTrack with an audio track
AliceJS->AliceUA: createDataChannel to get data channel AliceJS-&gt;AliceUA: createDataChannel to get data channel
AliceJS->AliceUA: createOffer to get |offer-B1| AliceJS-&gt;AliceUA: createOffer to get |offer-B1|
AliceJS->AliceUA: setLocalDescription with |offer-B1| AliceJS-&gt;AliceUA: setLocalDescription with |offer-B1|
// |offer-B1| is sent over signaling protocol to Bob // |offer-B1| is sent over signaling protocol to Bob
AliceJS->WebServer: signaling with |offer-B1| AliceJS-&gt;WebServer: signaling with |offer-B1|
WebServer->BobJS: signaling with |offer-B1| WebServer-&gt;BobJS: signaling with |offer-B1|
// |offer-B1| arrives at Bob // |offer-B1| arrives at Bob
BobJS->BobUA: create a PeerConnection BobJS-&gt;BobUA: create a PeerConnection
BobJS->BobUA: setRemoteDescription with |offer-B1| BobJS-&gt;BobUA: setRemoteDescription with |offer-B1|
BobUA->BobJS: ontrack with audio track from Alice BobUA-&gt;BobJS: ontrack event with audio track from Alice
// candidates are sent to Bob // candidates are sent to Bob
AliceUA->AliceJS: onicecandidate (host) |offer-B1-candidate-1| AliceUA-&gt;AliceJS: onicecandidate (host) |offer-B1-candidate-1|
AliceJS->WebServer: signaling with |offer-B1-candidate-1| AliceJS-&gt;WebServer: signaling with |offer-B1-candidate-1|
AliceUA->AliceJS: onicecandidate (srflx) |offer-B1-candidate-2| AliceUA-&gt;AliceJS: onicecandidate (srflx) |offer-B1-candidate-2|
AliceJS->WebServer: signaling with |offer-B1-candidate-2| AliceJS-&gt;WebServer: signaling with |offer-B1-candidate-2|
AliceUA->AliceJS: onicecandidate (relay) |offer-B1-candidate-3| AliceUA-&gt;AliceJS: onicecandidate (relay) |offer-B1-candidate-3|
AliceJS->WebServer: signaling with |offer-B1-candidate-3| AliceJS-&gt;WebServer: signaling with |offer-B1-candidate-3|
WebServer->BobJS: signaling with |offer-B1-candidate-1| WebServer-&gt;BobJS: signaling with |offer-B1-candidate-1|
BobJS->BobUA: addIceCandidate with |offer-B1-candidate-1| BobJS-&gt;BobUA: addIceCandidate with |offer-B1-candidate-1|
WebServer->BobJS: signaling with |offer-B1-candidate-2| WebServer-&gt;BobJS: signaling with |offer-B1-candidate-2|
BobJS->BobUA: addIceCandidate with |offer-B1-candidate-2| BobJS-&gt;BobUA: addIceCandidate with |offer-B1-candidate-2|
WebServer->BobJS: signaling with |offer-B1-candidate-3| WebServer-&gt;BobJS: signaling with |offer-B1-candidate-3|
BobJS->BobUA: addIceCandidate with |offer-B1-candidate-3| BobJS-&gt;BobUA: addIceCandidate with |offer-B1-candidate-3|
// Bob accepts call // Bob accepts call
BobJS->BobUA: addTrack with local audio BobJS-&gt;BobUA: addTrack with local audio
BobJS->BobUA: createDataChannel to get data channel BobJS-&gt;BobUA: createDataChannel to get data channel
BobJS->BobUA: createAnswer to get |answer-B1| BobJS-&gt;BobUA: createAnswer to get |answer-B1|
BobJS->BobUA: setLocalDescription with |answer-B1| BobJS-&gt;BobUA: setLocalDescription with |answer-B1|
// |answer-B1| is sent to Alice // |answer-B1| is sent to Alice
BobJS->WebServer: signaling with |answer-B1| BobJS-&gt;WebServer: signaling with |answer-B1|
WebServer->AliceJS: signaling with |answer-B1| WebServer-&gt;AliceJS: signaling with |answer-B1|
AliceJS->AliceUA: setRemoteDescription with |answer-B1| AliceJS-&gt;AliceUA: setRemoteDescription with |answer-B1|
AliceUA->AliceJS: ontrack event with audio track from Bob AliceUA-&gt;AliceJS: ontrack event with audio track from Bob
// candidates are sent to Alice // candidates are sent to Alice
BobUA->BobJS: onicecandidate (host) |answer-B1-candidate-1| BobUA-&gt;BobJS: onicecandidate (host) |answer-B1-candidate-1|
BobJS->WebServer: signaling with |answer-B1-candidate-1| BobJS-&gt;WebServer: signaling with |answer-B1-candidate-1|
BobUA->BobJS: onicecandidate (srflx) |answer-B1-candidate-2| BobUA-&gt;BobJS: onicecandidate (srflx) |answer-B1-candidate-2|
BobJS->WebServer: signaling with |answer-B1-candidate-2| BobJS-&gt;WebServer: signaling with |answer-B1-candidate-2|
BobUA->BobJS: onicecandidate (relay) |answer-B1-candidate-3| BobUA-&gt;BobJS: onicecandidate (relay) |answer-B1-candidate-3|
BobJS->WebServer: signaling with |answer-B1-candidate-3| BobJS-&gt;WebServer: signaling with |answer-B1-candidate-3|
WebServer->AliceJS: signaling with |answer-B1-candidate-1| WebServer-&gt;AliceJS: signaling with |answer-B1-candidate-1|
AliceJS->AliceUA: addIceCandidate with |answer-B1-candidate-1| AliceJS-&gt;AliceUA: addIceCandidate with |answer-B1-candidate-1|
WebServer->AliceJS: signaling with |answer-B1-candidate-2| WebServer-&gt;AliceJS: signaling with |answer-B1-candidate-2|
AliceJS->AliceUA: addIceCandidate with |answer-B1-candidate-2| AliceJS-&gt;AliceUA: addIceCandidate with |answer-B1-candidate-2|
WebServer->AliceJS: signaling with |answer-B1-candidate-3| WebServer-&gt;AliceJS: signaling with |answer-B1-candidate-3|
AliceJS->AliceUA: addIceCandidate with |answer-B1-candidate-3| AliceJS-&gt;AliceUA: addIceCandidate with |answer-B1-candidate-3|
// data channel opens // data channel opens
BobUA->BobJS: ondatachannel event BobUA-&gt;BobJS: ondatachannel event
AliceUA->AliceJS: ondatachannel event AliceUA-&gt;AliceJS: ondatachannel event
BobUA->BobJS: onopen BobUA-&gt;BobJS: onopen
AliceUA->AliceJS: onopen AliceUA-&gt;AliceJS: onopen
// media is flowing between endpoints // media is flowing between endpoints
BobUA->AliceUA: audio+data sent from Bob to Alice BobUA-&gt;AliceUA: audio+data sent from Bob to Alice
AliceUA->BobUA: audio+data sent from Alice to Bob AliceUA-&gt;BobUA: audio+data sent from Alice to Bob
// some time later Bob adds two video streams // some time later, Bob adds two video streams
// note, no candidates exchanged, because of bundle // note: no candidates exchanged, because of bundle
BobJS->BobUA: addTrack with first video stream BobJS-&gt;BobUA: addTrack with first video stream
BobJS->BobUA: addTrack with second video stream BobJS-&gt;BobUA: addTrack with second video stream
BobJS->BobUA: createOffer to get |offer-B2| BobJS-&gt;BobUA: createOffer to get |offer-B2|
BobJS->BobUA: setLocalDescription with |offer-B2| BobJS-&gt;BobUA: setLocalDescription with |offer-B2|
// |offer-B2| is sent to Alice // |offer-B2| is sent to Alice
BobJS->WebServer: signaling with |offer-B2| BobJS-&gt;WebServer: signaling with |offer-B2|
WebServer->AliceJS: signaling with |offer-B2| WebServer-&gt;AliceJS: signaling with |offer-B2|
AliceJS->AliceUA: setRemoteDescription with |offer-B2| AliceJS-&gt;AliceUA: setRemoteDescription with |offer-B2|
AliceUA->AliceJS: ontrack event with first video track AliceUA-&gt;AliceJS: ontrack event with first video track
AliceUA->AliceJS: ontrack event with second video track AliceUA-&gt;AliceJS: ontrack event with second video track
AliceJS->AliceUA: createAnswer to get |answer-B2| AliceJS-&gt;AliceUA: createAnswer to get |answer-B2|
AliceJS->AliceUA: setLocalDescription with |answer-B2| AliceJS-&gt;AliceUA: setLocalDescription with |answer-B2|
// |answer-B2| is sent over signaling protocol to Bob // |answer-B2| is sent over signaling protocol
AliceJS->WebServer: signaling with |answer-B2| // to Bob
WebServer->BobJS: signaling with |answer-B2| AliceJS-&gt;WebServer: signaling with |answer-B2|
BobJS->BobUA: setRemoteDescription with |answer-B2| WebServer-&gt;BobJS: signaling with |answer-B2|
BobJS-&gt;BobUA: setRemoteDescription with |answer-B2|
// media is flowing between endpoints // media is flowing between endpoints
BobUA->AliceUA: audio+video+data sent from Bob to Alice BobUA-&gt;AliceUA: audio+video+data sent from Bob to Alice
AliceUA->BobUA: audio+video+data sent from Alice to Bob AliceUA-&gt;BobUA: audio+video+data sent from Alice to Bob </artwork>
]]> <t indent="0" pn="section-7.2-3">The SDP for |offer-B1| looks like:</t>
</artwork> <sourcecode name="offer-B1" type="sdp" markers="false" pn="section-7.2-4
</figure> ">
</t>
<t>The SDP for |offer-B1| looks like:</t>
<t>
<figure>
<artwork alt="offer-B1">
<![CDATA[
v=0 v=0
o=- 4962303333179871723 1 IN IP4 0.0.0.0 o=- 4962303333179871723 1 IN IP4 0.0.0.0
s=- s=-
t=0 0 t=0 0
a=ice-options:trickle ice2 a=ice-options:trickle ice2
a=group:BUNDLE a1 d1 a=group:BUNDLE a1 d1
m=audio 9 UDP/TLS/RTP/SAVPF 96 0 8 97 98 m=audio 9 UDP/TLS/RTP/SAVPF 96 0 8 97 98
c=IN IP4 0.0.0.0 c=IN IP4 0.0.0.0
a=mid:a1 a=mid:a1
skipping to change at line 4508 skipping to change at line 4403
a=tls-id:17f0f4ba8a5f1213faca591b58ba52a7 a=tls-id:17f0f4ba8a5f1213faca591b58ba52a7
a=rtcp-mux a=rtcp-mux
a=rtcp-mux-only a=rtcp-mux-only
a=rtcp-rsize a=rtcp-rsize
m=application 0 UDP/DTLS/SCTP webrtc-datachannel m=application 0 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 0.0.0.0 c=IN IP4 0.0.0.0
a=mid:d1 a=mid:d1
a=sctp-port:5000 a=sctp-port:5000
a=max-message-size:65536 a=max-message-size:65536
a=bundle-only a=bundle-only</sourcecode>
]]> <t indent="0" pn="section-7.2-5">|offer-B1-candidate-1| looks like:</t>
</artwork> <sourcecode name="offer-B1-candidate-1" type="sdp" markers="false" pn="s
</figure> ection-7.2-6">
</t>
<t>|offer-B1-candidate-1| looks like:</t>
<t>
<figure>
<artwork alt="offer-B1-candidate-1">
<![CDATA[
ufrag ATEn ufrag ATEn
index 0 index 0
mid a1 mid a1
attr candidate:1 1 udp 2113929471 203.0.113.100 10100 typ host attr candidate:1 1 udp 2113929471 203.0.113.100 10100 typ host</sourcecode>
]]> <t indent="0" pn="section-7.2-7">|offer-B1-candidate-2| looks like:</t>
</artwork> <sourcecode name="offer-B1-candidate-2" type="sdp" markers="false" pn="s
</figure> ection-7.2-8">
</t>
<t>|offer-B1-candidate-2| looks like:</t>
<t>
<figure>
<artwork alt="offer-B1-candidate-2">
<![CDATA[
ufrag ATEn ufrag ATEn
index 0 index 0
mid a1 mid a1
attr candidate:1 1 udp 1845494015 198.51.100.100 11100 typ srflx attr candidate:1 1 udp 1845494015 198.51.100.100 11100 typ srflx
raddr 203.0.113.100 rport 10100 raddr 203.0.113.100 rport 10100</sourcecode>
]]> <t indent="0" pn="section-7.2-9">|offer-B1-candidate-3| looks like:</t>
</artwork> <sourcecode name="offer-B1-candidate-3" type="sdp" markers="false" pn="s
</figure> ection-7.2-10">
</t>
<t>|offer-B1-candidate-3| looks like:</t>
<t>
<figure>
<artwork alt="offer-B1-candidate-3">
<![CDATA[
ufrag ATEn ufrag ATEn
index 0 index 0
mid a1 mid a1
attr candidate:1 1 udp 255 192.0.2.100 12100 typ relay attr candidate:1 1 udp 255 192.0.2.100 12100 typ relay
raddr 198.51.100.100 rport 11100 raddr 198.51.100.100 rport 11100</sourcecode>
]]> <t indent="0" pn="section-7.2-11">The SDP for |answer-B1| looks like:</t
</artwork> >
</figure> <sourcecode name="answer-B1" type="sdp" markers="false" pn="section-7.2-
</t> 12">
<t>The SDP for |answer-B1| looks like:</t>
<t>
<figure>
<artwork alt="answer-B1">
<![CDATA[
v=0 v=0
o=- 7729291447651054566 1 IN IP4 0.0.0.0 o=- 7729291447651054566 1 IN IP4 0.0.0.0
s=- s=-
t=0 0 t=0 0
a=ice-options:trickle ice2 a=ice-options:trickle ice2
a=group:BUNDLE a1 d1 a=group:BUNDLE a1 d1
m=audio 9 UDP/TLS/RTP/SAVPF 96 0 8 97 98 m=audio 9 UDP/TLS/RTP/SAVPF 96 0 8 97 98
c=IN IP4 0.0.0.0 c=IN IP4 0.0.0.0
a=mid:a1 a=mid:a1
skipping to change at line 4604 skipping to change at line 4463
a=setup:active a=setup:active
a=tls-id:7a25ab85b195acaf3121f5a8ab4f0f71 a=tls-id:7a25ab85b195acaf3121f5a8ab4f0f71
a=rtcp-mux a=rtcp-mux
a=rtcp-mux-only a=rtcp-mux-only
a=rtcp-rsize a=rtcp-rsize
m=application 9 UDP/DTLS/SCTP webrtc-datachannel m=application 9 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 0.0.0.0 c=IN IP4 0.0.0.0
a=mid:d1 a=mid:d1
a=sctp-port:5000 a=sctp-port:5000
a=max-message-size:65536 a=max-message-size:65536</sourcecode>
]]> <t indent="0" pn="section-7.2-13">|answer-B1-candidate-1| looks like:</t
</artwork> >
</figure> <sourcecode name="answer-B1-candidate-1" type="sdp" markers="false" pn="
</t> section-7.2-14">
<t>|answer-B1-candidate-1| looks like:</t>
<t>
<figure>
<artwork alt="answer-B1-candidate-1">
<![CDATA[
ufrag 7sFv ufrag 7sFv
index 0 index 0
mid a1 mid a1
attr candidate:1 1 udp 2113929471 203.0.113.200 10200 typ host attr candidate:1 1 udp 2113929471 203.0.113.200 10200 typ host</sourcecode>
]]> <t indent="0" pn="section-7.2-15">|answer-B1-candidate-2| looks like:</t
</artwork> >
</figure> <sourcecode name="answer-B1-candidate-2" type="sdp" markers="false" pn="
</t> section-7.2-16">
<t>|answer-B1-candidate-2| looks like:</t>
<t>
<figure>
<artwork alt="answer-B1-candidate-2">
<![CDATA[
ufrag 7sFv ufrag 7sFv
index 0 index 0
mid a1 mid a1
attr candidate:1 1 udp 1845494015 198.51.100.200 11200 typ srflx attr candidate:1 1 udp 1845494015 198.51.100.200 11200 typ srflx
raddr 203.0.113.200 rport 10200 raddr 203.0.113.200 rport 10200</sourcecode>
]]> <t indent="0" pn="section-7.2-17">|answer-B1-candidate-3| looks like:</t
</artwork> >
</figure> <sourcecode name="answer-B1-candidate-3" type="sdp" markers="false" pn="
</t> section-7.2-18">
<t>|answer-B1-candidate-3| looks like:</t>
<t>
<figure>
<artwork alt="answer-B1-candidate-3">
<![CDATA[
ufrag 7sFv ufrag 7sFv
index 0 index 0
mid a1 mid a1
attr candidate:1 1 udp 255 192.0.2.200 12200 typ relay attr candidate:1 1 udp 255 192.0.2.200 12200 typ relay
raddr 198.51.100.200 rport 11200 raddr 198.51.100.200 rport 11200</sourcecode>
]]> <t indent="0" pn="section-7.2-19">The SDP for |offer-B2| is shown below.
