rfc8866v1.txt   rfc8866.txt 
Internet Engineering Task Force (IETF) A. Begen Internet Engineering Task Force (IETF) A. Begen
Request for Comments: 8866 Networked Media Request for Comments: 8866 Networked Media
Obsoletes: 4566 P. Kyzivat Obsoletes: 4566 P. Kyzivat
Category: Standards Track Category: Standards Track
ISSN: 2070-1721 C. Perkins ISSN: 2070-1721 C. Perkins
University of Glasgow University of Glasgow
M. Handley M. Handley
UCL UCL
July 2020 September 2020
SDP: Session Description Protocol SDP: Session Description Protocol
Abstract Abstract
This memo defines the Session Description Protocol (SDP). SDP is This memo defines the Session Description Protocol (SDP). SDP is
intended for describing multimedia sessions for the purposes of intended for describing multimedia sessions for the purposes of
session announcement, session invitation, and other forms of session announcement, session invitation, and other forms of
multimedia session initiation. This document obsoletes RFC 4566. multimedia session initiation. This document obsoletes RFC 4566.
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6.11. sdplang (SDP Language) 6.11. sdplang (SDP Language)
6.12. lang (Language) 6.12. lang (Language)
6.13. framerate (Frame Rate) 6.13. framerate (Frame Rate)
6.14. quality 6.14. quality
6.15. fmtp (Format Parameters) 6.15. fmtp (Format Parameters)
7. Security Considerations 7. Security Considerations
8. IANA Considerations 8. IANA Considerations
8.1. The "application/sdp" Media Type 8.1. The "application/sdp" Media Type
8.2. Registration of SDP Parameters with IANA 8.2. Registration of SDP Parameters with IANA
8.2.1. Registration Procedure 8.2.1. Registration Procedure
8.2.2. Media Types ("media") 8.2.2. Media Types (<media>)
8.2.3. Transport Protocols ("proto") 8.2.3. Transport Protocols (<proto>)
8.2.4. Attribute Names ("att-field") 8.2.4. Attribute Names (<attribute-name>)
8.2.5. Bandwidth Specifiers ("bwtype") 8.2.5. Bandwidth Specifiers (<bwtype>)
8.2.6. Network Types ("nettype") 8.2.6. Network Types (<nettype>)
8.2.7. Address Types ("addrtype") 8.2.7. Address Types (<addrtype>)
8.3. Encryption Key Access Methods (OBSOLETE) 8.3. Encryption Key Access Methods (OBSOLETE)
9. SDP Grammar 9. SDP Grammar
10. Summary of Changes from RFC 4566 10. Summary of Changes from RFC 4566
11. References 11. References
11.1. Normative References 11.1. Normative References
11.2. Informative References 11.2. Informative References
Acknowledgements Acknowledgements
Authors' Addresses Authors' Addresses
1. Introduction 1. Introduction
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Alternative means of conveying session descriptions include Alternative means of conveying session descriptions include
electronic mail and the World Wide Web (WWW). For both email and WWW electronic mail and the World Wide Web (WWW). For both email and WWW
distribution, the media type "application/sdp" is used. This enables distribution, the media type "application/sdp" is used. This enables
the automatic launching of applications for participation in the the automatic launching of applications for participation in the
session from the WWW client or mail reader in a standard manner. session from the WWW client or mail reader in a standard manner.
Note that descriptions of multicast sessions sent only via email or Note that descriptions of multicast sessions sent only via email or
the WWW do not have the property that the receiver of a session the WWW do not have the property that the receiver of a session
description can necessarily receive the session because the multicast description can necessarily receive the session because the multicast
sessions may be restricted in scope, and access to the WWW server or sessions may be restricted in scope, and access to the WWW server or
reception of email is possible outside this scope. reception of email is possibly outside this scope.
3.4. Multicast Session Announcement 3.4. Multicast Session Announcement
In order to assist the advertisement of multicast multimedia In order to assist the advertisement of multicast multimedia
conferences and other multicast sessions, and to communicate the conferences and other multicast sessions, and to communicate the
relevant session setup information to prospective participants, a relevant session setup information to prospective participants, a
distributed session directory may be used. An instance of such a distributed session directory may be used. An instance of such a
session directory periodically sends packets containing a description session directory periodically sends packets containing a description
of the session to a well-known multicast group. These advertisements of the session to a well-known multicast group. These advertisements
are received by other session directories such that potential remote are received by other session directories such that potential remote
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use of URIs to indicate remote resources is subject to the security use of URIs to indicate remote resources is subject to the security
considerations from [RFC3986].) considerations from [RFC3986].)
4.4. Internationalization 4.4. Internationalization
The SDP specification recommends the use of the ISO 10646 character The SDP specification recommends the use of the ISO 10646 character
set in the UTF-8 encoding [RFC3629] to allow many different languages set in the UTF-8 encoding [RFC3629] to allow many different languages
to be represented. However, to assist in compact representations, to be represented. However, to assist in compact representations,
SDP also allows other character sets such as [ISO.8859-1.1998] to be SDP also allows other character sets such as [ISO.8859-1.1998] to be
used when desired. Internationalization only applies to free-text used when desired. Internationalization only applies to free-text
sub-fields (session name and background information), and not to SDP subfields (session name and background information), and not to SDP
as a whole. as a whole.
5. SDP Specification 5. SDP Specification
An SDP description is denoted by the media type "application/sdp" An SDP description is denoted by the media type "application/sdp"
(See Section 8). (See Section 8).
An SDP description is entirely textual. SDP field names and An SDP description is entirely textual. SDP field names and
attribute names use only the US-ASCII subset of UTF-8 [RFC3629], but attribute names use only the US-ASCII subset of UTF-8 [RFC3629], but
textual fields and attribute values MAY use the full ISO 10646 textual fields and attribute values MAY use the full ISO 10646
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with strict order and formatting rules so that most errors would with strict order and formatting rules so that most errors would
result in malformed session descriptions that could be detected result in malformed session descriptions that could be detected
easily and discarded. easily and discarded.
An SDP description consists of a number of lines of text of the form: An SDP description consists of a number of lines of text of the form:
<type>=<value> <type>=<value>
where <type> is exactly one case-significant character and <value> is where <type> is exactly one case-significant character and <value> is
structured text whose format depends on <type>. In general, <value> structured text whose format depends on <type>. In general, <value>
is either a number of sub-fields delimited by a single space is either a number of subfields delimited by a single space character
character or a free format string, and is case-significant unless a or a free format string, and is case-significant unless a specific
specific field defines otherwise. Whitespace separators are not used field defines otherwise. Whitespace separators are not used on
on either side of the "=" sign, however, the value can contain a either side of the "=" sign, however, the value can contain a leading
leading whitespace as part of its syntax, i.e., that whitespace is whitespace as part of its syntax, i.e., that whitespace is part of
part of the value. the value.
An SDP description MUST conform to the syntax defined in Section 9. An SDP description MUST conform to the syntax defined in Section 9.
The following is an overview of the syntax. The following is an overview of the syntax.
An SDP description consists of a session-level section followed by An SDP description consists of a session-level section followed by
zero or more media descriptions. The session-level section starts zero or more media descriptions. The session-level section starts
with a "v=" line and continues to the first media description (or the with a "v=" line and continues to the first media description (or the
end of the whole description, whichever comes first). Each media end of the whole description, whichever comes first). Each media
description starts with an "m=" line and continues to the next media description starts with an "m=" line and continues to the next media
description or the end of the whole session description, whichever description or the end of the whole session description, whichever
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m=audio 49180 RTP/AVP 0 m=audio 49180 RTP/AVP 0
m=video 51372 RTP/AVP 99 m=video 51372 RTP/AVP 99
c=IN IP6 2001:db8::2 c=IN IP6 2001:db8::2
a=rtpmap:99 h263-1998/90000 a=rtpmap:99 h263-1998/90000
Text-containing fields such as the session-name-field and Text-containing fields such as the session-name-field and
information-field are octet strings that may contain any octet with information-field are octet strings that may contain any octet with
the exceptions of 0x00 (Nul), 0x0a (ASCII newline), and 0x0d (ASCII the exceptions of 0x00 (Nul), 0x0a (ASCII newline), and 0x0d (ASCII
carriage return). The sequence CRLF (0x0d0a) is used to end a line, carriage return). The sequence CRLF (0x0d0a) is used to end a line,
although parsers SHOULD be tolerant and also accept lines terminated although parsers SHOULD be tolerant and also accept lines terminated
with a single newline character. If the "a=charset" attribute is not with a single newline character. If the "a=charset:" attribute is
present, these octet strings MUST be interpreted as containing not present, these octet strings MUST be interpreted as containing
ISO-10646 characters in UTF-8 encoding. When the "a=charset" ISO-10646 characters in UTF-8 encoding. When the "a=charset:"
attribute is present the session-name-field, information-field, and attribute is present the session-name-field, information-field, and
some attribute fields are interpreted according to the selected some attribute fields are interpreted according to the selected
character set. character set.
A session description can contain domain names in the "o=", "u=", A session description can contain domain names in the "o=", "u=",
"e=", "c=", and "a=" lines. Any domain name used in SDP MUST comply "e=", "c=", and "a=" lines. Any domain name used in SDP MUST comply
with [RFC1034] and [RFC1035]. Internationalized domain names (IDNs) with [RFC1034] and [RFC1035]. Internationalized domain names (IDNs)
MUST be represented using the ASCII Compatible Encoding (ACE) form MUST be represented using the ASCII Compatible Encoding (ACE) form
defined in [RFC5890] and MUST NOT be directly represented in UTF-8 or defined in [RFC5890] and MUST NOT be directly represented in UTF-8 or
any other encoding (this requirement is for compatibility with any other encoding (this requirement is for compatibility with
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<nettype> is a text string giving the type of network. Initially, <nettype> is a text string giving the type of network. Initially,
"IN" is defined to have the meaning "Internet", but other values "IN" is defined to have the meaning "Internet", but other values
MAY be registered in the future (see Section 8). MAY be registered in the future (see Section 8).
<addrtype> is a text string giving the type of the address that <addrtype> is a text string giving the type of the address that
follows. Initially, "IP4" and "IP6" are defined, but other values follows. Initially, "IP4" and "IP6" are defined, but other values
MAY be registered in the future (see Section 8). MAY be registered in the future (see Section 8).
<unicast-address> is an address of the machine from which the <unicast-address> is an address of the machine from which the
session was created. For an address type of IP4, this is either a session was created. For an address type of "IP4", this is either
fully qualified domain name of the machine or the dotted-decimal a fully qualified domain name of the machine or the dotted-decimal
representation of an IP version 4 address of the machine. For an representation of an IP version 4 address of the machine. For an
address type of IP6, this is either a fully qualified domain name address type of "IP6", this is either a fully qualified domain
of the machine or the address of the machine represented as name of the machine or the address of the machine represented as
specified in Section 4 of [RFC5952]. For both IP4 and IP6, the specified in Section 4 of [RFC5952]. For both "IP4" and "IP6",
fully qualified domain name is the form that SHOULD be given the fully qualified domain name is the form that SHOULD be given
unless this is unavailable, in which case a globally unique unless this is unavailable, in which case a globally unique
address MAY be substituted. address MAY be substituted.
In general, the "o=" line serves as a globally unique identifier for In general, the "o=" line serves as a globally unique identifier for
this version of the session description, and the sub-fields excepting this version of the session description, and the subfields excepting
the version, taken together identify the session irrespective of any the version, taken together identify the session irrespective of any
modifications. modifications.
