rfc8848xml2.original.xml   rfc8848.xml 
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<front> <front>
<title abbrev="CLUE Signaling"> <title abbrev="CLUE Signaling">
Session Signaling for Controlling Multiple Streams for Telepresence (CLUE) Session Signaling for Controlling Multiple Streams for Telepresence (CLUE)
</title> </title>
<author initials="R." surname="Hanton" fullname="Robert Hanton"> <seriesInfo name="RFC" value="8848"/>
<author initials="R." surname="Hanton" fullname="Robert Hanton">
<organization>Cisco Systems</organization> <organization>Cisco Systems</organization>
<address> <address>
<email>rohanse2@cisco.com</email> <email>rohanse2@cisco.com</email>
</address> </address>
</author> </author>
<author initials="P." surname="Kyzivat" fullname="Paul Kyzivat"> <author initials="P." surname="Kyzivat" fullname="Paul Kyzivat">
<address> <address>
<email>pkyzivat@alum.mit.edu</email> <email>pkyzivat@alum.mit.edu</email>
</address> </address>
</author> </author>
<author initials="L." surname="Xiao" fullname="Lennard Xiao">
<organization>Huawei</organization> <author initials="L." surname="Xiao" fullname="Lennard Xiao">
<organization>Beijing Chuangshiyoulian</organization>
<address> <address>
<email>lennard.xiao@huawei.com</email> <email>lennard.xiao@outlook.com</email>
</address> </address>
</author> </author>
<author initials="C." surname="Groves" fullname="Christian Groves"> <author initials="C." surname="Groves" fullname="Christian Groves">
<address> <address>
<email>cngroves.std@gmail.com</email> <email>cngroves.std@gmail.com</email>
</address> </address>
</author> </author>
<date month="January" year="2021"/>
<date year="2019" /> <abstract>
<abstract>
<t> <t>
This document specifies how CLUE-specific signaling such as the CLUE This document is about Controlling Multiple Streams for Telepresence
protocol and the CLUE data channel are used in conjunction with each (CLUE) signaling. It specifies how the CLUE protocol and the CLUE
other and with existing signaling mechanisms such as SIP and SDP to data channel are used in conjunction with each other and with existing
produce a telepresence call. signaling mechanisms, such as SIP and the Session Description Protocol
(SDP), to produce a telepresence call.
</t> </t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<section title="Introduction"> <section numbered="true" toc="default">
<t> <name>Introduction</name>
To enable devices to participate in a telepresence call, selecting the sources <t>
they wish to view, receiving those media sources and displaying them in an To enable devices to participate in a telepresence call, where they select the s
optimal fashion, CLUE (ControLling mUltiple streams for tElepresence) employs ources
two principal and inter-related protocol negotiations. they wish to view, receive those media sources, and display them in an
<xref target="RFC4566">SDP</xref>, conveyed via optimal fashion, Controlling Multiple Streams for Telepresence (CLUE) employs
<xref target="RFC3261">SIP</xref>, is used to negotiate the specific media two principal and interrelated protocol negotiations.
SDP <xref target="RFC4566" format="default"/>, conveyed via
SIP <xref target="RFC3261" format="default"/>, is used to negotiate the specific
media
capabilities that can be delivered to specific addresses on a device. capabilities that can be delivered to specific addresses on a device.
Meanwhile, <xref target="I-D.ietf-clue-protocol">CLUE protocol</xref> Meanwhile, CLUE protocol messages <xref target="RFC8847" format="default"/>, tra
messages, transported via a nsported via a
<xref target="I-D.ietf-clue-datachannel">CLUE data channel</xref>, are used to CLUE data channel <xref target="RFC8850" format="default"/>, are used to
negotiate the Capture Sources available, their attributes and any constraints negotiate the Capture Sources available, their attributes, and any constraints
in their use. They also allow the far end device to specify which Captures in their use. They also allow the far-end device to specify which Captures
they wish to receive. It is recommended that those documents be read prior to they wish to receive. It is recommended that those documents be read prior to
this one as this document assumes familiarity with those protocols and hence this one as this document assumes familiarity with those protocols and hence
uses terminology from each with limited introduction. uses terminology from each with limited introduction.
</t> </t>
<t> <t>
Beyond negotiating the CLUE channel, SDP is also used to negotiate the details Beyond negotiating the CLUE channel, SDP is also used to negotiate the details
of supported media streams and the maximum capability of each of those of supported media streams and the maximum capability of each of those
streams. As the <xref target="I-D.ietf-clue-framework">CLUE Framework</xref> streams. As the CLUE Framework <xref target="RFC8845" format="default"/>
defines a manner in which the Media Provider expresses their maximum encoding defines a manner in which the Media Provider expresses their maximum Encoding
group capabilities, SDP is also used to express the encoding limits for each Group capabilities, SDP is also used to express the encoding limits for each
potential Encoding. potential Encoding.
</t> </t>
<t> <t>
Backwards-compatibility is an important consideration of the protocol: it is Backwards compatibility is an important consideration of the protocol: it is
vital that a CLUE-capable device contacting a device that does not support vital that a CLUE-capable device contacting a device that does not support
CLUE is able to fall back to a fully functional non-CLUE call. The document CLUE is able to fall back to a fully functional non-CLUE call. The document
also defines how a non-CLUE call may be upgraded to CLUE in mid-call, and also defines how a non-CLUE call may be upgraded to CLUE mid-call and,
similarly how CLUE functionality can be removed mid-call to return to a similarly, how CLUE functionality can be removed mid-call to return to a
standard non-CLUE call. standard non-CLUE call.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Terminology"> <name>Terminology</name>
<t> <t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQU
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", IRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
"MAY", and "OPTIONAL" in this document are to be interpreted as NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>
described in BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
and only when, they appear in all capitals, as shown here. "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
</t> be interpreted as
<t> described in BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/>
This document uses terminology defined in the when, and only when, they appear in all capitals, as shown here.
<xref target="I-D.ietf-clue-framework">CLUE Framework</xref>.
</t>
<t>
A few additional terms specific to this document are defined as follows:
</t>
<t>
<list style='hanging'>
<t hangText="non-CLUE device:">
A device that supports standard SIP and SDP, but either does not support CLUE,
or that does but does not currently wish to invoke CLUE capabilities.
</t> </t>
<t hangText="CLUE-controlled media:"> <t>
This document uses terminology defined in the CLUE Framework
<xref target="RFC8845" format="default"/>.
</t>
<t>
A few additional terms specific to this document are defined as follows:
</t>
<dl newline="false" spacing="normal">
<dt>CLUE-controlled media:</dt>
<dd>
A media "m=" line that is under CLUE control; the Capture Source that provides A media "m=" line that is under CLUE control; the Capture Source that provides
the media on this "m=" line is negotiated in CLUE. See the media on this "m=" line is negotiated in CLUE. See
<xref target="sec.group" /> for details of how this control is signaled in <xref target="sec.group" format="default"/> for details on how this control is s ignaled in
SDP. There is a corresponding "non-CLUE-controlled" media term. SDP. There is a corresponding "non-CLUE-controlled" media term.
</t> </dd>
</list> <dt>non-CLUE device:</dt>
</t> <dd>
</section> A device that supports standard SIP and SDP but either does not support CLUE
or does support CLUE but does not currently wish to invoke CLUE capabilities.
<section title="Media Feature Tag Definition" anchor="sec.tag"> </dd>
<t> <dt>RTCP:</dt><dd>RTP Control Protocol.</dd>
The "sip.clue" media feature tag <xref target="RFC3840"/> indicates <dt>SCTP:</dt><dd>Stream Control Transmission Protocol.</dd>
support for CLUE in <xref target="RFC3261">SIP</xref> calls. A CLUE-capable <dt>STUN:</dt><dd>Session Traversal Utilities for NAT.</dd>
device SHOULD include this media feature tag in its REGISTER requests and </dl>
OPTION responses. It SHOULD also include the media feature tag in INVITE and </section>
UPDATE <xref target="RFC3311" /> requests and responses. <section anchor="sec.tag" numbered="true" toc="default">
</t> <name>Media Feature Tag Definition</name>
<t>
Presence of the media feature tag in the contact field of a request or
response can be used to determine that the far end supports CLUE.
</t>
</section>
<section title="SDP Grouping Framework CLUE Extension Semantics" anchor="sec.g
roup">
<section title="General">
<t> <t>
This section defines a new SDP Grouping Framework <xref target="RFC5888" /> The "sip.clue" media feature tag <xref target="RFC3840" format="default"/> indic
extension called 'CLUE'. ates
support for CLUE in SIP <xref target="RFC3261" format="default"/> calls. A CLUE-
capable
device <bcp14>SHOULD</bcp14> include this media feature tag in its REGISTER requ
ests and
OPTION responses. It <bcp14>SHOULD</bcp14> also include the media feature tag in
INVITE and
UPDATE <xref target="RFC3311" format="default"/> requests and responses.
</t> </t>
<t> <t>
Presence of the media feature tag in the contact field of a request or
response can be used to determine that the far end supports CLUE.
</t>
</section>
<section anchor="sec.group" numbered="true" toc="default">
<name>SDP Grouping Framework CLUE Extension Semantics</name>
<section numbered="true" toc="default">
<name>General</name>
<t>
This section defines a new SDP Grouping Framework <xref target="RFC5888" format=
"default"/>
extension called 'CLUE'.
</t>
<t>
The CLUE extension can be indicated using an SDP session-level The CLUE extension can be indicated using an SDP session-level
'group' attribute. Each SDP media "m=" line that is included in this group, 'group' attribute. Each SDP media "m=" line that is included in this group,
using SDP media-level mid attributes, is CLUE-controlled, by a CLUE data using SDP media-level mid attributes, is CLUE controlled by a CLUE data
channel also included in this CLUE group. channel that is also included in this CLUE group.
</t> </t>
<t> <t>
Currently only support for a single CLUE group is specified; support for Currently, only support for a single CLUE group is specified; support for
multiple CLUE groups in a single session is outside the scope of this multiple CLUE groups in a single session is outside the scope of this
document. A device MUST NOT include more than one CLUE group in its SDP document. A device <bcp14>MUST NOT</bcp14> include more than one CLUE group in i ts SDP
message unless it is following a specification that defines how multiple CLUE message unless it is following a specification that defines how multiple CLUE
channels are signaled, and is either able to determine that the other side of channels are signaled and is able to either determine that the other side of
the SDP exchange supports multiple CLUE channels, or is able to fail the SDP exchange supports multiple CLUE channels or fail
gracefully in the event it does not. gracefully in the event it does not.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="The CLUE data channel and the CLUE grouping semantic"> <name>The CLUE Data Channel and the CLUE Grouping Semantic</name>
<t> <t>
The <xref target="I-D.ietf-clue-datachannel">CLUE data channel</xref> is a The CLUE data channel <xref target="RFC8850" format="default"/> is a
bidirectional <xref target="I-D.ietf-rtcweb-data-channel">data channel</xref> bidirectional data channel <xref target="RFC8831" format="default"/>
used for the transport of CLUE messages, conveyed within an SCTP over DTLS used for the transport of CLUE messages, conveyed within an SCTP over DTLS
connection. This channel must be established before CLUE protocol messages can connection. This channel must be established before CLUE protocol messages can
be exchanged and CLUE-controlled media can be sent. be exchanged and CLUE-controlled media can be sent.
</t> </t>
<t> <t>
The data channel is negotiated over SDP as described in The data channel is negotiated over SDP as described in
<xref target="I-D.ietf-mmusic-data-channel-sdpneg"/>. A CLUE-capable <xref target="RFC8864" format="default"/>. A CLUE-capable
device wishing to negotiate CLUE MUST also include a CLUE group in their SDP device wishing to negotiate CLUE <bcp14>MUST</bcp14> also include a CLUE group i
offer or answer and include the "mid" of the "m=" line for the data channel in n their SDP
that group. The CLUE group MUST include the "mid" of the "m=" line for one Offer or Answer and include the "mid" of the "m=" line for the data channel in
that group. The CLUE group <bcp14>MUST</bcp14> include the "mid" of the "m=" lin
e for one
(and only one) data channel. (and only one) data channel.
</t> </t>
<t> <t>
Presence of the data channel in the CLUE group in an SDP offer or answer also Presence of the data channel in the CLUE group in an SDP Offer or Answer also
serves, along with the "sip.clue" media feature tag, as an indication that the serves, along with the "sip.clue" media feature tag, as an indication that the
device supports CLUE and wishes to upgrade the call to include CLUE-controlled device supports CLUE and wishes to upgrade the call to include CLUE-controlled
media. A CLUE-capable device SHOULD include a data channel "m=" line in offers media. A CLUE-capable device <bcp14>SHOULD</bcp14> include a data channel "m=" l
and, when allowed by <xref target="RFC3264" />, answers. ine in offers
</t> and, when allowed by <xref target="RFC3264" format="default"/>, answers.
</section> </t>
</section>
<section title="CLUE-controlled media and the CLUE grouping semantic"> <section numbered="true" toc="default">
<t> <name>CLUE-Controlled Media and the CLUE Grouping Semantic</name>
<t>
CLUE-controlled media lines in an SDP are "m=" lines in which the content of CLUE-controlled media lines in an SDP are "m=" lines in which the content of
the media streams to be sent is negotiated via the the media streams to be sent is negotiated via the CLUE protocol
<xref target="I-D.ietf-clue-protocol">CLUE protocol</xref>. For an "m=" line <xref target="RFC8847" format="default"/>. For an "m=" line
to be CLUE-controlled, its "mid" value MUST be included in the CLUE group. to be CLUE controlled, its "mid" attribute value <bcp14>MUST</bcp14> be included
in the CLUE group.
CLUE-controlled media is controlled by the CLUE protocol as negotiated on the CLUE-controlled media is controlled by the CLUE protocol as negotiated on the
CLUE data channel with an "mid" included in the CLUE group. CLUE data channel with a "mid" included in the CLUE group.
</t> </t>
<t> <t>
"m=" lines not specified as under CLUE control follow normal rules for media "m=" lines not specified as being under CLUE control follow normal rules for med
ia
streams negotiated in SDP as defined in documents such as streams negotiated in SDP as defined in documents such as
<xref target="RFC3264" />. <xref target="RFC3264" format="default"/>.
</t> </t>
<t> <t>
The restrictions on CLUE-controlled media that are defined below always apply The restrictions on CLUE-controlled media that are defined below always apply
to "m=" lines in an SDP offer or answer, even if negotiation of the data to "m=" lines in an SDP Offer or Answer, even if negotiation of the data
channel in SDP failed due to lack of CLUE support by the remote device or for channel in SDP failed due to lack of CLUE support by the remote device or for
any other reason, or in an offer if the recipient does not include the "mid" any other reason, or in an offer if the recipient does not include the "mid"
of the corresponding "m=" line in their CLUE group. of the corresponding "m=" line in their CLUE group.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="SDP semantics for CLUE-controlled media"> <name>SDP Semantics for CLUE-Controlled Media</name>
<section title="Signaling CLUE Encodings" anchor="sec.sdp_encodings" <section anchor="sec.sdp_encodings" numbered="true" toc="default">
> <name>Signaling CLUE Encodings</name>
<t> <t>
The <xref target="I-D.ietf-clue-framework">CLUE Framework</xref> defines the The CLUE Framework <xref target="RFC8845" format="default"/> defines the
concept of "Encodings", which represent the sender's encode ability. Each concept of "Encodings", which represent the sender's encode ability. Each
Encoding the Media Provider wishes to signal is signaled via an "m=" line of Encoding the Media Provider wishes to signal is done so via an "m=" line of
the appropriate media type, which MUST be marked as sendonly with the the appropriate media type, which <bcp14>MUST</bcp14> be marked as sendonly with
the
"a=sendonly" attribute or as inactive with the "a=inactive" attribute. "a=sendonly" attribute or as inactive with the "a=inactive" attribute.