</artwork> In addition to the
</figure> new "m=" sections for video, both of which are offering FEC and
</t> one of which is offering simulcast, note the increment of the
version number in the "o=" line; changes to the "c=" line,
<t>The SDP for |offer-B2| is shown below. In addition to the indicating the local candidate that was selected; and the
new m= sections for video, both of which are offering FEC, and inclusion of gathered candidates as a=candidate lines.</t>
one of which is offering simulcast, note the increment of the <sourcecode name="offer-B2" type="sdp" markers="false" pn="section-7.2-2
version number in the o= line, changes to the c= line, 0">
indicating the local candidate that was selected, and the
inclusion of gathered candidates as a=candidate lines.</t>
<t>
<figure>
<artwork alt="offer-B2">
<![CDATA[
v=0 v=0
o=- 7729291447651054566 2 IN IP4 0.0.0.0 o=- 7729291447651054566 2 IN IP4 0.0.0.0
s=- s=-
t=0 0 t=0 0
a=ice-options:trickle ice2 a=ice-options:trickle ice2
a=group:BUNDLE a1 d1 v1 v2 a=group:BUNDLE a1 d1 v1 v2
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 12200 UDP/TLS/RTP/SAVPF 96 0 8 97 98 m=audio 12200 UDP/TLS/RTP/SAVPF 96 0 8 97 98
c=IN IP4 192.0.2.200 c=IN IP4 192.0.2.200
skipping to change at line 4723 skipping to change at line 4546
m=video 12200 UDP/TLS/RTP/SAVPF 100 101 102 103 104 m=video 12200 UDP/TLS/RTP/SAVPF 100 101 102 103 104
c=IN IP4 192.0.2.200 c=IN IP4 192.0.2.200
a=mid:v1 a=mid:v1
a=sendrecv a=sendrecv
a=rtpmap:100 VP8/90000 a=rtpmap:100 VP8/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=fmtp:101 packetization-mode=1;profile-level-id=42e01f a=fmtp:101 packetization-mode=1;profile-level-id=42e01f
a=rtpmap:102 rtx/90000 a=rtpmap:102 rtx/90000
a=fmtp:102 apt=100 a=fmtp:102 apt=100
=rtpmap:103 rtx/90000 a=rtpmap:103 rtx/90000
a=fmtp:103 apt=101 a=fmtp:103 apt=101
a=rtpmap:104 flexfec/90000 a=rtpmap:104 flexfec/90000
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=rtcp-fb:100 ccm fir a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli a=rtcp-fb:100 nack pli
a=msid:71317484-2ed4-49d7-9eb7-1414322a7aae a=msid:71317484-2ed4-49d7-9eb7-1414322a7aae
a=rid:1 send a=rid:1 send
a=rid:2 send a=rid:2 send
skipping to change at line 4746 skipping to change at line 4569
m=video 12200 UDP/TLS/RTP/SAVPF 100 101 102 103 104 m=video 12200 UDP/TLS/RTP/SAVPF 100 101 102 103 104
c=IN IP4 192.0.2.200 c=IN IP4 192.0.2.200
a=mid:v2 a=mid:v2
a=sendrecv a=sendrecv
a=rtpmap:100 VP8/90000 a=rtpmap:100 VP8/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=fmtp:101 packetization-mode=1;profile-level-id=42e01f a=fmtp:101 packetization-mode=1;profile-level-id=42e01f
a=rtpmap:102 rtx/90000 a=rtpmap:102 rtx/90000
a=fmtp:102 apt=100 a=fmtp:102 apt=100
=rtpmap:103 rtx/90000 a=rtpmap:103 rtx/90000
a=fmtp:103 apt=101 a=fmtp:103 apt=101
a=rtpmap:104 flexfec/90000 a=rtpmap:104 flexfec/90000
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=rtcp-fb:100 ccm fir a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli a=rtcp-fb:100 nack pli
a=msid:81317484-2ed4-49d7-9eb7-1414322a7aae a=msid:81317484-2ed4-49d7-9eb7-1414322a7aae</sourcecode>
]]> <t indent="0" pn="section-7.2-21">The SDP for |answer-B2| is shown below
</artwork> . In addition to the
</figure> acceptance of the video "m=" sections, the use of a=recvonly to
</t> indicate one-way video, and the use of a=imageattr to limit the
received resolution, note the use of setup:passive to maintain
<t>The SDP for |answer-B2| is shown below. In addition to the the existing DTLS roles.</t>
acceptance of the video m= sections, the use of a=recvonly to <sourcecode name="answer-B2" type="sdp" markers="false" pn="section-7.2-
indicate one-way video, and the use of a=imageattr to limit the 22">
received resolution, note the use of setup:passive to maintain
the existing DTLS roles.</t>
<t>
<figure>
<artwork alt="answer-B2">
<![CDATA[
v=0 v=0
o=- 4962303333179871723 2 IN IP4 0.0.0.0 o=- 4962303333179871723 2 IN IP4 0.0.0.0
s=- s=-
t=0 0 t=0 0
a=ice-options:trickle ice2 a=ice-options:trickle ice2
a=group:BUNDLE a1 d1 v1 v2 a=group:BUNDLE a1 d1 v1 v2
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 12100 UDP/TLS/RTP/SAVPF 96 0 8 97 98 m=audio 12100 UDP/TLS/RTP/SAVPF 96 0 8 97 98
c=IN IP4 192.0.2.100 c=IN IP4 192.0.2.100
skipping to change at line 4825 skipping to change at line 4639
m=video 12100 UDP/TLS/RTP/SAVPF 100 101 102 103 m=video 12100 UDP/TLS/RTP/SAVPF 100 101 102 103
c=IN IP4 192.0.2.100 c=IN IP4 192.0.2.100
a=mid:v1 a=mid:v1
a=recvonly a=recvonly
a=rtpmap:100 VP8/90000 a=rtpmap:100 VP8/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=fmtp:101 packetization-mode=1;profile-level-id=42e01f a=fmtp:101 packetization-mode=1;profile-level-id=42e01f
a=rtpmap:102 rtx/90000 a=rtpmap:102 rtx/90000
a=fmtp:102 apt=100 a=fmtp:102 apt=100
=rtpmap:103 rtx/90000 a=rtpmap:103 rtx/90000
a=fmtp:103 apt=101 a=fmtp:103 apt=101
a=imageattr:100 recv [x=[48:1920],y=[48:1080],q=1.0] a=imageattr:100 recv [x=[48:1920],y=[48:1080],q=1.0]
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=rtcp-fb:100 ccm fir a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli a=rtcp-fb:100 nack pli
m=video 12100 UDP/TLS/RTP/SAVPF 100 101 102 103 m=video 12100 UDP/TLS/RTP/SAVPF 100 101 102 103
c=IN IP4 192.0.2.100 c=IN IP4 192.0.2.100
a=mid:v2 a=mid:v2
a=recvonly a=recvonly
a=rtpmap:100 VP8/90000 a=rtpmap:100 VP8/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=fmtp:101 packetization-mode=1;profile-level-id=42e01f a=fmtp:101 packetization-mode=1;profile-level-id=42e01f
a=rtpmap:102 rtx/90000 a=rtpmap:102 rtx/90000
a=fmtp:102 apt=100 a=fmtp:102 apt=100
=rtpmap:103 rtx/90000 a=rtpmap:103 rtx/90000
a=fmtp:103 apt=101 a=fmtp:103 apt=101
a=imageattr:100 recv [x=[48:1920],y=[48:1080],q=1.0] a=imageattr:100 recv [x=[48:1920],y=[48:1080],q=1.0]
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=rtcp-fb:100 ccm fir a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli a=rtcp-fb:100 nack pli</sourcecode>
]]>
</artwork>
</figure>
</t>
</section> </section>
<section title="Early Transport Warmup Example" <section anchor="sec.warmup-example" numbered="true" toc="include" removeI
anchor="sec.warmup-example"> nRFC="false" pn="section-7.3">
<name slugifiedName="name-early-transport-warmup-exam">Early Transport W
<t>This example demonstrates the early warmup technique armup Example</name>
described in <t indent="0" pn="section-7.3-1">This example demonstrates the early-war
<xref target="sec.use-of-provisional-answer" />. Here, Alice's mup technique
endpoint sends an offer to Bob's endpoint to start an described in
audio/video call. Bob immediately responds with an answer that <xref target="sec.use-of-provisional-answer" format="default" sectionF
accepts the audio/video m= sections, but marks them as sendonly ormat="of" derivedContent="Section 4.1.10.1"/>. Here, Alice's
(from his perspective), meaning that Alice will not yet send endpoint sends an offer to Bob's endpoint to start an
media. This allows the JSEP implementation to start negotiating audio/video call. Bob immediately responds with an answer that
ICE and DTLS immediately. Bob's endpoint then prompts him to accepts the audio/video "m=" sections but marks them as sendonly
answer the call, and when he does, his endpoint sends a second (from his perspective), meaning that Alice will not yet send
offer which enables the audio and video m= sections, and media. This allows the JSEP implementation to start negotiating
thereby bidirectional media transmission. The advantage of such ICE and DTLS immediately. Bob's endpoint then prompts him to
a flow is that as soon as the first answer is received, the answer the call, and when he does, his endpoint sends a second
implementation can proceed with ICE and DTLS negotiation and offer, which enables the audio and video "m=" sections, and
establish the session transport. If the transport setup thereby bidirectional media transmission. The advantage of such
completes before the second offer is sent, then media can be a flow is that as soon as the first answer is received, the
transmitted immediately by the callee immediately upon implementation can proceed with ICE and DTLS negotiation and
answering the call, minimizing perceived post-dial-delay. The establish the session transport. If the transport setup
second offer/answer exchange can also change the preferred completes before the second offer is sent, then media can be
codecs or other session parameters.</t> transmitted by the callee immediately upon
answering the call, minimizing perceived post-dial delay. The
<t>This example also makes use of the "relay" ICE candidate second offer/answer exchange can also change the preferred
policy described in codecs or other session parameters.</t>
<xref target="sec.ice-candidate-policy" /> to minimize the ICE <t indent="0" pn="section-7.3-2">This example also makes use of the "rel
gathering and checking needed.</t> ay" ICE candidate
policy described in
<t> <xref target="sec.ice-candidate-policy" format="default" sectionFormat
<figure> ="of" derivedContent="Section 3.5.3"/> to minimize the ICE
<artwork> gathering and checking needed.</t>
<![CDATA[ <artwork name="" type="ascii-art" align="left" alt="" pn="section-7.3-3"
>
// set up local media state // set up local media state
AliceJS->AliceUA: create new PeerConnection with "relay" ICE policy AliceJS-&gt;AliceUA: create new PeerConnection with "relay" ICE policy
AliceJS->AliceUA: addTrack with two tracks: audio and video AliceJS-&gt;AliceUA: addTrack with two tracks: audio and video
AliceJS->AliceUA: createOffer to get |offer-C1| AliceJS-&gt;AliceUA: createOffer to get |offer-C1|
AliceJS->AliceUA: setLocalDescription with |offer-C1| AliceJS-&gt;AliceUA: setLocalDescription with |offer-C1|
// |offer-C1| is sent over signaling protocol to Bob // |offer-C1| is sent over signaling protocol to Bob
AliceJS->WebServer: signaling with |offer-C1| AliceJS-&gt;WebServer: signaling with |offer-C1|
WebServer->BobJS: signaling with |offer-C1| WebServer-&gt;BobJS: signaling with |offer-C1|
// |offer-C1| arrives at Bob // |offer-C1| arrives at Bob
BobJS->BobUA: create new PeerConnection with "relay" ICE policy BobJS-&gt;BobUA: create new PeerConnection with "relay" ICE policy
BobJS->BobUA: setRemoteDescription with |offer-C1| BobJS-&gt;BobUA: setRemoteDescription with |offer-C1|
BobUA->BobJS: ontrack events for audio and video BobUA-&gt;BobJS: ontrack events for audio and video
// a relay candidate is sent to Bob // a relay candidate is sent to Bob
AliceUA->AliceJS: onicecandidate (relay) |offer-C1-candidate-1| AliceUA-&gt;AliceJS: onicecandidate (relay) |offer-C1-candidate-1|
AliceJS->WebServer: signaling with |offer-C1-candidate-1| AliceJS-&gt;WebServer: signaling with |offer-C1-candidate-1|
WebServer->BobJS: signaling with |offer-C1-candidate-1| WebServer-&gt;BobJS: signaling with |offer-C1-candidate-1|
BobJS->BobUA: addIceCandidate with |offer-C1-candidate-1| BobJS-&gt;BobUA: addIceCandidate with |offer-C1-candidate-1|
// Bob prepares an early answer to warmup the transport // Bob prepares an early answer to warm up the
BobJS->BobUA: addTransceiver with null audio and video tracks // transport
BobJS->BobUA: transceiver.setDirection(sendonly) for both BobJS-&gt;BobUA: addTransceiver with null audio and video tracks
BobJS->BobUA: createAnswer BobJS-&gt;BobUA: transceiver.setDirection(sendonly) for both
BobJS->BobUA: setLocalDescription with answer BobJS-&gt;BobUA: createAnswer
BobJS-&gt;BobUA: setLocalDescription with answer
// |answer-C1| is sent over signaling protocol to Alice // |answer-C1| is sent over signaling protocol
BobJS->WebServer: signaling with |answer-C1| // to Alice
WebServer->AliceJS: signaling with |answer-C1| BobJS-&gt;WebServer: signaling with |answer-C1|
WebServer-&gt;AliceJS: signaling with |answer-C1|
// |answer-C1| (sendonly) arrives at Alice // |answer-C1| (sendonly) arrives at Alice
AliceJS->AliceUA: setRemoteDescription with |answer-C1| AliceJS-&gt;AliceUA: setRemoteDescription with |answer-C1|
AliceUA->AliceJS: ontrack events for audio and video AliceUA-&gt;AliceJS: ontrack events for audio and video
// a relay candidate is sent to Alice // a relay candidate is sent to Alice
BobUA->BobJS: onicecandidate (relay) |answer-B1-candidate-1| BobUA-&gt;BobJS: onicecandidate (relay) |answer-B1-candidate-1|
BobJS->WebServer: signaling with |answer-B1-candidate-1| BobJS-&gt;WebServer: signaling with |answer-B1-candidate-1|
WebServer->AliceJS: signaling with |answer-B1-candidate-1| WebServer-&gt;AliceJS: signaling with |answer-B1-candidate-1|
AliceJS->AliceUA: addIceCandidate with |answer-B1-candidate-1| AliceJS-&gt;AliceUA: addIceCandidate with |answer-B1-candidate-1|
// ICE and DTLS establish while call is ringing // ICE and DTLS establish while call is ringing
// Bob accepts call, starts media, and sends new offer // Bob accepts call, starts media, and sends
BobJS->BobUA: transceiver.setTrack with audio and video tracks // new offer
BobUA->AliceUA: media sent from Bob to Alice BobJS-&gt;BobUA: transceiver.setTrack with audio and video tracks
BobJS->BobUA: transceiver.setDirection(sendrecv) for both BobUA-&gt;AliceUA: media sent from Bob to Alice
BobJS-&gt;BobUA: transceiver.setDirection(sendrecv) for both
transceivers transceivers
BobJS->BobUA: createOffer BobJS-&gt;BobUA: createOffer
BobJS->BobUA: setLocalDescription with offer BobJS-&gt;BobUA: setLocalDescription with offer
// |offer-C2| is sent over signaling protocol to Alice // |offer-C2| is sent over signaling protocol
BobJS->WebServer: signaling with |offer-C2| // to Alice
WebServer->AliceJS: signaling with |offer-C2| BobJS-&gt;WebServer: signaling with |offer-C2|
WebServer-&gt;AliceJS: signaling with |offer-C2|
// |offer-C2| (sendrecv) arrives at Alice // |offer-C2| (sendrecv) arrives at Alice
AliceJS->AliceUA: setRemoteDescription with |offer-C2| AliceJS-&gt;AliceUA: setRemoteDescription with |offer-C2|
AliceJS->AliceUA: createAnswer AliceJS-&gt;AliceUA: createAnswer
AliceJS->AliceUA: setLocalDescription with |answer-C2| AliceJS-&gt;AliceUA: setLocalDescription with |answer-C2|
AliceUA->BobUA: media sent from Alice to Bob AliceUA-&gt;BobUA: media sent from Alice to Bob
// |answer-C2| is sent over signaling protocol to Bob
AliceJS->WebServer: signaling with |answer-C2|
WebServer->BobJS: signaling with |answer-C2|
BobJS->BobUA: setRemoteDescription with |answer-C2|
]]>
</artwork>
</figure>
</t>
<t>The SDP for |offer-C1| looks like:</t>
<t> // |answer-C2| is sent over signaling protocol
<figure> // to Bob
<artwork alt="offer-C1"> AliceJS-&gt;WebServer: signaling with |answer-C2|
<![CDATA[ WebServer-&gt;BobJS: signaling with |answer-C2|
BobJS-&gt;BobUA: setRemoteDescription with |answer-C2| </artwork>
<t indent="0" pn="section-7.3-4">The SDP for |offer-C1| looks like:</t>
<sourcecode name="offer-C1" type="sdp" markers="false" pn="section-7.3-5
">
v=0 v=0
o=- 1070771854436052752 1 IN IP4 0.0.0.0 o=- 1070771854436052752 1 IN IP4 0.0.0.0
s=- s=-
t=0 0 t=0 0
a=ice-options:trickle ice2 a=ice-options:trickle ice2
a=group:BUNDLE a1 v1 a=group:BUNDLE a1 v1
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 9 UDP/TLS/RTP/SAVPF 96 0 8 97 98 m=audio 9 UDP/TLS/RTP/SAVPF 96 0 8 97 98
c=IN IP4 0.0.0.0 c=IN IP4 0.0.0.0
skipping to change at line 5010 skipping to change at line 4810
m=video 0 UDP/TLS/RTP/SAVPF 100 101 102 103 m=video 0 UDP/TLS/RTP/SAVPF 100 101 102 103
c=IN IP4 0.0.0.0 c=IN IP4 0.0.0.0
a=mid:v1 a=mid:v1
a=sendrecv a=sendrecv
a=rtpmap:100 VP8/90000 a=rtpmap:100 VP8/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=fmtp:101 packetization-mode=1;profile-level-id=42e01f a=fmtp:101 packetization-mode=1;profile-level-id=42e01f
a=rtpmap:102 rtx/90000 a=rtpmap:102 rtx/90000
a=fmtp:102 apt=100 a=fmtp:102 apt=100
=rtpmap:103 rtx/90000 a=rtpmap:103 rtx/90000
a=fmtp:103 apt=101 a=fmtp:103 apt=101
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=rtcp-fb:100 ccm fir a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli a=rtcp-fb:100 nack pli