For privacy reasons, it is sometimes desirable to obfuscate the For privacy reasons, it is sometimes desirable to obfuscate the
username and IP address of the session originator. If this is a username and IP address of the session originator. If this is a
concern, an arbitrary <username> and private <unicast-address> MAY be concern, an arbitrary <username> and private <unicast-address> MAY be
chosen to populate the "o=" line, provided that these are selected in chosen to populate the "o=" line, provided that these are selected in
a manner that does not affect the global uniqueness of the field. a manner that does not affect the global uniqueness of the field.
5.3. Session Name ("s=") 5.3. Session Name ("s=")
s=<session name> s=<session name>
The "s=" line (session-name-field) is the textual session name. The "s=" line (session-name-field) is the textual session name.
There MUST be one and only one "s=" line per session description. There MUST be one and only one "s=" line per session description.
The "s=" line MUST NOT be empty. If a session has no meaningful The "s=" line MUST NOT be empty. If a session has no meaningful
name, then "s= " or "s=-" (i.e., a single space or dash as the name, then "s= " or "s=-" (i.e., a single space or dash as the
session name) is RECOMMENDED. If a session-level "a=charset" session name) is RECOMMENDED. If a session-level "a=charset:"
attribute is present, it specifies the character set used in the "s=" attribute is present, it specifies the character set used in the "s="
field. If a session-level "a=charset" attribute is not present, the field. If a session-level "a=charset:" attribute is not present, the
"s=" field MUST contain ISO 10646 characters in UTF-8 encoding. "s=" field MUST contain ISO 10646 characters in UTF-8 encoding.
5.4. Session Information ("i=") 5.4. Session Information ("i=")
i=<session information> i=<session information>
The "i=" line (information-field) provides textual information about The "i=" line (information-field) provides textual information about
the session. There can be at most one session-level "i=" line per the session. There can be at most one session-level "i=" line per
session description, and at most one "i=" line in each media session description, and at most one "i=" line in each media
description. Unless a media-level "i=" line is provided, the description. Unless a media-level "i=" line is provided, the
session-level "i=" line applies to that media description. If the session-level "i=" line applies to that media description. If the
"a=charset" attribute is present, it specifies the character set used "a=charset:" attribute is present, it specifies the character set
in the "i=" line. If the "a=charset" attribute is not present, the used in the "i=" line. If the "a=charset:" attribute is not present,
"i=" line MUST contain ISO 10646 characters in UTF-8 encoding. the "i=" line MUST contain ISO 10646 characters in UTF-8 encoding.
At most one "i=" line can be used for each media description. In At most one "i=" line can be used for each media description. In
media definitions, "i=" lines are primarily intended for labeling media definitions, "i=" lines are primarily intended for labeling
media streams. As such, they are most likely to be useful when a media streams. As such, they are most likely to be useful when a
single session has more than one distinct media stream of the same single session has more than one distinct media stream of the same
media type. An example would be two different whiteboards, one for media type. An example would be two different whiteboards, one for
slides and one for feedback and questions. slides and one for feedback and questions.
The "i=" line is intended to provide a free-form human-readable The "i=" line is intended to provide a free-form human-readable
description of the session or the purpose of a media stream. It is description of the session or the purpose of a media stream. It is
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e=j.doe@example.com (Jane Doe) e=j.doe@example.com (Jane Doe)
The alternative [RFC5322] name quoting convention is also allowed for The alternative [RFC5322] name quoting convention is also allowed for
both email addresses and phone numbers. For example: both email addresses and phone numbers. For example:
e=Jane Doe <j.doe@example.com> e=Jane Doe <j.doe@example.com>
The free text string SHOULD be in the ISO-10646 character set with The free text string SHOULD be in the ISO-10646 character set with
UTF-8 encoding, or alternatively in ISO-8859-1 or other encodings if UTF-8 encoding, or alternatively in ISO-8859-1 or other encodings if
the appropriate session-level "a=charset" attribute is set. the appropriate session-level "a=charset:" attribute is set.
5.7. Connection Information ("c=") 5.7. Connection Information ("c=")
c=<nettype> <addrtype> <connection-address> c=<nettype> <addrtype> <connection-address>
The "c=" line (connection-field) contains information necessary to The "c=" line (connection-field) contains information necessary to
establish a network connection. establish a network connection.
A session description MUST contain either at least one "c=" line in A session description MUST contain either at least one "c=" line in
each media description or a single "c=" line at the session level. each media description or a single "c=" line at the session level.
It MAY contain a single session-level "c=" line and additional media- It MAY contain a single session-level "c=" line and additional media-
level "c=" line(s) per-media-description, in which case the media- level "c=" line(s) per-media-description, in which case the media-
level values override the session-level settings for the respective level values override the session-level settings for the respective
media. media.
The first sub-field (<nettype>) is the network type, which is a text The first subfield (<nettype>) is the network type, which is a text
string giving the type of network. Initially, "IN" is defined to string giving the type of network. Initially, "IN" is defined to
have the meaning "Internet", but other values MAY be registered in have the meaning "Internet", but other values MAY be registered in
the future (see Section 8). the future (see Section 8).
The second sub-field (<addrtype>) is the address type. This allows The second subfield (<addrtype>) is the address type. This allows
SDP to be used for sessions that are not IP based. This memo only SDP to be used for sessions that are not IP based. This memo only
defines IP4 and IP6, but other values MAY be registered in the future defines "IP4" and "IP6", but other values MAY be registered in the
(see Section 8). future (see Section 8).
The third sub-field (<connection-address>) is the connection address. The third subfield (<connection-address>) is the connection address.
Additional sub-fields MAY be added after the connection address Additional subfields MAY be added after the connection address
depending on the value of the <addrtype> sub-field. depending on the value of the <addrtype> subfield.
When the <addrtype> is IP4 or IP6, the connection address is defined When the <addrtype> is "IP4" or "IP6", the connection address is
as follows: defined as follows:
* If the session is multicast, the connection address will be an IP * If the session is multicast, the connection address will be an IP
multicast group address. If the session is not multicast, then multicast group address. If the session is not multicast, then
the connection address contains the unicast IP address of the the connection address contains the unicast IP address of the
expected data source, data relay, or data sink as determined by expected data source, data relay, or data sink as determined by
additional attribute-fields (Section 5.13). It is not expected additional attribute-fields (Section 5.13). It is not expected
that unicast addresses will be given in a session description that that unicast addresses will be given in a session description that
is communicated by a multicast announcement, though this is not is communicated by a multicast announcement, though this is not
prohibited. prohibited.
* Sessions using an IP4 multicast connection address MUST also have * Sessions using an "IP4" multicast connection address MUST also
a time to live (TTL) value present in addition to the multicast have a time to live (TTL) value present in addition to the
address. The TTL and the address together define the scope with multicast address. The TTL and the address together define the
which multicast packets sent in this session will be sent. TTL scope with which multicast packets sent in this session will be
values MUST be in the range 0-255. Although the TTL MUST be sent. TTL values MUST be in the range 0-255. Although the TTL
specified, its use to scope multicast traffic is deprecated; MUST be specified, its use to scope multicast traffic is
applications SHOULD use an administratively scoped address deprecated; applications SHOULD use an administratively scoped
instead. address instead.
The TTL for the session is appended to the address using a slash as a The TTL for the session is appended to the address using a slash as a
separator. An example is: separator. An example is:
c=IN IP4 233.252.0.1/127 c=IN IP4 233.252.0.1/127
IP6 multicast does not use TTL scoping, and hence the TTL value MUST "IP6" multicast does not use TTL scoping, and hence the TTL value
NOT be present for IP6 multicast. It is expected that IPv6 scoped MUST NOT be present for "IP6" multicast. It is expected that IPv6
addresses will be used to limit the scope of multimedia conferences. scoped addresses will be used to limit the scope of multimedia
conferences.
Hierarchical or layered encoding schemes are data streams where the Hierarchical or layered encoding schemes are data streams where the
encoding from a single media source is split into a number of layers. encoding from a single media source is split into a number of layers.
The receiver can choose the desired quality (and hence bandwidth) by The receiver can choose the desired quality (and hence bandwidth) by
only subscribing to a subset of these layers. Such layered encodings only subscribing to a subset of these layers. Such layered encodings
are normally transmitted in multiple multicast groups to allow are normally transmitted in multiple multicast groups to allow
multicast pruning. This technique keeps unwanted traffic from sites multicast pruning. This technique keeps unwanted traffic from sites
only requiring certain levels of the hierarchy. For applications only requiring certain levels of the hierarchy. For applications
requiring multiple multicast groups, we allow the following notation requiring multiple multicast groups, we allow the following notation
to be used for the connection address: to be used for the connection address:
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Similarly, an IPv6 example would be: Similarly, an IPv6 example would be:
c=IN IP6 ff00::db8:0:101/3 c=IN IP6 ff00::db8:0:101/3
which is semantically equivalent to: which is semantically equivalent to:
c=IN IP6 ff00::db8:0:101 c=IN IP6 ff00::db8:0:101
c=IN IP6 ff00::db8:0:102 c=IN IP6 ff00::db8:0:102
c=IN IP6 ff00::db8:0:103 c=IN IP6 ff00::db8:0:103
(remember that the TTL sub-field is not present in IP6 multicast). (remember that the TTL subfield is not present in "IP6" multicast).
Multiple addresses or "c=" lines MAY be specified on a per media Multiple addresses or "c=" lines MAY be specified on a per media
description basis only if they provide multicast addresses for description basis only if they provide multicast addresses for
different layers in a hierarchical or layered encoding scheme. different layers in a hierarchical or layered encoding scheme.
Multiple addresses or "c=" lines MUST NOT be specified at session Multiple addresses or "c=" lines MUST NOT be specified at session
level. level.
The slash notation for multiple addresses described above MUST NOT be The slash notation for multiple addresses described above MUST NOT be
used for IP unicast addresses. used for IP unicast addresses.
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b=<bwtype>:<bandwidth> b=<bwtype>:<bandwidth>
The OPTIONAL "b=" line (bandwidth-field) denotes the proposed The OPTIONAL "b=" line (bandwidth-field) denotes the proposed
bandwidth to be used by the session or media description. The bandwidth to be used by the session or media description. The
<bwtype> is an alphanumeric modifier that provides the meaning of the <bwtype> is an alphanumeric modifier that provides the meaning of the
<bandwidth> number. Two values are defined in this specification, <bandwidth> number. Two values are defined in this specification,
but other values MAY be registered in the future (see Section 8 and but other values MAY be registered in the future (see Section 8 and
[RFC3556], [RFC3890]): [RFC3556], [RFC3890]):
CT If the bandwidth of a session is different from the bandwidth CT If the bandwidth of a session is different from the bandwidth
implicit from the scope, a "b=CT:..." line SHOULD be supplied for implicit from the scope, a "b=CT:" line SHOULD be supplied for the
the session giving the proposed upper limit to the bandwidth used session giving the proposed upper limit to the bandwidth used (the
(the "conference total" bandwidth). Similarly, if the bandwidth "conference total" bandwidth). Similarly, if the bandwidth of
of bundled media streams [RFC8843] in an "m=" line is different bundled media streams [RFC8843] in an "m=" line is different from
from the implicit value from the scope, a "b=CT:..." line SHOULD the implicit value from the scope, a "b=CT:" line SHOULD be
be supplied in the media level. The primary purpose of this is to supplied in the media level. The primary purpose of this is to
give an approximate idea as to whether two or more sessions (or give an approximate idea as to whether two or more sessions (or
bundled media streams) can coexist simultaneously. Note that CT bundled media streams) can coexist simultaneously. Note that a
gives a total bandwidth figure for all the media at all endpoints. "b=CT:" line gives a total bandwidth figure for all the media at
all endpoints.