</t> </t>
<t> <t>
The encoder limits of active (eg, "a=sendonly") Encodings can then be The encoder limits of active (e.g., "a=sendonly") Encodings can then be
expressed using existing SDP syntax. For instance, for H.264 see Table 6 in expressed using existing SDP syntax. For instance, for H.264, see Table 6 in
<xref target="RFC6184" /> for a list of valid parameters for representing <xref target="RFC6184" sectionFormat="of" section="8.2.2"/> for a list of valid
parameters for representing
encoder sender stream limits. encoder sender stream limits.
</t> </t>
<t> <t>
These Encodings are CLUE-controlled and hence MUST include an "mid" in the These Encodings are CLUE controlled and hence <bcp14>MUST</bcp14> include a "mid
" in the
CLUE group as defined above. CLUE group as defined above.
</t> </t>
<t> <t>
As well as the normal restrictions defined in <xref target="RFC3264" /> the In addition to the normal restrictions defined in <xref target="RFC3264" format=
stream MUST be treated as if the "m=" line direction attribute had been set to "default"/>, the
stream <bcp14>MUST</bcp14> be treated as if the "m=" line direction attribute ha
d been set to
"a=inactive" until the Media Provider has received a valid CLUE 'configure' "a=inactive" until the Media Provider has received a valid CLUE 'configure'
message specifying the Capture to be used for this stream. This means that message specifying the Capture to be used for this stream. This means that
RTP packets MUST NOT be sent until configuration is complete, while RTP packets <bcp14>MUST NOT</bcp14> be sent until configuration is complete, whi
non-media packets such as STUN, RTCP and DTLS MUST be sent as per their le
relevant specifications if negotiated. non-media packets such as STUN, RTCP, and DTLS <bcp14>MUST</bcp14> be sent as pe
</t> r their
<t> relevant specifications, if negotiated.
Every "m=" line representing a CLUE Encoding MUST contain a "label" attribute </t>
as defined in <xref target="RFC4574" />. This label is used to identify the <t>
Every "m=" line representing a CLUE Encoding <bcp14>MUST</bcp14> contain a "labe
l" attribute
as defined in <xref target="RFC4574" format="default"/>. This label is used to i
dentify the
Encoding by the sender in CLUE 'advertisement' messages and by the receiver in Encoding by the sender in CLUE 'advertisement' messages and by the receiver in
CLUE 'configure' messages. Each label used for a CLUE-controlled "m=" line CLUE 'configure' messages. Each label used for a CLUE-controlled "m=" line
MUST be different from the label on all other "m=" lines in the CLUE group, <bcp14>MUST</bcp14> be different from the label on all other "m=" lines in the C LUE group,
unless an "m=" line represents a dependent stream related to another "m=" line unless an "m=" line represents a dependent stream related to another "m=" line
(such as an FEC stream), in which case it MUST have the same label value as (such as a Forward Error Correction (FEC) stream), in which case it <bcp14>MUST< /bcp14> have the same label value as
the "m=" line on which it depends. the "m=" line on which it depends.
</t> </t>
<section title="Referencing Encodings in the CLUE protocol"> <section numbered="true" toc="default">
<t> <name>Referencing Encodings in the CLUE Protocol</name>
CLUE Encodings are defined in SDP, but can be referenced from CLUE protocol <t>
messages - this is how the protocol defines which Encodings are part of an CLUE Encodings are defined in SDP but can be referenced from CLUE protocol
Encoding Group (in 'advertisement' messages) and which Encoding with which to messages -- this is how the protocol defines which Encodings are a part of an
encode a specific Capture (in 'configure' messages). The labels on the Encoding Group (in 'advertisement' messages) and which Encoding is used to encod
e
a specific Capture (in 'configure' messages). The labels on the
CLUE-controlled "m=" lines are the references that are used in the CLUE CLUE-controlled "m=" lines are the references that are used in the CLUE
protocol. protocol.
</t> </t>
<t> <t>
Each &lt;encID&gt; (in encodingIDList) in a CLUE 'advertisement' message Each &lt;encID&gt; (in encodingIDList) in a CLUE 'advertisement' message
SHOULD represent an Encoding defined in SDP; the specific Encoding referenced <bcp14>SHOULD</bcp14> represent an Encoding defined in SDP; the specific Encodin g referenced
is a CLUE-controlled "m=" line in the most recent SDP Offer/Answer message is a CLUE-controlled "m=" line in the most recent SDP Offer/Answer message
sent by the sender of the 'advertisement' message with a label value sent by the sender of the 'advertisement' message with a label value
corresponding to the text content of the &lt;encID&gt;. If the &lt;encID&gt; corresponding to the text content of the &lt;encID&gt;. If the &lt;encID&gt;
is not defined in SDP it MUST be one it anticipates sending in a subsequent is not defined in SDP, it <bcp14>MUST</bcp14> be one it anticipates sending in a subsequent
SDP Offer/Answer exchange. SDP Offer/Answer exchange.
</t> </t>
<t> <t>
Each &lt;encodingID&gt; (in captureEncodingType) in a CLUE 'configure' message Each &lt;encodingID&gt; (in captureEncodingType) in a CLUE 'configure' message
MUST represent an Encoding defined in SDP; the specific Encoding referenced is <bcp14>MUST</bcp14> represent an Encoding defined in SDP; the specific Encoding referenced is
a CLUE-controlled "m=" line in the most recent SDP Offer/Answer message a CLUE-controlled "m=" line in the most recent SDP Offer/Answer message
received by the sender of the 'configure' message with a label value received by the sender of the 'configure' message with a label value
corresponding to the text content of the &lt;encodingID&gt;. corresponding to the text content of the &lt;encodingID&gt;.
</t> </t>
<t> <t>
Note that the non-atomic nature of SDP/CLUE protocol interaction may mean that Note that the non-atomic nature of SDP/CLUE protocol interaction may mean that
there are temporary periods where an &lt;encID&gt;/&lt;encodingID&gt; in a there are temporary periods where an &lt;encID&gt;/&lt;encodingID&gt; in a
CLUE message does not reference an SDP "m=" line, or where an Encoding CLUE message does not reference an SDP "m=" line, or where an Encoding
represented in SDP is not referenced in a CLUE protocol message. represented in SDP is not referenced in a CLUE protocol message.
See <xref target="sec.coordination" /> for specifics. See <xref target="sec.coordination" format="default"/> for specifics.
</t> </t>
</section> </section>
</section> </section>
<section title="Negotiating receipt of CLUE Capture Encodings in SDP <section numbered="true" toc="default">
"> <name>Negotiating Receipt of CLUE Capture Encodings in SDP</name>
<t> <t>
A receiver who wishes to receive a CLUE stream via a specific Encoding A receiver who wishes to receive a CLUE stream via a specific Encoding
requires an "a=recvonly" "m=" line that matches the "a=sendonly" Encoding. requires an "a=recvonly" "m=" line that matches the "a=sendonly" Encoding.
</t> </t>
<t> <t>
These "m=" lines are CLUE-controlled and hence MUST include their "mid" in the These "m=" lines are CLUE controlled and hence <bcp14>MUST</bcp14> include their
CLUE group. They MAY include a "label" attribute, but this is not required by "mid" in the
CLUE group. They <bcp14>MAY</bcp14> include a "label" attribute, but this is not
required by
CLUE, as only label values associated with "a=sendonly" Encodings are CLUE, as only label values associated with "a=sendonly" Encodings are
referenced by CLUE protocol messages. referenced by CLUE protocol messages.
</t> </t>
</section> </section>
</section> </section>
<section numbered="true" toc="default">
<section title="SDP Offer/Answer Procedures"> <name>SDP Offer/Answer Procedures</name>
<section title="Generating the Initial Offer"> <section numbered="true" toc="default">
<t> <name>Generating the Initial Offer</name>
A CLUE-capable device sending an initial SDP offer of a SIP session and <t>
A CLUE-capable device sending an initial SDP Offer of a SIP session and
wishing to negotiate CLUE will include an "m=" line for the data channel to wishing to negotiate CLUE will include an "m=" line for the data channel to
convey the CLUE protocol, along with a CLUE group containing the "mid" of the convey the CLUE protocol, along with a CLUE group containing the "mid" of the
data channel "m=" line. data channel "m=" line.
</t> </t>
<t> <t>
For interoperability with non-CLUE devices a CLUE-capable device sending an For interoperability with non-CLUE devices, a CLUE-capable device sending an
initial SDP offer SHOULD NOT include any "m=" line for CLUE-controlled media initial SDP Offer <bcp14>SHOULD NOT</bcp14> include any "m=" line for CLUE-contr
beyond the "m=" line for the CLUE data channel, and SHOULD include at least olled media
beyond the "m=" line for the CLUE data channel, and it <bcp14>SHOULD</bcp14> inc
lude at least
one non-CLUE-controlled media "m=" line. one non-CLUE-controlled media "m=" line.
</t> </t>
<t> <t>
If the device has evidence that the receiver is also CLUE-capable, for If the device has evidence that the receiver is also CLUE capable, for
instance due to receiving an initial INVITE with no SDP but including a instance, due to receiving an initial INVITE with no SDP but including a
"sip.clue" media feature tag, the above recommendation is waived, and the "sip.clue" media feature tag, the above recommendation is waived, and the
initial offer MAY contain "m=" lines for CLUE-controlled media. initial offer <bcp14>MAY</bcp14> contain "m=" lines for CLUE-controlled media.
</t> </t>
<t> <t>
With the same interoperability recommendations as for Encodings, the sender of With the same interoperability recommendations as for Encodings, the sender of
the initial SDP offer MAY also include "a=recvonly" media lines to the initial SDP Offer <bcp14>MAY</bcp14> also include "a=recvonly" media lines t
preallocate "m=" lines to receive media. Alternatively, it MAY wait until CLUE o
preallocate "m=" lines to receive media. Alternatively, it <bcp14>MAY</bcp14> wa
it until CLUE
protocol negotiation has completed before including these lines in a new protocol negotiation has completed before including these lines in a new
offer/answer exchange - see <xref target="sec.coordination" /> for offer/answer exchange -- see <xref target="sec.coordination" format="default"/> for
recommendations. recommendations.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Generating the Answer"> <name>Generating the Answer</name>
<section title="Negotiating use of CLUE and the CLUE data channe <section numbered="true" toc="default">
l"> <name>Negotiating Use of CLUE and the CLUE Data Channel</name>
<t> <t>
If the recipient of an initial offer is CLUE-capable, and the offer contains If the recipient of an initial offer is CLUE capable, and the offer contains
both an "m=" line for a data channel and a CLUE group containing the "mid" for both an "m=" line for a data channel and a CLUE group containing the "mid" for
that "m=" line, they SHOULD negotiate data channel support for an "m=" line, that "m=" line, they <bcp14>SHOULD</bcp14> negotiate data channel support for an "m=" line
and include the "mid" of that "m=" line in a corresponding CLUE group. and include the "mid" of that "m=" line in a corresponding CLUE group.
</t> </t>
<t> <t>
A CLUE-capable recipient that receives an "m=" line for a data channel but no A CLUE-capable recipient that receives an "m=" line for a data channel but no
corresponding CLUE group containing the "mid" of that "m=" line MAY still corresponding CLUE group containing the "mid" of that "m=" line <bcp14>MAY</bcp1 4> still
include a corresponding data channel "m=" line if there are any other non-CLUE include a corresponding data channel "m=" line if there are any other non-CLUE
protocols it can convey over that channel, but MUST NOT negotiate use of the protocols it can convey over that channel, but the use of the CLUE protocol <bcp
CLUE protocol on this channel. 14>MUST NOT</bcp14> be negotiated on this channel.
</t> </t>
</section> </section>
<section title="Negotiating CLUE-controlled media"> <section numbered="true" toc="default">
<t> <name>Negotiating CLUE-Controlled Media</name>
If the initial offer contained "a=recvonly" CLUE-controlled media lines the <t>
recipient SHOULD include corresponding "a=sendonly" CLUE-controlled media If the initial offer contained "a=recvonly" CLUE-controlled media lines, the
recipient <bcp14>SHOULD</bcp14> include corresponding "a=sendonly" CLUE-controll
ed media
lines for accepted Encodings, up to the maximum number of Encodings it lines for accepted Encodings, up to the maximum number of Encodings it
wishes to advertise. As CLUE-controlled media, the "mid" of these "m=" lines wishes to advertise. As CLUE-controlled media, the "mid" of these "m=" lines
MUST be included in the corresponding CLUE group. The recipient MUST set the <bcp14>MUST</bcp14> be included in the corresponding CLUE group. The recipient < bcp14>MUST</bcp14> set the
direction of the corresponding "m=" lines of any remaining "a=recvonly" direction of the corresponding "m=" lines of any remaining "a=recvonly"
CLUE-controlled media lines received in the offer to "a=inactive". CLUE-controlled media lines received in the offer to "a=inactive".
</t> </t>
<t> <t>
If the initial offer contained "a=sendonly" CLUE-controlled media lines the If the initial offer contained "a=sendonly" CLUE-controlled media lines, the
recipient MAY include corresponding "a=recvonly" CLUE-controlled media lines, recipient <bcp14>MAY</bcp14> include corresponding "a=recvonly" CLUE-controlled
media lines,
up to the maximum number of Capture Encodings it wishes to receive. up to the maximum number of Capture Encodings it wishes to receive.
Alternatively, it MAY wait until CLUE protocol negotiation has completed Alternatively, it <bcp14>MAY</bcp14> wait until CLUE protocol negotiation has co
before including these lines in a new offer/answer exchange - see mpleted
<xref target="sec.coordination" /> for recommendations. The recipient MUST set before including these lines in a new offer/answer exchange -- see
<xref target="sec.coordination" format="default"/> for recommendations. The reci
pient <bcp14>MUST</bcp14> set
the direction of the corresponding "m=" lines of any remaining "a=sendonly" the direction of the corresponding "m=" lines of any remaining "a=sendonly"
CLUE-controlled media lines received in the offer to "a=inactive" CLUE-controlled media lines received in the offer to "a=inactive".
</t> </t>
</section> </section>
<section title="Negotiating non-CLUE controlled media"> <section numbered="true" toc="default">
<t> <name>Negotiating Non-CLUE-controlled Media</name>
A CLUE-controlled device implementation MAY prefer to render initial, <t>
A CLUE-controlled device implementation <bcp14>MAY</bcp14> prefer to render init
ial,
single-stream audio and/or video for the user as rapidly as possible, single-stream audio and/or video for the user as rapidly as possible,
transitioning to CLUE-controlled media once that has been negotiated. transitioning to CLUE-controlled media once that has been negotiated.
Alternatively, an implementation MAY wish to suppress initial media, only Alternatively, an implementation <bcp14>MAY</bcp14> wish to suppress initial med ia, only
providing media once the final, CLUE-controlled streams have been negotiated. providing media once the final, CLUE-controlled streams have been negotiated.
</t> </t>
<t> <t>
The receiver of the initial offer, if making the call CLUE-enabled with their The receiver of the initial offer, if making the call CLUE-enabled with their
SDP answer, can make their preference clear by their action in accepting or SDP Answer, can make their preference clear by their action in accepting or
rejecting non-CLUE-controlled media lines. Rejecting these "m=" lines will rejecting non-CLUE-controlled media lines. Rejecting these "m=" lines will
ensure that no non-CLUE-controlled media flows before the CLUE-controlled ensure that no non-CLUE-controlled media flows before the CLUE-controlled
media is negotiated. In contrast, accepting one or more non-CLUE-controlled media is negotiated. In contrast, accepting one or more non-CLUE-controlled
"m=" lines in this initial answer will enable initial media to flow. "m=" lines in this initial answer will enable initial media to flow.