a=msid:bbce3ba6-abfc-ac63-d00a-e15b286f8fce a=msid:bbce3ba6-abfc-ac63-d00a-e15b286f8fce
a=bundle-only a=bundle-only</sourcecode>
]]> <t indent="0" pn="section-7.3-6">|offer-C1-candidate-1| looks like:</t>
</artwork> <sourcecode name="offer-C1-candidate-1" type="sdp" markers="false" pn="s
</figure> ection-7.3-7">
</t>
<t>|offer-C1-candidate-1| looks like:</t>
<t>
<figure>
<artwork alt="offer-C1-candidate-1">
<![CDATA[
ufrag 4ZcD ufrag 4ZcD
index 0 index 0
mid a1 mid a1
attr candidate:1 1 udp 255 192.0.2.100 12100 typ relay attr candidate:1 1 udp 255 192.0.2.100 12100 typ relay
raddr 0.0.0.0 rport 0 raddr 0.0.0.0 rport 0</sourcecode>
]]> <t indent="0" pn="section-7.3-8">The SDP for |answer-C1| looks like:</t>
</artwork> <sourcecode name="answer-C1" type="sdp" markers="false" pn="section-7.3-
</figure> 9">
</t>
<t>The SDP for |answer-C1| looks like:</t>
<t>
<figure>
<artwork alt="answer-C1">
<![CDATA[
v=0 v=0
o=- 6386516489780559513 1 IN IP4 0.0.0.0 o=- 6386516489780559513 1 IN IP4 0.0.0.0
s=- s=-
t=0 0 t=0 0
a=ice-options:trickle ice2 a=ice-options:trickle ice2
a=group:BUNDLE a1 v1 a=group:BUNDLE a1 v1
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 9 UDP/TLS/RTP/SAVPF 96 0 8 97 98 m=audio 9 UDP/TLS/RTP/SAVPF 96 0 8 97 98
c=IN IP4 0.0.0.0 c=IN IP4 0.0.0.0
skipping to change at line 5089 skipping to change at line 4871
m=video 9 UDP/TLS/RTP/SAVPF 100 101 102 103 m=video 9 UDP/TLS/RTP/SAVPF 100 101 102 103
c=IN IP4 0.0.0.0 c=IN IP4 0.0.0.0
a=mid:v1 a=mid:v1
a=sendonly a=sendonly
a=rtpmap:100 VP8/90000 a=rtpmap:100 VP8/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=fmtp:101 packetization-mode=1;profile-level-id=42e01f a=fmtp:101 packetization-mode=1;profile-level-id=42e01f
a=rtpmap:102 rtx/90000 a=rtpmap:102 rtx/90000
a=fmtp:102 apt=100 a=fmtp:102 apt=100
=rtpmap:103 rtx/90000 a=rtpmap:103 rtx/90000
a=fmtp:103 apt=101 a=fmtp:103 apt=101
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=rtcp-fb:100 ccm fir a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli a=rtcp-fb:100 nack pli
a=msid:751f239e-4ae0-c549-aa3d-890de772998b a=msid:751f239e-4ae0-c549-aa3d-890de772998b</sourcecode>
]]> <t indent="0" pn="section-7.3-10">|answer-C1-candidate-1| looks like:</t
</artwork> >
</figure> <sourcecode name="answer-C1-candidate-1" type="sdp" markers="false" pn="
</t> section-7.3-11">
<t>|answer-C1-candidate-1| looks like:</t>
<t>
<figure>
<artwork alt="answer-C1-candidate-1">
<![CDATA[
ufrag TpaA ufrag TpaA
index 0 index 0
mid a1 mid a1
attr candidate:1 1 udp 255 192.0.2.200 12200 typ relay attr candidate:1 1 udp 255 192.0.2.200 12200 typ relay
raddr 0.0.0.0 rport 0 raddr 0.0.0.0 rport 0</sourcecode>
]]> <t indent="0" pn="section-7.3-12">The SDP for |offer-C2| looks like:</t>
</artwork> <sourcecode name="offer-C2" type="sdp" markers="false" pn="section-7.3-1
</figure> 3">
</t>
<t>The SDP for |offer-C2| looks like:</t>
<t>
<figure>
<artwork alt="offer-C2">
<![CDATA[
v=0 v=0
o=- 6386516489780559513 2 IN IP4 0.0.0.0 o=- 6386516489780559513 2 IN IP4 0.0.0.0
s=- s=-
t=0 0 t=0 0
a=ice-options:trickle ice2 a=ice-options:trickle ice2
a=group:BUNDLE a1 v1 a=group:BUNDLE a1 v1
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 12200 UDP/TLS/RTP/SAVPF 96 0 8 97 98 m=audio 12200 UDP/TLS/RTP/SAVPF 96 0 8 97 98
c=IN IP4 192.0.2.200 c=IN IP4 192.0.2.200
skipping to change at line 5170 skipping to change at line 4934
m=video 12200 UDP/TLS/RTP/SAVPF 100 101 102 103 m=video 12200 UDP/TLS/RTP/SAVPF 100 101 102 103
c=IN IP4 192.0.2.200 c=IN IP4 192.0.2.200
a=mid:v1 a=mid:v1
a=sendrecv a=sendrecv
a=rtpmap:100 VP8/90000 a=rtpmap:100 VP8/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=fmtp:101 packetization-mode=1;profile-level-id=42e01f a=fmtp:101 packetization-mode=1;profile-level-id=42e01f
a=rtpmap:102 rtx/90000 a=rtpmap:102 rtx/90000
a=fmtp:102 apt=100 a=fmtp:102 apt=100
=rtpmap:103 rtx/90000 a=rtpmap:103 rtx/90000
a=fmtp:103 apt=101 a=fmtp:103 apt=101
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=rtcp-fb:100 ccm fir a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli a=rtcp-fb:100 nack pli
a=msid:751f239e-4ae0-c549-aa3d-890de772998b a=msid:751f239e-4ae0-c549-aa3d-890de772998b</sourcecode>
]]> <t indent="0" pn="section-7.3-14">The SDP for |answer-C2| looks like:</t
</artwork> >
</figure> <sourcecode name="answer-C2" type="sdp" markers="false" pn="section-7.3-
</t> 15">
<t>The SDP for |answer-C2| looks like:</t>
<t>
<figure>
<artwork alt="answer-C2">
<![CDATA[
v=0 v=0
o=- 1070771854436052752 2 IN IP4 0.0.0.0 o=- 1070771854436052752 2 IN IP4 0.0.0.0
s=- s=-
t=0 0 t=0 0
a=ice-options:trickle ice2 a=ice-options:trickle ice2
a=group:BUNDLE a1 v1 a=group:BUNDLE a1 v1
a=group:LS a1 v1 a=group:LS a1 v1
m=audio 12100 UDP/TLS/RTP/SAVPF 96 0 8 97 98 m=audio 12100 UDP/TLS/RTP/SAVPF 96 0 8 97 98
c=IN IP4 192.0.2.100 c=IN IP4 192.0.2.100
skipping to change at line 5235 skipping to change at line 4990
m=video 12100 UDP/TLS/RTP/SAVPF 100 101 102 103 m=video 12100 UDP/TLS/RTP/SAVPF 100 101 102 103
c=IN IP4 192.0.2.100 c=IN IP4 192.0.2.100
a=mid:v1 a=mid:v1
a=sendrecv a=sendrecv
a=rtpmap:100 VP8/90000 a=rtpmap:100 VP8/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=fmtp:101 packetization-mode=1;profile-level-id=42e01f a=fmtp:101 packetization-mode=1;profile-level-id=42e01f
a=rtpmap:102 rtx/90000 a=rtpmap:102 rtx/90000
a=fmtp:102 apt=100 a=fmtp:102 apt=100
=rtpmap:103 rtx/90000 a=rtpmap:103 rtx/90000
a=fmtp:103 apt=101 a=fmtp:103 apt=101
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=rtcp-fb:100 ccm fir a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli a=rtcp-fb:100 nack pli
a=msid:bbce3ba6-abfc-ac63-d00a-e15b286f8fce a=msid:bbce3ba6-abfc-ac63-d00a-e15b286f8fce</sourcecode>
]]>
</artwork>
</figure>
</t>
</section> </section>
</section> </section>
<section title="Security Considerations" <section anchor="sec.security-considerations" numbered="true" toc="include"
anchor="sec.security-considerations"> removeInRFC="false" pn="section-8">
<name slugifiedName="name-security-considerations">Security Considerations
<t>The IETF has published separate documents </name>
<xref target="I-D.ietf-rtcweb-security-arch" /> <t indent="0" pn="section-8-1">The IETF has published separate documents
<xref target="I-D.ietf-rtcweb-security" /> describing the security <xref target="RFC8827" format="default" sectionFormat="of" derivedConten
architecture for WebRTC as a whole. The remainder of this section t="RFC8827"/>
describes security considerations for this document.</t> <xref target="RFC8826" format="default" sectionFormat="of" derivedConten
t="RFC8826"/> describing the security
<t>While formally the JSEP interface is an API, it is better to architecture for WebRTC as a whole. The remainder of this section
think of it as an Internet protocol, with the application describes security considerations for this document.</t>
JavaScript being untrustworthy from the perspective of the JSEP <t indent="0" pn="section-8-2">While formally the JSEP interface is an API
implementation. Thus, the threat model of , it is better to
<xref target="RFC3552" /> applies. In particular, JavaScript can think of it as an Internet protocol, with the application
call the API in any order and with any inputs, including JavaScript being untrustworthy from the perspective of the JSEP
malicious ones. This is particularly relevant when we consider implementation. Thus, the threat model of
the SDP which is passed to setLocalDescription(). While correct <xref target="RFC3552" format="default" sectionFormat="of" derivedConten
API usage requires that the application pass in SDP which was t="RFC3552"/> applies. In particular, JavaScript can
derived from createOffer() or createAnswer(), there is no call the API in any order and with any inputs, including
guarantee that applications do so. The JSEP implementation MUST malicious ones. This is particularly relevant when we consider
be prepared for the JavaScript to pass in bogus data instead.</t> the SDP that is passed to setLocalDescription. While correct
API usage requires that the application pass in SDP that was
<t>Conversely, the application programmer needs to be aware that derived from createOffer or createAnswer, there is no
the JavaScript does not have complete control of endpoint guarantee that applications do so. The JSEP implementation <bcp14>MUST</
behavior. One case that bears particular mention is that editing bcp14>
ICE candidates out of the SDP or suppressing trickled candidates be prepared for the JavaScript to pass in bogus data instead.</t>
does not have the expected behavior: implementations will still <t indent="0" pn="section-8-3">Conversely, the application programmer need
perform checks from those candidates even if they are not sent to s to be aware that
the other side. Thus, for instance, it is not possible to prevent the JavaScript does not have complete control of endpoint
the remote peer from learning your public IP address by removing behavior. One case that bears particular mention is that editing
server reflexive candidates. Applications which wish to conceal ICE candidates out of the SDP or suppressing trickled candidates
their public IP address should instead configure the ICE agent to does not have the expected behavior: implementations will still
use only relay candidates.</t> perform checks from those candidates even if they are not sent to
</section> the other side. Thus, for instance, it is not possible to prevent
<section title="IANA Considerations" the remote peer from learning your public IP address by removing
anchor="sec.iana-considerations"> server-reflexive candidates. Applications that wish to conceal
their public IP address <bcp14>MUST</bcp14> instead configure the ICE ag
<t>This document requires no actions from IANA.</t> ent to
use only relay candidates.</t>
</section> </section>
<section title="Acknowledgements" anchor="sec.acknowledgements"> <section anchor="sec.iana-considerations" numbered="true" toc="include" remo
veInRFC="false" pn="section-9">
<t>Harald Alvestrand, Taylor Brandstetter, Suhas Nandakumar, and <name slugifiedName="name-iana-considerations">IANA Considerations</name>
Peter Thatcher provided significant text for this draft. Bernard <t indent="0" pn="section-9-1">This document has no IANA actions.</t>
Aboba, Adam Bergkvist, Dan Burnett, Ben Campbell, Alissa Cooper,
Richard Ejzak, Stefan Hakansson, Ted Hardie, Christer Holmberg
Andrew Hutton, Randell Jesup, Matthew Kaufman, Anant Narayanan,
Adam Roach, Robert Sparks, Neil Stratford, Martin Thomson, Sean
Turner, and Magnus Westerlund all provided valuable feedback on
this proposal.</t>
</section> </section>
</middle> </middle>
<back> <back>
<references title="Normative References"> <displayreference target="I-D.ietf-rtcweb-sdp" to="SDP4WebRTC"/>
<?rfc include='reference.I-D.ietf-avtext-rid'?> <references pn="section-10">
<?rfc include='reference.I-D.ietf-ice-trickle'?> <name slugifiedName="name-references">References</name>
<?rfc include='reference.I-D.ietf-mmusic-dtls-sdp'?> <references pn="section-10.1">
<?rfc include='reference.I-D.ietf-mmusic-ice-sip-sdp'?> <name slugifiedName="name-normative-references">Normative References</na
<?rfc include='reference.I-D.ietf-mmusic-msid'?> me>
<?rfc include='reference.I-D.ietf-mmusic-mux-exclusive'?> <reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2
<?rfc include='reference.I-D.ietf-mmusic-rid'?> 119" quoteTitle="true" derivedAnchor="RFC2119">
<?rfc include='reference.I-D.ietf-mmusic-sctp-sdp'?> <front>
<?rfc include='reference.I-D.ietf-mmusic-sdp-bundle-negotiation'?> <title>Key words for use in RFCs to Indicate Requirement Levels</tit
<?rfc include='reference.I-D.ietf-mmusic-sdp-mux-attributes'?> le>
<?rfc include='reference.I-D.ietf-mmusic-sdp-simulcast'?> <author initials="S." surname="Bradner" fullname="S. Bradner">
<?rfc include='reference.I-D.ietf-rtcweb-fec'?> <organization showOnFrontPage="true"/>
<?rfc include='reference.I-D.ietf-rtcweb-rtp-usage'?> </author>
<?rfc include='reference.I-D.ietf-rtcweb-security'?> <date year="1997" month="March"/>
<?rfc include='reference.I-D.ietf-rtcweb-security-arch'?> <abstract>
<?rfc include='reference.RFC.2119.xml'?> <t indent="0">In many standards track documents several words are
<?rfc include='reference.RFC.3261.xml'?> used to signify the requirements in the specification. These words are often ca
<?rfc include='reference.RFC.3264.xml'?> pitalized. This document defines these words as they should be interpreted in IE
<?rfc include='reference.RFC.3552.xml'?> TF documents. This document specifies an Internet Best Current Practices for th
<?rfc include='reference.RFC.3605.xml'?> e Internet Community, and requests discussion and suggestions for improvements.<
<?rfc include='reference.RFC.3890.xml'?> /t>
<?rfc include='reference.RFC.4145.xml'?> </abstract>
<?rfc include='reference.RFC.4566.xml'?> </front>
<?rfc include='reference.RFC.4585.xml'?> <seriesInfo name="BCP" value="14"/>
<?rfc include='reference.RFC.5124.xml'?> <seriesInfo name="RFC" value="2119"/>
<?rfc include='reference.RFC.5285.xml'?> <seriesInfo name="DOI" value="10.17487/RFC2119"/>
<?rfc include='reference.RFC.5761.xml'?> </reference>
<?rfc include='reference.RFC.5888.xml'?> <reference anchor="RFC3261" target="https://www.rfc-editor.org/info/rfc3
<?rfc include='reference.RFC.6236.xml'?> 261" quoteTitle="true" derivedAnchor="RFC3261">
<?rfc include='reference.RFC.6347.xml'?> <front>
<?rfc include='reference.RFC.6716.xml'?> <title>SIP: Session Initiation Protocol</title>
<?rfc include='reference.RFC.6904.xml'?> <author initials="J." surname="Rosenberg" fullname="J. Rosenberg">
<?rfc include='reference.RFC.7160.xml'?> <organization showOnFrontPage="true"/>
<?rfc include='reference.RFC.7587.xml'?> </author>
<?rfc include='reference.RFC.7742.xml'?> <author initials="H." surname="Schulzrinne" fullname="H. Schulzrinne
<?rfc include='reference.RFC.7850.xml'?> ">
<?rfc include='reference.RFC.7874.xml'?> <organization showOnFrontPage="true"/>
<?rfc include='reference.RFC.8108.xml'?> </author>
<?rfc include='reference.RFC.8122.xml'?> <author initials="G." surname="Camarillo" fullname="G. Camarillo">
<?rfc include='reference.RFC.8445.xml'?> <organization showOnFrontPage="true"/>
<?rfc include='reference.RFC.3711.xml'?> </author>
</references> <author initials="A." surname="Johnston" fullname="A. Johnston">
<references title="Informative References"> <organization showOnFrontPage="true"/>
<?rfc include='reference.I-D.ietf-rtcweb-ip-handling'?> </author>
<?rfc include='reference.I-D.ietf-mmusic-trickle-ice-sip'?> <author initials="J." surname="Peterson" fullname="J. Peterson">
<?rfc include='reference.I-D.ietf-rtcweb-sdp'?> <organization showOnFrontPage="true"/>
<?rfc include='reference.RFC.3389.xml'?> </author>
<?rfc include='reference.RFC.3960.xml'?> <author initials="R." surname="Sparks" fullname="R. Sparks">
<?rfc include='reference.RFC.4568.xml'?> <organization showOnFrontPage="true"/>
<?rfc include='reference.RFC.4588.xml'?> </author>
<?rfc include='reference.RFC.4733.xml'?> <author initials="M." surname="Handley" fullname="M. Handley">
<?rfc include='reference.RFC.5245.xml'?> <organization showOnFrontPage="true"/>
<?rfc include='reference.RFC.5506.xml'?> </author>
<?rfc include='reference.RFC.5576.xml'?> <author initials="E." surname="Schooler" fullname="E. Schooler">
<?rfc include='reference.RFC.5763.xml'?> <organization showOnFrontPage="true"/>
<?rfc include='reference.RFC.5764.xml'?> </author>
<?rfc include='reference.RFC.6464.xml'?> <date year="2002" month="June"/>
<?rfc include='reference.RFC.6544.xml'?> <abstract>
<?rfc include='reference.RFC.3556.xml'?> <t indent="0">This document describes Session Initiation Protocol
<reference anchor="W3C.webrtc" (SIP), an application-layer control (signaling) protocol for creating, modifying
target="https://www.w3.org/TR/2017/WD-webrtc-20170515/"> , and terminating sessions with one or more participants. These sessions includ
<front> e Internet telephone calls, multimedia distribution, and multimedia conferences.