The Mux Category for CT is NORMAL. This is discussed in The Mux Category for "b=CT:" is NORMAL. This is discussed in
[RFC8859]. [RFC8859].
AS The bandwidth is interpreted to be application specific (it will AS The bandwidth is interpreted to be application specific (it will
be the application's concept of maximum bandwidth). Normally, be the application's concept of maximum bandwidth). Normally,
this will coincide with what is set on the application's "maximum this will coincide with what is set on the application's "maximum
bandwidth" control if applicable. For RTP-based applications, AS bandwidth" control if applicable. For RTP-based applications, the
gives the RTP "session bandwidth" as defined in Section 6.2 of "b=AS:" line gives the RTP "session bandwidth" as defined in
[RFC3550]. Note that AS gives a bandwidth figure for a single Section 6.2 of [RFC3550]. Note that a "b=AS:" line gives a
media at a single endpoint, although there may be many endpoints bandwidth figure for a single media at a single endpoint, although
sending simultaneously. there may be many endpoints sending simultaneously.
The Mux Category for AS is SUM. This is discussed in [RFC8859]. The Mux Category for "b=AS:" is SUM. This is discussed in
[RFC8859].
[RFC4566] defined an "X-" prefix for <bwtype> names. This was [RFC4566] defined an "X-" prefix for <bwtype> names. This was
intended for experimental purposes only. For example: intended for experimental purposes only. For example:
b=X-YZ:128 b=X-YZ:128
Use of the "X-" prefix is NOT RECOMMENDED. Instead new (non "X-" Use of the "X-" prefix is NOT RECOMMENDED. Instead new (non "X-"
prefix) <bwtype> names SHOULD be defined, and then MUST be registered prefix) <bwtype> names SHOULD be defined, and then MUST be registered
with IANA in the standard namespace. SDP parsers MUST ignore with IANA in the standard namespace. SDP parsers MUST ignore
bandwidth-fields with unknown <bwtype> names. The <bwtype> names bandwidth-fields with unknown <bwtype> names. The <bwtype> names
skipping to change at line 828 skipping to change at line 831
regular repeat times, a repeat description, begun by an "r=" line regular repeat times, a repeat description, begun by an "r=" line
(see Section 5.10) can be included following the time-field -- in (see Section 5.10) can be included following the time-field -- in
which case the time-field specifies the start and stop times of the which case the time-field specifies the start and stop times of the
entire repeat sequence. entire repeat sequence.
The following example specifies two active intervals: The following example specifies two active intervals:
t=3724394400 3724398000 ; Mon 8-Jan-2018 10:00-11:00 UTC t=3724394400 3724398000 ; Mon 8-Jan-2018 10:00-11:00 UTC
t=3724484400 3724488000 ; Tue 9-Jan-2018 11:00-12:00 UTC t=3724484400 3724488000 ; Tue 9-Jan-2018 11:00-12:00 UTC
The first and second sub-fields of the time-field give the start and The first and second subfields of the time-field give the start and
stop times, respectively, for the session. These are the decimal stop times, respectively, for the session. These are the decimal
representation of time values in seconds since January 1, 1900 UTC. representation of time values in seconds since January 1, 1900 UTC.
To convert these values to Unix time (UTC), subtract decimal To convert these values to Unix time (UTC), subtract decimal
2208988800. 2208988800.
Some time representations will wrap in the year 2036. Because SDP Some time representations will wrap in the year 2036. Because SDP
uses an arbitrary length decimal representation, it does not have uses an arbitrary length decimal representation, it does not have
this issue. Implementations of SDP need to be prepared to handle this issue. Implementations of SDP need to be prepared to handle
these larger values. these larger values.
skipping to change at line 852 skipping to change at line 855
User interfaces SHOULD strongly discourage the creation of unbounded User interfaces SHOULD strongly discourage the creation of unbounded
and permanent sessions as they give no information about when the and permanent sessions as they give no information about when the
session is actually going to terminate, and so make scheduling session is actually going to terminate, and so make scheduling
difficult. difficult.
The general assumption may be made, when displaying unbounded The general assumption may be made, when displaying unbounded
sessions that have not timed out to the user, that an unbounded sessions that have not timed out to the user, that an unbounded
session will only be active until half an hour from the current time session will only be active until half an hour from the current time
or the session start time, whichever is the later. If behavior other or the session start time, whichever is the later. If behavior other
than this is required, an end-time SHOULD be given and modified as than this is required, a <stop-time> SHOULD be given and modified as
appropriate when new information becomes available about when the appropriate when new information becomes available about when the
session should really end. session should really end.
Permanent sessions may be shown to the user as never being active Permanent sessions may be shown to the user as never being active
unless there are associated repeat times that state precisely when unless there are associated repeat times that state precisely when
the session will be active. the session will be active.
5.10. Repeat Times ("r=") 5.10. Repeat Times ("r=")
r=<repeat interval> <active duration> <offsets from start-time> r=<repeat interval> <active duration> <offsets from start-time>
An"r=" line (repeat-field) specifies repeat times for a session. If An"r=" line (repeat-field) specifies repeat times for a session. If
needed to express complex schedules, multiple repeat-fields may be needed to express complex schedules, multiple repeat-fields may be
included. For example, if a session is active at 10am on Monday and included. For example, if a session is active at 10am on Monday and
11am on Tuesday for one hour each week for three months, then the 11am on Tuesday for one hour each week for three months, then the
<start-time> in the corresponding "t=" line would be the <start-time> in the corresponding "t=" line would be the
representation of 10am on the first Monday, the <repeat interval> representation of 10am on the first Monday, the <repeat interval>
would be 1 week, the <active duration> would be 1 hour, and the would be 1 week, the <active duration> would be 1 hour, and the
offsets would be zero and 25 hours. The corresponding "t=" line stop offsets would be zero and 25 hours. The corresponding "t=" line stop
time would be the representation of the end of the last session three time would be the representation of the end of the last session three
months later. By default, all sub-fields are in seconds, so the "r=" months later. By default, all subfields are in seconds, so the "r="
and "t=" lines might be the following: and "t=" lines might be the following:
t=3724394400 3730536000 ; Mon 8-Jan-2018 10:00-11:00 UTC t=3724394400 3730536000 ; Mon 8-Jan-2018 10:00-11:00 UTC
; Tues 20-Mar-2018 12:00 UTC ; Tues 20-Mar-2018 12:00 UTC
r=604800 3600 0 90000 ; 1 week, 1 hour, zero, 25 hours r=604800 3600 0 90000 ; 1 week, 1 hour, zero, 25 hours
To make the description more compact, times may also be given in To make the description more compact, times may also be given in
units of days, hours, or minutes. The syntax for these is a number units of days, hours, or minutes. The syntax for these is a number
immediately followed by a single case-sensitive character. immediately followed by a single case-sensitive character.
Fractional units are not allowed -- a smaller unit should be used Fractional units are not allowed -- a smaller unit should be used
skipping to change at line 896 skipping to change at line 899
+---+------------------------------------+ +---+------------------------------------+
| d | days (86400 seconds) | | d | days (86400 seconds) |
+---+------------------------------------+ +---+------------------------------------+
| h | hours (3600 seconds) | | h | hours (3600 seconds) |
+---+------------------------------------+ +---+------------------------------------+
| m | minutes (60 seconds) | | m | minutes (60 seconds) |
+---+------------------------------------+ +---+------------------------------------+
| s | seconds (allowed for completeness) | | s | seconds (allowed for completeness) |
+---+------------------------------------+ +---+------------------------------------+
Table 1: Time unit specification Table 1: Time Unit Specification
characters Characters
Thus, the above repeat-field could also have been written: Thus, the above repeat-field could also have been written:
r=7d 1h 0 25h r=7d 1h 0 25h
Monthly and yearly repeats cannot be directly specified with a single Monthly and yearly repeats cannot be directly specified with a single
SDP repeat time; instead, separate time-descriptions should be used SDP repeat time; instead, separate time-descriptions should be used
to explicitly list the session times. to explicitly list the session times.
5.11. Time Zone Adjustment ("z=") 5.11. Time Zone Adjustment ("z=")
skipping to change at line 964 skipping to change at line 967
k=<method> k=<method>
k=<method>:<encryption key> k=<method>:<encryption key>
The "k=" line (key-field) is obsolete and MUST NOT be used. It is The "k=" line (key-field) is obsolete and MUST NOT be used. It is
included in this document for legacy reasons. One MUST NOT include a included in this document for legacy reasons. One MUST NOT include a
"k=" line in an SDP, and MUST discard it if it is received in an SDP. "k=" line in an SDP, and MUST discard it if it is received in an SDP.
5.13. Attributes ("a=") 5.13. Attributes ("a=")
a=<attribute> a=<attribute-name>
a=<attribute>:<value> a=<attribute-name>:<attribute-value>
Attributes are the primary means for extending SDP. Attributes may Attributes are the primary means for extending SDP. Attributes may
be defined to be used as session-level attributes, media-level be defined to be used as session-level attributes, media-level
attributes, or both. (Attribute scopes in addition to media-level attributes, or both. (Attribute scopes in addition to media-level
and session-level scopes may also be defined in extensions to this and session-level scopes may also be defined in extensions to this
document, e.g., [RFC5576] and [RFC8864].) document, e.g., [RFC5576] and [RFC8864].)
A media description may contain any number of "a=" lines (attribute- A media description may contain any number of "a=" lines (attribute-
fields) that are media description specific. These are referred to fields) that are media description specific. These are referred to
as media-level attributes and add information about the media as media-level attributes and add information about the media
description. Attribute-fields can also be added before the first description. Attribute-fields can also be added before the first
media description; these session-level attributes convey additional media description; these session-level attributes convey additional
information that applies to the session as a whole rather than to information that applies to the session as a whole rather than to
individual media descriptions. individual media descriptions.
Attribute-fields may be of two forms: Attribute-fields may be of two forms:
* A property attribute is simply of the form "a=<attribute>". These * A property attribute is simply of the form "a=<attribute-name>".
are binary attributes, and the presence of the attribute conveys These are binary attributes, and the presence of the attribute
that the attribute is a property of the session. An example might conveys that the attribute is a property of the session. An
be "a=recvonly". example might be "a=recvonly".
* A value attribute is of the form "a=<attribute>:<value>". For * A value attribute is of the form "a=<attribute-name>:<attribute-
example, a whiteboard could have the value attribute value>". For example, a whiteboard could have the value attribute
"a=orient:landscape". "a=orient:landscape".
Attribute interpretation depends on the media tool being invoked. Attribute interpretation depends on the media tool being invoked.
Thus receivers of session descriptions should be configurable in Thus receivers of session descriptions should be configurable in
their interpretation of session descriptions in general and of their interpretation of session descriptions in general and of
attributes in particular. attributes in particular.
Attribute names MUST use the US-ASCII subset of ISO-10646/UTF-8. Attribute names MUST use the US-ASCII subset of ISO-10646/UTF-8.