</t> </t>
<t> <t>
If the answerer chooses to send initial non-CLUE-controlled media in a If the answerer chooses to send initial non-CLUE-controlled media in a
CLUE-enabled call, <xref target="sec.clue-media" /> addresses the need to CLUE-enabled call, <xref target="sec.clue-media" format="default"/> addresses th
disable it once CLUE-controlled media is fully negotiated. e need to
</t> disable it once the CLUE-controlled media is fully negotiated.
</section> </t>
</section> </section>
</section>
<section title="Processing the initial Offer/Answer negotiation"> <section numbered="true" toc="default">
<t> <name>Processing the Initial Offer/Answer Negotiation</name>
In the event that both offer and answer include a data channel "m=" line with <t>
a mid value included in corresponding CLUE groups, CLUE has been successfully In the event that both the offer and answer include a data channel "m=" line wit
negotiated and the call is now CLUE-enabled. If not then the call is not h
CLUE-enabled. a "mid" value included in corresponding CLUE groups, CLUE has been successfully
</t> negotiated, and the call is now CLUE enabled. If not, then the call is not
<section title="Successful CLUE negotiation"> CLUE enabled.
<t> </t>
In the event of successful CLUE-enablement of the call, devices MUST now begin <section numbered="true" toc="default">
negotiation of the CLUE channel, see <name>Successful CLUE Negotiation</name>
<xref target="I-D.ietf-clue-datachannel" /> for negotiation details. If <t>
negotiation is successful, sending of <xref target="I-D.ietf-clue-protocol"> In the event of successful CLUE enablement of the call, devices <bcp14>MUST</bcp
CLUE protocol</xref> messages can begin. 14> now begin
</t> negotiation of the CLUE channel; see
<t> <xref target="RFC8850" format="default"/> for negotiation details. If
A CLUE-capable device MAY choose not to send RTP on the non-CLUE-controlled negotiation is successful, the sending of CLUE protocol messages <xref target="R
FC8847" format="default"/> can begin.
</t>
<t>
A CLUE-capable device <bcp14>MAY</bcp14> choose not to send RTP on the non-CLUE-
controlled
channels during the period in which control of the CLUE-controlled media lines channels during the period in which control of the CLUE-controlled media lines
is being negotiated (though RTCP MUST still be sent and received as normal). is being negotiated (though RTCP <bcp14>MUST</bcp14> still be sent and received
However, a CLUE-capable device MUST still be prepared to receive media on as normal).
However, a CLUE-capable device <bcp14>MUST</bcp14> still be prepared to receive
media on
non-CLUE-controlled media lines that have been successfully negotiated as non-CLUE-controlled media lines that have been successfully negotiated as
defined in <xref target="RFC3264" />. defined in <xref target="RFC3264" format="default"/>.
</t> </t>
<t> <t>
If either side of the call wishes to add additional CLUE-controlled "m=" lines If either side of the call wishes to add additional CLUE-controlled "m=" lines
to send or receive CLUE-controlled media they MAY now send a SIP request with to send or receive CLUE-controlled media, they <bcp14>MAY</bcp14> now send a SIP
a new SDP offer following the normal rules of SDP offer/answer and any request with
a new SDP Offer following the normal rules of SDP Offer/Answer and any
negotiated extensions. negotiated extensions.
</t> </t>
</section> </section>
<section title="CLUE negotiation failure"> <section numbered="true" toc="default">
<t> <name>CLUE Negotiation Failure</name>
<t>
In the event that the negotiation of CLUE fails and the call is not In the event that the negotiation of CLUE fails and the call is not
CLUE-enabled once the initial offer/answer negotiation completes then CLUE is CLUE enabled once the initial offer/answer negotiation completes, then CLUE is
not in use in the call. The CLUE-capable devices MUST either revert to not in use in the call. CLUE-capable devices <bcp14>MUST</bcp14> either revert t
non-CLUE behaviour or terminate the call. o
</t> non-CLUE behavior or terminate the call.
</section> </t>
</section> </section>
</section>
<section title="Modifying the session"> <section numbered="true" toc="default">
<section title="Adding and removing CLUE-controlled media" ancho <name>Modifying the Session</name>
r="sec.clue-media"> <section anchor="sec.clue-media" numbered="true" toc="default">
<t> <name>Adding and Removing CLUE-Controlled Media</name>
Subsequent offer/answer exchanges MAY add additional "m=" lines for <t>
CLUE-controlled media, or activate or deactivate existing "m=" lines per the Subsequent offer/answer exchanges <bcp14>MAY</bcp14> add additional "m=" lines f
or
CLUE-controlled media or activate or deactivate existing "m=" lines per the
standard SDP mechanisms. standard SDP mechanisms.
</t> </t>
<t> <t>
In most cases at least one additional exchange after the initial offer/answer In most cases, at least one additional exchange after the initial offer/answer
exchange will be required before both sides have added all the Encodings and exchange will be required before both sides have added all the Encodings and
ability to receive Encodings that they desire. Devices MAY delay adding the ability to receive Encodings that they desire. Devices <bcp14>MAY</bcp14> de lay adding
"a=recvonly" CLUE-controlled "m=" lines until after CLUE protocol negotiation "a=recvonly" CLUE-controlled "m=" lines until after CLUE protocol negotiation
completes - see <xref target="sec.coordination" /> for recommendations. completes -- see <xref target="sec.coordination" format="default"/> for recommen
</t> dations.
<t> </t>
Once CLUE media has been successfully negotiated devices SHOULD ensure that <t>
Once CLUE media has been successfully negotiated, devices <bcp14>SHOULD</bcp14>
ensure that
non-CLUE-controlled media is deactivated by setting their ports to 0 in cases non-CLUE-controlled media is deactivated by setting their ports to 0 in cases
where it corresponds to the media type of CLUE-controlled media that has been where it corresponds to the media type of CLUE-controlled media that has been
successfully negotiated. This deactivation may require an additional SDP successfully negotiated. This deactivation may require an additional SDP
exchange, or may be incorporated into one that is part of the CLUE exchange or may be incorporated into one that is part of the CLUE
negotiation. negotiation.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Enabling CLUE mid-call"> <name>Enabling CLUE Mid-Call</name>
<t> <t>
A CLUE-capable device that receives an initial SDP offer from a non-CLUE A CLUE-capable device that receives an initial SDP Offer from a non-CLUE
device SHOULD include a new data channel "m=" line and corresponding CLUE device <bcp14>SHOULD</bcp14> include a new data channel "m=" line and correspond
group in any subsequent offers it sends, to indicate that it is CLUE-capable. ing CLUE
</t> group in any subsequent offers it sends, to indicate that it is CLUE capable.
<t> </t>
If, in an ongoing non-CLUE call, an SDP offer/answer exchange completes with <t>
If, in an ongoing non-CLUE call, an SDP Offer/Answer exchange completes with
both sides having included a data channel "m=" line in their SDP and with the both sides having included a data channel "m=" line in their SDP and with the
"mid" for that channel in a corresponding CLUE group then the call is now "mid" for that channel in a corresponding CLUE group, then the call is now
CLUE-enabled; negotiation of the data channel and subsequently the CLUE CLUE enabled; negotiation of the data channel and subsequently the CLUE
protocol begins. protocol begins.
</t> </t>
</section> </section>
<section anchor="sec.clue-disable" numbered="true" toc="default">
<section title="Disabling CLUE mid-call" anchor="sec.clue-disabl <name>Disabling CLUE Mid-Call</name>
e"> <t>
<t> If, during an ongoing CLUE-enabled call, a device wishes to disable CLUE, it
If, during an ongoing CLUE-enabled call a device wishes to disable CLUE, it can do so by following the procedures for closing a data channel as defined in
can do so by following the procedures for closing a data channel defined in <xref target="RFC8864" sectionFormat="of" section="6.6.1"/>: sending
Section 5.2.4 of <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/>: sending a new SDP Offer/Answer exchange and subsequent SCTP Stream Sequence Number (SSN)
a new SDP offer/answer exchange and subsequent SCTP SSN reset for the CLUE reset for the CLUE
channel. It MUST also remove the CLUE group. Without the CLUE group any "m=" channel. It <bcp14>MUST</bcp14> also remove the CLUE group. Without the CLUE gro
lines that were previously CLUE-controlled no longer are; implementations MAY up, any "m="
disable them by setting their ports to 0 or MAY continue to use them - in the lines that were previously CLUE controlled no longer are; implementations <bcp14
latter case how they are used is outside the scope of this document. >MAY</bcp14>
</t> disable them by setting their ports to 0 or <bcp14>MAY</bcp14> continue to use t
<t> hem -- in the
If a device follows the procedure above, or an SDP offer-answer negotiation latter case, how they are used is outside the scope of this document.
</t>
<t>
If a device follows the procedure above, or an SDP Offer/Answer negotiation
completes in a fashion in which either the "m=" CLUE data channel line was not completes in a fashion in which either the "m=" CLUE data channel line was not
successfully negotiated, and/or one side did not include the data channel in successfully negotiated and/or one side did not include the data channel in
the CLUE group then CLUE for this call is disabled. In the event that this the CLUE group, then CLUE for this call is disabled. In the event that this
occurs, CLUE is no longer enabled. Any active "m=" lines still included in the occurs, CLUE is no longer enabled. Any active "m=" lines still included in the
CLUE group are no longer CLUE-controlled and the implementation MAY either CLUE group are no longer CLUE controlled, and the implementation <bcp14>MAY</bcp 14> either
disable them in a subsequent negotiation or continue to use them in some other disable them in a subsequent negotiation or continue to use them in some other
fashion. If the data channel is still present but not included in the CLUE fashion. If the data channel is still present but not included in the CLUE
group semantic CLUE protocol messages MUST no longer be sent. group semantic, CLUE protocol messages <bcp14>MUST</bcp14> no longer be sent.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="CLUE protocol failure mid-call"> <name>CLUE Protocol Failure Mid-Call</name>
<t> <t>
In contrast to the specific disablement of the use of CLUE described above, In contrast to the specific disablement of the use of CLUE described above,
the CLUE channel may fail unexpectedly. Two circumstances where this can occur the CLUE channel may fail unexpectedly. Two circumstances where this can occur
are: are:
<list style='symbols'> </t>
<t> <ul spacing="normal">
<li>
The CLUE data channel terminates, either gracefully or ungracefully, without The CLUE data channel terminates, either gracefully or ungracefully, without
any corresponding SDP renegotiation. any corresponding SDP renegotiation.
</t> </li>
<t> <li>
A channel error of the CLUE protocol causes it to return to the IDLE state as A channel error of the CLUE protocol causes it to return to the IDLE state as
defined in Section 6. of <xref target="I-D.ietf-clue-protocol" />. defined in <xref target="RFC8847" sectionFormat="of" section="6"/>.
</t> </li>
</list> </ul>
</t> <t>
<t> In this circumstance, implementations <bcp14>SHOULD</bcp14> continue to transmit
In this circumstance implementations SHOULD continue to transmit and receive and receive
CLUE-controlled media on the basis of the last negotiated CLUE messages, CLUE-controlled media on the basis of the last negotiated CLUE messages,
until the CLUE protocol is re-established (in the event of a channel error) or until the CLUE protocol is re-established (in the event of a channel error) or
disabled mid-call by an SDP exchange as defined in disabled mid-call by an SDP exchange as defined in
<xref target="sec.clue-disable" />. Implementations MAY choose to send such <xref target="sec.clue-disable" format="default"/>. Implementations <bcp14>MAY</
an SDP request to disable CLUE immediately or MAY continue on in a bcp14> choose to send such
an SDP request to disable CLUE immediately or <bcp14>MAY</bcp14> continue on in
a
call-preservation mode. call-preservation mode.
</t> </t>
</section> </section>
</section>
</section> </section>
</section>
</section> </section>
<section anchor="sec.coordination" numbered="true" toc="default">
<section title="Interaction of CLUE protocol and SDP negotiations" anchor="s <name>Interaction of the CLUE Protocol and SDP Negotiations</name>
ec.coordination">
<t> <t>
Information about media streams in CLUE is split between two message types: Information about media streams in CLUE is split between two message types:
SDP, which defines media addresses and limits, and the CLUE channel, SDP, which defines media addresses and limits, and the CLUE channel,
which defines properties of Capture Devices available, scene information and which defines properties of Capture Devices available, scene information, and
additional constraints. As a result certain operations, such as advertising additional constraints. As a result, certain operations, such as advertising
support for a new transmissible Capture with associated stream, cannot be support for a new transmissible Capture with an associated stream, cannot be
performed atomically, as they require changes to both SDP and CLUE messaging. performed atomically, as they require changes to both SDP and CLUE messaging.
</t> </t>
<t> <t>
This section defines how the negotiation of the two protocols interact, This section defines how the negotiation of the two protocols interact,
provides some recommendations on dealing with intermediate stages in provides some recommendations on dealing with intermediate stages in
non-atomic operations, and mandates additional constraints on when non-atomic operations, and mandates additional constraints on when
CLUE-configured media can be sent. CLUE-configured media can be sent.
</t> </t>
<section title="Independence of SDP and CLUE negotiation"> <section numbered="true" toc="default">
<t> <name>Independence of SDP and CLUE Negotiation</name>
<t>
To avoid the need to implement interlocking state machines with the potential To avoid the need to implement interlocking state machines with the potential
to reach invalid states if messages were to be lost, or be rewritten en-route to reach invalid states if messages were to be lost, or be rewritten en route
by middle boxes, the state machines in SDP and CLUE operate independently. The by middleboxes, the state machines in SDP and CLUE operate independently. The
state of the CLUE channel does not restrict when an implementation may send a state of the CLUE channel does not restrict when an implementation may send a
new SDP offer or answer, and likewise the implementation’s ability to send a new SDP Offer or Answer; likewise, the implementation's ability to send a
new CLUE 'advertisement' or 'configure' message is not restricted by the new CLUE 'advertisement' or 'configure' message is not restricted by the
results of or the state of the most recent SDP negotiation (unless the SDP results of or the state of the most recent SDP negotiation (unless the SDP
negotiation has removed the CLUE channel). negotiation has removed the CLUE channel).
</t> </t>
<t> <t>
The primary implication of this is that a device may receive an SDP The primary implication of this is that a device may receive an SDP
Offer/Answer message with a CLUE Encoding for which it does not yet have Offer/Answer message with a CLUE Encoding for which it does not yet have
Capture information, or receive a CLUE 'configure' message specifying a Capture information or receive a CLUE 'configure' message specifying a
Capture Encoding for which the far end has not negotiated a media stream in Capture Encoding for which the far end has not negotiated a media stream in
SDP. SDP.
</t> </t>
<t> <t>
CLUE messages contain an &lt;encID&gt; (in encodingIDList) or CLUE messages contain an &lt;encID&gt; (in encodingIDList) or
&lt;encodingID&gt; (in captureEncodingType), which is used to identify a &lt;encodingID&gt; (in captureEncodingType), which is used to identify a
specific encoding or captureEncoding in SDP; see specific Encoding or captureEncoding in SDP; see
<xref target="I-D.ietf-clue-data-model-schema" /> for specifics. <xref target="RFC8846" format="default"/> for specifics.
The non-atomic nature of CLUE negotiation means that a sender may wish to send The non-atomic nature of CLUE negotiation means that a sender may wish to send
a new CLUE 'advertisement' message before the corresponding SDP message. As a new CLUE 'advertisement' message before the corresponding SDP message. As
such the sender of the CLUE message MAY include an &lt;encID&gt; which does such, the sender of the CLUE message <bcp14>MAY</bcp14> include an &lt;encID&gt;
not currently match a CLUE-controlled "m=" line label in SDP; A CLUE-capable that does
implementation MUST NOT reject a CLUE protocol message solely because it not currently match a CLUE-controlled "m=" line label in SDP; a CLUE-capable
implementation <bcp14>MUST NOT</bcp14> reject a CLUE protocol message solely bec
ause it
contains &lt;encID&gt; elements that do not match a label in SDP. contains &lt;encID&gt; elements that do not match a label in SDP.