<title>WebRTC 1.0: Real-time Communication Between [STANDARDS-TRACK]</t>
Browsers</title> </abstract>
<author fullname="Adam Bergkvist" initials="A." </front>
surname="Bergkvist"> <seriesInfo name="RFC" value="3261"/>
<organization>Ericsson</organization> <seriesInfo name="DOI" value="10.17487/RFC3261"/>
</author> </reference>
<author fullname="Daniel C. Burnett" initials="D." <reference anchor="RFC3264" target="https://www.rfc-editor.org/info/rfc3
surname="Burnett"> 264" quoteTitle="true" derivedAnchor="RFC3264">
<organization></organization> <front>
</author> <title>An Offer/Answer Model with Session Description Protocol (SDP)
<author fullname="Cullen Jennings" initials="C." </title>
surname="Jennings"> <author initials="J." surname="Rosenberg" fullname="J. Rosenberg">
<organization>Cisco</organization> <organization showOnFrontPage="true"/>
</author> </author>
<author fullname="Anant Narayanan" initials="A." <author initials="H." surname="Schulzrinne" fullname="H. Schulzrinne
surname="Narayanan"> ">
<organization>Mozilla</organization> <organization showOnFrontPage="true"/>
</author> </author>
<author fullname="Bernard Aboba" initials="B." <date year="2002" month="June"/>
surname="Aboba"> <abstract>
<organization>Microsoft Corporation</organization> <t indent="0">This document defines a mechanism by which two entit
</author> ies can make use of the Session Description Protocol (SDP) to arrive at a common
<author fullname="Taylor Brandstetter" initials="T." view of a multimedia session between them. In the model, one participant offer
surname="Brandstetter"> s the other a description of the desired session from their perspective, and the
<organization>Google</organization> other participant answers with the desired session from their perspective. Thi
</author> s offer/answer model is most useful in unicast sessions where information from b
<date day="15" month="May" year="2017" /> oth participants is needed for the complete view of the session. The offer/answ
</front> er model is used by protocols like the Session Initiation Protocol (SIP). [STAN
<seriesInfo name="World Wide Web Consortium WD" DARDS-TRACK]</t>
value="WD-webrtc-20170515" /> </abstract>
<format target="https://www.w3.org/TR/2017/WD-webrtc-20170515/" </front>
type="HTML" /> <seriesInfo name="RFC" value="3264"/>
</reference> <seriesInfo name="DOI" value="10.17487/RFC3264"/>
<reference anchor="TS26.114" </reference>
target="http://www.3gpp.org/DynaReport/26114.htm"> <reference anchor="RFC3552" target="https://www.rfc-editor.org/info/rfc3
<front> 552" quoteTitle="true" derivedAnchor="RFC3552">
<title>3rd Generation Partnership Project; Technical <front>
Specification Group Services and System Aspects; IP <title>Guidelines for Writing RFC Text on Security Considerations</t
Multimedia Subsystem (IMS); Multimedia Telephony; Media itle>
handling and interaction (Release 12)</title> <author initials="E." surname="Rescorla" fullname="E. Rescorla">
<author> <organization showOnFrontPage="true"/>
<organization>3GPP TS 26.114 V12.8.0</organization> </author>
</author> <author initials="B." surname="Korver" fullname="B. Korver">
<date year="2014" month="December" /> <organization showOnFrontPage="true"/>
</front> </author>
</reference> <date year="2003" month="July"/>
<abstract>
<t indent="0">All RFCs are required to have a Security Considerati
ons section. Historically, such sections have been relatively weak. This docume
nt provides guidelines to RFC authors on how to write a good Security Considerat
ions section. This document specifies an Internet Best Current Practices for t
he Internet Community, and requests discussion and suggestions for improvements.
</t>
</abstract>
</front>
<seriesInfo name="BCP" value="72"/>
<seriesInfo name="RFC" value="3552"/>
<seriesInfo name="DOI" value="10.17487/RFC3552"/>
</reference>
<reference anchor="RFC3605" target="https://www.rfc-editor.org/info/rfc3
605" quoteTitle="true" derivedAnchor="RFC3605">
<front>
<title>Real Time Control Protocol (RTCP) attribute in Session Descri
ption Protocol (SDP)</title>
<author initials="C." surname="Huitema" fullname="C. Huitema">
<organization showOnFrontPage="true"/>
</author>
<date year="2003" month="October"/>
<abstract>
<t indent="0">The Session Description Protocol (SDP) is used to de
scribe the parameters of media streams used in multimedia sessions. When a sess
ion requires multiple ports, SDP assumes that these ports have consecutive numbe
rs. However, when the session crosses a network address translation device that
also uses port mapping, the ordering of ports can be destroyed by the translati
on. To handle this, we propose an extension attribute to SDP.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="3605"/>
<seriesInfo name="DOI" value="10.17487/RFC3605"/>
</reference>
<reference anchor="RFC3711" target="https://www.rfc-editor.org/info/rfc3
711" quoteTitle="true" derivedAnchor="RFC3711">
<front>
<title>The Secure Real-time Transport Protocol (SRTP)</title>
<author initials="M." surname="Baugher" fullname="M. Baugher">
<organization showOnFrontPage="true"/>
</author>
<author initials="D." surname="McGrew" fullname="D. McGrew">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Naslund" fullname="M. Naslund">
<organization showOnFrontPage="true"/>
</author>
<author initials="E." surname="Carrara" fullname="E. Carrara">
<organization showOnFrontPage="true"/>
</author>
<author initials="K." surname="Norrman" fullname="K. Norrman">
<organization showOnFrontPage="true"/>
</author>
<date year="2004" month="March"/>
<abstract>
<t indent="0">This document describes the Secure Real-time Transpo
rt Protocol (SRTP), a profile of the Real-time Transport Protocol (RTP), which c
an provide confidentiality, message authentication, and replay protection to the
RTP traffic and to the control traffic for RTP, the Real-time Transport Control
Protocol (RTCP). [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="3711"/>
<seriesInfo name="DOI" value="10.17487/RFC3711"/>
</reference>
<reference anchor="RFC3890" target="https://www.rfc-editor.org/info/rfc3
890" quoteTitle="true" derivedAnchor="RFC3890">
<front>
<title>A Transport Independent Bandwidth Modifier for the Session De
scription Protocol (SDP)</title>
<author initials="M." surname="Westerlund" fullname="M. Westerlund">
<organization showOnFrontPage="true"/>
</author>
<date year="2004" month="September"/>
<abstract>
<t indent="0">This document defines a Session Description Protocol
(SDP) Transport Independent Application Specific Maximum (TIAS) bandwidth modif
ier that does not include transport overhead; instead an additional packet rate
attribute is defined. The transport independent bit-rate value together with th
e maximum packet rate can then be used to calculate the real bit-rate over the t
ransport actually used. </t>
<t indent="0"> The existing SDP bandwidth modifiers and their valu
es include the bandwidth needed for the transport and IP layers. When using SDP
with protocols like the Session Announcement Protocol (SAP), the Session Initia
tion Protocol (SIP), and the Real-Time Streaming Protocol (RTSP), and when the i
nvolved hosts has different transport overhead, for example due to different IP
versions, the interpretation of what lower layer bandwidths are included is not
clear. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="3890"/>
<seriesInfo name="DOI" value="10.17487/RFC3890"/>
</reference>
<reference anchor="RFC4145" target="https://www.rfc-editor.org/info/rfc4
145" quoteTitle="true" derivedAnchor="RFC4145">
<front>
<title>TCP-Based Media Transport in the Session Description Protocol
(SDP)</title>
<author initials="D." surname="Yon" fullname="D. Yon">
<organization showOnFrontPage="true"/>
</author>
<author initials="G." surname="Camarillo" fullname="G. Camarillo">
<organization showOnFrontPage="true"/>
</author>
<date year="2005" month="September"/>
<abstract>
<t indent="0">This document describes how to express media transpo
rt over TCP using the Session Description Protocol (SDP). It defines the SDP 'T
CP' protocol identifier, the SDP 'setup' attribute, which describes the connecti
on setup procedure, and the SDP 'connection' attribute, which handles connection
reestablishment. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4145"/>
<seriesInfo name="DOI" value="10.17487/RFC4145"/>
</reference>
<reference anchor="RFC4566" target="https://www.rfc-editor.org/info/rfc4
566" quoteTitle="true" derivedAnchor="RFC4566">
<front>
<title>SDP: Session Description Protocol</title>
<author initials="M." surname="Handley" fullname="M. Handley">
<organization showOnFrontPage="true"/>
</author>
<author initials="V." surname="Jacobson" fullname="V. Jacobson">
<organization showOnFrontPage="true"/>
</author>
<author initials="C." surname="Perkins" fullname="C. Perkins">
<organization showOnFrontPage="true"/>
</author>
<date year="2006" month="July"/>
<abstract>
<t indent="0">This memo defines the Session Description Protocol (
SDP). SDP is intended for describing multimedia sessions for the purposes of se
ssion announcement, session invitation, and other forms of multimedia session in
itiation. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4566"/>
<seriesInfo name="DOI" value="10.17487/RFC4566"/>
</reference>
<reference anchor="RFC4585" target="https://www.rfc-editor.org/info/rfc4
585" quoteTitle="true" derivedAnchor="RFC4585">
<front>
<title>Extended RTP Profile for Real-time Transport Control Protocol
(RTCP)-Based Feedback (RTP/AVPF)</title>
<author initials="J." surname="Ott" fullname="J. Ott">
<organization showOnFrontPage="true"/>
</author>
<author initials="S." surname="Wenger" fullname="S. Wenger">
<organization showOnFrontPage="true"/>
</author>
<author initials="N." surname="Sato" fullname="N. Sato">
<organization showOnFrontPage="true"/>
</author>
<author initials="C." surname="Burmeister" fullname="C. Burmeister">
<organization showOnFrontPage="true"/>
</author>
<author initials="J." surname="Rey" fullname="J. Rey">
<organization showOnFrontPage="true"/>
</author>
<date year="2006" month="July"/>
<abstract>
<t indent="0">Real-time media streams that use RTP are, to some de
gree, resilient against packet losses. Receivers may use the base mechanisms of
the Real-time Transport Control Protocol (RTCP) to report packet reception stat
istics and thus allow a sender to adapt its transmission behavior in the mid-ter
m. This is the sole means for feedback and feedback-based error repair (besides
a few codec-specific mechanisms). This document defines an extension to the Au
dio-visual Profile (AVP) that enables receivers to provide, statistically, more
immediate feedback to the senders and thus allows for short-term adaptation and
efficient feedback-based repair mechanisms to be implemented. This early feedba
ck profile (AVPF) maintains the AVP bandwidth constraints for RTCP and preserves
scalability to large groups. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4585"/>
<seriesInfo name="DOI" value="10.17487/RFC4585"/>
</reference>
<reference anchor="RFC5124" target="https://www.rfc-editor.org/info/rfc5
124" quoteTitle="true" derivedAnchor="RFC5124">
<front>
<title>Extended Secure RTP Profile for Real-time Transport Control P
rotocol (RTCP)-Based Feedback (RTP/SAVPF)</title>
<author initials="J." surname="Ott" fullname="J. Ott">
<organization showOnFrontPage="true"/>
</author>
<author initials="E." surname="Carrara" fullname="E. Carrara">
<organization showOnFrontPage="true"/>
</author>
<date year="2008" month="February"/>
<abstract>
<t indent="0">An RTP profile (SAVP) for secure real-time communica
tions and another profile (AVPF) to provide timely feedback from the receivers t
o a sender are defined in RFC 3711 and RFC 4585, respectively. This memo specif
ies the combination of both profiles to enable secure RTP communications with fe
edback. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5124"/>
<seriesInfo name="DOI" value="10.17487/RFC5124"/>
</reference>
<reference anchor="RFC5285" target="https://www.rfc-editor.org/info/rfc5
285" quoteTitle="true" derivedAnchor="RFC5285">
<front>
<title>A General Mechanism for RTP Header Extensions</title>
<author initials="D." surname="Singer" fullname="D. Singer">
<organization showOnFrontPage="true"/>
</author>
<author initials="H." surname="Desineni" fullname="H. Desineni">
<organization showOnFrontPage="true"/>
</author>
<date year="2008" month="July"/>
<abstract>
<t indent="0">This document provides a general mechanism to use th
e header extension feature of RTP (the Real-Time Transport Protocol). It provid
es the option to use a small number of small extensions in each RTP packet, wher
e the universe of possible extensions is large and registration is de-centralize
d. The actual extensions in use in a session are signaled in the setup informat
ion for that session. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5285"/>
<seriesInfo name="DOI" value="10.17487/RFC5285"/>
</reference>
<reference anchor="RFC5761" target="https://www.rfc-editor.org/info/rfc5
761" quoteTitle="true" derivedAnchor="RFC5761">
<front>
<title>Multiplexing RTP Data and Control Packets on a Single Port</t
itle>
<author initials="C." surname="Perkins" fullname="C. Perkins">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Westerlund" fullname="M. Westerlund">
<organization showOnFrontPage="true"/>
</author>
<date year="2010" month="April"/>
<abstract>
<t indent="0">This memo discusses issues that arise when multiplex
ing RTP data packets and RTP Control Protocol (RTCP) packets on a single UDP por
t. It updates RFC 3550 and RFC 3551 to describe when such multiplexing is and is
not appropriate, and it explains how the Session Description Protocol (SDP) can
be used to signal multiplexed sessions. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5761"/>
<seriesInfo name="DOI" value="10.17487/RFC5761"/>
</reference>
<reference anchor="RFC5888" target="https://www.rfc-editor.org/info/rfc5
888" quoteTitle="true" derivedAnchor="RFC5888">
<front>
<title>The Session Description Protocol (SDP) Grouping Framework</ti
tle>
<author initials="G." surname="Camarillo" fullname="G. Camarillo">
<organization showOnFrontPage="true"/>
</author>
<author initials="H." surname="Schulzrinne" fullname="H. Schulzrinne
">
<organization showOnFrontPage="true"/>
</author>
<date year="2010" month="June"/>
<abstract>
<t indent="0">In this specification, we define a framework to grou
p "m" lines in the Session Description Protocol (SDP) for different purposes. T
his framework uses the "group" and "mid" SDP attributes, both of which are defin
ed in this specification. Additionally, we specify how to use the framework for
two different purposes: for lip synchronization and for receiving a media flow