Attribute values are octet strings, and MAY use any octet value Attribute values are octet strings, and MAY use any octet value
except 0x00 (Nul), 0x0A (LF), and 0x0D (CR). By default, attribute except 0x00 (Nul), 0x0A (LF), and 0x0D (CR). By default, attribute
values are to be interpreted as in ISO-10646 character set with UTF-8 values are to be interpreted as in ISO-10646 character set with UTF-8
encoding. Unlike other text fields, attribute values are NOT encoding. Unlike other text fields, attribute values are NOT
normally affected by the "charset" attribute as this would make normally affected by the "a=charset:" attribute as this would make
comparisons against known values problematic. However, when an comparisons against known values problematic. However, when an
attribute is defined, it can be defined to be charset dependent, in attribute is defined, it can be defined to be charset dependent, in
which case its value should be interpreted in the session charset which case its value should be interpreted in the session charset
rather than in ISO-10646. rather than in ISO-10646.
Attributes MUST be registered with IANA (see Section 8). If an Attributes MUST be registered with IANA (see Section 8). If an
attribute is received that is not understood, it MUST be ignored by attribute is received that is not understood, it MUST be ignored by
the receiver. the receiver.
5.14. Media Descriptions ("m=") 5.14. Media Descriptions ("m=")
m=<media> <port> <proto> <fmt> ... m=<media> <port> <proto> <fmt> ...
A session description may contain a number of media descriptions. A session description may contain a number of media descriptions.
Each media description starts with an "m=" line (media-field) and is Each media description starts with an "m=" line (media-field) and is
terminated by either the next "m=" line or by the end of the session terminated by either the next "m=" line or by the end of the session
description. A media-field has several sub-fields: description. A media-field has several subfields:
<media> is the media type. This document defines the values <media> is the media type. This document defines the values
"audio", "video", "text", "application", and "message". This list "audio", "video", "text", "application", and "message". This list
is extended by other memos and may be further extended by is extended by other memos and may be further extended by
additional memos registering media types in the future (see additional memos registering media types in the future (see
Section 8). For example, [RFC6466] defined the "image" media Section 8). For example, [RFC6466] defined the "image" media
type. type.
<port> is the transport port to which the media stream is sent. The <port> is the transport port to which the media stream is sent. The
meaning of the transport port depends on the network being used as meaning of the transport port depends on the network being used as
specified in the relevant "c=" line, and on the transport protocol specified in the relevant "c=" line, and on the transport protocol
defined in the <proto> sub-field of the media-field. Other ports defined in the <proto> subfield of the media-field. Other ports
used by the media application (such as the RTP Control Protocol used by the media application (such as the RTP Control Protocol
(RTCP) port [RFC3550]) MAY be derived algorithmically from the (RTCP) port [RFC3550]) MAY be derived algorithmically from the
base media port or MAY be specified in a separate attribute (for base media port or MAY be specified in a separate attribute (for
example, "a=rtcp:" as defined in [RFC3605]). example, the "a=rtcp:" attribute as defined in [RFC3605]).
If noncontiguous ports are used or if they don't follow the parity If noncontiguous ports are used or if they don't follow the parity
rule of even RTP ports and odd RTCP ports, the "a=rtcp:" attribute rule of even RTP ports and odd RTCP ports, the "a=rtcp:" attribute
MUST be used. Applications that are requested to send media to a MUST be used. Applications that are requested to send media to a
<port> that is odd and where the "a=rtcp:" is present MUST NOT <port> that is odd and where the "a=rtcp:" attribute is present
subtract 1 from the RTP port: that is, they MUST send the RTP to MUST NOT subtract 1 from the RTP port: that is, they MUST send the
the port indicated in <port> and send the RTCP to the port RTP to the port indicated in <port> and send the RTCP to the port
indicated in the "a=rtcp" attribute. indicated in the "a=rtcp:" attribute.
For applications where hierarchically encoded streams are being For applications where hierarchically encoded streams are being
sent to a unicast address, it may be necessary to specify multiple sent to a unicast address, it may be necessary to specify multiple
transport ports. This is done using a similar notation to that transport ports. This is done using a similar notation to that
used for IP multicast addresses in the "c=" line: used for IP multicast addresses in the "c=" line:
m=<media> <port>/<number of ports> <proto> <fmt> ... m=<media> <port>/<number of ports> <proto> <fmt> ...
In such a case, the ports used depend on the transport protocol. In such a case, the ports used depend on the transport protocol.
For RTP, the default is that only the even-numbered ports are used For RTP, the default is that only the even-numbered ports are used
skipping to change at line 1069 skipping to change at line 1072
m=video 49170/2 RTP/AVP 31 m=video 49170/2 RTP/AVP 31
would specify that ports 49170 and 49171 form one RTP/RTCP pair, would specify that ports 49170 and 49171 form one RTP/RTCP pair,
and 49172 and 49173 form the second RTP/RTCP pair. RTP/AVP is the and 49172 and 49173 form the second RTP/RTCP pair. RTP/AVP is the
transport protocol, and 31 is the format (see the description of transport protocol, and 31 is the format (see the description of
<fmt> below). <fmt> below).
This document does not include a mechanism for declaring This document does not include a mechanism for declaring
hierarchically encoded streams using noncontiguous ports. (There hierarchically encoded streams using noncontiguous ports. (There
is currently no attribute defined that can accomplish this. The is currently no attribute defined that can accomplish this. The
"a=rtcp:" defined in [RFC3605] does not handle hierarchical "a=rtcp:" attribute defined in [RFC3605] does not handle
encoding.) If a need arises to declare noncontiguous ports then hierarchical encoding.) If a need arises to declare noncontiguous
it will be necessary to define a new attribute to do so. ports then it will be necessary to define a new attribute to do
so.
If multiple addresses are specified in the "c=" line and multiple If multiple addresses are specified in the "c=" line and multiple
ports are specified in the "m=" line, a one-to-one mapping from ports are specified in the "m=" line, a one-to-one mapping from
port to the corresponding address is implied. For example: port to the corresponding address is implied. For example:
m=video 49170/2 RTP/AVP 31 m=video 49170/2 RTP/AVP 31
c=IN IP4 233.252.0.1/127/2 c=IN IP4 233.252.0.1/127/2
would imply that address 233.252.0.1 is used with ports 49170 and would imply that address 233.252.0.1 is used with ports 49170 and
49171, and address 233.252.0.2 is used with ports 49172 and 49173. 49171, and address 233.252.0.2 is used with ports 49172 and 49173.
skipping to change at line 1101 skipping to change at line 1105
and 49171, and address ff00::db8:0:102 is used with ports 49172 and 49171, and address ff00::db8:0:102 is used with ports 49172
and 49173. and 49173.
This document gives no meaning to assigning the same media address This document gives no meaning to assigning the same media address
to multiple media descriptions. Doing so does not implicitly to multiple media descriptions. Doing so does not implicitly
group those media descriptions in any way. An explicit grouping group those media descriptions in any way. An explicit grouping
framework (for example, [RFC5888]) should instead be used to framework (for example, [RFC5888]) should instead be used to
express the intended semantics. For instance, see [RFC8843]. express the intended semantics. For instance, see [RFC8843].
<proto> is the transport protocol. The meaning of the transport <proto> is the transport protocol. The meaning of the transport
protocol is dependent on the address type sub-field in the protocol is dependent on the address type subfield in the relevant
relevant "c=" line. Thus a "c=" line with an address type of IP4 "c=" line. Thus a "c=" line with an address type of "IP4"
indicates that the transport protocol runs over IPv4. The indicates that the transport protocol runs over IPv4. The
following transport protocols are defined, but may be extended following transport protocols are defined, but may be extended
through registration of new protocols with IANA (see Section 8): through registration of new protocols with IANA (see Section 8):
* udp: denotes that the data is transported directly in UDP with * udp: denotes that the data is transported directly in UDP with
no additional framing. no additional framing.
* RTP/AVP: denotes RTP [RFC3550] used under the RTP Profile for * RTP/AVP: denotes RTP [RFC3550] used under the RTP Profile for
Audio and Video Conferences with Minimal Control [RFC3551] Audio and Video Conferences with Minimal Control [RFC3551]
running over UDP. running over UDP.
* RTP/SAVP: denotes the Secure Real-time Transport Protocol * RTP/SAVP: denotes the Secure Real-time Transport Protocol
[RFC3711] running over UDP. [RFC3711] running over UDP.
* RTP/SAVPF: denotes SRTP with the Extended SRTP Profile for
RTCP-Based Feedback [RFC5124] running over UDP.
The main reason to specify the transport protocol in addition to The main reason to specify the transport protocol in addition to
the media format is that the same standard media formats may be the media format is that the same standard media formats may be
carried over different transport protocols even when the network carried over different transport protocols even when the network
protocol is the same -- a historical example is VAT (MBone's protocol is the same -- a historical example is vat (MBone's
popular multimedia audio tool) Pulse Code Modulation (PCM) audio popular multimedia audio tool) Pulse Code Modulation (PCM) audio
and RTP PCM audio; another might be TCP/RTP PCM audio. In and RTP PCM audio; another might be TCP/RTP PCM audio. In
addition, relays and monitoring tools that are transport-protocol- addition, relays and monitoring tools that are transport-protocol-
specific but format-independent are possible. specific but format-independent are possible.
<fmt> is a media format description. The fourth and any subsequent <fmt> is a media format description. The fourth and any subsequent
sub-fields describe the format of the media. The interpretation subfields describe the format of the media. The interpretation of
of the media format depends on the value of the <proto> sub-field. the media format depends on the value of the <proto> subfield.
If the <proto> sub-field is "RTP/AVP" or "RTP/SAVP", the <fmt> If the <proto> subfield is "RTP/AVP" or "RTP/SAVP", the <fmt>
sub-fields contain RTP payload type numbers. When a list of subfields contain RTP payload type numbers. When a list of
payload type numbers is given, this implies that all of these payload type numbers is given, this implies that all of these
payload formats MAY be used in the session, but the first of these payload formats MAY be used in the session, and these payload
formats SHOULD be used as the default format for the session. For formats are listed in order of preference, with the first format
dynamic payload type assignments, the "a=rtpmap:" attribute (see listed being preferred. When multiple payload formats are listed,
Section 6) SHOULD be used to map from an RTP payload type number the first acceptable payload format from the beginning of the list
to a media encoding name that identifies the payload format. The SHOULD be used for the session. For dynamic payload type
"a=fmtp:" attribute MAY be used to specify format parameters (see assignments, the "a=rtpmap:" attribute (see Section 6.6) SHOULD be
Section 6). used to map from an RTP payload type number to a media encoding
name that identifies the payload format. The "a=fmtp:" attribute
MAY be used to specify format parameters (see Section 6.15).
If the <proto> sub-field is "udp", the <fmt> sub-fields MUST If the <proto> subfield is "udp", the <fmt> subfields MUST
reference a media type describing the format under the "audio", reference a media type describing the format under the "audio",
"video", "text", "application", or "message" top-level media "video", "text", "application", or "message" top-level media
types. The media type registration SHOULD define the packet types. The media type registration SHOULD define the packet
format for use with UDP transport. format for use with UDP transport.
For media using other transport protocols, the <fmt> sub-field is For media using other transport protocols, the <fmt> subfield is
protocol specific. Rules for interpretation of the <fmt> sub- protocol specific. Rules for interpretation of the <fmt> subfield
field MUST be defined when registering new protocols (see MUST be defined when registering new protocols (see
Section 8.2.2). Section 8.2.2).