</t> </t>
<t> <t>
The current state of the CLUE participant or Media Provider/Consumer The current state of the CLUE Participant or Media Provider/Consumer
state machines do not affect compliance with any of the normative language of state machines does not affect compliance with any of the normative language of
<xref target="RFC3264" />. That is, they MUST NOT delay an ongoing SDP <xref target="RFC3264" format="default"/>. That is, they <bcp14>MUST NOT</bcp14>
exchange as part of a SIP server or client transaction; an implementation MUST delay an ongoing SDP
NOT delay an SDP exchange while waiting for CLUE negotiation to complete or exchange as part of a SIP server or client transaction; an implementation <bcp14
>MUST
NOT</bcp14> delay an SDP exchange while waiting for CLUE negotiation to complete
or
for a 'configure' message to arrive. for a 'configure' message to arrive.
</t> </t>
<t> <t>
Similarly, a device in a CLUE-enabled call MUST NOT delay any mandatory state Similarly, a device in a CLUE-enabled call <bcp14>MUST NOT</bcp14> delay any man datory state
transitions in the CLUE Participant or Media Provider/Consumer state machines transitions in the CLUE Participant or Media Provider/Consumer state machines
due to the presence or absence of an ongoing SDP exchange. due to the presence or absence of an ongoing SDP exchange.
</t> </t>
<t> <t>
A device with the CLUE Participant state machine in the ACTIVE state A device with the CLUE Participant state machine in the ACTIVE state
MAY choose to delay moving from ESTABLISHED to ADV (Media Provider <bcp14>MAY</bcp14> choose to delay moving from ESTABLISHED to ADV (Media Provide r
state machine) or from ESTABLISHED to WAIT FOR CONF RESPONSE (Media Consumer state machine) or from ESTABLISHED to WAIT FOR CONF RESPONSE (Media Consumer
state machine) based on the SDP state. See state machine) based on the SDP state. See
<xref target="I-D.ietf-clue-protocol"/> for CLUE state machine specifics. <xref target="RFC8847" format="default"/> for CLUE state machine specifics.
Similarly, a device MAY choose to delay initiating a new SDP exchange based on Similarly, a device <bcp14>MAY</bcp14> choose to delay initiating a new SDP exch
ange based on
the state of their CLUE state machines. the state of their CLUE state machines.
</t> </t>
</section> </section>
<section title="Constraints on sending media"> <section numbered="true" toc="default">
<t> <name>Constraints on Sending Media</name>
<t>
While SDP and CLUE message states do not impose constraints on each other, While SDP and CLUE message states do not impose constraints on each other,
both impose constraints on the sending of media - CLUE-controlled media MUST both impose constraints on the sending of media -- CLUE-controlled media <bcp14>
NOT be sent unless it has been negotiated in both CLUE and SDP: an MUST
implementation MUST NOT send a specific CLUE Capture Encoding unless its most NOT</bcp14> be sent unless it has been negotiated in both CLUE and SDP: an
implementation <bcp14>MUST NOT</bcp14> send a specific CLUE Capture Encoding unl
ess its most
recent SDP exchange contains an active media channel for that Encoding AND recent SDP exchange contains an active media channel for that Encoding AND
it has received a CLUE 'configure' message specifying a valid Capture for that it has received a CLUE 'configure' message specifying a valid Capture for that
Encoding. Encoding.
</t> </t>
</section> </section>
<section title="Recommendations for operating with non-atomic operations"> <section numbered="true" toc="default">
<name>Recommendations for Operating with Non-atomic Operations</name>
<t> <t>
CLUE-capable devices MUST be able to handle states in which CLUE messages make CLUE-capable devices <bcp14>MUST</bcp14> be able to handle states in which CLUE messages make
reference to EncodingIDs that do not match the most recently received SDP, reference to EncodingIDs that do not match the most recently received SDP,
irrespective of the order in which SDP and CLUE messages are received. While irrespective of the order in which SDP and CLUE messages are received. While
these mismatches will usually be transitory a device MUST be able to cope these mismatches will usually be transitory, a device <bcp14>MUST</bcp14> be abl e to cope
with such mismatches remaining indefinitely. However, this document makes some with such mismatches remaining indefinitely. However, this document makes some
recommendations on message ordering for these non-atomic transitions. recommendations on message ordering for these non-atomic transitions.
</t> </t>
<t> <t>
CLUE-capable devices MUST ensure that any inconsistencies between SDP and CLUE-capable devices <bcp14>MUST</bcp14> ensure that any inconsistencies between SDP and
CLUE signaling are temporary by sending updated SDP or CLUE messages as soon CLUE signaling are temporary by sending updated SDP or CLUE messages as soon
as the relevant state machines and other constraints permit. as the relevant state machines and other constraints permit.
</t> </t>
<t> <t>
Generally, implementations that receive messages for which they have Generally, implementations that receive messages with
incomplete information will be most efficient if they wait until they have the incomplete information will be most efficient if they wait until they have the
corresponding information they lack before sending messages to make changes corresponding information they lack before sending messages to make changes
related to that information. For example, an answerer that receives a new SDP related to that information. For example, an answerer that receives a new SDP
offer with three new "a=sendonly" CLUE "m=" lines for which it has received no Offer with three new "a=sendonly" CLUE "m=" lines for which it has received no
CLUE 'advertisement' message providing the corresponding capture information CLUE 'advertisement' message providing the corresponding capture information
would typically inclue corresponding "a=inactive" lines in its answer, and would typically include corresponding "a=inactive" lines in its answer, and
only make a new SDP offer with "a=recvonly" when and if a new 'advertisement' it would only make a new SDP Offer with "a=recvonly" when and if a new 'advertis
ement'
message arrives with Captures relevant to those Encodings. message arrives with Captures relevant to those Encodings.
</t> </t>
<t> <t>
Because of the constraints of SDP offer/answer and because new SDP Because of the constraints of SDP Offer/Answer and because new SDP
negotiations are generally more 'costly' than sending a new CLUE message, negotiations are generally more 'costly' than sending a new CLUE message,
implementations needing to make changes to both channels SHOULD prioritize implementations needing to make changes to both channels <bcp14>SHOULD</bcp14> p rioritize
sending the updated CLUE message over sending the new SDP message. The aim is sending the updated CLUE message over sending the new SDP message. The aim is
for the recipient to receive the CLUE changes before the SDP changes, allowing for the recipient to receive the CLUE changes before the SDP changes, allowing
the recipient to send their SDP answers without incomplete information, the recipient to send their SDP Answers without incomplete information and
reducing the number of new SDP offers required. reducing the number of new SDP Offers required.
</t> </t>
</section> </section>
</section> </section>
<section anchor="sec.capture-id" numbered="true" toc="default">
<section title="Interaction of CLUE protocol and RTP/RTCP CaptureID" anchor=" <name>Interaction of the CLUE Protocol and RTP/RTCP CaptureID</name>
sec.capture-id">
<t> <t>
The <xref target="I-D.ietf-clue-framework">CLUE Framework</xref> allows for The CLUE Framework <xref target="RFC8845" format="default"/> allows for
Multiple Content Captures (MCCs): Captures which contain multiple source Multiple Content Captures (MCCs): Captures that contain multiple source
Captures, whether composited into a single stream or switched based on some Captures, whether composited into a single stream or switched based on some
metric. metric.
</t> </t>
<t> <t>
The Captures that contribute to these MCCs may or may not be defined in the The Captures that contribute to these MCCs may or may not be defined in the
'advertisement' message. If they are defined and the MCC is providing them in 'advertisement' message. If they are defined and the MCC is providing them in
a switched format the recipient may wish to determine which originating source a switched format, the recipient may wish to determine which originating source
Capture is currently being provided, so that they can apply geometric Capture is currently being provided, so that they can apply geometric
corrections based on that Capture's geometry, or take some other action based corrections based on that Capture's geometry or take some other action based
on the original Capture information. on the original Capture information.
</t> </t>
<t> <t>
To do this, <xref target="I-D.ietf-clue-rtp-mapping" /> allows for the To do this, <xref target="RFC8849" format="default"/> allows for the CaptureID o
CaptureID of the originating Capture to be conveyed via RTP or RTCP. A Media f the originating Capture to be conveyed via RTP or RTCP. A Media
Provider sending switched media for an MCC with defined originating sources Provider sending switched media for an MCC with defined originating sources
MUST send the CaptureID in both RTP and RTCP, as described <bcp14>MUST</bcp14> send the CaptureID in both RTP and RTCP, as described
in the mapping document. in the mapping document.
</t> </t>
<section title="CaptureID reception during MCC redefinition"> <section numbered="true" toc="default">
<t> <name>CaptureID Reception during MCC Redefinition</name>
<t>
Because the RTP/RTCP CaptureID is delivered via a different channel to the Because the RTP/RTCP CaptureID is delivered via a different channel to the
'advertisement' message in which in the contents of the MCC are defined there 'advertisement' message in which in the contents of the MCC are defined, there
is an intrinsic race condition in cases in which the contents of an MCC are is an intrinsic race condition in cases where the contents of an MCC are
redefined. redefined.
</t> </t>
<t> <t>
When a Media Provider redefines an MCC which involves CaptureIDs, the When a Media Provider redefines an MCC that involves CaptureIDs, the
reception of the relevant CaptureIDs by the recipient will either lead or lag reception of the relevant CaptureIDs by the recipient will either lead or lag re
reception and processing of the new 'advertisement' message by the recipient. ception and the processing of the new 'advertisement' message by the recipient.
As such, a Media Consumer MUST NOT be disrupted by any of the following in any As such, a Media Consumer <bcp14>MUST NOT</bcp14> be disrupted by any of the fol
lowing scenarios in any
CLUE-controlled media stream it is receiving, whether that stream is for a CLUE-controlled media stream it is receiving, whether that stream is for a
static Capture or for an MCC (as any static Capture may be redefined to an MCC static Capture or for an MCC (as any static Capture may be redefined to an MCC
in a later 'advertisement' message): in a later 'advertisement' message):
<list style='symbols'> </t>
<t> <ul spacing="normal">
Receiving RTP or RTCP containing a CaptureID when the most recently processed <li>
'advertisement' message means that none are expected. By receiving RTP or RTCP containing a CaptureID when the most recently processed
</t> 'advertisement' message means that no media CaptureIDs are expected.
<t> </li>
Receiving RTP or RTCP without CaptureIDs when the most recently processed <li>
By receiving RTP or RTCP without CaptureIDs when the most recently processed
'advertisement' message means that media CaptureIDs are expected. 'advertisement' message means that media CaptureIDs are expected.
</t> </li>
<t> <li>
Receiving a CaptureID in RTP or RTCP for a Capture defined in the most By receiving a CaptureID in RTP or RTCP for a Capture defined in the most
recently processed 'advertisement' message, but which the same 'advertisement' recently processed 'advertisement' message, but which the same 'advertisement'
message does not include in the MCC. message does not include in the MCC.
</t> </li>
<t> <li>
Receiving a CaptureID in RTP or RTCP for a Capture not defined in the most By receiving a CaptureID in RTP or RTCP for a Capture not defined in the most
recently processed 'advertisement' message. recently processed 'advertisement' message.
</t> </li>
</list> </ul>
</t>
</section> </section>
</section> </section>
<section anchor="sec-bundle" numbered="true" toc="default">
<section title="Multiplexing of CLUE-controlled media using BUNDLE" anchor="s <name>Multiplexing of CLUE-Controlled Media Using BUNDLE</name>
ec-bundle"> <section numbered="true" toc="default">
<section title="Overview"> <name>Overview</name>
<t> <t>
A CLUE call may involve sending and/or receiving significant numbers of media A CLUE call may involve sending and/or receiving significant numbers of media
streams. Conventionally, media streams are sent and received on unique ports. streams. Conventionally, media streams are sent and received on unique ports.
However, each separate port used for this purpose may impose costs that a However, each separate port used for this purpose may impose costs that a
device wishes to avoid, such as the need to open that port on firewalls and device wishes to avoid, such as the need to open that port on firewalls and
NATs, the need to collect <xref target="RFC8445">ICE candidates</xref>, etc. NATs, the need to collect Interactive Connectivity Establishment (ICE) candidate
</t> s <xref target="RFC8445" format="default"/>, etc.
<t> </t>
The <xref target="I-D.ietf-mmusic-sdp-bundle-negotiation">BUNDLE</xref> <t>
extension can be used to negotiate the multiplexing of multiple media lines The BUNDLE extension <xref target="RFC8843" format="default"/> can be used to ne
gotiate the multiplexing of multiple media lines
onto a single 5-tuple for sending and receiving media, allowing devices in onto a single 5-tuple for sending and receiving media, allowing devices in
calls to another BUNDLE-supporting device to potentially avoid some of the calls to another BUNDLE-supporting device to potentially avoid some of the
above costs. above costs.
</t> </t>
<t> <t>
While CLUE-capable devices MAY support the BUNDLE extension for this purpose While CLUE-capable devices <bcp14>MAY</bcp14> support the BUNDLE extension for t
supporting the extension is not mandatory for a device to be CLUE-compliant. his purpose,
</t> supporting the extension is not mandatory for a device to be CLUE compliant.
<t> </t>
A CLUE-capable device that supports BUNDLE SHOULD also support <t>
<xref target="RFC5761">rtcp-mux</xref>. However, a CLUE-capable device that A CLUE-capable device that supports BUNDLE <bcp14>SHOULD</bcp14> also support rt
cp-mux
<xref target="RFC5761" format="default"/>. However, a CLUE-capable device that
supports rtcp-mux may or may not support BUNDLE. supports rtcp-mux may or may not support BUNDLE.
</t> </t>
</section> </section>
<section title="Usage of BUNDLE with CLUE"> <section numbered="true" toc="default">
<t> <name>Usage of BUNDLE with CLUE</name>
<t>
This specification imposes no additional requirements or restrictions on the This specification imposes no additional requirements or restrictions on the
usage of BUNDLE when used with CLUE. There is no restriction on combining usage of BUNDLE when used with CLUE. There is no restriction on combining
CLUE-controlled media lines and non-CLUE-controlled media lines in the same CLUE-controlled media lines and non-CLUE-controlled media lines in the same
BUNDLE group or in multiple such groups. However, there are several steps an BUNDLE group or in multiple such groups. However, there are several steps an
implementation may wish to take to ameliorate the cost and time requirements implementation may wish to take to ameliorate the cost and time requirements
of extra SDP offer/answer exchanges between CLUE and BUNDLE. of extra SDP Offer/Answer exchanges between CLUE and BUNDLE.
</t> </t>
<section title="Generating the Initial Offer"> <section numbered="true" toc="default">
<t> <name>Generating the Initial Offer</name>
BUNDLE mandates that the initial SDP offer MUST use a unique address for each <t>
BUNDLE mandates that the initial SDP Offer <bcp14>MUST</bcp14> use a unique addr
ess for each
"m=" line with a non-zero port. Because CLUE implementations generally will "m=" line with a non-zero port. Because CLUE implementations generally will
not include CLUE-controlled media lines with the exception of the data not include CLUE-controlled media lines, with the exception of the data
channel in the initial SDP offer, CLUE devices that support large numbers of channel in the initial SDP Offer, CLUE devices that support large numbers of
streams can avoid ever having to open large numbers of ports if they streams can avoid ever having to open large numbers of ports if they
successfully negotiate BUNDLE. successfully negotiate BUNDLE.