consisting of several media streams on different transport addresses. This docu
ment obsoletes RFC 3388. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5888"/>
<seriesInfo name="DOI" value="10.17487/RFC5888"/>
</reference>
<reference anchor="RFC6236" target="https://www.rfc-editor.org/info/rfc6
236" quoteTitle="true" derivedAnchor="RFC6236">
<front>
<title>Negotiation of Generic Image Attributes in the Session Descri
ption Protocol (SDP)</title>
<author initials="I." surname="Johansson" fullname="I. Johansson">
<organization showOnFrontPage="true"/>
</author>
<author initials="K." surname="Jung" fullname="K. Jung">
<organization showOnFrontPage="true"/>
</author>
<date year="2011" month="May"/>
<abstract>
<t indent="0">This document proposes a new generic session setup a
ttribute to make it possible to negotiate different image attributes such as ima
ge size. A possible use case is to make it possible for a \%low-end \%hand- hel
d terminal to display video without the need to rescale the image, something tha
t may consume large amounts of memory and processing power. The document also h
elps to maintain an optimal bitrate for video as only the image size that is des
ired by the receiver is transmitted. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6236"/>
<seriesInfo name="DOI" value="10.17487/RFC6236"/>
</reference>
<reference anchor="RFC6347" target="https://www.rfc-editor.org/info/rfc6
347" quoteTitle="true" derivedAnchor="RFC6347">
<front>
<title>Datagram Transport Layer Security Version 1.2</title>
<author initials="E." surname="Rescorla" fullname="E. Rescorla">
<organization showOnFrontPage="true"/>
</author>
<author initials="N." surname="Modadugu" fullname="N. Modadugu">
<organization showOnFrontPage="true"/>
</author>
<date year="2012" month="January"/>
<abstract>
<t indent="0">This document specifies version 1.2 of the Datagram
Transport Layer Security (DTLS) protocol. The DTLS protocol provides communicat
ions privacy for datagram protocols. The protocol allows client/server applicat
ions to communicate in a way that is designed to prevent eavesdropping, tamperin
g, or message forgery. The DTLS protocol is based on the Transport Layer Securi
ty (TLS) protocol and provides equivalent security guarantees. Datagram semanti
cs of the underlying transport are preserved by the DTLS protocol. This documen
t updates DTLS 1.0 to work with TLS version 1.2. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6347"/>
<seriesInfo name="DOI" value="10.17487/RFC6347"/>
</reference>
<reference anchor="RFC6716" target="https://www.rfc-editor.org/info/rfc6
716" quoteTitle="true" derivedAnchor="RFC6716">
<front>
<title>Definition of the Opus Audio Codec</title>
<author initials="JM." surname="Valin" fullname="JM. Valin">
<organization showOnFrontPage="true"/>
</author>
<author initials="K." surname="Vos" fullname="K. Vos">
<organization showOnFrontPage="true"/>
</author>
<author initials="T." surname="Terriberry" fullname="T. Terriberry">
<organization showOnFrontPage="true"/>
</author>
<date year="2012" month="September"/>
<abstract>
<t indent="0">This document defines the Opus interactive speech an
d audio codec. Opus is designed to handle a wide range of interactive audio appl
ications, including Voice over IP, videoconferencing, in-game chat, and even liv
e, distributed music performances. It scales from low bitrate narrowband speech
at 6 kbit/s to very high quality stereo music at 510 kbit/s. Opus uses both Li
near Prediction (LP) and the Modified Discrete Cosine Transform (MDCT) to achiev
e good compression of both speech and music. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6716"/>
<seriesInfo name="DOI" value="10.17487/RFC6716"/>
</reference>
<reference anchor="RFC6904" target="https://www.rfc-editor.org/info/rfc6
904" quoteTitle="true" derivedAnchor="RFC6904">
<front>
<title>Encryption of Header Extensions in the Secure Real-time Trans
port Protocol (SRTP)</title>
<author initials="J." surname="Lennox" fullname="J. Lennox">
<organization showOnFrontPage="true"/>
</author>
<date year="2013" month="April"/>
<abstract>
<t indent="0">The Secure Real-time Transport Protocol (SRTP) provi
des authentication, but not encryption, of the headers of Real-time Transport Pr
otocol (RTP) packets. However, RTP header extensions may carry sensitive inform
ation for which participants in multimedia sessions want confidentiality. This
document provides a mechanism, extending the mechanisms of SRTP, to selectively
encrypt RTP header extensions in SRTP.</t>
<t indent="0">This document updates RFC 3711, the Secure Real-time
Transport Protocol specification, to require that all future SRTP encryption tr
ansforms specify how RTP header extensions are to be encrypted.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6904"/>
<seriesInfo name="DOI" value="10.17487/RFC6904"/>
</reference>
<reference anchor="RFC7160" target="https://www.rfc-editor.org/info/rfc7
160" quoteTitle="true" derivedAnchor="RFC7160">
<front>
<title>Support for Multiple Clock Rates in an RTP Session</title>
<author initials="M." surname="Petit-Huguenin" fullname="M. Petit-Hu
guenin">
<organization showOnFrontPage="true"/>
</author>
<author initials="G." surname="Zorn" fullname="G. Zorn" role="editor
">
<organization showOnFrontPage="true"/>
</author>
<date year="2014" month="April"/>
<abstract>
<t indent="0">This document clarifies the RTP specification regard
ing the use of different clock rates in an RTP session. It also provides guidan
ce on how legacy RTP implementations that use multiple clock rates can interoper
ate with RTP implementations that use the algorithm described in this document.
It updates RFC 3550.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="7160"/>
<seriesInfo name="DOI" value="10.17487/RFC7160"/>
</reference>
<reference anchor="RFC7587" target="https://www.rfc-editor.org/info/rfc7
587" quoteTitle="true" derivedAnchor="RFC7587">
<front>
<title>RTP Payload Format for the Opus Speech and Audio Codec</title
>
<author initials="J." surname="Spittka" fullname="J. Spittka">
<organization showOnFrontPage="true"/>
</author>
<author initials="K." surname="Vos" fullname="K. Vos">
<organization showOnFrontPage="true"/>
</author>
<author initials="JM." surname="Valin" fullname="JM. Valin">
<organization showOnFrontPage="true"/>
</author>
<date year="2015" month="June"/>
<abstract>
<t indent="0">This document defines the Real-time Transport Protoc
ol (RTP) payload format for packetization of Opus-encoded speech and audio data
necessary to integrate the codec in the most compatible way. It also provides a
n applicability statement for the use of Opus over RTP. Further, it describes me
dia type registrations for the RTP payload format.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="7587"/>
<seriesInfo name="DOI" value="10.17487/RFC7587"/>
</reference>
<reference anchor="RFC7742" target="https://www.rfc-editor.org/info/rfc7
742" quoteTitle="true" derivedAnchor="RFC7742">
<front>
<title>WebRTC Video Processing and Codec Requirements</title>
<author initials="A.B." surname="Roach" fullname="A.B. Roach">
<organization showOnFrontPage="true"/>
</author>
<date year="2016" month="March"/>
<abstract>
<t indent="0">This specification provides the requirements and con
siderations for WebRTC applications to send and receive video across a network.
It specifies the video processing that is required as well as video codecs and
their parameters.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="7742"/>
<seriesInfo name="DOI" value="10.17487/RFC7742"/>
</reference>
<reference anchor="RFC7850" target="https://www.rfc-editor.org/info/rfc7
850" quoteTitle="true" derivedAnchor="RFC7850">
<front>
<title>Registering Values of the SDP 'proto' Field for Transporting
RTP Media over TCP under Various RTP Profiles</title>
<author initials="S." surname="Nandakumar" fullname="S. Nandakumar">
<organization showOnFrontPage="true"/>
</author>
<date year="2016" month="April"/>
<abstract>
<t indent="0">The Real-time Transport Protocol (RTP) specification
establishes a registry of profile names for use by higher-level control protoco
ls, such as the Session Description Protocol (SDP), to refer to the transport me
thods. This specification describes the following new SDP transport protocol id
entifiers for transporting RTP Media over TCP: 'TCP/RTP/AVPF', 'TCP/RTP/SAVP', '
TCP/RTP/SAVPF', 'TCP/DTLS/RTP/SAVP', 'TCP/DTLS/RTP/SAVPF', 'TCP/TLS/RTP/AVP', an
d 'TCP/TLS/RTP/AVPF'.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="7850"/>
<seriesInfo name="DOI" value="10.17487/RFC7850"/>
</reference>
<reference anchor="RFC7874" target="https://www.rfc-editor.org/info/rfc7
874" quoteTitle="true" derivedAnchor="RFC7874">
<front>
<title>WebRTC Audio Codec and Processing Requirements</title>
<author initials="JM." surname="Valin" fullname="JM. Valin">
<organization showOnFrontPage="true"/>
</author>
<author initials="C." surname="Bran" fullname="C. Bran">
<organization showOnFrontPage="true"/>
</author>
<date year="2016" month="May"/>
<abstract>
<t indent="0">This document outlines the audio codec and processin
g requirements for WebRTC endpoints.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="7874"/>
<seriesInfo name="DOI" value="10.17487/RFC7874"/>
</reference>
<reference anchor="RFC8108" target="https://www.rfc-editor.org/info/rfc8
108" quoteTitle="true" derivedAnchor="RFC8108">
<front>
<title>Sending Multiple RTP Streams in a Single RTP Session</title>
<author initials="J." surname="Lennox" fullname="J. Lennox">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Westerlund" fullname="M. Westerlund">
<organization showOnFrontPage="true"/>
</author>
<author initials="Q." surname="Wu" fullname="Q. Wu">
<organization showOnFrontPage="true"/>
</author>
<author initials="C." surname="Perkins" fullname="C. Perkins">
<organization showOnFrontPage="true"/>
</author>
<date year="2017" month="March"/>
<abstract>
<t indent="0">This memo expands and clarifies the behavior of Real
-time Transport Protocol (RTP) endpoints that use multiple synchronization sourc
es (SSRCs). This occurs, for example, when an endpoint sends multiple RTP strea
ms in a single RTP session. This memo updates RFC 3550 with regard to handling
multiple SSRCs per endpoint in RTP sessions, with a particular focus on RTP Cont
rol Protocol (RTCP) behavior. It also updates RFC 4585 to change and clarify th
e calculation of the timeout of SSRCs and the inclusion of feedback messages.</t
>
</abstract>
</front>
<seriesInfo name="RFC" value="8108"/>
<seriesInfo name="DOI" value="10.17487/RFC8108"/>
</reference>
<reference anchor="RFC8122" target="https://www.rfc-editor.org/info/rfc8
122" quoteTitle="true" derivedAnchor="RFC8122">
<front>
<title>Connection-Oriented Media Transport over the Transport Layer
Security (TLS) Protocol in the Session Description Protocol (SDP)</title>
<author initials="J." surname="Lennox" fullname="J. Lennox">
<organization showOnFrontPage="true"/>
</author>
<author initials="C." surname="Holmberg" fullname="C. Holmberg">
<organization showOnFrontPage="true"/>
</author>
<date year="2017" month="March"/>
<abstract>
<t indent="0">This document specifies how to establish secure conn
ection-oriented media transport sessions over the Transport Layer Security (TLS)
protocol using the Session Description Protocol (SDP). It defines the SDP prot
ocol identifier, 'TCP/TLS'. It also defines the syntax and semantics for an SDP
'fingerprint' attribute that identifies the certificate that will be presented
for the TLS session. This mechanism allows media transport over TLS connections
to be established securely, so long as the integrity of session descriptions is
assured.</t>
<t indent="0">This document obsoletes RFC 4572 by clarifying the u
sage of multiple fingerprints.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="8122"/>
<seriesInfo name="DOI" value="10.17487/RFC8122"/>
</reference>
<reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8
174" quoteTitle="true" derivedAnchor="RFC8174">
<front>
<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</ti
tle>
<author initials="B." surname="Leiba" fullname="B. Leiba">
<organization showOnFrontPage="true"/>
</author>
<date year="2017" month="May"/>
<abstract>
<t indent="0">RFC 2119 specifies common key words that may be used
in protocol specifications. This document aims to reduce the ambiguity by cla
rifying that only UPPERCASE usage of the key words have the defined special mea
nings.</t>
</abstract>
</front>
<seriesInfo name="BCP" value="14"/>
<seriesInfo name="RFC" value="8174"/>
<seriesInfo name="DOI" value="10.17487/RFC8174"/>
</reference>
<reference anchor="RFC8445" target="https://www.rfc-editor.org/info/rfc8
445" quoteTitle="true" derivedAnchor="RFC8445">
<front>
<title>Interactive Connectivity Establishment (ICE): A Protocol for
Network Address Translator (NAT) Traversal</title>
<author initials="A." surname="Keranen" fullname="A. Keranen">
<organization showOnFrontPage="true"/>
</author>
<author initials="C." surname="Holmberg" fullname="C. Holmberg">
<organization showOnFrontPage="true"/>
</author>
<author initials="J." surname="Rosenberg" fullname="J. Rosenberg">
<organization showOnFrontPage="true"/>
</author>
<date year="2018" month="July"/>
<abstract>
<t indent="0">This document describes a protocol for Network Addre
ss Translator (NAT) traversal for UDP-based communication. This protocol is cal
led Interactive Connectivity Establishment (ICE). ICE makes use of the Session
Traversal Utilities for NAT (STUN) protocol and its extension, Traversal Using R
elay NAT (TURN).</t>
<t indent="0">This document obsoletes RFC 5245.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="8445"/>
<seriesInfo name="DOI" value="10.17487/RFC8445"/>
</reference>
<reference anchor="RFC8826" target="https://www.rfc-editor.org/info/rfc8
826" quoteTitle="true" derivedAnchor="RFC8826">
<front>
<title>Security Considerations for WebRTC</title>
<author initials="E." surname="Rescorla" fullname="Eric Rescorla">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8826"/>
<seriesInfo name="DOI" value="10.17487/RFC8826"/>
</reference>
<reference anchor="RFC8827" target="https://www.rfc-editor.org/info/rfc8
827" quoteTitle="true" derivedAnchor="RFC8827">
<front>
<title>WebRTC Security Architecture</title>
<author initials="E." surname="Rescorla" fullname="Eric Rescorla">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8827"/>
<seriesInfo name="DOI" value="10.17487/RFC8827"/>
</reference>
<reference anchor="RFC8830" target="https://www.rfc-editor.org/info/rfc8
830" quoteTitle="true" derivedAnchor="RFC8830">
<front>
<title>WebRTC MediaStream Identification in the Session Description