Section 3 of [RFC4855] states that the payload format (encoding) Section 3 of [RFC4855] states that the payload format (encoding)
names defined in the RTP profile are commonly shown in upper case, names defined in the RTP profile are commonly shown in upper case,
while media subtype names are commonly shown in lower case. It while media subtype names are commonly shown in lower case. It
also states that both of these names are case-insensitive in both also states that both of these names are case-insensitive in both
places, similar to parameter names which are case-insensitive both places, similar to parameter names which are case-insensitive both
in media type strings and in the default mapping to the SDP in media type strings and in the default mapping to the SDP
"a=fmtp:" attribute. "a=fmtp:" attribute.
skipping to change at line 1212 skipping to change at line 1221
Syntax: Syntax:
keywds-value = keywords keywds-value = keywords
keywords = text keywords = text
Example: Example:
a=keywds:SDP session description protocol a=keywds:SDP session description protocol
Like the "cat" attribute, this was intended to assist identifying Like the "a=cat:" attribute, this was intended to assist identifying
wanted sessions at the receiver, and to allow a receiver to select wanted sessions at the receiver, and to allow a receiver to select
interesting sessions based on keywords describing the purpose of the interesting sessions based on keywords describing the purpose of the
session; however, there is no central registry of keywords. Its session; however, there is no central registry of keywords. Its
value should be interpreted in the charset specified for the session value should be interpreted in the charset specified for the session
description if one is specified, or by default in ISO 10646/UTF-8. description if one is specified, or by default in ISO 10646/UTF-8.
This attribute is obsolete and SHOULD NOT be used. It SHOULD be This attribute is obsolete and SHOULD NOT be used. It SHOULD be
ignored if received. ignored if received.
6.3. tool 6.3. tool
skipping to change at line 1264 skipping to change at line 1273
ptime-value = non-zero-int-or-real ptime-value = non-zero-int-or-real
Example: Example:
a=ptime:20 a=ptime:20
This gives the length of time in milliseconds represented by the This gives the length of time in milliseconds represented by the
media in a packet. This is probably only meaningful for audio data, media in a packet. This is probably only meaningful for audio data,
but may be used with other media types if it makes sense. It should but may be used with other media types if it makes sense. It should
not be necessary to know ptime to decode RTP or VAT audio, and it is not be necessary to know "a=ptime:" to decode RTP or vat audio, and
intended as a recommendation for the encoding/packetization of audio. it is intended as a recommendation for the encoding/packetization of
audio.
6.5. maxptime (Maximum Packet Time) 6.5. maxptime (Maximum Packet Time)
Name: maxptime Name: maxptime
Value: maxptime-value Value: maxptime-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
skipping to change at line 1340 skipping to change at line 1350
m=audio 49232 RTP/AVP 0 m=audio 49232 RTP/AVP 0
An example of a dynamic payload type is 16-bit linear encoded stereo An example of a dynamic payload type is 16-bit linear encoded stereo
audio sampled at 16 kHz. If we wish to use the dynamic RTP/AVP audio sampled at 16 kHz. If we wish to use the dynamic RTP/AVP
payload type 98 for this stream, additional information is required payload type 98 for this stream, additional information is required
to decode it: to decode it:
m=audio 49232 RTP/AVP 98 m=audio 49232 RTP/AVP 98
a=rtpmap:98 L16/16000/2 a=rtpmap:98 L16/16000/2
Up to one rtpmap attribute can be defined for each media format Up to one "a=rtpmap:" attribute can be defined for each media format
specified. Thus, we might have the following: specified. Thus, we might have the following:
m=audio 49230 RTP/AVP 96 97 98 m=audio 49230 RTP/AVP 96 97 98
a=rtpmap:96 L8/8000 a=rtpmap:96 L8/8000
a=rtpmap:97 L16/8000 a=rtpmap:97 L16/8000
a=rtpmap:98 L16/11025/2 a=rtpmap:98 L16/11025/2
RTP profiles that specify the use of dynamic payload types MUST RTP profiles that specify the use of dynamic payload types MUST
define the set of valid encoding names and/or a means to register define the set of valid encoding names and/or a means to register
encoding names if that profile is to be used with SDP. The "RTP/AVP" encoding names if that profile is to be used with SDP. The "RTP/AVP"
skipping to change at line 1372 skipping to change at line 1382
Additional encoding parameters MAY be defined in the future, but Additional encoding parameters MAY be defined in the future, but
codec-specific parameters SHOULD NOT be added. Parameters added to codec-specific parameters SHOULD NOT be added. Parameters added to
an "a=rtpmap:" attribute SHOULD only be those required for a session an "a=rtpmap:" attribute SHOULD only be those required for a session
directory to make the choice of appropriate media to participate in a directory to make the choice of appropriate media to participate in a
session. Codec-specific parameters should be added in other session. Codec-specific parameters should be added in other
attributes (for example, "a=fmtp:"). attributes (for example, "a=fmtp:").
Note: RTP audio formats typically do not include information about Note: RTP audio formats typically do not include information about
the number of samples per packet. If a non-default (as defined in the number of samples per packet. If a non-default (as defined in
the RTP Audio/Video Profile [RFC3551]) packetization is required, the the RTP Audio/Video Profile [RFC3551]) packetization is required, the
"ptime" attribute is used as given in Section 6.4. "a=ptime:" attribute is used as given in Section 6.4.
6.7. Media Direction Attributes 6.7. Media Direction Attributes
At most one occurrence of recvonly, sendrecv, sendonly, or inactive At most one occurrence of "a=recvonly", "a=sendrecv", "a=sendonly",
MAY appear at session level, and at most one MAY appear in each media or "a=inactive" MAY appear at session level, and at most one MAY
description. appear in each media description.
If any one of these appears in a media description, then it applies If any one of these appears in a media description, then it applies
for that media description. If none appears in a media description, for that media description. If none appears in a media description,
then the one from session level, if any, applies to that media then the one from session level, if any, applies to that media
description. description.
If none of the media direction attributes is present at either If none of the media direction attributes is present at either
session level or media level, "sendrecv" SHOULD be assumed as the session level or media level, "a=sendrecv" SHOULD be assumed as the
default. default.
Within the following SDP example, the "sendrecv" attribute applies to Within the following SDP example, the "a=sendrecv" attribute applies
the first audio media and the "inactive" attribute applies to the to the first audio media and the "a=inactive" attribute applies to
others. the others.
v=0 v=0
o=jdoe 3724395000 3724395001 IN IP6 2001:db8::1 o=jdoe 3724395000 3724395001 IN IP6 2001:db8::1
s=- s=-
c=IN IP6 2001:db8::1 c=IN IP6 2001:db8::1
t=0 0 t=0 0
a=inactive a=inactive
m=audio 49170 RTP/AVP 0 m=audio 49170 RTP/AVP 0
a=sendrecv a=sendrecv
m=audio 49180 RTP/AVP 0 m=audio 49180 RTP/AVP 0
skipping to change at line 1420 skipping to change at line 1430
Usage Level: session, media Usage Level: session, media
Charset Dependent: no Charset Dependent: no
Example: Example:
a=recvonly a=recvonly
This specifies that the tools should be started in receive-only mode This specifies that the tools should be started in receive-only mode
where applicable. Note that recvonly applies to the media only, not where applicable. Note that receive-only mode applies to the media
to any associated control protocol. An RTP-based system in recvonly only, not to any associated control protocol. An RTP-based system in
mode MUST still send RTCP packets as described in [RFC3550], receive-only mode MUST still send RTCP packets as described in
Section 6. [RFC3550], Section 6.
6.7.2. sendrecv (Send-Receive) 6.7.2. sendrecv (Send-Receive)
Name: sendrecv Name: sendrecv
Value: Value:
Usage Level: session, media Usage Level: session, media
Charset Dependent: no Charset Dependent: no
skipping to change at line 1460 skipping to change at line 1470
Charset Dependent: no Charset Dependent: no
Example: Example:
a=sendonly a=sendonly
This specifies that the tools should be started in send-only mode. This specifies that the tools should be started in send-only mode.
An example may be where a different unicast address is to be used for An example may be where a different unicast address is to be used for
a traffic destination than for a traffic source. In such a case, two a traffic destination than for a traffic source. In such a case, two
media descriptions may be used, one sendonly and one recvonly. Note media descriptions may be used, one in send-only mode and one in
that sendonly applies only to the media, and any associated control receive-vonly mode. Note that send-only mode applies only to the
protocol (e.g., RTCP) SHOULD still be received and processed as media, and any associated control protocol (e.g., RTCP) SHOULD still
normal. be received and processed as normal.
6.7.4. inactive 6.7.4. inactive
Name: inactive Name: inactive
Value: Value:
Usage Level: session, media Usage Level: session, media
Charset Dependent: no Charset Dependent: no
Example: Example:
a=inactive a=inactive
This specifies that the tools should be started in inactive mode. This specifies that the tools should be started in inactive mode.
This is necessary for interactive multimedia conferences where users This is necessary for interactive multimedia conferences where users
can put other users on hold. No media is sent over an inactive media can put other users on hold. No media is sent over an inactive media
stream. Note that an RTP-based system MUST still send RTCP (if RTCP stream. Note that an RTP-based system MUST still send RTCP (if RTCP
is used), even if started inactive. is used), even if started in inactive mode.
6.8. orient (Orientation) 6.8. orient (Orientation)
Name: orient Name: orient
Value: orient-value Value: orient-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
skipping to change at line 1617 skipping to change at line 1627
Syntax: Syntax:
sdplang-value = Language-Tag sdplang-value = Language-Tag
; Language-Tag defined in RFC 5646 ; Language-Tag defined in RFC 5646
Example: Example:
a=sdplang:fr a=sdplang:fr
Multiple sdplang attributes can be provided either at session or Multiple "a=sdplang:" attributes can be provided either at session or
media level if the session description or media use multiple media level if the session description or media use multiple
languages. languages.
As a session-level attribute, it specifies the language for the As a session-level attribute, it specifies the language for the
session description (not the language of the media). As a media- session description (not the language of the media). As a media-
level attribute, it specifies the language for any media-level SDP level attribute, it specifies the language for any media-level SDP
information-field associated with that media (again not the language information-field associated with that media (again not the language
of the media), overriding any sdplang attributes specified at session of the media), overriding any "a=sdplang:" attributes specified at
level. session level.
In general, sending session descriptions consisting of multiple In general, sending session descriptions consisting of multiple
languages is discouraged. Instead, multiple session descriptions languages is discouraged. Instead, multiple session descriptions
SHOULD be sent describing the session, one in each language. SHOULD be sent describing the session, one in each language.
However, this is not possible with all transport mechanisms, and so However, this is not possible with all transport mechanisms, and so
multiple sdplang attributes are allowed although NOT RECOMMENDED. multiple "a=sdplang:" attributes are allowed although NOT
RECOMMENDED.
The "sdplang" attribute value must be a single language tag The "a=sdplang:" attribute value must be a single language tag
[RFC5646]. An "sdplang" attribute SHOULD be specified when a session [RFC5646]. An "a=sdplang:" attribute SHOULD be specified when a
is distributed with sufficient scope to cross geographic boundaries, session is distributed with sufficient scope to cross geographic
where the language of recipients cannot be assumed, or where the boundaries, where the language of recipients cannot be assumed, or
session is in a different language from the locally assumed norm. where the session is in a different language from the locally assumed
norm.
6.12. lang (Language) 6.12. lang (Language)
Name: lang Name: lang
Value: lang-value Value: lang-value
Usage Level: session, media Usage Level: session, media
Charset Dependent: no Charset Dependent: no
Syntax: Syntax:
lang-value = Language-Tag lang-value = Language-Tag
; Language-Tag defined in RFC 5646 ; Language-Tag defined in RFC 5646
Example: Example:
a=lang:de a=lang:de
Multiple lang attributes can be provided either at session or media Multiple "a=lang:" attributes can be provided either at session or
level if the session or media has capabilities in more than one media level if the session or media has capabilities in more than one
language, in which case the order of the attributes indicates the language, in which case the order of the attributes indicates the
order of preference of the various languages in the session or media, order of preference of the various languages in the session or media,
from most preferred to least preferred. from most preferred to least preferred.