</t> </t>
<t> <t>
An implementation that does include CLUE-controlled media lines in its initial An implementation that does include CLUE-controlled media lines in its initial
SDP offer while also using BUNDLE must take care to avoid renderings its SDP Offer while also using BUNDLE must take care to avoid rendering its
CLUE-controlled media lines unusable in the event the far end does not CLUE-controlled media lines unusable in the event the far end does not
negotiate BUNDLE if it wishes to avoid the risk of additional SDP exchanges to negotiate BUNDLE if it wishes to avoid the risk of additional SDP exchanges to
resolve this issue. This is best achieved by not sending any CLUE-controlled resolve this issue. This is best achieved by not sending any CLUE-controlled
media lines in an initial offer with the 'bundle-only' attribute unless it has media lines in an initial offer with the 'bundle-only' attribute unless it has
been established via some other channel that the recipient supports and is been established via some other channel that the recipient supports and is
able to use BUNDLE. able to use BUNDLE.
</t> </t>
</section> </section>
<section title="Multiplexing of the data channel and RTP media"> <section numbered="true" toc="default">
<t> <name>Multiplexing of the Data Channel and RTP Media</name>
BUNDLE-supporting CLUE-capable devices MAY include the data channel in the <t>
same BUNDLE group as RTP media. In this case the device MUST be able to BUNDLE-supporting CLUE-capable devices <bcp14>MAY</bcp14> include the data chann
demultiplex the various transports - see section 9.2 of the el in the
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation">BUNDLE draft</xref>. If same BUNDLE group as RTP media. In this case, the device <bcp14>MUST</bcp14> be
the BUNDLE group includes other protocols than the data channel transported able to
via DTLS the device MUST also be able to differentiate the various protocols. demultiplex the various transports -- see Section <xref target="RFC8843" section
</t> ="9.2" sectionFormat="bare"/> of the BUNDLE specification <xref target="RFC8843"
</section> />. If
the BUNDLE group includes protocols other than the data channel transported
via DTLS, the device <bcp14>MUST</bcp14> also be able to differentiate the vario
us protocols.
</t>
</section>
</section> </section>
</section> </section>
<section title="Example: A call between two CLUE-capable Endpoints" anchor="s <section anchor="sec-clueexample" numbered="true" toc="default">
ec-clueexample"> <name>Example: A Call between Two CLUE-Capable Endpoints</name>
<t> <t>
This example illustrates a call between two CLUE-capable Endpoints. This example illustrates a call between two CLUE-capable Endpoints.
Alice, initiating the call, is a system with three cameras and three screens. Alice, initiating the call, is a system with three cameras and three screens.
Bob, receiving the call, is a system with two cameras and two screens. Bob, receiving the call, is a system with two cameras and two screens.
A call-flow diagram is presented, followed by a summary of each message. A call-flow diagram is presented, followed by a summary of each message.
</t> </t>
<t> <t keepWithPrevious="true">
To manage the size of this section the SDP snippets only illustrate video "m=" To manage the size of this section, the SDP snippets only illustrate video "m="
lines. SIP ACKs are not always discussed. Note that BUNDLE is not in use. lines. SIP ACKs are not always discussed. Note that BUNDLE is not in use.
</t> </t>
<t> <artwork name="" type="" align="left" alt=""><![CDATA[
<vspace blankLines="100" />
<figure>
<artwork>
<![CDATA[
+----------+ +-----------+ +----------+ +-----------+
| Alice | | Bob | | Alice | | Bob |
| | | | | | | |
+----+-----+ +-----+-----+ +----+-----+ +-----+-----+
| | | |
| | | |
| SIP INVITE 1 | | SIP INVITE 1 |
|--------------------------------->| |--------------------------------->|
| | | |
| | | |
skipping to change at line 879 skipping to change at line 891
|<---------------------------------| |<---------------------------------|
| | | |
| | | |
| | | |
|<########### MEDIA 3 ############>| |<########### MEDIA 3 ############>|
| 2 video A->B, 2 video B->A | | 2 video A->B, 2 video B->A |
|<################################>| |<################################>|
| | | |
| | | |
| | | |
v v v v ]]></artwork>
]]>
</artwork>
</figure>
</t>
<t> <t>
In SIP INVITE 1, Alice sends Bob a SIP INVITE including in the SDP body the In SIP INVITE 1, Alice sends Bob a SIP INVITE with the
basic audio and video capabilities and the data channel as per basic audio and video capabilities and data channel included in the SIP body as
<xref target="I-D.ietf-mmusic-sctp-sdp"/>. Alice also includes the "sip.clue" per
<xref target="RFC8841" format="default"/>. Alice also includes the "sip.clue"
media feature tag in the INVITE. A snippet of the SDP showing the grouping media feature tag in the INVITE. A snippet of the SDP showing the grouping
attribute and the video "m=" line are shown below. Alice has included a "CLUE" attribute and the video "m=" line are shown below. Alice has included a "CLUE"
group, and included the mid corresponding to a data channel in the group (3). group and the mid corresponding to a data channel in the group (3).
Note that Alice has chosen not to include any CLUE-controlled media in the Note that Alice has chosen not to include any CLUE-controlled media in the
initial offer - the mid value of the video line is not included in the "CLUE" initial offer -- the "mid" value of the video line is not included in the "CLUE"
group. group.
<figure> </t>
<artwork> <sourcecode type="sdp"><![CDATA[ ...
<![CDATA[
...
a=group:CLUE 3 a=group:CLUE 3
... ...
m=video 6002 RTP/AVP 96 m=video 6002 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600 a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv a=sendrecv
a=mid:2 a=mid:2
... ...
m=application 6100 UDP/DTLS/SCTP webrtc-datachannel m=application 6100 UDP/DTLS/SCTP webrtc-datachannel
a=setup:actpass a=setup:actpass
a=sctp-port: 5000 a=sctp-port: 5000
a=dcmap:2 subprotocol="CLUE";ordered=true a=dcmap:2 subprotocol="CLUE";ordered=true
a=mid:3 a=mid:3 ]]></sourcecode>
]]>
</artwork>
</figure>
</t>
<t> <t>
Bob responds with a similar SDP in SIP 200 OK 1, which also has a "CLUE" group Bob responds with a similar SDP in SIP 200 OK 1, which also has a "CLUE" group
including the mid value of a data channel; due to their similarity no SDP including the "mid" value of a data channel; due to their similarity, no SDP
snippet is shown here. Bob wishes to receive initial media, and so includes snippet is shown here. Bob wishes to receive initial media and thus includes
corresponding non-CLUE-controlled audio and video lines. Bob also includes the corresponding non-CLUE-controlled audio and video lines. Bob also includes the
"sip.clue" media feature tag in the 200 OK. Alice and Bob are each now able to "sip.clue" media feature tag in the 200 OK. Alice and Bob are each now able to
send a single audio and video stream. This is illustrated as MEDIA 1. send a single audio and video stream. This is illustrated as MEDIA 1.
</t> </t>
<t> <t>
With the successful initial SDP Offer/Answer exchange complete Alice and Bob With the successful initial SDP Offer/Answer exchange complete, Alice and Bob
are also free to negotiate the CLUE data channel. This is illustrated as CLUE are also free to negotiate the CLUE data channel. This is illustrated as CLUE
DATA CHANNEL ESTABLISHED. DATA CHANNEL ESTABLISHED.
</t> </t>
<t> <t>
Once the data channel is established CLUE protocol negotiation begins. In this Once the data channel is established, CLUE protocol negotiation begins. In this
case Bob was the DTLS client (sending a=active in his SDP answer) and hence is case, Bob was the DTLS client (sending "a=active" in his SDP Answer) and hence i
the CLUE Channel Initiator and sends a CLUE OPTIONS message describing his s
version support. On receiving that message Alice sends her corresponding CLUE the CLUE Channel Initiator. He sends a CLUE OPTIONS message describing his
version support. On receiving that message, Alice sends her corresponding CLUE
OPTIONS RESPONSE. OPTIONS RESPONSE.
</t> </t>
<t> <t>
With the OPTIONS phase complete Alice now sends her CLUE 'advertisement' With the OPTIONS phase complete, Alice now sends her CLUE 'advertisement'
message (CLUE ADVERTISEMENT 1). She advertises three static Captures message (CLUE ADVERTISEMENT 1). She advertises three static Captures
representing her three cameras. She also includes switched Captures suitable representing her three cameras. She also includes switched Captures suitable
for two- and one-screen systems. All of these Captures are in a single Capture for systems with one or two screens. All of these Captures are in a single Captu
Scene, with suitable Capture Scene Views to tell Bob that he should either re
subscribe to the three static Captures, the two switched Captures or the one Scene, with suitable Capture Scene Views that tell Bob he should
switched Capture. Alice has no simultaneity constraints, so includes all six subscribe to the three static Captures, the two switched Captures, or the one
Captures in one simultaneous set. Finally, Alice includes an Encoding Group switched Capture. Alice has no simultaneity constraints, so all six
with three Encoding IDs: "enc1", "enc2" and "enc3". These Encoding IDs aren't Captures are included in one simultaneous set. Finally, Alice includes an Encodi
currently valid, but will match the next SDP offer she sends. ng Group
with three Encoding IDs: "enc1", "enc2", and "enc3". These Encoding IDs aren't
currently valid but will match the next SDP Offer she sends.
</t> </t>
<t> <t>
Bob received CLUE ADVERTISEMENT 1 but does not yet send a 'configure' message, Bob received CLUE ADVERTISEMENT 1 but does not yet send a 'configure' message,
because he has not yet received Alice's Encoding information, so as yet he because he has not yet received Alice's Encoding information; thus, he
does not know if she will have sufficient resources to send him the two does not know if she will have sufficient resources in order to send him the two
streams he ideally wants at a quality he is happy with. Because Bob is not streams he ideally wants at a quality he is happy with. Because Bob is not
sending an immediate 'configure' message with the "ack" element set he must sending an immediate 'configure' message with the "ack" element set, he must
send an explicit 'ack' message (CLUE ACK 1) to signal receipt of CLUE send an explicit 'ack' message (CLUE ACK 1) to signal receipt of CLUE
ADVERTISEMENT 1. ADVERTISEMENT 1.
</t> </t>
<t> <t>
Bob also sends his CLUE 'advertisement' message (CLUE ADVERTISEMENT 2) - Bob also sends his CLUE 'advertisement' message (CLUE ADVERTISEMENT 2) --
though the diagram shows that this occurs after Alice sends CLUE ADVERTISEMENT though the diagram shows that this occurs after Alice sends CLUE ADVERTISEMENT
1 Bob sends his 'advertisement' message independently and does not wait for 1, Bob sends his 'advertisement' message independently and does not wait for
CLUE ADVERTISEMENT 1 to arrive. He advertises two static Captures representing CLUE ADVERTISEMENT 1 to arrive. He advertises two static Captures representing
his cameras. He also includes a single composed Capture for single-screen his cameras. He also includes a single composed Capture for single-screen
systems, in which he will composite the two camera views into a single video systems, in which he will composite the two camera views into a single video
stream. All three Captures are in a single Capture Scene, with suitable stream. All three Captures are in a single Capture Scene, with suitable
Capture Scene Views to tell Alice that she should either subscribe to the two Capture Scene Views that tell Alice she should subscribe to either the two
static Captures, or the single composed Capture. Bob also has no simultaneity static Captures or the single composed Capture. Bob also has no simultaneity
constraints, so includes all three Captures in one simultaneous set. Bob also constraints, so he includes all three Captures in one simultaneous set. Bob also
includes a single Encoding Group with two Encoding IDs: "foo" and "bar". includes a single Encoding Group with two Encoding IDs: "foo" and "bar".
</t> </t>
<t> <t>
Similarly, Alice receives CLUE ADVERTISEMENT 2 but does not yet send a Similarly, Alice receives CLUE ADVERTISEMENT 2 but does not yet send a
'configure' message, because she has not yet received Bob's Encoding 'configure' message, because she has not yet received Bob's Encoding
information, sending instead an 'ack' message (CLUE ACK 2). information; instead, she sends an 'ack' message (CLUE ACK 2).
</t> </t>
<t> <t>
Both sides have now sent their CLUE 'advertisement' messages and an SDP Both sides have now sent their CLUE 'advertisement' messages, and an SDP
exchange is required to negotiate Encodings. For simplicity, in this case exchange is required to negotiate Encodings. For simplicity, in this case,
Alice is shown sending an INVITE with a new offer; in many implementations Alice is shown sending an INVITE with a new offer; in many implementations,
both sides might send an INVITE, which would be resolved by use of the 491 both sides might send an INVITE, which would be resolved by use of the 491
Request Pending resolution mechanism from <xref target="RFC3261"/>. Request Pending resolution mechanism from <xref target="RFC3261" format="default "/>.
</t> </t>
<t> <t>
Alice now sends SIP INVITE 2. She maintains the sendrecv audio, video and CLUE Alice now sends SIP INVITE 2. She maintains the sendrecv audio, video, and CLUE
"m=" lines, and she adds three new sendonly "m=" lines to represent the three "m=" lines, and she adds three new sendonly "m=" lines to represent the three
CLUE-controlled Encodings she can send. Each of these "m=" lines has a label CLUE-controlled Encodings she can send. Each of these "m=" lines has a label
corresponding to one of the Encoding IDs from CLUE ADVERTISEMENT 1. Each also corresponding to one of the Encoding IDs from CLUE ADVERTISEMENT 1. Each also
has its mid added to the grouping attribute to show they are controlled by the has its mid added to the grouping attribute to show they are controlled by the
CLUE data channel. A snippet of the SDP showing the grouping attribute, data CLUE data channel. A snippet of the SDP showing the grouping attribute, data
channel and the video "m=" lines are shown below: channel, and video "m=" lines are shown below:
<figure> </t>
<artwork> <sourcecode type="sdp"><![CDATA[ ...
<![CDATA[
...
a=group:CLUE 3 4 5 6 a=group:CLUE 3 4 5 6
... ...
m=video 6002 RTP/AVP 96 m=video 6002 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600 a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv a=sendrecv
a=mid:2 a=mid:2
... ...
m=application 6100 UDP/DTLS/SCTP webrtc-datachannel m=application 6100 UDP/DTLS/SCTP webrtc-datachannel
a=sctp-port: 5000 a=sctp-port: 5000
skipping to change at line 1023 skipping to change at line 1023
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016 a=fmtp:96 profile-level-id=42e016
a=sendonly a=sendonly
a=mid:5 a=mid:5
a=label:enc2 a=label:enc2
m=video 6008 RTP/AVP 96 m=video 6008 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016 a=fmtp:96 profile-level-id=42e016
a=sendonly a=sendonly
a=mid:6 a=mid:6
a=label:enc3 a=label:enc3 ]]></sourcecode>
]]>
</artwork>
</figure>
</t>
<t> <t>
Bob now has all the information he needs to decide which streams to configure, Bob now has all the information he needs to decide which streams to configure,
allowing him to send both a CLUE 'configure' message and his SDP answer. As allowing him to send both a CLUE 'configure' message and his SDP Answer. As
such he now sends CLUE CONFIGURE 1. This requests the pair of switched such, he now sends CLUE CONFIGURE 1. This requests the pair of switched
Captures that represent Alice's scene, and he configures them with encoder ids Captures that represent Alice's scene, and he configures them with encoder ids
"enc1" and "enc2". "enc1" and "enc2".
</t> </t>
<t> <t>
Bob also sends his SDP answer as part of SIP 200 OK 2. Alongside his original Bob also sends his SDP Answer as part of SIP 200 OK 2. Alongside his original
audio, video and CLUE "m=" lines he includes three additional "m=" lines audio, video, and CLUE "m=" lines, he includes three additional "m=" lines
corresponding to the three added by Alice; two active recvonly "m= "lines and corresponding to the three added by Alice: two active recvonly "m= "lines and
an inactive "m=" line for the third. He adds their mid values to the grouping an inactive "m=" line for the third. He adds their "mid" values to the grouping
attribute to show they are controlled by the CLUE data channel. A snippet of attribute to show they are controlled by the CLUE data channel. A snippet of
the SDP showing the grouping attribute and the video "m=" lines are shown the SDP showing the grouping attribute and the video "m=" lines are shown
below (mid 100 represents the CLUE data channel, not shown): below (mid 100 represents the CLUE data channel, which is not shown):
<figure> </t>
<artwork> <sourcecode type="sdp"><![CDATA[ ...