Protocol</title>
<author initials="H" surname="Alvestrand" fullname="Harald Alvestran
d">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8830"/>
<seriesInfo name="DOI" value="10.17487/RFC8830"/>
</reference>
<reference anchor="RFC8834" target="https://www.rfc-editor.org/info/rfc8
834" quoteTitle="true" derivedAnchor="RFC8834">
<front>
<title>Media Transport and Use of RTP in WebRTC</title>
<author initials="C." surname="Perkins" fullname="Colin Perkins">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Westerlund" fullname="Magnus Westerlu
nd">
<organization showOnFrontPage="true"/>
</author>
<author initials="J." surname="Ott" fullname="Jörg Ott">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8834"/>
<seriesInfo name="DOI" value="10.17487/RFC8834"/>
</reference>
<reference anchor="RFC8838" target="https://www.rfc-editor.org/info/rfc8
838" quoteTitle="true" derivedAnchor="RFC8838">
<front>
<title>Trickle ICE: Incremental Provisioning of Candidates for the I
nteractive Connectivity Establishment (ICE) Protocol</title>
<author initials="E" surname="Ivov" fullname="Emil Ivov">
<organization showOnFrontPage="true"/>
</author>
<author initials="J" surname="Uberti" fullname="Justin Uberti">
<organization showOnFrontPage="true"/>
</author>
<author initials="P" surname="Saint-Andre" fullname="Peter Saint-And
re">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8838"/>
<seriesInfo name="DOI" value="10.17487/RFC8838"/>
</reference>
<reference anchor="RFC8839" target="https://www.rfc-editor.org/info/rfc8
839" quoteTitle="true" derivedAnchor="RFC8839">
<front>
<title>Session Description Protocol (SDP) Offer/Answer Procedures fo
r Interactive Connectivity Establishment (ICE)</title>
<author initials="M" surname="Petit-Huguenin" fullname="Marc Petit-H
uguenin">
<organization showOnFrontPage="true"/>
</author>
<author initials="S" surname="Nandakumar" fullname="Suhas Nandakumar
">
<organization showOnFrontPage="true"/>
</author>
<author initials="C" surname="Holmberg" fullname="Christer Holmberg"
>
<organization showOnFrontPage="true"/>
</author>
<author initials="A" surname="Keränen" fullname="Ari Keränen">
<organization showOnFrontPage="true"/>
</author>
<author initials="R" surname="Shpount" fullname="Roman Shpount">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8839"/>
<seriesInfo name="DOI" value="10.17487/RFC8839"/>
</reference>
<reference anchor="RFC8840" target="https://www.rfc-editor.org/info/rfc8
840" quoteTitle="true" derivedAnchor="RFC8840">
<front>
<title>A Session Initiation Protocol (SIP) Usage for Incremental Pro
visioning of Candidates for the Interactive Connectivity Establishment (Trickle
ICE)</title>
<author initials="E" surname="Ivov" fullname="Emil Ivov">
<organization showOnFrontPage="true"/>
</author>
<author initials="T" surname="Stach" fullname="Thomas Stach">
<organization showOnFrontPage="true"/>
</author>
<author initials="E" surname="Marocco" fullname="Enrico Marocco">
<organization showOnFrontPage="true"/>
</author>
<author initials="C" surname="Holmberg" fullname="Christer Holmberg"
>
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8840"/>
<seriesInfo name="DOI" value="10.17487/RFC8840"/>
</reference>
<reference anchor="RFC8841" target="https://www.rfc-editor.org/info/rfc8
841" quoteTitle="true" derivedAnchor="RFC8841">
<front>
<title>Session Description Protocol (SDP) Offer/Answer Procedures fo
r Stream Control Transmission Protocol (SCTP) over Datagram Transport Layer Secu
rity (DTLS) Transport</title>
<author initials="C." surname="Holmberg" fullname="Christer Holmberg
">
<organization showOnFrontPage="true"/>
</author>
<author initials="R." surname="Shpount" fullname="Roman Shpount">
<organization showOnFrontPage="true"/>
</author>
<author initials="S." surname="Loreto" fullname="Salvatore Loreto">
<organization showOnFrontPage="true"/>
</author>
<author initials="G." surname="Camarillo" fullname="Gonzalo Camarill
o">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8841"/>
<seriesInfo name="DOI" value="10.17487/RFC8841"/>
</reference>
<reference anchor="RFC8842" target="https://www.rfc-editor.org/info/rfc8
842" quoteTitle="true" derivedAnchor="RFC8842">
<front>
<title>Session Description Protocol (SDP) Offer/Answer Consideration
s for Datagram Transport Layer Security (DTLS) and Transport Layer Security (TLS
)</title>
<author initials="C." surname="Holmberg" fullname="Christer Holmberg
">
<organization showOnFrontPage="true"/>
</author>
<author initials="R." surname="Shpount" fullname="Roman Shpount">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8842"/>
<seriesInfo name="DOI" value="10.17487/RFC8842"/>
</reference>
<reference anchor="RFC8843" target="https://www.rfc-editor.org/info/rfc8
843" quoteTitle="true" derivedAnchor="RFC8843">
<front>
<title>Negotiating Media Multiplexing Using the Session Description
Protocol (SDP)</title>
<author initials="C" surname="Holmberg" fullname="Christer Holmberg"
>
<organization showOnFrontPage="true"/>
</author>
<author initials="H" surname="Alvestrand" fullname="Harald Alvestran
d">
<organization showOnFrontPage="true"/>
</author>
<author initials="C" surname="Jennings" fullname="Cullen Jennings">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8843"/>
<seriesInfo name="DOI" value="10.17487/RFC8843"/>
</reference>
<reference anchor="RFC8851" target="https://www.rfc-editor.org/info/rfc8
851" quoteTitle="true" derivedAnchor="RFC8851">
<front>
<title>RTP Payload Format Restrictions</title>
<author initials="A.B." surname="Roach" fullname="Adam Roach" role="
editor">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8851"/>
<seriesInfo name="DOI" value="10.17487/RFC8851"/>
</reference>
<reference anchor="RFC8852" target="https://www.rfc-editor.org/info/rfc8
852" quoteTitle="true" derivedAnchor="RFC8852">
<front>
<title>RTP Stream Identifier Source Description (SDES)</title>
<author initials="A.B." surname="Roach" fullname="Adam Roach"/>
<author initials="S" surname="Nandakumar" fullname="Suhas Nandakumar
"/>
<author initials="P" surname="Thatcher" fullname="Peter Thatcher"/>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8852"/>
<seriesInfo name="DOI" value="10.17487/RFC8852"/>
</reference>
<reference anchor="RFC8853" target="https://www.rfc-editor.org/info/rfc8
853" quoteTitle="true" derivedAnchor="RFC8853">
<front>
<title>Using Simulcast in Session Description Protocol (SDP) and RTP
Sessions</title>
<author initials="B" surname="Burman" fullname="Bo Burman">
<organization showOnFrontPage="true"/>
</author>
<author initials="M" surname="Westerlund" fullname="Magnus Westerlun
d">
<organization showOnFrontPage="true"/>
</author>
<author initials="S" surname="Nandakumar" fullname="Suhas Nandakumar
">
<organization showOnFrontPage="true"/>
</author>
<author initials="M" surname="Zanaty" fullname="Mo Zanaty">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8853"/>
<seriesInfo name="DOI" value="10.17487/RFC8853"/>
</reference>
<reference anchor="RFC8854" target="https://www.rfc-editor.org/info/rfc8
854" quoteTitle="true" derivedAnchor="RFC8854">
<front>
<title>WebRTC Forward Error Correction Requirements</title>
<author initials="J." surname="Uberti" fullname="Justin Uberti">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8854"/>
<seriesInfo name="DOI" value="10.17487/RFC8854"/>
</reference>
<reference anchor="RFC8858" target="https://www.rfc-editor.org/info/rfc8
858" quoteTitle="true" derivedAnchor="RFC8858">
<front>
<title>Indicating Exclusive Support of RTP and RTP Control Protocol
(RTCP) Multiplexing Using the Session Description Protocol (SDP)</title>
<author initials="C." surname="Holmberg" fullname="Christer Holmberg
">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8858"/>
<seriesInfo name="DOI" value="10.17487/RFC8858"/>
</reference>
<reference anchor="RFC8859" target="https://www.rfc-editor.org/info/rfc8
859" quoteTitle="true" derivedAnchor="RFC8859">
<front>
<title>A Framework for Session Description Protocol (SDP) Attributes
When Multiplexing</title>
<author initials="S" surname="Nandakumar" fullname="Suhas Nandakumar
">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8859"/>
<seriesInfo name="DOI" value="10.17487/RFC8859"/>
</reference>
</references>
<references pn="section-10.2">
<name slugifiedName="name-informative-references">Informative References
</name>
<reference anchor="RFC3389" target="https://www.rfc-editor.org/info/rfc3
389" quoteTitle="true" derivedAnchor="RFC3389">
<front>
<title>Real-time Transport Protocol (RTP) Payload for Comfort Noise
(CN)</title>
<author initials="R." surname="Zopf" fullname="R. Zopf">
<organization showOnFrontPage="true"/>
</author>
<date year="2002" month="September"/>
</front>
<seriesInfo name="RFC" value="3389"/>
<seriesInfo name="DOI" value="10.17487/RFC3389"/>
</reference>
<reference anchor="RFC3556" target="https://www.rfc-editor.org/info/rfc3
556" quoteTitle="true" derivedAnchor="RFC3556">
<front>
<title>Session Description Protocol (SDP) Bandwidth Modifiers for RT
P Control Protocol (RTCP) Bandwidth</title>
<author initials="S." surname="Casner" fullname="S. Casner">
<organization showOnFrontPage="true"/>
</author>
<date year="2003" month="July"/>
<abstract>
<t indent="0">This document defines an extension to the Session De
scription Protocol (SDP) to specify two additional modifiers for the bandwidth a
ttribute. These modifiers may be used to specify the bandwidth allowed for RTP C
ontrol Protocol (RTCP) packets in a Real-time Transport Protocol (RTP) session.
[STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="3556"/>
<seriesInfo name="DOI" value="10.17487/RFC3556"/>
</reference>
<reference anchor="RFC3960" target="https://www.rfc-editor.org/info/rfc3
960" quoteTitle="true" derivedAnchor="RFC3960">
<front>
<title>Early Media and Ringing Tone Generation in the Session Initia
tion Protocol (SIP)</title>
<author initials="G." surname="Camarillo" fullname="G. Camarillo">
<organization showOnFrontPage="true"/>
</author>
<author initials="H." surname="Schulzrinne" fullname="H. Schulzrinne
">
<organization showOnFrontPage="true"/>
</author>
<date year="2004" month="December"/>
<abstract>
<t indent="0">This document describes how to manage early media in
the Session Initiation Protocol (SIP) using two models: the gateway model and t
he application server model. It also describes the inputs one needs to consider
in defining local policies for ringing tone generation. This memo provides inf
ormation for the Internet community.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="3960"/>
<seriesInfo name="DOI" value="10.17487/RFC3960"/>
</reference>
<reference anchor="RFC4568" target="https://www.rfc-editor.org/info/rfc4
568" quoteTitle="true" derivedAnchor="RFC4568">
<front>
<title>Session Description Protocol (SDP) Security Descriptions for
Media Streams</title>
<author initials="F." surname="Andreasen" fullname="F. Andreasen">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Baugher" fullname="M. Baugher">
<organization showOnFrontPage="true"/>
</author>
<author initials="D." surname="Wing" fullname="D. Wing">
<organization showOnFrontPage="true"/>
</author>
<date year="2006" month="July"/>
<abstract>
<t indent="0">This document defines a Session Description Protocol
(SDP) cryptographic attribute for unicast media streams. The attribute describ
es a cryptographic key and other parameters that serve to configure security for
a unicast media stream in either a single message or a roundtrip exchange. The
attribute can be used with a variety of SDP media transports, and this document
defines how to use it for the Secure Real-time Transport Protocol (SRTP) unicas
t media streams. The SDP crypto attribute requires the services of a data secur
ity protocol to secure the SDP message. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4568"/>
<seriesInfo name="DOI" value="10.17487/RFC4568"/>
</reference>
<reference anchor="RFC4588" target="https://www.rfc-editor.org/info/rfc4
588" quoteTitle="true" derivedAnchor="RFC4588">
<front>
<title>RTP Retransmission Payload Format</title>
<author initials="J." surname="Rey" fullname="J. Rey">
<organization showOnFrontPage="true"/>
</author>
<author initials="D." surname="Leon" fullname="D. Leon">
<organization showOnFrontPage="true"/>
</author>
<author initials="A." surname="Miyazaki" fullname="A. Miyazaki">
<organization showOnFrontPage="true"/>
</author>
<author initials="V." surname="Varsa" fullname="V. Varsa">
<organization showOnFrontPage="true"/>
</author>
<author initials="R." surname="Hakenberg" fullname="R. Hakenberg">
<organization showOnFrontPage="true"/>
</author>
<date year="2006" month="July"/>
<abstract>
<t indent="0">RTP retransmission is an effective packet loss recov
ery technique for real-time applications with relaxed delay bounds. This docume
nt describes an RTP payload format for performing retransmissions. Retransmitted
RTP packets are sent in a separate stream from the original RTP stream. It is
assumed that feedback from receivers to senders is available. In particular, it
is assumed that Real-time Transport Control Protocol (RTCP) feedback as defined
in the extended RTP profile for RTCP-based feedback (denoted RTP/AVPF) is avail
able in this memo. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4588"/>
<seriesInfo name="DOI" value="10.17487/RFC4588"/>
</reference>
<reference anchor="RFC4733" target="https://www.rfc-editor.org/info/rfc4
733" quoteTitle="true" derivedAnchor="RFC4733">
<front>
<title>RTP Payload for DTMF Digits, Telephony Tones, and Telephony S
ignals</title>
<author initials="H." surname="Schulzrinne" fullname="H. Schulzrinne
">
<organization showOnFrontPage="true"/>
</author>
<author initials="T." surname="Taylor" fullname="T. Taylor">
<organization showOnFrontPage="true"/>
</author>
<date year="2006" month="December"/>
<abstract>
<t indent="0">This memo describes how to carry dual-tone multifreq
uency (DTMF) signalling, other tone signals, and telephony events in RTP packets
. It obsoletes RFC 2833.</t>
<t indent="0">This memo captures and expands upon the basic framew
ork defined in RFC 2833, but retains only the most basic event codes. It sets u
p an IANA registry to which other event code assignments may be added. Companion
documents add event codes to this registry relating to modem, fax, text telepho
ny, and channel-associated signalling events. The remainder of the event codes d
efined in RFC 2833 are conditionally reserved in case other documents revive the
ir use.</t>
<t indent="0">This document provides a number of clarifications to
the original document. However, it specifically differs from RFC 2833 by remov
ing the requirement that all compliant implementations support the DTMF events.