As a session-level attribute, lang specifies a language capability As a session-level attribute, "a=lang:" specifies a language
for the session being described. As a media-level attribute, it capability for the session being described. As a media-level
specifies a language capability for that media, overriding any attribute, it specifies a language capability for that media,
session-level language(s) specified. overriding any session-level language(s) specified.
The "lang" attribute value must be a single [RFC5646] language tag. The "a=lang:" attribute value must be a single [RFC5646] language
A "lang" attribute SHOULD be specified when a session is of tag. An "a=lang:" attribute SHOULD be specified when a session is of
sufficient scope to cross geographic boundaries where the language of sufficient scope to cross geographic boundaries where the language of
participants cannot be assumed, or where the session has capabilities participants cannot be assumed, or where the session has capabilities
in languages different from the locally assumed norm. in languages different from the locally assumed norm.
The "lang" attribute is supposed to be used for setting the initial The "a=lang:" attribute is supposed to be used for setting the
language(s) used in the session. Events during the session may initial language(s) used in the session. Events during the session
influence which language(s) are used, and the participants are not may influence which language(s) are used, and the participants are
strictly bound to only use the declared languages. not strictly bound to only use the declared languages.
Most real-time use cases start with just one language used, while Most real-time use cases start with just one language used, while
other cases involve a range of languages, e.g., an interpreted or other cases involve a range of languages, e.g., an interpreted or
subtitled session. When more than one "lang" attribute is specified, subtitled session. When more than one "a=lang:" attribute is
the "lang" attribute itself does not provide any information about specified, the "a=lang:" attribute itself does not provide any
multiple languages being intended to be used during the session, or information about multiple languages being intended to be used during
if the intention is to only select one of the languages. If needed, the session, or if the intention is to only select one of the
a new attribute can be defined and used to indicate such intentions. languages. If needed, a new attribute can be defined and used to
Without such semantics, it is assumed that for a negotiated session indicate such intentions. Without such semantics, it is assumed that
one of the declared languages will be selected and used. for a negotiated session one of the declared languages will be
selected and used.
6.13. framerate (Frame Rate) 6.13. framerate (Frame Rate)
Name: framerate Name: framerate
Value: framerate-value Value: framerate-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
skipping to change at line 1749 skipping to change at line 1762
| 10 | the best still-image quality the | | 10 | the best still-image quality the |
| | compression scheme can give. | | | compression scheme can give. |
+----+----------------------------------------+ +----+----------------------------------------+
| 5 | the default behavior given no quality | | 5 | the default behavior given no quality |
| | suggestion. | | | suggestion. |
+----+----------------------------------------+ +----+----------------------------------------+
| 0 | the worst still-image quality the | | 0 | the worst still-image quality the |
| | codec designer thinks is still usable. | | | codec designer thinks is still usable. |
+----+----------------------------------------+ +----+----------------------------------------+
Table 2: Encoding quality values Table 2: Encoding Quality Values
6.15. fmtp (Format Parameters) 6.15. fmtp (Format Parameters)
Name: fmtp Name: fmtp
Value: fmtp-value Value: fmtp-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
skipping to change at line 1781 skipping to change at line 1794
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
This attribute allows parameters that are specific to a particular This attribute allows parameters that are specific to a particular
format to be conveyed in a way that SDP does not have to understand format to be conveyed in a way that SDP does not have to understand
them. The format must be one of the formats specified for the media. them. The format must be one of the formats specified for the media.
Format-specific parameters, semicolon separated, may be any set of Format-specific parameters, semicolon separated, may be any set of
parameters required to be conveyed by SDP and given unchanged to the parameters required to be conveyed by SDP and given unchanged to the
media tool that will use this format. At most one instance of this media tool that will use this format. At most one instance of this
attribute is allowed for each format. attribute is allowed for each format.
The fmtp attribute may be used to specify parameters for any protocol The "a=fmtp:" attribute may be used to specify parameters for any
and format that defines use of such parameters. protocol and format that defines use of such parameters.
7. Security Considerations 7. Security Considerations
SDP is frequently used with the Session Initiation Protocol [RFC3261] SDP is frequently used with the Session Initiation Protocol [RFC3261]
using the offer/answer model [RFC3264] to agree on parameters for using the offer/answer model [RFC3264] to agree on parameters for
unicast sessions. When used in this manner, the security unicast sessions. When used in this manner, the security
considerations of those protocols apply. considerations of those protocols apply.
SDP is a session description format that describes multimedia SDP is a session description format that describes multimedia
sessions. Entities receiving and acting upon an SDP message SHOULD sessions. Entities receiving and acting upon an SDP message SHOULD
skipping to change at line 1859 skipping to change at line 1872
are NOT RECOMMENDED unless the session description is conveyed in are NOT RECOMMENDED unless the session description is conveyed in
such a manner that allows the intermediary system to conduct proper such a manner that allows the intermediary system to conduct proper
checks to establish the authenticity of the session description, and checks to establish the authenticity of the session description, and
the authority of its source to establish such communication sessions. the authority of its source to establish such communication sessions.
SDP by itself does not include sufficient information to enable these SDP by itself does not include sufficient information to enable these
checks: they depend on the encapsulating protocol (e.g., SIP or checks: they depend on the encapsulating protocol (e.g., SIP or
RTSP). The use of some procedures and SDP extensions (e.g., RTSP). The use of some procedures and SDP extensions (e.g.,
Interactive Connectivity Establishment (ICE) [RFC8445] and ICE-SIP- Interactive Connectivity Establishment (ICE) [RFC8445] and ICE-SIP-
SDP [RFC8839]) may avoid the need for intermediaries to modify SDP. SDP [RFC8839]) may avoid the need for intermediaries to modify SDP.
SDP MUST NOT be used to convey keying material (e.g., using SDP MUST NOT be used to convey keying material (e.g., using the
"a=crypto" [RFC4568]) unless it can be guaranteed that the channel "a=crypto:" attribute [RFC4568]) unless it can be guaranteed that the
over which the SDP is delivered is both private and authenticated. channel over which the SDP is delivered is both private and
authenticated.
8. IANA Considerations 8. IANA Considerations
8.1. The "application/sdp" Media Type 8.1. The "application/sdp" Media Type
One media type registration from [RFC4566] is to be updated, as One media type registration from [RFC4566] is to be updated, as
defined below. defined below.
Type name: application Type name: application
skipping to change at line 1918 skipping to change at line 1932
Restrictions on usage: None Restrictions on usage: None
Author/Change controller: Author/Change controller:
Authors of RFC 8866 Authors of RFC 8866
IETF MMUSIC working group delegated from the IESG IETF MMUSIC working group delegated from the IESG
8.2. Registration of SDP Parameters with IANA 8.2. Registration of SDP Parameters with IANA
This document specifies IANA parameter registries for six named SDP This document specifies IANA parameter registries for six named SDP
sub-fields. Using the terminology in the SDP specification Augmented subfields. Using the terminology in the SDP specification Augmented
Backus-Naur Form (ABNF), they are "media", "proto", "att-field", Backus-Naur Form (ABNF), they are <media>, <proto>, <attribute-name>,
"bwtype", "nettype", and "addrtype". <bwtype>, <nettype>, and <addrtype>.
This document also replaces and updates the definitions of all those This document also replaces and updates the definitions of all those
parameters previously defined by [RFC4566]. parameters previously defined by [RFC4566].
IANA: Please change all references to RFC4566 in these registries to IANA: Please change all references to RFC4566 in these registries to
instead refer to this document. instead refer to this document.
The contact name and email address for all parameters registered in The contact name and email address for all parameters registered in
this document is: this document is:
The IETF MMUSIC working group <mmusic@ietf.org> or its successor The IETF MMUSIC working group <mmusic@ietf.org> or its successor
as designated by the IESG. as designated by the IESG.
All of these registries have a common format: All of these registries have a common format:
+======+==========+================+===========+ +======+==========+================+===========+
| Type | SDP Name | [other fields] | Reference | | Type | SDP Name | [other fields] | Reference |
+======+==========+================+===========+ +======+==========+================+===========+
Table 3: Common format for SDP registries Table 3: Common Format for SDP Registries
8.2.1. Registration Procedure 8.2.1. Registration Procedure
A specification document that defines values for SDP "media", A specification document that defines values for SDP <media>,
"proto", "att-field", "bwtype", "nettype", and "addrtype" parameters <proto>, <attribute-name>, <bwtype>, <nettype>, and <addrtype>
MUST include the following information: parameters MUST include the following information:
* Contact name * Contact name
* Contact email address * Contact email address
* Name being defined (as it will appear in SDP) * Name being defined (as it will appear in SDP)
* Type of name ("media", "proto", "bwtype", "nettype", or * Type of name (<media>, <proto>, <bwtype>, <nettype>, or
"addrtype") <addrtype>)
* A description of the purpose of the defined name * A description of the purpose of the defined name
* A stable reference to the document containing this information and * A stable reference to the document containing this information and
the definition of the value. (This will typically be an RFC the definition of the value. (This will typically be an RFC
number.) number.)
The subsections below specify what other information (if any) must be The subsections below specify what other information (if any) must be
specified for particular parameters, and what other fields are to be specified for particular parameters, and what other fields are to be
included in the registry. included in the registry.
8.2.2. Media Types ("media") 8.2.2. Media Types (<media>)
The set of media types is intended to be small and SHOULD NOT be The set of media types is intended to be small and SHOULD NOT be
extended except under rare circumstances. The same rules should extended except under rare circumstances. The same rules should
apply for media names as well as for top-level media types, and where apply for media names as well as for top-level media types, and where
possible the same name should be registered for SDP as for MIME. For possible the same name should be registered for SDP as for MIME. For
media other than existing top-level media types, a Standards Track media other than existing top-level media types, a Standards Track
RFC MUST be produced for a new top-level media type to be registered, RFC MUST be produced for a new top-level media type to be registered,
and the registration MUST provide good justification why no existing and the registration MUST provide good justification why no existing
media name is appropriate (the "Standards Action" policy of media name is appropriate (the "Standards Action" policy of
[RFC8126]). [RFC8126]).
skipping to change at line 1994 skipping to change at line 2008
semantics were never fully specified, and they are not widely used. semantics were never fully specified, and they are not widely used.
These media types have been removed in this specification, although These media types have been removed in this specification, although
they still remain valid media type capabilities for a SIP user agent they still remain valid media type capabilities for a SIP user agent
as defined in [RFC3840]. If these media types are considered useful as defined in [RFC3840]. If these media types are considered useful
in the future, a Standards Track RFC MUST be produced to document in the future, a Standards Track RFC MUST be produced to document
their use. Until that is done, applications SHOULD NOT use these their use. Until that is done, applications SHOULD NOT use these
types and SHOULD NOT declare support for them in SIP capabilities types and SHOULD NOT declare support for them in SIP capabilities
declarations (even though they exist in the registry created by declarations (even though they exist in the registry created by
[RFC3840]). Also note that [RFC6466] defined the "image" media type. [RFC3840]). Also note that [RFC6466] defined the "image" media type.
8.2.3. Transport Protocols ("proto") 8.2.3. Transport Protocols (<proto>)
The "proto" sub-field describes the transport protocol used. The The <proto> subfield describes the transport protocol used. The
registration procedure for this registry is "RFC Required". registration procedure for this registry is "RFC Required".