<![CDATA[
...
a=group:CLUE 11 12 13 100 a=group:CLUE 11 12 13 100
... ...
m=video 58722 RTP/AVP 96 m=video 58722 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600 a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv a=sendrecv
a=mid:10 a=mid:10
... ...
m=video 58724 RTP/AVP 96 m=video 58724 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
skipping to change at line 1069 skipping to change at line 1063
a=mid:11 a=mid:11
m=video 58726 RTP/AVP 96 m=video 58726 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600 a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=recvonly a=recvonly
a=mid:12 a=mid:12
m=video 58728 RTP/AVP 96 m=video 58728 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600 a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=inactive a=inactive
a=mid:13 a=mid:13 ]]></sourcecode>
]]>
</artwork>
</figure>
</t>
<t> <t>
Alice receives Bob's message CLUE CONFIGURE 1 and sends CLUE CONFIGURE Alice receives Bob's CLUE CONFIGURE 1 message and sends CLUE CONFIGURE
RESPONSE 1 to ack its reception. She does not yet send the Capture Encodings RESPONSE 1 to acknowledge its reception. She does not yet send the Capture Encod
specified, because at this stage she hasn't processed Bob's answer SDP and so ings
specified, because at this stage, she hasn't processed Bob's answer SDP and thus
hasn't negotiated the ability for Bob to receive these streams. hasn't negotiated the ability for Bob to receive these streams.
</t> </t>
<t> <t>
On receiving SIP 200 OK 2 from Bob Alice sends her SIP ACK (SIP ACK 2). She is On receiving SIP 200 OK 2 from Bob, Alice sends her SIP ACK (SIP ACK 2). She is
now able to send the two streams of video Bob requested - this is illustrated now able to send the two streams of video Bob requested -- this is illustrated
as MEDIA 2. as MEDIA 2.
</t> </t>
<t> <t>
The constraints of offer/answer meant that Bob could not include his encoding The constraints of offer/answer meant that Bob could not include his Encoding
information as new "m=" lines in SIP 200 OK 2. As such Bob now sends SIP information as new "m=" lines in SIP 200 OK 2. As such, Bob now sends SIP
INVITE 3 to generate a new offer. Along with all the streams from SIP 200 OK 2 INVITE 3 to generate a new offer. Along with all the streams from SIP 200 OK 2,
Bob also includes two new sendonly streams. Each stream has a label Bob also includes two new sendonly streams. Each stream has a label
corresponding to the Encoding IDs in his CLUE ADVERTISEMENT 2 message. He also corresponding to the Encoding IDs in his CLUE ADVERTISEMENT 2 message. He also
adds their mid values to the grouping attribute to show they are controlled by adds their "mid" values to the grouping attribute to show they are controlled by
the CLUE data channel. A snippet of the SDP showing the grouping attribute and the CLUE data channel. A snippet of the SDP showing the grouping attribute and
the video "m=" lines are shown below (mid 100 represents the CLUE data the video "m=" lines are shown below (mid 100 represents the CLUE data
channel, not shown): channel, which is not shown):
<figure> </t>
<artwork> <sourcecode type="sdp"><![CDATA[ ...
<![CDATA[
...
a=group:CLUE 11 12 14 15 100 a=group:CLUE 11 12 14 15 100
... ...
m=video 58722 RTP/AVP 96 m=video 58722 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600 a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv a=sendrecv
a=mid:10 a=mid:10
... ...
m=video 58724 RTP/AVP 96 m=video 58724 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
skipping to change at line 1130 skipping to change at line 1118
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016 a=fmtp:96 profile-level-id=42e016
a=sendonly a=sendonly
a=label:foo a=label:foo
a=mid:14 a=mid:14
m=video 58730 RTP/AVP 96 m=video 58730 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016 a=fmtp:96 profile-level-id=42e016
a=sendonly a=sendonly
a=label:bar a=label:bar
a=mid:15 a=mid:15 ]]></sourcecode>
]]>
</artwork>
</figure>
</t>
<t> <t>
Having received this, Alice now has all the information she needs to send Having received this, Alice now has all the information she needs to send
her CLUE 'configure' message and her SDP answer. In CLUE CONFIGURE 2 she her CLUE 'configure' message and her SDP Answer. In CLUE CONFIGURE 2, she
requests the two static Captures from Bob, to be sent on Encodings "foo" and requests the two static Captures from Bob to be sent on Encodings "foo" and
"bar". "bar".
</t> </t>
<t> <t>
Alice also sends SIP 200 OK 3, matching two recvonly "m=" lines to Bob's new Alice also sends SIP 200 OK 3, matching two recvonly "m=" lines to Bob's new
sendonly lines. She includes their mid values in the grouping attribute to sendonly lines. She includes their "mid" values in the grouping attribute to
show they are controlled by the CLUE cdata hannel. Alice also now deactivates show they are controlled by the CLUE data channel. Alice then deactivates
the initial non-CLUE-controlled media, as bidirectional CLUE-controlled media the initial non-CLUE-controlled media, as bidirectional CLUE-controlled media
is now available. A snippet of the SDP showing the grouping attribute and the is now available. A snippet of the SDP showing the grouping attribute and the
video "m=" lines are shown below (mid 3 represents the data channel, not video "m=" lines are shown below (mid 3 represents the data channel, not
shown): shown):
<figure> </t>
<artwork> <sourcecode type="sdp"><![CDATA[ ...
<![CDATA[
...
a=group:CLUE 3 4 5 7 8 a=group:CLUE 3 4 5 7 8
... ...
m=video 0 RTP/AVP 96 m=video 0 RTP/AVP 96
a=mid:2 a=mid:2
... ...
m=video 6004 RTP/AVP 96 m=video 6004 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016 a=fmtp:96 profile-level-id=42e016
a=sendonly a=sendonly
a=mid:4 a=mid:4
skipping to change at line 1181 skipping to change at line 1163
a=mid:6 a=mid:6
m=video 6010 RTP/AVP 96 m=video 6010 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600 a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=recvonly a=recvonly
a=mid:7 a=mid:7
m=video 6012 RTP/AVP 96 m=video 6012 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600 a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=recvonly a=recvonly
a=mid:8 a=mid:8 ]]></sourcecode>
]]>
</artwork>
</figure>
</t>
<t> <t>
Bob receives Alice's message CLUE CONFIGURE 2 and sends CLUE CONFIGURE Bob receives Alice's CLUE CONFIGURE 2 message and sends CLUE CONFIGURE
RESPONSE 2 to ack its reception. Bob does not yet send the Capture Encodings RESPONSE 2 to acknowledge its reception. Bob does not yet send the Capture Encod
specified, because he hasn't yet received and processed Alice's SDP answer ings
specified, because he hasn't yet received and processed Alice's SDP Answer
and negotiated the ability to send these streams. and negotiated the ability to send these streams.
</t> </t>
<t> <t>
Finally, on receiving SIP 200 OK 3 Bob is now able to send the two streams of Finally, on receiving SIP 200 OK 3, Bob is now able to send the two streams of
video Alice requested - this is illustrated as MEDIA 3. video Alice requested -- this is illustrated as MEDIA 3.
</t> </t>
<t> <t>
Both sides of the call are now sending multiple video streams with their Both sides of the call are now sending multiple video streams with their
sources defined via CLUE negotiation. As the call progresses either side can sources defined via CLUE negotiation. As the call progresses, either side can
send new 'advertisement' or 'configure' message or new SDP offer/answers to send a new 'advertisement' or 'configure' message or the new SDP Offers/Answers
add, remove or change what they have available or want to receive. to
add, remove, or change what they have available or want to receive.
</t> </t>
</section> </section>
<section anchor="sec-nonclueexample" numbered="true" toc="default">
<section title="Example: A call between a CLUE-capable and non-CLUE Endpoint" <name>Example: A Call between a CLUE-Capable and Non-CLUE Endpoint</name>
anchor="sec-nonclueexample">
<t> <t>
In this brief example Alice is a CLUE-capable Endpoint making a call to Bob, In this brief example, Alice is a CLUE-capable Endpoint making a call to Bob,
who is not CLUE-capable (i.e. is not able to use the CLUE protocol). who is not CLUE capable (i.e., is not able to use the CLUE protocol).
</t> </t>
<figure> <artwork name="" type="" align="left" alt=""><![CDATA[
<artwork>
<![CDATA[
+----------+ +-----------+ +----------+ +-----------+
| Alice | | Bob | | Alice | | Bob |
| | | | | | | |
+----+-----+ +-----+-----+ +----+-----+ +-----+-----+
| | | |
| | | |
| SIP INVITE 1 | | SIP INVITE 1 |
|--------------------------------->| |--------------------------------->|
| | | |
| | | |
skipping to change at line 1239 skipping to change at line 1214
| | | |
| | | |
| | | |
|<########### MEDIA 1 ############>| |<########### MEDIA 1 ############>|
| 1 video A->B, 1 video B->A | | 1 video A->B, 1 video B->A |
|<################################>| |<################################>|
| | | |
| | | |
| | | |
| | | |
v v v v ]]></artwork>
]]>
</artwork>
</figure>
<t> <t>
In SIP INVITE 1, Alice sends Bob a SIP INVITE including in the SDP body the In SIP INVITE 1, Alice sends Bob a SIP INVITE including the
basic audio and video capabilities and the data channel as per basic audio and video capabilities and data channel in the SDP body as per
<xref target="I-D.ietf-mmusic-sctp-sdp"/>. Alice also includes the "sip.clue" <xref target="RFC8841" format="default"/>. Alice also includes the "sip.clue"
media feature tag in the INVITE. A snippet of the SDP showing the grouping media feature tag in the INVITE. A snippet of the SDP showing the grouping
attribute and the video "m=" line are shown below. Alice has included a "CLUE" attribute and the video "m=" line are shown below. Alice has included a "CLUE"
group, and included the mid corresponding to a data channel in the group (3). group and the mid corresponding to a data channel in the group (3).
Note that Alice has chosen not to include any CLUE-controlled media in the Note that Alice has chosen not to include any CLUE-controlled media in the
initial offer - the mid value of the video line is not included in the "CLUE" initial offer -- the "mid" value of the video line is not included in the "CLUE"
group. group.
<figure> </t>
<artwork> <sourcecode type="sdp"><![CDATA[ ...
<![CDATA[
...
a=group:CLUE 3 a=group:CLUE 3
... ...
m=video 6002 RTP/AVP 96 m=video 6002 RTP/AVP 96
a=rtpmap:96 H264/90000 a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600 a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv a=sendrecv
a=mid:2 a=mid:2
... ...
m=application 6100 UDP/DTLS/SCTP webrtc-datachannel m=application 6100 UDP/DTLS/SCTP webrtc-datachannel
a=sctp-port: 5000 a=sctp-port: 5000
a=dcmap:2 subprotocol="CLUE";ordered=true a=dcmap:2 subprotocol="CLUE";ordered=true
a=mid:3 a=mid:3 ]]></sourcecode>
]]>
</artwork>
</figure>
</t>
<t> <t>
Bob is not CLUE-capable, and hence does not recognize the "CLUE" semantic for Bob is not CLUE capable and hence does not recognize the "CLUE" semantic for
grouping attribute, nor does he support the data channel. IN SIP 200 OK 1 he the grouping attribute, nor does he support the data channel. IN SIP 200 OK 1, h
responds with an answer with audio and video, but with the data channel e
responds with an answer that includes audio and video, but with the data channel
zeroed. zeroed.
</t> </t>
<t> <t>
From the lack of a CLUE group Alice understands that Bob does not support From the lack of a CLUE group, Alice understands that Bob does not support
CLUE, or does not wish to use it. Both sides are now able to send a single CLUE, or does not wish to use it. Both sides are now able to send a single
audio and video stream to each other. Alice at this point begins to send her audio and video stream to each other. At this point, Alice begins to send her
fallback video: in this case likely a switched view from whichever camera fallback video: in this case, it's likely a switched view from whichever camera
shows the current loudest participant on her side. shows the current loudest participant on her side.
</t> </t>
</section> </section>
<section title="Acknowledgements">
<t>
Besides the authors, the team focusing on this draft consists of:
Roni Even,
Simon Pietro-Romano,
Roberta Presta.
</t>
<t>
Christian Groves, Jonathan Lennox and Adam Roach have contributed detailed
comments and suggestions.
</t>
</section>
<section title="IANA Considerations"> <section numbered="true" toc="default">
<section title="New SDP Grouping Framework Attribute"> <name>IANA Considerations</name>
<t> <section numbered="true" toc="default">
<name>New SDP Grouping Framework Attribute</name>
<t>
This document registers the following semantics with IANA in the This document registers the following semantics with IANA in the
"Semantics for the "group" SDP Attribute" subregistry (under the "Semantics for the 'group' SDP Attribute" subregistry (under the
"Session Description Protocol (SDP) Parameters" registry per "Session Description Protocol (SDP) Parameters" registry) per
<xref target="RFC5888"/>: <xref target="RFC5888" format="default"/>:
</t> </t>
<figure>
<artwork> <table anchor="IANA_table_1" align="left">
<![CDATA[ <thead>
Semantics Token Reference <tr>
CLUE-controlled m-line CLUE [this draft] <th align='center'>Semantics</th>
]]> <th align='center'>Token</th>
</artwork> <th align='center'>Mux Category</th>
</figure> <th align='center'>Reference</th>
</tr>
</thead>
<tbody>
<tr>
<td align="center">CLUE-controlled "m=" line</td>
<td align="left">CLUE</td>
<td align="left">NORMAL</td>
<td align="left">RFC 8848</td>
</tr>
</tbody>
</table>
</section> </section>
<section title="New SIP Media Feature Tag"> <section numbered="true" toc="default">
<t> <name>New SIP Media Feature Tag</name>
This specification registers a new media feature tag in the <t>
<xref target="RFC3261">SIP</xref> tree per the procedures defined in This specification registers a new media feature tag in the SIP
<xref target="RFC2506"/> and <xref target="RFC3840"/>. <xref target="RFC3261" format="default"/> tree per the procedures defined in
</t> <xref target="RFC2506" format="default"/> and <xref target="RFC3840" format="def
<t> ault"/>.
Media feature tag name: sip.clue </t>
</t> <dl newline="false" spacing="normal">
<t> <dt>Media feature tag name:</dt><dd>sip.clue</dd>
ASN.1 Identifier: [to be assigned]
</t> <dt>ASN.1 Identifier:</dt><dd>30</dd>
<t>
Summary of the media feature indicated by this tag: This feature tag indicates <dt>Summary of the media feature indicated by this tag:</dt><dd>This feature tag
that the device supports CLUE-controlled media. indicates
</t> that the device supports CLUE-controlled media.</dd>
<t>
Values appropriate for use with this feature tag: Boolean. <dt>Values appropriate for use with this feature tag:</dt><dd>Boolean.</dd>
</t>
<t> <dt>The feature tag is intended primarily for use in the following
The feature tag is intended primarily for use in the following applications, protocols, services, or negotiation mechanisms:</dt>
applications, protocols, services, or negotiation mechanisms: <dd><t><br/>This feature tag is most useful in a communications application for
</t> describing the capabilities of a device to use the CLUE control protocol to nego
<t> tiate the use of multiple media streams.</t></dd>
This feature tag is most useful in a communications application for
describing the capabilities of a device to use the CLUE control protocol to <dt>Related standards or documents:</dt><dd>RFC 8848</dd>
negotiate the use of multiple media streams.