Instead, compliant implementations taking part in out-of-band negotiations of m
edia stream content indicate what events they support. This memo adds three new
procedures to the RFC 2833 framework: subdivision of long events into segments,
reporting of multiple events in a single packet, and the concept and reporting
of state events. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4733"/>
<seriesInfo name="DOI" value="10.17487/RFC4733"/>
</reference>
<reference anchor="RFC5245" target="https://www.rfc-editor.org/info/rfc5
245" quoteTitle="true" derivedAnchor="RFC5245">
<front>
<title>Interactive Connectivity Establishment (ICE): A Protocol for
Network Address Translator (NAT) Traversal for Offer/Answer Protocols</title>
<author initials="J." surname="Rosenberg" fullname="J. Rosenberg">
<organization showOnFrontPage="true"/>
</author>
<date year="2010" month="April"/>
<abstract>
<t indent="0">This document describes a protocol for Network Addre
ss Translator (NAT) traversal for UDP-based multimedia sessions established with
the offer/answer model. This protocol is called Interactive Connectivity Estab
lishment (ICE). ICE makes use of the Session Traversal Utilities for NAT (STUN)
protocol and its extension, Traversal Using Relay NAT (TURN). ICE can be used
by any protocol utilizing the offer/answer model, such as the Session Initiation
Protocol (SIP). [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5245"/>
<seriesInfo name="DOI" value="10.17487/RFC5245"/>
</reference>
<reference anchor="RFC5506" target="https://www.rfc-editor.org/info/rfc5
506" quoteTitle="true" derivedAnchor="RFC5506">
<front>
<title>Support for Reduced-Size Real-Time Transport Control Protocol
(RTCP): Opportunities and Consequences</title>
<author initials="I." surname="Johansson" fullname="I. Johansson">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Westerlund" fullname="M. Westerlund">
<organization showOnFrontPage="true"/>
</author>
<date year="2009" month="April"/>
<abstract>
<t indent="0">This memo discusses benefits and issues that arise w
hen allowing Real-time Transport Protocol (RTCP) packets to be transmitted with
reduced size. The size can be reduced if the rules on how to create compound pa
ckets outlined in RFC 3550 are removed or changed. Based on that analysis, this
memo defines certain changes to the rules to allow feedback messages to be sent
as Reduced-Size RTCP packets under certain conditions when using the RTP/AVPF (
Real-time Transport Protocol / Audio-Visual Profile with Feedback) profile (RFC
4585). This document updates RFC 3550, RFC 3711, and RFC 4585. [STANDARDS-TRACK
]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5506"/>
<seriesInfo name="DOI" value="10.17487/RFC5506"/>
</reference>
<reference anchor="RFC5576" target="https://www.rfc-editor.org/info/rfc5
576" quoteTitle="true" derivedAnchor="RFC5576">
<front>
<title>Source-Specific Media Attributes in the Session Description P
rotocol (SDP)</title>
<author initials="J." surname="Lennox" fullname="J. Lennox">
<organization showOnFrontPage="true"/>
</author>
<author initials="J." surname="Ott" fullname="J. Ott">
<organization showOnFrontPage="true"/>
</author>
<author initials="T." surname="Schierl" fullname="T. Schierl">
<organization showOnFrontPage="true"/>
</author>
<date year="2009" month="June"/>
<abstract>
<t indent="0">The Session Description Protocol (SDP) provides mech
anisms to describe attributes of multimedia sessions and of individual media str
eams (e.g., Real-time Transport Protocol (RTP) sessions) within a multimedia ses
sion, but does not provide any mechanism to describe individual media sources wi
thin a media stream. This document defines a mechanism to describe RTP media so
urces, which are identified by their synchronization source (SSRC) identifiers,
in SDP, to associate attributes with these sources, and to express relationships
among sources. It also defines several source-level attributes that can be use
d to describe properties of media sources. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5576"/>
<seriesInfo name="DOI" value="10.17487/RFC5576"/>
</reference>
<reference anchor="RFC5763" target="https://www.rfc-editor.org/info/rfc5
763" quoteTitle="true" derivedAnchor="RFC5763">
<front>
<title>Framework for Establishing a Secure Real-time Transport Proto
col (SRTP) Security Context Using Datagram Transport Layer Security (DTLS)</titl
e>
<author initials="J." surname="Fischl" fullname="J. Fischl">
<organization showOnFrontPage="true"/>
</author>
<author initials="H." surname="Tschofenig" fullname="H. Tschofenig">
<organization showOnFrontPage="true"/>
</author>
<author initials="E." surname="Rescorla" fullname="E. Rescorla">
<organization showOnFrontPage="true"/>
</author>
<date year="2010" month="May"/>
<abstract>
<t indent="0">This document specifies how to use the Session Initi
ation Protocol (SIP) to establish a Secure Real-time Transport Protocol (SRTP) s
ecurity context using the Datagram Transport Layer Security (DTLS) protocol. It
describes a mechanism of transporting a fingerprint attribute in the Session De
scription Protocol (SDP) that identifies the key that will be presented during t
he DTLS handshake. The key exchange travels along the media path as opposed to
the signaling path. The SIP Identity mechanism can be used to protect the integ
rity of the fingerprint attribute from modification by intermediate proxies. [S
TANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5763"/>
<seriesInfo name="DOI" value="10.17487/RFC5763"/>
</reference>
<reference anchor="RFC5764" target="https://www.rfc-editor.org/info/rfc5
764" quoteTitle="true" derivedAnchor="RFC5764">
<front>
<title>Datagram Transport Layer Security (DTLS) Extension to Establi
sh Keys for the Secure Real-time Transport Protocol (SRTP)</title>
<author initials="D." surname="McGrew" fullname="D. McGrew">
<organization showOnFrontPage="true"/>
</author>
<author initials="E." surname="Rescorla" fullname="E. Rescorla">
<organization showOnFrontPage="true"/>
</author>
<date year="2010" month="May"/>
<abstract>
<t indent="0">This document describes a Datagram Transport Layer S
ecurity (DTLS) extension to establish keys for Secure RTP (SRTP) and Secure RTP
Control Protocol (SRTCP) flows. DTLS keying happens on the media path, independ
ent of any out-of-band signalling channel present. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5764"/>
<seriesInfo name="DOI" value="10.17487/RFC5764"/>
</reference>
<reference anchor="RFC6120" target="https://www.rfc-editor.org/info/rfc6
120" quoteTitle="true" derivedAnchor="RFC6120">
<front>
<title>Extensible Messaging and Presence Protocol (XMPP): Core</titl
e>
<author initials="P." surname="Saint-Andre" fullname="P. Saint-Andre
">
<organization showOnFrontPage="true"/>
</author>
<date year="2011" month="March"/>
<abstract>
<t indent="0">The Extensible Messaging and Presence Protocol (XMPP
) is an application profile of the Extensible Markup Language (XML) that enables
the near-real-time exchange of structured yet extensible data between any two o
r more network entities. This document defines XMPP's core protocol methods: se
tup and teardown of XML streams, channel encryption, authentication, error handl
ing, and communication primitives for messaging, network availability ("presence
"), and request-response interactions. This document obsoletes RFC 3920. [STAN
DARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6120"/>
<seriesInfo name="DOI" value="10.17487/RFC6120"/>
</reference>
<reference anchor="RFC6464" target="https://www.rfc-editor.org/info/rfc6
464" quoteTitle="true" derivedAnchor="RFC6464">
<front>
<title>A Real-time Transport Protocol (RTP) Header Extension for Cli
ent-to-Mixer Audio Level Indication</title>
<author initials="J." surname="Lennox" fullname="J. Lennox" role="ed
itor">
<organization showOnFrontPage="true"/>
</author>
<author initials="E." surname="Ivov" fullname="E. Ivov">
<organization showOnFrontPage="true"/>
</author>
<author initials="E." surname="Marocco" fullname="E. Marocco">
<organization showOnFrontPage="true"/>
</author>
<date year="2011" month="December"/>
<abstract>
<t indent="0">This document defines a mechanism by which packets o
f Real-time Transport Protocol (RTP) audio streams can indicate, in an RTP heade
r extension, the audio level of the audio sample carried in the RTP packet. In
large conferences, this can reduce the load on an audio mixer or other middlebox
that wants to forward only a few of the loudest audio streams, without requirin
g it to decode and measure every stream that is received. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6464"/>
<seriesInfo name="DOI" value="10.17487/RFC6464"/>
</reference>
<reference anchor="RFC8828" target="https://www.rfc-editor.org/info/rfc8
828" quoteTitle="true" derivedAnchor="RFC8828">
<front>
<title>WebRTC IP Address Handling Requirements</title>
<author initials="J" surname="Uberti" fullname="Justin Uberti">
<organization showOnFrontPage="true"/>
</author>
<author initials="G" surname="Shieh" fullname="Guo-wei Shieh">
<organization showOnFrontPage="true"/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8828"/>
<seriesInfo name="DOI" value="10.17487/RFC8828"/>
</reference>
<reference anchor="I-D.ietf-rtcweb-sdp" quoteTitle="true" target="https:
//tools.ietf.org/html/draft-ietf-rtcweb-sdp-14" derivedAnchor="SDP4WebRTC">
<front>
<title>Annotated Example SDP for WebRTC</title>
<author initials="S" surname="Nandakumar" fullname="Suhas Nandakumar
">
<organization showOnFrontPage="true"/>
</author>
<author initials="C" surname="Jennings" fullname="Cullen Jennings">
<organization showOnFrontPage="true"/>
</author>
<date month="December" day="17" year="2020"/>
<abstract>
<t indent="0">The Web Real Time Communications (WebRTC) family of
protocols defines mechanism for direct interactive rich communication using audi
o, video, and data between two peers' web browsers. With in the WebRTC framewor
k, the Session Description Protocol (SDP) is used for negotiating session capabi
lities between the peers. Such a negotiation happens based on the SDP offer/ans
wer exchange mechanism This document provides an informational reference in des
cribing the role of SDP and the offer/answer exchange mechanism for the most com
mon WebRTC use cases. This document makes no changes to the SDP offer/answer ex
change mechanism.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-rtcweb-sdp-14"/>
<format type="TXT" target="http://www.ietf.org/internet-drafts/draft-i
etf-rtcweb-sdp-14.txt"/>
<refcontent>Work in Progress</refcontent>
</reference>
<reference anchor="TS26.114" target="https://www.3gpp.org/DynaReport/261
14.htm" quoteTitle="true" derivedAnchor="TS26.114">
<front>
<title>3rd Generation Partnership Project; Technical Specification G
roup Services and System Aspects; IP Multimedia Subsystem (IMS); Multimedia Tele
phony; Media handling and interaction (Release 16)</title>
<seriesInfo name="3GPP TS" value="26.114 V16.3.0"/>
<author>
<organization showOnFrontPage="true">3GPP</organization>
</author>
<date year="2019" month="September"/>
</front>
</reference>
<reference anchor="W3C.webrtc" target="https://www.w3.org/TR/2020/PR-web
rtc-20201215/" quoteTitle="true" derivedAnchor="W3C.webrtc">
<front>
<title>WebRTC 1.0: Real-time Communication Between Browsers</title>
<author fullname="Cullen Jennings" initials="C." surname="Jennings"
role="editor">
<organization showOnFrontPage="true">Cisco</organization>
</author>
<author fullname="Henrik Boström" asciiFullname="Henrik Bostrom" ini
tials="H." surname="Boström" asciiSurname="Bostrom" role="editor">
<organization showOnFrontPage="true">Google</organization>
</author>
<author fullname="Jan-Ivar Bruaroey" initials="J." surname="Bruaroey
" role="editor">
<organization showOnFrontPage="true">Mozilla</organization>
</author>
<date month="Dec" year="2020"/>
</front>
<refcontent>World Wide Web Consortium PR PR-webrtc-20201215</refconten
t>
</reference>
</references>
</references> </references>
<section title="Appendix A" anchor="sec.appendix-a"> <section anchor="sec.appendix-a" numbered="true" toc="include" removeInRFC="
false" pn="section-appendix.a">
<t>For the syntax validation performed in <name slugifiedName="name-sdp-abnf-syntax">SDP ABNF Syntax</name>
<xref target="sec.parsing-a-desc" />, the following list of ABNF <t indent="0" pn="section-appendix.a-1">For the syntax validation performe
d in
<xref target="sec.parsing-a-desc" format="default" sectionFormat="of" deri
vedContent="Section 5.8"/>, the following list of ABNF
definitions is used:</t> definitions is used:</t>
<texttable anchor="sdp-abnf" title="SDP ABNF References"> <table anchor="sdp-abnf" align="center" pn="table-1">
<ttcol align='left'>Attribute</ttcol> <name slugifiedName="name-sdp-abnf-references">SDP ABNF References</name
<ttcol align='left'>Reference</ttcol> >
<c>ptime</c> <thead>
<c> <tr>
<xref target="RFC4566" /> Section 9</c> <th align="left" colspan="1" rowspan="1">Attribute</th>
<c>maxptime</c> <th align="left" colspan="1" rowspan="1">Reference</th>
<c> </tr>
<xref target="RFC4566" /> Section 9</c> </thead>
<c>rtpmap</c> <tbody>
<c> <tr>
<xref target="RFC4566" /> Section 9</c> <td align="left" colspan="1" rowspan="1">ptime</td>
<c>recvonly</c> <td align="left" colspan="1" rowspan="1">
<c> <xref target="RFC4566" sectionFormat="of" section="6" format="defa
<xref target="RFC4566" /> Section 9</c> ult" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedContent="
<c>sendrecv</c> RFC4566"/></td>
<c> </tr>
<xref target="RFC4566" /> Section 9</c> <tr>
<c>sendonly</c> <td align="left" colspan="1" rowspan="1">maxptime</td>
<c> <td align="left" colspan="1" rowspan="1">
<xref target="RFC4566" /> Section 9</c> <xref target="RFC4566" sectionFormat="of" section="6" format="defa
<c>inactive</c> ult" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedContent="
<c> RFC4566"/></td>
<xref target="RFC4566" /> Section 9</c> </tr>
<c>framerate</c> <tr>
<c> <td align="left" colspan="1" rowspan="1">rtpmap</td>
<xref target="RFC4566" /> Section 9</c> <td align="left" colspan="1" rowspan="1">
<c>fmtp</c> <xref target="RFC4566" sectionFormat="of" section="6" format="defa
<c> ult" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-6" derivedContent="
<xref target="RFC4566" /> Section 9</c> RFC4566"/></td>
<c>quality</c> </tr>
<c> <tr>
<xref target="RFC4566" /> Section 9</c> <td align="left" colspan="1" rowspan="1">recvonly</td>
<c>rtcp</c> <td align="left" colspan="1" rowspan="1">
<c> <xref target="RFC4566" sectionFormat="of" section="9" format="defa
<xref target="RFC3605" /> Section 2.1</c> ult" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-9" derivedContent="
<c>setup</c> RFC4566"/></td>
<c> </tr>
<xref target="RFC4145" /> Sections 3, 4, and 5</c> <tr>
<c>connection</c> <td align="left" colspan="1" rowspan="1">sendrecv</td>
<c> <td align="left" colspan="1" rowspan="1">
<xref target="RFC4145" /> Sections 3, 4, and 5</c> <xref target="RFC4566" sectionFormat="of" section="9" format="defa
<c>fingerprint</c> ult" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-9" derivedContent="
<c> RFC4566"/></td>
<xref target="RFC8122" /> Section 5</c> </tr>
<c>rtcp-fb</c> <tr>
<c> <td align="left" colspan="1" rowspan="1">sendonly</td>
<xref target="RFC4585" /> Section 4.2</c> <td align="left" colspan="1" rowspan="1">
<c>extmap</c> <xref target="RFC4566" sectionFormat="of" section="9" format="defa
<c> ult" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-9" derivedContent="
<xref target="RFC5285" /> Section 7</c> RFC4566"/></td>
<c>mid</c> </tr>
<c> <tr>
<xref target="RFC5888" /> Sections 4 and 5</c> <td align="left" colspan="1" rowspan="1">inactive</td>
<c>group</c> <td align="left" colspan="1" rowspan="1">
<c> <xref target="RFC4566" sectionFormat="of" section="9" format="defa
<xref target="RFC5888" /> Sections 4 and 5</c> ult" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-9" derivedContent="
<c>imageattr</c> RFC4566"/></td>
<c> </tr>
<xref target="RFC6236" /> Section 3.1</c> <tr>
<c>extmap (encrypt option)</c> <td align="left" colspan="1" rowspan="1">fmtp</td>
<c> <td align="left" colspan="1" rowspan="1">
<xref target="RFC6904" /> Section 4</c> <xref target="RFC4566" sectionFormat="of" section="9" format="defa
<c>candidate</c> ult" derivedLink="https://rfc-editor.org/rfc/rfc4566#section-9" derivedContent="
<c> RFC4566"/></td>
<xref target="I-D.ietf-mmusic-ice-sip-sdp" /> Section 4.1</c> </tr>
<c>remote-candidates</c> <tr>
<c> <td align="left" colspan="1" rowspan="1">rtcp</td>
<xref target="I-D.ietf-mmusic-ice-sip-sdp" /> Section 4.2</c> <td align="left" colspan="1" rowspan="1">
<c>ice-lite</c> <xref target="RFC3605" sectionFormat="of" section="2.1" format="de
<c> fault" derivedLink="https://rfc-editor.org/rfc/rfc3605#section-2.1" derivedConte
<xref target="I-D.ietf-mmusic-ice-sip-sdp" /> Section 4.3</c> nt="RFC3605"/></td>
<c>ice-ufrag</c> </tr>
<c> <tr>
<xref target="I-D.ietf-mmusic-ice-sip-sdp" /> Section 4.4</c> <td align="left" colspan="1" rowspan="1">setup</td>
<c>ice-pwd</c> <td align="left" colspan="1" rowspan="1">
<c> <xref target="RFC4145" section="4" sectionFormat="of" format="defa
<xref target="I-D.ietf-mmusic-ice-sip-sdp" /> Section 4.4</c> ult" derivedLink="https://rfc-editor.org/rfc/rfc4145#section-4" derivedContent="
<c>ice-options</c> RFC4145"/></td>
<c> </tr>
<xref target="I-D.ietf-mmusic-ice-sip-sdp" /> Section 4.6</c> <tr>
<c>msid</c> <td align="left" colspan="1" rowspan="1">fingerprint</td>
<c> <td align="left" colspan="1" rowspan="1">
<xref target="I-D.ietf-mmusic-msid" /> Section 2</c> <xref target="RFC8122" sectionFormat="of" section="5" format="defa
<c>rid</c> ult" derivedLink="https://rfc-editor.org/rfc/rfc8122#section-5" derivedContent="
<c> RFC8122"/></td>
<xref target="I-D.ietf-mmusic-rid" /> Section 10</c> </tr>
<c>simulcast</c> <tr>
<c> <td align="left" colspan="1" rowspan="1">rtcp-fb</td>
<xref target="I-D.ietf-mmusic-sdp-simulcast" /> Section 6.1</c> <td align="left" colspan="1" rowspan="1">
<c>tls-id</c> <xref target="RFC4585" sectionFormat="of" section="4.2" format="de
<c> fault" derivedLink="https://rfc-editor.org/rfc/rfc4585#section-4.2" derivedConte
<xref target="I-D.ietf-mmusic-dtls-sdp" /> Section 4</c> nt="RFC4585"/></td>
</texttable> </tr>
<tr>
<td align="left" colspan="1" rowspan="1">extmap</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC5285" sectionFormat="of" section="7" format="defa
ult" derivedLink="https://rfc-editor.org/rfc/rfc5285#section-7" derivedContent="
RFC5285"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">mid</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC5888" section="4" sectionFormat="of" format="defa
ult" derivedLink="https://rfc-editor.org/rfc/rfc5888#section-4" derivedContent="
RFC5888"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">group</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC5888" section="5" sectionFormat="of" format="defa
ult" derivedLink="https://rfc-editor.org/rfc/rfc5888#section-5" derivedContent="
RFC5888"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">imageattr</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC6236" sectionFormat="of" section="3.1" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc6236#section-3.1" derivedConte