This document registers two values: This document registers two values:
* "RTP/AVP" is a reference to [RFC3550] used under the RTP Profile * "RTP/AVP" is a reference to [RFC3550] used under the RTP Profile
for Audio and Video Conferences with Minimal Control [RFC3551] for Audio and Video Conferences with Minimal Control [RFC3551]
running over UDP/IP. running over UDP/IP.
* "udp" indicates direct use of UDP. * "udp" indicates direct use of UDP.
New transport protocols MAY be defined, and MUST be registered with New transport protocols MAY be defined, and MUST be registered with
IANA. Registrations MUST reference an RFC describing the protocol. IANA. Registrations MUST reference an RFC describing the protocol.
Such an RFC MAY be Experimental or Informational, although it is Such an RFC MAY be Experimental or Informational, although it is
preferable that it be Standards Track. The RFC defining a new preferable that it be Standards Track. The RFC defining a new
protocol MUST define the rules by which the "fmt" (see below) protocol MUST define the rules by which the <fmt> (see below)
namespace is managed. namespace is managed.
"proto" names starting with "RTP/" MUST only be used for defining <proto> names starting with "RTP/" MUST only be used for defining
transport protocols that are profiles of RTP. For example, a profile transport protocols that are profiles of RTP. For example, a profile
whose short name is "XYZ" would be denoted by a "proto" sub-field of whose short name is "XYZ" would be denoted by a <proto> subfield of
"RTP/XYZ". "RTP/XYZ".
Each transport protocol, defined by the "proto" sub-field, has an Each transport protocol, defined by the <proto> subfield, has an
associated "fmt" namespace that describes the media formats that may associated <fmt> namespace that describes the media formats that may
be conveyed by that protocol. Formats cover all the possible be conveyed by that protocol. Formats cover all the possible
encodings that could be transported in a multimedia session. encodings that could be transported in a multimedia session.
RTP payload formats under the "RTP/AVP" and other "RTP/*" profiles RTP payload formats under the "RTP/AVP" and other "RTP/*" profiles
MUST use the payload type number as their "fmt" value. If the MUST use the payload type number as their <fmt> value. If the
payload type number is dynamically assigned by this session payload type number is dynamically assigned by this session
description, an additional "rtpmap" attribute MUST be included to description, an additional "a=rtpmap:" attribute MUST be included to
specify the format name and parameters as defined by the media type specify the format name and parameters as defined by the media type
registration for the payload format. It is RECOMMENDED that other registration for the payload format. It is RECOMMENDED that other
RTP profiles that are registered (in combination with RTP) as SDP RTP profiles that are registered (in combination with RTP) as SDP
transport protocols specify the same rules for the "fmt" namespace. transport protocols specify the same rules for the <fmt> namespace.
For the "udp" protocol, the allowed "fmt" values are media subtypes For the "udp" protocol, the allowed <fmt> values are media subtypes
from the IANA Media Types registry. The media type and subtype from the IANA Media Types registry. The media type and subtype
combination <media>/<fmt> specifies the format of the body of UDP combination <media>/<fmt> specifies the format of the body of UDP
packets. Use of an existing media subtype for the format is packets. Use of an existing media subtype for the format is
encouraged. If no suitable media subtype exists, it is RECOMMENDED encouraged. If no suitable media subtype exists, it is RECOMMENDED
that a new one be registered through the IETF process [RFC6838] by that a new one be registered through the IETF process [RFC6838] by
production of, or reference to, a Standards Track RFC that defines production of, or reference to, a Standards Track RFC that defines
the format. the format.
For other protocols, formats MAY be registered according to the rules For other protocols, formats MAY be registered according to the rules
of the associated "proto" specification. of the associated <proto> specification.
Registrations of new formats MUST specify which transport protocols Registrations of new formats MUST specify which transport protocols
they apply to. they apply to.
8.2.4. Attribute Names ("att-field") 8.2.4. Attribute Names (<attribute-name>)
Attribute-field names ("att-field") MUST be registered with IANA and Attribute-field names (<attribute-name>) MUST be registered with IANA
documented to avoid any issues due to conflicting attribute and documented to avoid any issues due to conflicting attribute
definitions under the same name. (While unknown attributes in SDP definitions under the same name. (While unknown attributes in SDP
are simply ignored, conflicting ones that fragment the protocol are a are simply ignored, conflicting ones that fragment the protocol are a
serious problem.) serious problem.)
The format of the attribute registry is: The format of the <attribute-name> registry is:
+======+==========+=============+==============+===========+ +======+==========+=============+==============+===========+
| Type | SDP Name | Usage Level | Mux Category | Reference | | Type | SDP Name | Usage Level | Mux Category | Reference |
+======+==========+=============+==============+===========+ +======+==========+=============+==============+===========+
Table 4: Format of the attribute registry Table 4: Format of the <attribute-name> Registry
For example, the attribute "setup", which is defined for both session For example, the attribute "lang", which is defined for both session
and media level, will be listed in the new registry as follows: and media level, will be listed in the new registry as follows:
+===========+=======+=============+===========+====================+ +===========+======+==========+===========+========================+
| Type | SDP | Usage Level | Mux | Reference | | Type | SDP | Usage | Mux | Reference |
| | Name | | Category | | | | Name | Level | Category | |
+===========+=======+=============+===========+====================+ +===========+======+==========+===========+========================+
| attribute | setup | session, | IDENTICAL | [RFC4145] | | attribute | lang | session, | TRANSPORT | [RFC8866] [RFC8859] |
| | | media, dcsa | | [RFC6135] | | | | media | | |
| | | (msrp) | | [MSRP-DATACHANNEL] | +-----------+------+----------+-----------+------------------------+
+-----------+-------+-------------+-----------+--------------------+
Table 5: Attribute registry example Table 5: <attribute-name> Registry Example
This one registry combines all of the previous usage-level-specific This one <attribute-name> registry combines all of the previous
"att-field" registries, including updates made by [RFC8859]. IANA is usage-level-specific "att-field" registries, including updates made
requested to do the necessary reformatting. by [RFC8859]. IANA is requested to do the necessary reformatting.
Section 6 of this document replaces the initial set of attribute Section 6 of this document replaces the initial set of attribute
definitions made by [RFC4566]. IANA is requested to update the definitions made by [RFC4566]. IANA is requested to update the
registry accordingly. registry accordingly.
Documents can define new attributes and can also extend the Documents can define new attributes and can also extend the
definitions of previously defined attributes. definitions of previously defined attributes.
8.2.4.1. New Attributes 8.2.4.1. New Attributes
New attribute registrations are accepted according to the New attribute registrations are accepted according to the
"Specification Required" policy of [RFC8126], provided that the "Specification Required" policy of [RFC8126], provided that the
specification includes the following information: specification includes the following information:
* Contact name * Contact name
* Contact email address * Contact email address
* Attribute name: the name of the attribute that will appear in SDP. * Attribute name: the name of the attribute that will appear in SDP.
This MUST conform to the definition of <att-field>. This MUST conform to the definition of <attribute-name>.
* Attribute syntax: for a value attribute (see Section 5.13), an * Attribute syntax: for a value attribute (see Section 5.13), an
ABNF definition of the attribute value <att-value> syntax (see ABNF definition of the attribute value <attribute-value> syntax
Section 9) MUST be provided. The syntax MUST follow the rule form (see Section 9) MUST be provided. The syntax MUST follow the rule
per Section 2.2 of [RFC5234] and [RFC7405]. This SHALL define the form per Section 2.2 of [RFC5234] and [RFC7405]. This SHALL
allowable values that the attribute might take. It MAY also define the allowable values that the attribute might take. It MAY
define an extension method for the addition of future values. For also define an extension method for the addition of future values.
a property attribute, the ABNF definition is omitted as the For a property attribute, the ABNF definition is omitted as the
property attribute takes no values. property attribute takes no values.
* Attribute semantics: for a value attribute, a semantic description * Attribute semantics: for a value attribute, a semantic description
of the values that the attribute might take MUST be provided. The of the values that the attribute might take MUST be provided. The
usage of a property attribute is described under Purpose below. usage of a property attribute is described under Purpose below.
* Attribute value: the name of an ABNF syntax rule defining the * Attribute value: the name of an ABNF syntax rule defining the
syntax of the value. Absence of a rule name indicates that the syntax of the value. Absence of a rule name indicates that the
attribute takes no values. Enclosing the rule name in "[" and "]" attribute takes no values. Enclosing the rule name in "[" and "]"
indicates that a value is optional. indicates that a value is optional.
* Usage level: the usage level(s) of the attribute. This MUST be * Usage level: the usage level(s) of the attribute. This MUST be
one or more of the following: session, media, source, dcsa, and one or more of the following: session, media, source, dcsa, and
dcsa(subprotocol). For a definition of source-level attributes, dcsa(subprotocol). For a definition of source-level attributes,
see [RFC5576]. For a definition of dcsa attributes see [RFC8864]. see [RFC5576]. For a definition of dcsa attributes see [RFC8864].
* Charset dependent: this MUST be "Yes" or "No" depending on whether * Charset dependent: this MUST be "Yes" or "No" depending on whether
the attribute value is subject to the charset attribute. the attribute value is subject to the "a=charset:" attribute.
* Purpose: an explanation of the purpose and usage of the attribute. * Purpose: an explanation of the purpose and usage of the attribute.
* O/A procedures: offer/answer procedures as explained in [RFC3264]. * O/A procedures: offer/answer procedures as explained in [RFC3264].
* Mux Category: this MUST indicate one of the following categories: * Mux Category: this MUST indicate one of the following categories:
NORMAL, NOT RECOMMENDED, IDENTICAL, SUM, TRANSPORT, INHERIT, NORMAL, NOT RECOMMENDED, IDENTICAL, SUM, TRANSPORT, INHERIT,
IDENTICAL-PER-PT, SPECIAL, or TBD as defined by [RFC8859]. IDENTICAL-PER-PT, SPECIAL, or TBD as defined by [RFC8859].
* Reference: a reference to the specification defining the * Reference: a reference to the specification defining the
skipping to change at line 2161 skipping to change at line 2174
attribute usage level. They should not choose only "session" when attribute usage level. They should not choose only "session" when
the attribute can have different values when media is disaggregated, the attribute can have different values when media is disaggregated,
i.e., when each "m=" section has its own IP address on a different i.e., when each "m=" section has its own IP address on a different
endpoint. In that case, the attribute type chosen should be endpoint. In that case, the attribute type chosen should be
"session, media" or "media" (depending on desired semantics). The "session, media" or "media" (depending on desired semantics). The
default rule is that for all new SDP attributes that can occur both default rule is that for all new SDP attributes that can occur both
in session and media level, the media level overrides the session in session and media level, the media level overrides the session
level. When this is not the case for a new SDP attribute, it MUST be level. When this is not the case for a new SDP attribute, it MUST be
explicitly stated. explicitly stated.
IANA has registered the initial set of attribute names ("att-field" IANA has registered the initial set of attribute names (<attribute-
values) with definitions as in Section 6 of this memo (these name> values) with definitions as in Section 6 of this memo (these
definitions replace those in [RFC4566]). definitions replace those in [RFC4566]).
8.2.4.2. Updates to Existing Attributes 8.2.4.2. Updates to Existing Attributes
Updated attribute registrations are accepted according to the Updated attribute registrations are accepted according to the
"Specification Required" policy of [RFC8126]. "Specification Required" policy of [RFC8126].