</t> <dt>Security Considerations:</dt><dd>Security considerations for this media
<t> feature tag are discussed in <xref target="sec.security" format="default"/> of
Related standards or documents: [this draft] RFC 8848.</dd>
</t>
<t> <dt>Name(s) &amp; email address(es) of person(s) to contact for further
Security Considerations: Security considerations for this media information:</dt><dd>Internet Engineering Steering Group &lt;iesg@ietf.org&gt;</
feature tag are discussed in <xref target="sec.security" /> of dd>
[this draft].
</t> <dt>Intended usage:</dt><dd>COMMON</dd>
<t> </dl>
Name(s) &amp; email address(es) of person(s) to contact for further
information:
</t>
<t><list style='symbols'>
<t>
Internet Engineering Steering Group: iesg@ietf.org
</t>
</list></t>
<t>
Intended usage: COMMON
</t>
</section> </section>
</section> </section>
<section title="Security Considerations" anchor="sec.security"> <section anchor="sec.security" numbered="true" toc="default">
<name>Security Considerations</name>
<t> <t>
CLUE makes use of a number of protocols and mechanisms, either defined by CLUE CLUE makes use of a number of protocols and mechanisms, either defined by CLUE
or long-standing. The security considerations section of the or long-standing. The Security Considerations section of the
<xref target="I-D.ietf-clue-framework">CLUE Framework</xref> addresses the CLUE Framework document <xref target="RFC8845" format="default"/> addresses the
need to secure these mechanisms by following the recommendations of the need to secure these mechanisms by following the recommendations of the
individual protocols. individual protocols.
</t> </t>
<t> <t>
Beyond the need to secure the constituent protocols, the use of CLUE does Beyond the need to secure the constituent protocols, the use of CLUE does
impose additional security concerns. One area of increased risk involves the impose additional security concerns. One area of increased risk involves the
potential for a malicious party to subvert a CLUE-capable device to attack a potential for a malicious party to subvert a CLUE-capable device to attack a
third party by driving large volumes of media (particularly video) traffic at third party by driving large volumes of media (particularly video) traffic at
them by establishing a connection to the CLUE-capable device and directing the them by establishing a connection to the CLUE-capable device and directing the
media to the victim. While this is a risk for all media devices, a media to the victim. While this is a risk for all media devices, a
CLUE-capable device may allow the attacker to configure multiple media streams CLUE-capable device may allow the attacker to configure multiple media streams
to be sent, significantly increasing the volume of traffic directed at the to be sent, significantly increasing the volume of traffic directed at the
victim. victim.
</t> </t>
<t> <t>
This attack can be prevented by ensuring that the media recipient intends to This attack can be prevented by ensuring that the media recipient intends to
receive the media packets. As such all CLUE-capable devices MUST support key receive the media packets. As such, all CLUE-capable devices <bcp14>MUST</bcp14>
negotiation and receiver intent assurance via support key
<xref target="RFC5763">DTLS-SRTP</xref> on CLUE-controlled RTP "m=" lines, and negotiation and receiver intent assurance via DTLS / Secure Real-time Transport
MUST use it or some other mechanism that provides receiver intent assurance. Protocol (SRTP) <xref target="RFC5763" format="default"/> on CLUE-controlled RTP
"m=" lines, and they
<bcp14>MUST</bcp14> use it or some other mechanism that provides receiver intent
assurance.
All CLUE-controlled RTP "m" lines must be secured and implemented using All CLUE-controlled RTP "m" lines must be secured and implemented using
mechanisms such as <xref target="RFC3711">SRTP</xref>. CLUE implementations mechanisms such as SRTP <xref target="RFC3711" format="default"/>. CLUE implemen
MAY choose not to require the use of SRTP to secure legacy tations
<bcp14>MAY</bcp14> choose not to require the use of SRTP to secure legacy
(non-CLUE-controlled) media for backwards compatibility with older SIP clients (non-CLUE-controlled) media for backwards compatibility with older SIP clients
that are incapable of supporting it. that are incapable of supporting it.
</t> </t>
<t> <t>
CLUE also defines a new media feature tag that indicates CLUE support. This CLUE also defines a new media feature tag that indicates CLUE support. This
tag may be present even in non-CLUE calls, which increases the metadata tag may be present even in non-CLUE calls, which increases the metadata
available about the sending device, which can help an attacker differentiate available about the sending device; this can help an attacker differentiate
between multiple devices and help them identify otherwise anonymised users between multiple devices and identify otherwise anonymized users
via the fingerprint of features their device supports. To prevent this, SIP via the fingerprint of features their device supports. To prevent this, SIP
signaling used to set up CLUE sessions SHOULD always be encrypted using signaling used to set up CLUE sessions <bcp14>SHOULD</bcp14> always be encrypted
<xref target="RFC5630">TLS</xref>. using
TLS <xref target="RFC5630" format="default"/>.
</t> </t>
<t> <t>
The CLUE protocol also carries additional information that could be used to The CLUE protocol also carries additional information that could be used to
help fingerprint a particular user or to identify the specific version of help fingerprint a particular user or to identify the specific version of
software being used. software being used.
<xref target="I-D.ietf-clue-protocol">CLUE Framework</xref> provides details The CLUE Framework <xref target="RFC8847" format="default"/> provides details
of these issues and how to mitigate them. about these issues and how to mitigate them.
</t> </t>
</section> </section>
</middle>
<back>
<section title="Change History"> <references>
<t>
Note to RFC Editor: please remove this section prior to publication
</t>
<t><list style='hanging'>
<t hangText="-15:"> Revision by Rob Hanton
<list style='symbols'>
<t>
Clarified that using an 'EncID' defined in SDP in an CLUE ADVERTISEMENT message
is only a SHOULD because of the inherent race conditions about the ordering of t
he SDP and CLUE message. In contrast, changed the use of 'EncID' in a CLUE CONFI
GURE message to a MUST as that is defined by the far end and so there is no way
for the sending of the CONFIGURE to anticipate it.
</t>
<t>
Updated the description of handling the failure of the CLUE channel to reflect t
he fact that the protocol state machine now returns to the IDLE state on failure
rather than a specific termination state, which also means defining an allowanc
e for the CLUE channel being recovered.
</t>
<t>
Updated all instances of advertisment, configure and ack messages throughout to
match the styling of the protocol document
</t>
<t>
Security section updated to make DTLs-SRTP mandatory to use as well as support u
nless intent assurance is provided by some other mechanism per mailing list prop
osal (to resolve the concern from a previous IETF session of those wanting to us
e CLUE in a closed environment where intent assurance was provided by other pror
ietary mechanisms).
</t>
<t>
Removed OID value for "sip.clue" media feature tag pending its actual assignment
on registration, leaving a placeholder
</t>
<t>
All lower-case uses of 'must', 'should' and 'may' reviewed and a few made normat
ive
</t>
<t>
Fixed various spelling mistakes, clarified grammar, and fixed a copy/paste error
.
</t>
<t>
Updated boilerplate to RFC 8174
</t>
<t>
Some informative references moved to normative.
</t>
</list>
</t>
<t hangText="-14:"> Revision by Rob Hanton
<list style='symbols'>
<t>
Reference to RFC5245 updated to RFC8445
</t>
<t>
Updated my name to reflect surname change (Hansen to Hanton).
</t>
<t>
Reviewed recent changes to clue protocol document and concluded that none
affected this document
</t>
<t>
Added recommendation that the SDP O/A spec and clue protocol be read prior to
this document
</t>
<t>
Several acronyms expanded at the point of initial use
</t>
<t>
Some unnecessary normative language replaced with prose
</t>
</list>
</t>
<t hangText="-13:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Added a section on handling failures of the protocol channel or data channel mid
-call -
instructions are that media must continue as if the clue channel were still esta
blished
and unchanged until CLUE is disabled by either side via SDP exchange.
</t>
<t>
Example in section on efficient operation with non-atomic transactions has had a
ll
normative language removed and is now entirely descriptive (normative language r
etained
in the non-example portion).
</t>
<t>
draft-ietf-clue-protocol-14 reviewed for relevant changes, and use of CLUE ACK a
nd
RESPONSE messages made consistent with that document (ADVERTISEMENT ACKNOWLEDGEM
ENT and
CONFIGURE RESPONSE respectively).
</t>
<t>
Order of authors revised to reflect updates since Jan 2014.
</t>
</list>
</t>
<t hangText="-12:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Title change to expand and elucidate our totally-not-contrived acronym
</t>
<t>
Explicit reference to RFC3840 added when first mentioning media feature tags
</t>
<t>
Have standardised references to Clue protocol messages to ADVERTISEMENT, CONFIGU
RE and ACK, in line with section 12.4.1. of the protocol document (though the pr
otocol document also uses ADV and CONF).
</t>
<t>
'MUST' in opening paragraph of 4.2 changed from normative 'MUST' to logical 'mus
t'
</t>
<t>
Per his request, removed Cristian's company affiliation and changed his email ad
dress
</t>
<t>
Clarified that an implementation that chooses not to send media during the initi
al negotiation process must still send RTCP as normal
</t>
<t>
Rewrote the section on adding/remove clue m-lines after the initial exchange to
make clear that this is just standard SDP. For non-clue controlled lines, recomm
ended they are deactivated by zeroing the port when turning them off after clue
is successfully negotiated.
</t>
<t>
Added guidance that an initial offer containing clue-controlled m-lines MUST NOT
set them bundle-only unless they somehow know the far end actually supports BUN
DLE
</t>
<t>
Added section saying that CLUE devices that do BUNDLE SHOULD do rtcp-mux, but th
at the requirement doesn't exist in the other direction (eg, supporting rtcp-mux
does not require or imply the need to implement BUNDLE)
</t>
<t>
For clue-controlled m-lines where the sender included more encodings than the re
cipient wants, have standardised on using "a=inactive" to not receive RTP on the
m (previously had a mix of "a=inactive" or port 0, or in some cases did not spec
ify).
</t>
<t>
Page break added before the big ladder diagram in the example
</t>
<t>
Have added a direction attribute to the SDP example in the data channel, and mad
e explicit that Bob is the DTLS client and hence the CLUE Channel Initiator.
</t>
<t>
Have removed all language that referenced the possibility of having multiple CLU
E groups
</t>
<t>
Removed names appearing in the authors list from the acknowledgements
</t>
<t>
Changed the contact for the IANA registration to iesg@ietf.org
</t>
<t>
Security section updated to clarify that DTLS-SRTP must be supported (as opposed
to DTLS) and removed the reference to RFC7202.
</t>
<t>
Other syntactic tweaks based on Paul and Adam's feedback
</t>
</list>
</t>
<t hangText="-11:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Some informative references added for SIP and SDP.
</t>
<t>
'a=mid' lines added to example m-lines with port 0, per RFC5888 section 6.
</t>
<t>
Instace of 'must' changed to normative 'MUST', along with various minor
clarifications and corrections.
</t>
<t>
Abstract made standalone without citations, per RFC7322 section 4.3.
</t>
<t>
RFC editor note added to remove this section.
</t>
</list>
</t>
<t hangText="-10:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Changes to draft-ietf-clue-protocol between 07 and 11 reviewed to ensure
compatibility between documents has been maintained.
</t>
<t>
Expanded the portion of the document related to fingerprinting with info on
the CLUE channel as well as SIP.
</t>
</list>
</t>
<t hangText="-09:"> Revision by Rob Hansen
<list style='symbols'>
<t>
A few minor spelling tweaks
</t>
<t>
Made removing the CLUE group mandatory when disabling CLUE mid-call. Made
clear that any CLUE-controlled m-lines should be disabled or else how they're
used is up to the implementation.
</t>
</list>
</t>
<t hangText="-08:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Spelling and grammar fixes from Paul and Christian gratefully adopted
</t>
<t>
Expanded the section on disabling CLUE mid-call to make explicit the actions
required to disable the CLUE channel gracefully, or to handle someone else
doing the same.
</t>
<t>
Made a number of fixes to the example call flow to better reflect the
recommendations in the document.
</t>
</list>
</t>
<t hangText="-07:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Removed the entire 'Media line directionality' section as a discussion of the
pros/cons of using bidirectional vs unidirectional schemes wasn't suitable for
a finalised version. The unidirectionality requirement is covered normatively
in an earlier section.
</t>
<t>
BUNDLE no longer includes an address synchronisation step so the suggestion
to wait until that done has been replaced with some general language about
following any negotiated extensions.
</t>
<t>
Added OPTIONS negotiation to the example flow, and revised the flow to ensure
it matched protocol document.
</t>
<t>
Section on not sending CLUE control media until CLUE negotiation completes
narrowed to notify that only RTP should not be sent until negotiation
completes and add RTCP to the list of things that should be sent as normal, in
line with a=inactive.
</t>
<t>
Make explicit that m=recvonly lines don't need to have a label, as only
m=sendonly lines are referenced by CLUE protocol messages.
</t>
<t>
Fix formatting of IANA sections. Improve syntax of feature tag section in line
with Paul's suggestions. Definition of feature tag narrowed to be multiple
media lines *negotiated via CLUE protocol* rather than more generic 'multiple
media lines'.
</t>
<t>
General corrections to grammar, spelling and readability based on Christian,
Paul and Mark; in many cases suggested text was gratefully accepted.
</t>
</list>
</t>
<t hangText="-06:"> Revision by Rob Hansen
<list style='symbols'>
<t>
State machine interactions updated to match versions in -04 of protocol doc.
</t>
<t>
Section on encoding updated to specify both encID and encodingID from data
model doc.
</t>
<t>
Removed the limitations on describing H264 encoding limits using SDP syntax
as an open issue.
</t>
<t>
Previous draft had SRTP and DTLS mandatory to implement and to use on CLUE-
controlled m lines. Current version has DTLS mandatory to implement, and
'security' mandatory to use but does not define what that security is.
</t>
<t>
Terminology reference to framework doc reinforced. All terminology that
duplicates framework removed. All text updated with capitalisation that
matches framework document's terminology.
</t>
<t>
SDP example syntax updated to match that of ietf-clue-datachannel
and hence ietf-mmusic-data-channel-sdpneg.
</t>
</list>
</t>
<t hangText="-05:"> Revision by Rob Hansen
<list style='symbols'>
<t>
SRTP/DTLS made mandatory for CLUE-controlled media lines.
</t>
<t>
IANA consideration section added (text as proposed by Christian Groves).
</t>
<t>
Includes provision for dependent streams on seperate "m" lines having the same
encID as their parent "m" line.
</t>
<t>
References to putting CLUE-controlled media and data channels in more than one
CLUE group removed, since the document no longer supports using more than one
CLUE group.
</t>
<t>
Section on CLUE controlled media restrictions still applying even if the call
does not end up being CLUE enabled being rewritten to hopefully be clearer.
</t>
<t>
Other minor syntax improvements.
</t>
</list>
</t>
<t hangText="-04:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Updated DTLS/SCTP channel syntax in examples to fix errors and match latest
format defined in draft-ietf-mmusic-sctp-sdp-07.
</t>
<t>
Clarified the behaviour if an SDP offer includes a CLUE-controlled "m" line
and the answer accepts that "m" line but without CLUE control of that line.
</t>
<t>
Added a new section on the sending and receiving of CaptureIDs in RTP and
RTCP. Includes a section on the necessity of the receiver coping with
unexpected CaptureIDs (or the lack thereof) due to MCCs being redefined in
new Advertisement messages.
</t>
<t>
Added reminder on IANA section on registering grouping semantic and media
feature tag, removed the less formal sections that did the same job.
</t>
<t>
Fixed and clarified issues raised by Christian's document review.
</t>
<t>
Added a number of security considerations.
</t>
</list>
</t>
<t hangText="-03:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Clarified text on not rejecting messages because they contain unknown encIDs.