nt="RFC6236"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">extmap (encrypt option)</td
>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC6904" sectionFormat="of" section="4" format="defa
ult" derivedLink="https://rfc-editor.org/rfc/rfc6904#section-4" derivedContent="
RFC6904"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">candidate</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC8839" sectionFormat="of" section="5.1" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.1" derivedConte
nt="RFC8839"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">remote-candidates</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC8839" sectionFormat="of" section="5.2" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.2" derivedConte
nt="RFC8839"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">ice-lite</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC8839" sectionFormat="of" section="5.3" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.3" derivedConte
nt="RFC8839"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">ice-ufrag</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC8839" sectionFormat="of" section="5.4" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.4" derivedConte
nt="RFC8839"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">ice-pwd</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC8839" sectionFormat="of" section="5.4" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.4" derivedConte
nt="RFC8839"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">ice-options</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC8839" sectionFormat="of" section="5.6" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc8839#section-5.6" derivedConte
nt="RFC8839"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">msid</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC8830" sectionFormat="of" section="3" format="defa
ult" derivedLink="https://rfc-editor.org/rfc/rfc8830#section-3" derivedContent="
RFC8830"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">rid</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC8851" sectionFormat="of" section="10" format="def
ault" derivedLink="https://rfc-editor.org/rfc/rfc8851#section-10" derivedContent
="RFC8851"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">simulcast</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC8853" sectionFormat="of" section="5.1" format="de
fault" derivedLink="https://rfc-editor.org/rfc/rfc8853#section-5.1" derivedConte
nt="RFC8853"/></td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">tls-id</td>
<td align="left" colspan="1" rowspan="1">
<xref target="RFC8842" sectionFormat="of" section="4" format="defa
ult" derivedLink="https://rfc-editor.org/rfc/rfc8842#section-4" derivedContent="
RFC8842"/></td>
</tr>
</tbody>
</table>
</section> </section>
<section title="Change log" anchor="sec.change-log"> <section anchor="sec.acknowledgements" numbered="false" toc="include" remove
InRFC="false" pn="section-appendix.b">
<t>Note to RFC Editor: Please remove this section before <name slugifiedName="name-acknowledgements">Acknowledgements</name>
publication.</t> <t indent="0" pn="section-appendix.b-1"><contact fullname="Harald Alvestra
nd"/>, <contact fullname="Taylor Brandstetter"/>, <contact fullname="Suhas
<t>Changes in draft-26:</t> Nandakumar"/>, and
<contact fullname="Peter Thatcher"/> provided significant text for this
<t> document. <contact fullname="Bernard Aboba"/>, <contact fullname="Adam
<list style="symbols"> Bergkvist"/>, <contact fullname="Jan-Ivar Bruaroey"/>,
<t>Update guidance on generation of the m= proto value to be <contact fullname="Dan Burnett"/>, <contact fullname="Ben Campbell"/
consistent with ice-sip-sdp.</t> >, <contact fullname="Alissa Cooper"/>,
</list> <contact fullname="Richard Ejzak"/>, <contact fullname="Stefan Håkan
</t> sson"/>, <contact fullname="Ted Hardie"/>, <contact fullname="Christer Holmberg"
/>,
<t>Changes in draft-25:</t> <contact fullname="Andrew Hutton"/>, <contact fullname="Randell Jesu
p"/>, <contact fullname="Matthew Kaufman"/>, <contact fullname="Anant Narayanan"
<t> />,
<list style="symbols"> <contact fullname="Adam Roach"/>, <contact fullname="Robert Sparks"/>,
<contact fullname="Neil Stratford"/>, <contact fullname="Martin Thom
<t>Remove MSID track ID from offers and answers.</t> son"/>, <contact fullname="Sean Turner"/>, and <contact fullname="Magnus W
esterlund"/> all provided valuable feedback on
<t>Add note about rejecting all m= sections in a BUNDLE group.</t> this document.</t>
</section>
<t>Update ICE references to RFC 8445 and mention ice2.</t> <section anchor="authors-addresses" numbered="false" removeInRFC="false" toc
</list> ="include" pn="section-appendix.c">
</t> <name slugifiedName="name-authors-addresses">Authors' Addresses</name>
<author fullname="Justin Uberti" initials="J." surname="Uberti">
<t>Changes in draft-24:</t> <organization showOnFrontPage="true">Google</organization>
<address>
<t> <postal>
<list style="symbols"> <street>747 6th Street South</street>
<city>Kirkland</city>
<t>Clarify that rounding is permitted when trying to maintain <region>WA</region>
aspect ratio.</t> <code>98033</code>
<country>United States of America</country>
<t>Update tls-id handling to match what is specified in </postal>
dtls-sdp.</t> <email>justin@uberti.name</email>
</list> </address>
</t> </author>
<author fullname="Cullen Jennings" initials="C." surname="Jennings">
<t>Changes in draft-23:</t> <organization showOnFrontPage="true">Cisco</organization>
<address>
<t> <postal>
<list style="symbols"> <street>400 3rd Avenue SW</street>
<city>Calgary</city>
<t>Clarify rollback handling, and treat it similarly to other <region>AB</region>
setLocal/setRemote usages.</t> <code>T2P 4H2</code>
<country>Canada</country>
<t>Adopt a first-fit policy for handling multiple remote </postal>
a=imageattr attributes.</t> <email>fluffy@iii.ca</email>
</address>
<t>Clarify that a session description with zero m= sections </author>
is legal.</t> <author fullname="Eric Rescorla" initials="E." surname="Rescorla" role="ed
</list> itor">
</t> <organization showOnFrontPage="true">Mozilla</organization>
<address>
<t>Changes in draft-22:</t> <email>ekr@rtfm.com</email>
</address>
<t> </author>
<list style="symbols">
<t>Clarify currentDirection versus direction.</t>
<t>Correct session-id text so that it aligns with RFC
3264.</t>
<t>Clarify that generated ICE candidate objects must have all
four fields.</t>
<t>Make rollback work from any state besides stable and
regardless of whether setLocalDescription or
setRemoteDescription is used.</t>
<t>Allow modifying SDP before sending or after receiving
either offers or answers (previously this was forbidden for
answers).</t>
<t>Provide rationale for several design choices.</t>
</list>
</t>
<t>Changes in draft-21:</t>
<t>
<list style="symbols">
<t>Change dtls-id to tls-id to match MMUSIC draft.</t>
<t>Replace regular expression for proto field with a list and
clarify that the answer must exactly match the offer.</t>
<t>Remove text about how to error check on setLocal because
local descriptions cannot be changed.</t>
<t>Rework silence suppression support to always require that
both sides agree to silence suppression or none is used.</t>
<t>Remove instructions to parse "a=ssrc-group".</t>
<t>Allow the addition of new codecs in answers and in
subsequent offers.</t>
<t>Clarify imageattr processing. Replace use of [x=0,y=0]
with direction indicators.</t>
<t>Document when early media can occur.</t>
<t>Fix ICE default port handling when bundle-only is
used.</t>
<t>Forbid duplicating IDENTICAL/TRANSPORT attributes when you
are bundling.</t>
<t>Clarify the number of components to gather when bundle is
involved.</t>
<t>Explicitly state that PTs and SSRCs are to be used for
demuxing.</t>
<t>Update guidance on "a=setup" line. This should now match
the MMUSIC draft.</t>
<t>Update guidance on certificate/digest matching to conform
to RFC8122.</t>
<t>Update examples.</t>
</list>
</t>
<t>Changes in draft-20:</t>
<t>
<list style="symbols">
<t>Remove Appendix-B.</t>
</list>
</t>
<t>Changes in draft-19:</t>
<t>
<list style="symbols">
<t>Examples are now machine-generated for correctness, and
use IETF-approved example IP addresses.</t>
<t>Add early transport warmup example, and add missing
attributes to existing examples.</t>
<t>Only send "a=rtcp-mux-only" and "a=bundle-only" on new m=
sections.</t>
<t>Update references.</t>
<t>Add coverage of a=identity.</t>
<t>Explain the lipsync group algorithm more thoroughly.</t>
<t>Remove unnecessary list of MTI specs.</t>
<t>Allow codecs which weren't offered to appear in answers
and which weren't selected to appear in subsequent
offers.</t>
<t>Codec preferences now are applied on both initial and
subsequent offers and answers.</t>
<t>Clarify a=msid handling for recvonly m= sections.</t>
<t>Clarify behavior of attributes for bundle-only data
channels.</t>
<t>Allow media attributes to appear in data m= sections when
all the media m= sections are bundle-only.</t>
<t>Use consistent terminology for JSEP implementations.</t>
<t>Describe how to handle failed API calls.</t>
<t>Some cleanup on routing rules.</t>
</list>
</t>
<t>Changes in draft-18:</t>
<t>
<list style="symbols">
<t>Update demux algorithm and move it to an appendix in
preparation for merging it into BUNDLE.</t>
<t>Clarify why we can't handle an incoming offer to send
simulcast.</t>
<t>Expand IceCandidate object text.</t>
<t>Further document use of ICE candidate pool.</t>
<t>Document removeTrack.</t>
<t>Update requirements to only accept the last generated
offer/answer as an argument to setLocalDescription.</t>
<t>Allow round pixels.</t>
<t>Fix code around default timing when AVPF is not
specified.</t>
<t>Clean up terminology around m= line and m=section.</t>
<t>Provide a more realistic example for minimum decoder
capabilities.</t>
<t>Document behavior when rtcp-mux policy is require but
rtcp-mux attribute not provided.</t>
<t>Expanded discussion of RtpSender and RtpReceiver.</t>
<t>Add RtpTransceiver.currentDirection and document
setDirection.</t>
<t>Require imageattr x=0, y=0 to indicate that there are no
valid resolutions.</t>
<t>Require a privacy-preserving MID/RID construction.</t>
<t>Require support for RFC 3556 bandwidth modifiers.</t>
<t>Update maxptime description.</t>
<t>Note that endpoints may encounter extra codecs in answers
and subsequent offers from non-JSEP peers.</t>
<t>Update references.</t>
</list>
</t>
<t>Changes in draft-17:</t>
<t>
<list style="symbols">
<t>Split createOffer and createAnswer sections to clearly
indicate attributes which always appear and which only appear
when not bundled into another m= section.</t>
<t>Add descriptions of RtpTransceiver methods.</t>
<t>Describe how to process RTCP feedback attributes.</t>
<t>Clarify transceiver directions and their interaction with
3264.</t>
<t>Describe setCodecPreferences.</t>
<t>Update RTP demux algorithm. Include RTCP.</t>
<t>Update requirements for when a=rtcp is included, limiting
to cases where it is needed for backward compatibility.</t>
<t>Clarify SAR handling.</t>
<t>Updated addTrack matching algorithm.</t>
<t>Remove a=ssrc requirements.</t>
<t>Handle a=setup in reoffers.</t>
<t>Discuss how RTX/FEC should be handled.</t>
<t>Discuss how telephone-event should be handled.</t>
<t>Discuss how CN/DTX should be handled.</t>
<t>Add missing references to ABNF table.</t>
</list>
</t>
<t>Changes in draft-16:</t>
<t>
<list style="symbols">
<t>Update addIceCandidate to indicate ICE generation and
allow per-m= section end-of-candidates.</t>
<t>Update fingerprint handling to use
draft-ietf-mmusic-4572-update.</t>
<t>Update text around SDP processing of RTP header extensions
and payload formats.</t>
<t>Add sections on simulcast, addTransceiver, and
createDataChannel.</t>
<t>Clarify text to ensure that the session ID is a positive
63 bit integer.</t>
<t>Clarify SDP processing for direction indication.</t>
<t>Describe SDP processing for rtcp-mux-only.</t>
<t>Specify how SDP session version in o= line.</t>
<t>Require that when doing an re-offer, the capabilities of
the new session are mostly required to be a subset of the
previously negotiated session.</t>
<t>Clarified ICE restart interaction with bundle-only.</t>
<t>Remove support for changing SDP before calling
setLocalDescription.</t>
<t>Specify algorithm for demuxing RTP based on MID, PT, and
SSRC.</t>
<t>Clarify rules for rejecting m= lines when bundle policy is
balanced or max-bundle.</t>
</list>
</t>
<t>Changes in draft-15:</t>
<t>
<list style="symbols">
<t>Clarify text around codecs offered in subsequent
transactions to refer to what's been negotiated.</t>
<t>Rewrite LS handling text to indicate edge cases and that
we're living with them.</t>
<t>Require that answerer reject m= lines when there are no
codecs in common.</t>
<t>Enforce max-bundle on offer processing.</t>
<t>Fix TIAS formula to handle bits vs. kilobits.</t>
<t>Describe addTrack algorithm.</t>
<t>Clean up references.</t>
</list>
</t>
<t>Changes in draft-14:</t>
<t>
<list style="symbols">
<t>Added discussion of RtpTransceivers + RtpSenders +
RtpReceivers, and how they interact with
createOffer/createAnswer.</t>
<t>Removed obsolete OfferToReceiveX options.</t>
<t>Explained how addIceCandidate can be used for
end-of-candidates.</t>
</list>
</t>
<t>Changes in draft-13:</t>
<t>
<list style="symbols">
<t>Clarified which SDP lines can be ignored.</t>
<t>Clarified how to handle various received attributes.</t>
<t>Revised how attributes should be generated for bundled m=
lines.</t>
<t>Remove unused references.</t>
<t>Remove text advocating use of unilateral PTs.</t>
<t>Trigger an ICE restart even if the ICE candidate policy is
being made more strict.</t>
<t>Remove the 'public' ICE candidate policy.</t>
<t>Move open issues into GitHub issues.</t>
<t>Split local/remote description accessors into
current/pending.</t>
<t>Clarify a=imageattr handling.</t>
<t>Add more detail on VoiceActivityDetection handling.</t>
<t>Reference draft-shieh-rtcweb-ip-handling.</t>
<t>Make it clear when an ICE restart should occur.</t>
<t>Resolve changes needed in references.</t>
<t>Remove MSID semantics.</t>
<t>ice-options are now at session level.</t>
<t>Default RTCP mux policy is now 'require'.</t>
</list>
</t>
<t>Changes in draft-12:</t>
<t>
<list style="symbols">
<t>Filled in sections on applying local and remote
descriptions.</t>
<t>Discussed downscaling and upscaling to fulfill imageattr
requirements.</t>
<t>Updated what SDP can be modified by the application.</t>
<t>Updated to latest datachannel SDP.</t>
<t>Allowed multiple fingerprint lines.</t>
<t>Switched back to IPv4 for dummy candidates.</t>
<t>Added additional clarity on ICE default candidates.</t>
</list>
</t>
<t>Changes in draft-11:</t>
<t>
<list style="symbols">
<t>Clarified handling of RTP CNAMEs.</t>
<t>Updated what SDP lines should be processed or ignored.</t>
<t>Specified how a=imageattr should be used.</t>
</list>
</t>
<t>Changes in draft-10:</t>
<t>
<list style="symbols">
<t>Described video size negotiation with imageattr.</t>
<t>Clarified rejection of sections that do not have
mux-only.</t>
<t>Add handling of LS groups</t>
</list>
</t>
<t>Changes in draft-09:</t>
<t>
<list style="symbols">
<t>Don't return null for {local,remote}Description after
close().</t>
<t>Changed TCP/TLS to UDP/DTLS in RTP profile names.</t>
<t>Separate out bundle and mux policy.</t>
<t>Added specific references to FEC mechanisms.</t>
<t>Added canTrickle mechanism.</t>
<t>Added section on subsequent answers and, answer
options.</t>
<t>Added text defining set{Local,Remote}Description
behavior.</t>
</list>
</t>
<t>Changes in draft-08:
<list style="symbols">
<t>Added new example section and removed old examples in
appendix.</t>
<t>Fixed &lt;proto&gt; field handling.</t>
<t>Added text describing a=rtcp attribute.</t>
<t>Reworked handling of OfferToReceiveAudio and
OfferToReceiveVideo per discussion at IETF 90.</t>
<t>Reworked trickle ICE handling and its impact on m= and c=
lines per discussion at interim.</t>
<t>Added max-bundle-and-rtcp-mux policy.</t>
<t>Added description of maxptime handling.</t>
<t>Updated ICE candidate pool default to 0.</t>
<t>Resolved open issues around AppID/receiver-ID.</t>
<t>Reworked and expanded how changes to the ICE configuration
are handled.</t>
<t>Some reference updates.</t>
<t>Editorial clarification.</t>
</list></t>
<t>Changes in draft-07:
<list style="symbols">
<t>Expanded discussion of VAD and Opus DTX.</t>
<t>Added a security considerations section.</t>
<t>Rewrote the section on modifying SDP to require
implementations to clearly indicate whether any given
modification is allowed.</t>
<t>Clarified impact of IceRestart on CreateOffer in local-offer
state.</t>
<t>Guidance on whether attributes should be defined at the
media level or the session level.</t>
<t>Renamed "default" bundle policy to "balanced".</t>
<t>Removed default ICE candidate pool size and clarify how it
works.</t>
<t>Defined a canonical order for assignment of MSTs to m=
lines.</t>
<t>Removed discussion of rehydration.</t>
<t>Added Eric Rescorla as a draft editor.</t>
<t>Cleaned up references.</t>
<t>Editorial cleanup</t>
</list></t>
<t>Changes in draft-06:
<list style="symbols">
<t>Reworked handling of m= line recycling.</t>
<t>Added handling of BUNDLE and bundle-only.</t>
<t>Clarified handling of rollback.</t>
<t>Added text describing the ICE Candidate Pool and its
behavior.</t>
<t>Allowed OfferToReceiveX to create multiple recvonly m=
sections.</t>
</list></t>
<t>Changes in draft-05:
<list style="symbols">
<t>Fixed several issues identified in the createOffer/Answer
sections during document review.</t>
<t>Updated references.</t>
</list></t>
<t>Changes in draft-04:
<list style="symbols">
<t>Filled in sections on createOffer and createAnswer.</t>
<t>Added SDP examples.</t>
<t>Fixed references.</t>
</list></t>
<t>Changes in draft-03:
<list style="symbols">
<t>Added text describing relationship to W3C specification</t>
</list></t>
<t>Changes in draft-02:
<list style="symbols">
<!-- A -->
<t>Converted from nroff</t>
<!-- B -->
<t>Removed comparisons to old approaches abandoned by the
working group</t>
<!-- C -->
<t>Removed stuff that has moved to W3C specification</t>
<!-- D -->
<t>Align SDP handling with W3C draft</t>
<!-- E -->
<t>Clarified section on forking.</t>
<!-- F -->
<!-- G -->
<!-- H -->
<!-- I -->
<!-- J -->
<!-- K -->
<!-- L -->
</list></t>
<t>Changes in draft-01:
<list style="symbols">
<t>Added diagrams for architecture and state machine.</t>
<t>Added sections on forking and rehydration.</t>
<t>Clarified meaning of "pranswer" and "answer".</t>
<t>Reworked how ICE restarts and media directions are
controlled.</t>
<t>Added list of parameters that can be changed in a
description.</t>
<t>Updated suggested API and examples to match latest
thinking.</t>
<t>Suggested API and examples have been moved to an
appendix.</t>
</list></t>
<t>Changes in draft -00:
<list style="symbols">
<t>Migrated from draft-uberti-rtcweb-jsep-02.</t>
</list></t>
</section> </section>
</back> </back>
</rfc> </rfc>
 End of changes. 699 change blocks. 
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