</t>
<t>
Removed normative language in section on accepting/rejecting
non-CLUE-controlled media in the initial answer.
</t>
<t>
Example SDP updated to include the data channel "m" lines.
</t>
<t>
Example call flow updated to show disablement of non-CLUE-controlled media
once CLUE-controlled media is flowing.
</t>
</list>
</t>
<t hangText="-02:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Added section on not accepting non-CLUE-controlled "m" lines in the initial
answer when CLUE is to be negotiated.
</t>
<t>
Removed previous language attempting to describe media restrictions
for CLUE-controlled "m" lines that had not been configured, and replaced
it with much more accurate 'treat as "a=inactive" was set'.
</t>
<t>
Made label element mandatory for CLUE-controlled media (was previously
"SHOULD include", but there didn't seem a good reason for this - anyone
wishing to include the "m" line but not immediately use it in CLUE can simply
leave it out of the &lt;encodingIDList&gt;.)
</t>
<t>
Added a section on the specifics of relating encodings in SDP to &lt;encID&gt;
elements in the CLUE protocol, including the fact that both Advertisement and
Configure messages reference the *encoding* (eg, in the Configure case the
sender of the Configure message includes the labels of the recipient's "m"
lines as their &lt;encID&gt; contents).
</t>
<t>
Minor revisions to the section on complying with normative SDP/CLUEstate
machine language to clarify that these were not new normative language, merely
that existing normative language still applies.
</t>
<t>
Removed appendices which previously contained information to be transferred
to the protocol and data channel drafts. Removed other text that
discussed alternatives to the current approach.
</t>
<t>
Cleaned up some 'todo' text.
</t>
</list>
</t>
<t hangText="-01:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Revised terminology - removed the term 'CLUE-enabled' device as insufficiently
distinct from 'CLUE-capable' and instead added a term for 'CLUE-enabled'
calls.
</t>
<t>
Removed text forbidding RTCP and instead added text that ICE/DTLS negotiation
for CLUE controlled media must be done as normal irrespective of CLUE
negotiation.
</t>
<t>
Changed 'sip.telepresence' to 'sip.clue' and 'TELEPRESENCE' grouping semantic
back to CLUE.
</t>
<t>
Made it mandatory to have exactly one mid corresponding to a data channel in a
CLUE group
</t>
<t>
Forbade having multiple CLUE groups unless a specification for doing so is
published.
</t>
<t>
Refactored SDP-related text; previously the encoding information had been in
the "initial offer" section despite the fact that we recommend that the
initial offer doesn't actually include any encodings. I moved the
specifications of encodings and how they're received to an earlier, seperate
section.
</t>
<t>
Added text on how the state machines in CLUE and SDP are allowed to affect one
another, and further recommendations on how a device should handle the sending
of CLUE and SDP changes.
</t>
</list>
</t>
<t hangText="-00:"> Revision by Rob Hansen
<list style='symbols'>
<t>
Submitted as -00 working group document
</t>
</list>
</t>
<t hangText="draft-kyzivat-08:"> Revisions by Rob Hansen
<list style='symbols'>
<t>
Added media feature tag for CLUE support ('sip.telepresence')
</t>
<t>
Changed grouping semantic from 'CLUE' to 'TELEPRESENCE'
</t>
<t>
Restructured document to be more centred on the grouping semantic and its use
with O/A
</t>
<t>
Lots of additional text on usage of the grouping semantic
</t>
<t>
Stricter definition of CLUE-controlled m lines and how they work
</t>
<t>
Some additional text on defining what happens when CLUE supports is added or
removed
</t>
<t>
Added details on when to not send RTCP for CLUE-controlled "m" lines.
</t>
<t>
Added a section on using BUNDLE with CLUE
</t>
<t>
Updated data channel references to point at new WG document rather than
indivual draft
</t>
</list>
</t>
<t hangText="draft-kyzivat-07:"> Revisions by Rob Hansen
<list style='symbols'>
<t>
Removed the text providing arguments for encoding limits being in SDP and
Encoding Groups in the CLUE protocol in favor of the specifics of how to
negotiate encodings in SDP
</t>
<t>
Added normative language on the setting up of a CLUE call, and added sections
on mid-call changes to the
CLUE status.
</t>
<t>
Added references to <xref target="I-D.ietf-clue-datachannel" /> where
appropriate.
</t>
<t>
Added some terminology for various types of CLUE and non-CLUE states of
operation.
</t>
<t>
Moved language related to topics that should be in
<xref target="I-D.ietf-clue-datachannel" /> and
<xref target="I-D.ietf-clue-protocol" />, but that has not yet been resolved
in those documents, into
an appendix.
</t>
</list>
</t>
<t hangText="draft-kyzivat-06:"> Revisions by Rob Hansen
<list style='symbols'>
<t>
Removed CLUE message XML schema and details that are now in
draft-presta-clue-protocol
</t>
<t>
Encoding limits in SDP section updated to note that this has been investigated
and discussed and is the current working assumption of the WG, though
consensus has not been fully achieved.
</t>
<t>
A section has also been added on the current mandation of unidirectional
"m" lines.
</t>
<t>
Updated CLUE messaging in example call flow to match
draft-presta-clue-protocol-03
</t>
</list>
</t>
<t hangText="draft-kyzivat-05:"> Revisions by pkyzivat:
<list style='symbols'>
<t>
Specified versioning model and mechanism.
</t>
<t>
Added explicit response to all messages.
</t>
<t>
Rearranged text to work with the above changes.
(Which rendered diff almost useless.)
</t>
</list>
</t>
<t hangText="draft-kyzivat-04:"> Revisions by Rob Hansen: ???</t>
<t hangText="draft-kyzivat-03:"> Revisions by pkyzivat:
<list style='symbols'>
<t>
Added a syntax section with an XML schema for CLUE messages.
This is a strawhorse, and is very incomplete, but it establishes
a template for doing this based on elements defined in the data model.
(Thanks to Roberta for help with this!)
</t>
<t>
Did some rewording to fit the syntax section in and reference it.
</t>
<t>
Did some relatively minor restructuring of the document to make
it flow better in a logical way.
</t>
</list>
</t> <name>References</name>
<t hangText="draft-kyzivat-02:"> A bunch of revisions by pkyzivat: <references>
<list style='symbols'> <name>Normative References</name>
<t>
Moved roberta's call flows to a more appropriate place in the document.
</t>
<t>
New section on versioning.
</t>
<t>
New section on NAK.
</t>
<t>
A couple of possible alternatives for message acknowledgment.
</t>
<t>
Some discussion of when/how to signal changes in provider state.
</t>
<t>
Some discussion about the handling of transport errors.
</t>
<t>
Added a change history section.
</t>
</list>
These were developed by Lennard Xiao, Christian Groves and Paul,
so added Lennard and Christian as authors.
</t> <!--draft-ietf-clue-framework-25 is 8845 -->
<t hangText="draft-kyzivat-01:"> <reference anchor='RFC8845' target='https://www.rfc-editor.org/info/rfc8845'>
<front>
<title>Framework for Telepresence Multi-Streams</title>
<author initials='M' surname='Duckworth' fullname='Mark Duckworth' role='editor'
>
<organization />
</author>
<author initials='A' surname='Pepperell' fullname='Andrew Pepperell'>
<organization />
</author>
<author initials='S' surname='Wenger' fullname='Stephan Wenger'>
<organization />
</author>
<date month='January' year='2021' />
</front>
<seriesInfo name='RFC' value='8845' />
<seriesInfo name='DOI' value='10.17487/RFC8845' />
</reference>
Updated by roberta to include some sample call flows. <!-- &I-D.ietf-clue-data-model-schema; is 8846-->
<reference anchor="RFC8846" target="http://www.rfc-editor.org/info/rfc8846">
<front>
<title>An XML Schema for the Controlling Multiple Streams for Telepr
esence (CLUE) Data Model</title>
<author initials="R" surname="Presta" fullname="Roberta Presta">
<organization/>
</author>
<author initials="S P." surname="Romano" fullname="Simon Romano">
<organization/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8846"/>
<seriesInfo name="DOI" value="10.17487/RFC8846"/>
</reference>
</t> <!--draft-ietf-clue-protocol-19 is 8847 -->
<t hangText="draft-kyzivat-00:"> <reference anchor='RFC8847' target='https://www.rfc-editor.org/info/rfc8847'>
<front>
<title>Protocol for Controlling Multiple Streams for Telepresence (CLUE)</title>
<author initials='R' surname='Presta' fullname='Roberta Presta'>
<organization />
</author>
<author initials='S P.' surname='Romano' fullname='Simon Pietro Romano'>
<organization />
</author>
<date month='January' year='2021' />
</front>
<seriesInfo name="RFC" value="8847" />
<seriesInfo name='DOI' value='10.17487/RFC8847' />
</reference>
Initial version by pkyzivat. Established general outline for the document, <!--draft-ietf-clue-datachannel-18 is 8850 -->
and specified a few things thought to represent wg consensus. <reference anchor="RFC8850" target="https://www.rfc-editor.org/info/rfc8850">
<front>
<title>Controlling Multiple Streams for Telepresence (CLUE) Protocol Data
Channel</title>
<author initials="C." surname="Holmberg" fullname="Christer Holmberg">
<organization/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8850"/>
<seriesInfo name="DOI" value="10.17487/RFC8850"/>
</reference>
</t> <!--draft-ietf-clue-rtp-mapping-14: 8849 -->
</list></t> <reference anchor='RFC8849' target="https://www.rfc-editor.org/info/rfc8849">
</section> <front>
<title>Mapping RTP Streams to Controlling Multiple Streams for Telepresence
(CLUE) Media Captures</title>
<author initials='R' surname='Even' fullname='Roni Even'>
<organization />
</author>
<author initials='J' surname='Lennox' fullname='Jonathan Lennox'>
<organization />
</author>
<date month='January' year='2021' />
</front>
<seriesInfo name='RFC' value='8849' />
<seriesInfo name="DOI" value="10.17487/RFC8849"/>
</reference>
</middle> <!-- draft-ietf-mmusic-sctp-sdp -->
<reference anchor="RFC8841" target="https://www.rfc-editor.org/info/rfc8841">
<front>
<title>Session Description Protocol (SDP) Offer/Answer Procedures for
Stream Control Transmission Protocol (SCTP) over Datagram Transport Layer
Security (DTLS) Transport</title>
<author initials="C." surname="Holmberg" fullname="Christer Holmberg">
<organization />
</author>
<author initials="R." surname="Shpount" fullname="Roman Shpount">
<organization />
</author>
<author initials="S." surname="Loreto" fullname="Salvatore Loreto">
<organization />
</author>
<author initials="G." surname="Camarillo" fullname="Gonzalo Camarillo">
<organization />
</author>
<date month="January" year="2021" />
</front>
<seriesInfo name="RFC" value="8841" />
<seriesInfo name="DOI" value="10.17487/RFC8841"/>
</reference>
<back> <!--draft-ietf-mmusic-data-channel-sdpneg-28; in REF - part of C238-->
<references title="Normative References"> <reference anchor="RFC8864" target="https://www.rfc-editor.org/info/rfc8864">
<?rfc include="reference.I-D.ietf-clue-framework"?> <front>
<?rfc include="reference.I-D.ietf-clue-data-model-schema"?> <title>Negotiation Data Channels Using the Session Description
<?rfc include="reference.I-D.ietf-clue-protocol"?> Protocol (SDP)</title>
<?rfc include="reference.I-D.ietf-clue-datachannel"?> <author fullname="Keith Drage" initials="K." surname="Drage">
<?rfc include="reference.I-D.ietf-clue-rtp-mapping"?> <organization>Unaffiliated</organization>
<?rfc include="reference.I-D.ietf-rtcweb-data-channel"?> </author>
<?rfc include="reference.I-D.ietf-mmusic-sctp-sdp"?> <author fullname="Raju Makaraju" initials="M." surname="Makaraju">
<?rfc include="reference.I-D.ietf-mmusic-data-channel-sdpneg"?> <organization>Nokia</organization>
<?rfc include="reference.I-D.ietf-mmusic-sdp-bundle-negotiation"?> </author>
<?rfc include="reference.RFC.2119"?> <author fullname="Richard Ejzak" initials="R." surname="Ejzak">
<?rfc include="reference.RFC.3711"?> <organization>Unaffiliated</organization>
<?rfc include="reference.RFC.3840"?> </author>
<?rfc include="reference.RFC.4574"?> <author fullname="Jerome Marcon" initials="J." surname="Marcon">
<?rfc include="reference.RFC.5763"?> <organization>Unaffiliated</organization>
<?rfc include="reference.RFC.5888"?> </author>
<?rfc include="reference.RFC.8174"?> <author fullname="Roni Even" initials="R." surname="Even" role="editor">
</references> <organization>Huawei</organization>
<references title="Informative References"> </author>
<?rfc include="reference.RFC.2506"?> <date month="January" year="2021"/>
<?rfc include="reference.RFC.3261"?> </front>
<?rfc include="reference.RFC.3264"?> <seriesInfo name="RFC" value="8864"/>
<?rfc include="reference.RFC.3311"?> <seriesInfo name="DOI" value="10.17487/RFC8864"/>
<?rfc include="reference.RFC.4566"?> </reference>
<?rfc include="reference.RFC.8445"?>
<?rfc include="reference.RFC.5630"?>
<?rfc include="reference.RFC.5761"?>
<?rfc include="reference.RFC.6184"?>
</references>
</back> <!-- draft-ietf-mmusic-sdp-bundle-negotiation (RFC 8843) -->
<reference anchor="RFC8843" target="https://www.rfc-editor.org/info/rfc8843"
>
<front>
<title>Negotiating Media Multiplexing Using the Session Description Prot
ocol (SDP)</title>
<author initials="C" surname="Holmberg" fullname="Christer Holmberg">
<organization/>
</author>
<author initials="H" surname="Alvestrand" fullname="Harald Alvestrand">
<organization/>
</author>
<author initials="C" surname="Jennings" fullname="Cullen Jennings">
<organization/>
</author>
<date month="January" year="2021"/>
</front>
<seriesInfo name="RFC" value="8843"/>
<seriesInfo name="DOI" value="10.17487/RFC8843"/>
</reference>
<!-- draft-ietf-rtcweb-data-channel: 8831 -->
<reference anchor="RFC8831" target="https://www.rfc-editor.org/info/rfc8831">
<front>
<title>WebRTC Data Channels</title>
<author initials="R" surname="Jesup" fullname="Randell Jesup">
<organization/>
</author>
<author initials="S" surname="Loreto" fullname="Salvatore Loreto">
<organization/>
</author>
<author initials="M" surname="Tüxen" fullname="Michael Tüxen">
<organization/>
</author>
<date month='January' year='2021'/>
</front>
<seriesInfo name="RFC" value="8831"/>
<seriesInfo name="DOI" value="10.17487/RFC8831"/>
</reference>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.2119.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.3711.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.3840.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.4574.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.5763.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.5888.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.8174.xml"/>
</references>
<references>
<name>Informative References</name>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.2506.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.3261.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.3264.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.3311.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.4566.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.5630.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.5761.xml"/>
<xi:include
href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.
6184.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.8445.xml"/>
</references>
</references>
<section numbered="false" toc="default">
<name>Acknowledgements</name>
<t>
Besides the authors, the team focusing on this document consists of:
<contact fullname="Roni Even"/>, <contact fullname="Simon Pietro Romano"/>, and
<contact fullname="Roberta Presta"/>.
</t>
<t>
<contact fullname="Christian Groves"/>, <contact fullname="Jonathan Lennox"/>, a
nd <contact fullname="Adam Roach"/> have contributed detailed
comments and suggestions.
</t>
</section>
</back>
</rfc> </rfc>
 End of changes. 225 change blocks. 
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