The Designated Expert reviewing the update is requested to evaluate The Designated Expert reviewing the update is requested to evaluate
whether the update is compatible with the prior intent and use of the whether the update is compatible with the prior intent and use of the
attribute, and whether the new document is of sufficient maturity and attribute, and whether the new document is of sufficient maturity and
skipping to change at line 2217 skipping to change at line 2230
* Mux Category: no change unless from "TBD" to another value (see * Mux Category: no change unless from "TBD" to another value (see
[RFC8859]. It MAY also change if media level is being added to [RFC8859]. It MAY also change if media level is being added to
the definition of an attribute that previously did not include it. the definition of an attribute that previously did not include it.
* Reference: a new (additional or replacement) reference MUST be * Reference: a new (additional or replacement) reference MUST be
provided. provided.
Items SHOULD be omitted if there is no impact to them as a result of Items SHOULD be omitted if there is no impact to them as a result of
the attribute update. the attribute update.
8.2.5. Bandwidth Specifiers ("bwtype") 8.2.5. Bandwidth Specifiers (<bwtype>)
A proliferation of bandwidth specifiers is strongly discouraged. A proliferation of bandwidth specifiers is strongly discouraged.
New bandwidth specifiers (<bwtype> sub-field values) MUST be New bandwidth specifiers (<bwtype> subfield values) MUST be
registered with IANA. The submission MUST reference a Standards registered with IANA. The submission MUST reference a Standards
Track RFC specifying the semantics of the bandwidth specifier Track RFC specifying the semantics of the bandwidth specifier
precisely, and indicating when it should be used, and why the precisely, and indicating when it should be used, and why the
existing registered bandwidth specifiers do not suffice. existing registered bandwidth specifiers do not suffice.
The RFC MUST specify the Mux Category for this value as defined by The RFC MUST specify the Mux Category for this value as defined by
[RFC8859]. [RFC8859].
The format of the "bwtype" registry is: The format of the <bwtype> registry is:
+======+==========+==============+===========+ +======+==========+==============+===========+
| Type | SDP Name | Mux Category | Reference | | Type | SDP Name | Mux Category | Reference |
+======+==========+==============+===========+ +======+==========+==============+===========+
Table 6: Format of the "bwtype" registry Table 6: Format of the <bwtype> Registry
IANA is requested to update the "bwtype" registry entries for the IANA is requested to update the <bwtype> registry entries for the
bandwidth specifiers "CT" and "AS" with the definitions in bandwidth specifiers "CT" and "AS" with the definitions in
Section 5.8 of this memo (these definitions replace those in Section 5.8 of this memo (these definitions replace those in
[RFC4566]). [RFC4566]).
8.2.6. Network Types ("nettype") 8.2.6. Network Types (<nettype>)
Network type "IN", representing the Internet, is defined in Network type "IN", representing the Internet, is defined in
Section 5.2 and Section 5.7 of this memo (this definition replaces Section 5.2 and Section 5.7 of this memo (this definition replaces
that in [RFC4566]). that in [RFC4566]).
To enable SDP to reference a new non-Internet environment, a new To enable SDP to reference a new non-Internet environment, a new
network type (<nettype> sub-field value) MUST be registered with network type (<nettype> subfield value) MUST be registered with IANA.
IANA. The registration is subject to the "RFC Required" policy of The registration is subject to the "RFC Required" policy of
[RFC8126]. Although non-Internet environments are not normally the [RFC8126]. Although non-Internet environments are not normally the
preserve of IANA, there may be circumstances when an Internet preserve of IANA, there may be circumstances when an Internet
application needs to interoperate with a non-Internet application, application needs to interoperate with a non-Internet application,
such as when gatewaying an Internet telephone call into the Public such as when gatewaying an Internet telephone call into the Public
Switched Telephone Network (PSTN). The number of network types Switched Telephone Network (PSTN). The number of network types
should be small and should be rarely extended. A new network type should be small and should be rarely extended. A new network type
registration MUST reference an RFC that gives details of the network registration MUST reference an RFC that gives details of the network
type and the address type(s) that may be used with it. type and the address type(s) that may be used with it.
The format of the "nettype" registry is: The format of the <nettype> registry is:
+======+==========+========================+===========+ +======+==========+========================+===========+
| Type | SDP Name | Usable addrtype Values | Reference | | Type | SDP Name | Usable addrtype Values | Reference |
+======+==========+========================+===========+ +======+==========+========================+===========+
Table 7: Format of the "nettype" registry Table 7: Format of the <nettype> Registry
IANA is requested to update the "nettype" registry to this new IANA is requested to update the <nettype> registry to this new
format. The following is the updated content of the registry: format. The following is the updated content of the registry:
+=========+==========+========================+===========+ +=========+==========+========================+===========+
| Type | SDP Name | Usable addrtype Values | Reference | | Type | SDP Name | Usable addrtype Values | Reference |
+=========+==========+========================+===========+ +=========+==========+========================+===========+
| nettype | IN | IP4, IP6 | RFC 8866 | | nettype | IN | IP4, IP6 | [RFC8866] |
+---------+----------+------------------------+-----------+ +---------+----------+------------------------+-----------+
| nettype | TN | RFC2543 | [RFC2848] | | nettype | TN | RFC2543 | [RFC2848] |
+---------+----------+------------------------+-----------+ +---------+----------+------------------------+-----------+
| nettype | ATM | NSAP, GWID, E164 | [RFC3108] | | nettype | ATM | NSAP, GWID, E164 | [RFC3108] |
+---------+----------+------------------------+-----------+ +---------+----------+------------------------+-----------+
| nettype | PSTN | E164 | [RFC7195] | | nettype | PSTN | E164 | [RFC7195] |
+---------+----------+------------------------+-----------+ +---------+----------+------------------------+-----------+
Table 8: Content of the "nettype" registry Table 8: Content of the <nettype> registry
Note that both [RFC7195] and [RFC3108] registered "E164" as an Note that both [RFC7195] and [RFC3108] registered "E164" as an
address type, although [RFC7195] mentions that the "E164" address address type, although [RFC7195] mentions that the "E164" address
type has a different context for ATM and PSTN networks. type has a different context for ATM and PSTN networks.
8.2.7. Address Types ("addrtype") 8.2.7. Address Types (<addrtype>)
New address types ("addrtype") MUST be registered with IANA. The New address types (<addrtype>) MUST be registered with IANA. The
registration is subject to the "RFC Required" policy of [RFC8126]. A registration is subject to the "RFC Required" policy of [RFC8126]. A
new address type registration MUST reference an RFC, giving details new address type registration MUST reference an RFC, giving details
of the syntax of the address type. Address types are not expected to of the syntax of the address type. Address types are not expected to
be registered frequently. be registered frequently.
Section 5.7 of this document gives new definitions of address types Section 5.7 of this document gives new definitions of address types
"IP4" and "IP6". "IP4" and "IP6".
8.3. Encryption Key Access Methods (OBSOLETE) 8.3. Encryption Key Access Methods (OBSOLETE)
skipping to change at line 2455 skipping to change at line 2468
%s"base64:" base64 / %s"base64:" base64 /
%s"uri:" uri %s"uri:" uri
; NOTE: These names are case-sensitive. ; NOTE: These names are case-sensitive.
base64 = *base64-unit [base64-pad] base64 = *base64-unit [base64-pad]
base64-unit = 4base64-char base64-unit = 4base64-char
base64-pad = 2base64-char "==" / 3base64-char "=" base64-pad = 2base64-char "==" / 3base64-char "="
base64-char = ALPHA / DIGIT / "+" / "/" base64-char = ALPHA / DIGIT / "+" / "/"
; sub-rules of 'a=' ; sub-rules of 'a='
attribute = (att-field ":" att-value) / att-field attribute = (attribute-name ":" attribute-value) /
attribute-name
att-field = token attribute-name = token
att-value = byte-string attribute-value = byte-string
att-field = attribute-name ; for backward compatibility
; sub-rules of 'm=' ; sub-rules of 'm='
media = token media = token
;typically "audio", "video", "text", "image" ;typically "audio", "video", "text", "image"
;or "application" ;or "application"
fmt = token fmt = token
;typically an RTP payload type for audio ;typically an RTP payload type for audio
;and video media ;and video media
proto = token *("/" token) proto = token *("/" token)
;typically "RTP/AVP" or "udp" ;typically "RTP/AVP", "RTP/SAVP", "udp",
;or "RTP/SAVPF"
port = 1*DIGIT port = 1*DIGIT
; generic sub-rules: addressing ; generic sub-rules: addressing
unicast-address = IP4-address / IP6-address / FQDN / extn-addr unicast-address = IP4-address / IP6-address / FQDN / extn-addr
multicast-address = IP4-multicast / IP6-multicast / FQDN multicast-address = IP4-multicast / IP6-multicast / FQDN
/ extn-addr / extn-addr
IP4-multicast = m1 3( "." decimal-uchar ) IP4-multicast = m1 3( "." decimal-uchar )
skipping to change at line 2578 skipping to change at line 2595
DIGIT = <DIGIT definition from RFC 5234> DIGIT = <DIGIT definition from RFC 5234>
CRLF = <CRLF definition from RFC 5234> CRLF = <CRLF definition from RFC 5234>
HEXDIG = <HEXDIG definition from RFC 5234> HEXDIG = <HEXDIG definition from RFC 5234>
SP = <SP definition from RFC 5234> SP = <SP definition from RFC 5234>
VCHAR = <VCHAR definition from RFC 5234> VCHAR = <VCHAR definition from RFC 5234>
URI-reference = <URI-reference definition from RFC 3986> URI-reference = <URI-reference definition from RFC 3986>
addr-spec = <addr-spec definition from RFC 5322> addr-spec = <addr-spec definition from RFC 5322>
10. Summary of Changes from RFC 4566 10. Summary of Changes from RFC 4566
* Generally clarified and refined terminology. * Generally clarified and refined terminology. Aligned terms used
in text with the ABNF. The terms <attribute>, <att-field>, and
"att-field" are now <attribute-name>. The terms <value> and <att-
value> are now <attribute-value>. The term "media" is now
<media>.
* Identified now-obsolete items: "a=cat" (Section 6.1), "a=keywds" * Identified now-obsolete items: "a=cat:" (Section 6.1), "a=keywds:"
(Section 6.2), and "k=" (Section 5.12). (Section 6.2), and "k=" (Section 5.12).
* Updated normative and informative references, and added references * Updated normative and informative references, and added references
to additional relevant related RFCs. to additional relevant related RFCs.
* Reformatted the SDP Attributes section (Section 6) for * Reformatted the SDP Attributes section (Section 6) for
readability. The syntax of attribute values is now given in ABNF. readability. The syntax of attribute values is now given in ABNF.
* Made mandatory the sending of RTCP with inactive media streams * Made mandatory the sending of RTCP with inactive media streams
(Section 6.7.4). (Section 6.7.4).
* Removed the section "Private Sessions". That section dated back * Removed the section "Private Sessions". That section dated back
to a time when the primary use of SDP was with SAP (Session to a time when the primary use of SDP was with SAP (Session
Announcement Protocol), which has fallen out of use. Now the vast Announcement Protocol), which has fallen out of use. Now the vast
majority of uses of SDP is for establishment of private sessions. majority of uses of SDP is for establishment of private sessions.
The considerations for that are covered in Section 7. The considerations for that are covered in Section 7.
* Expanded and clarified the specification of the "lang" * Expanded and clarified the specification of the "a=lang:"
(Section 6.12) and "sdplang" (Section 6.11) attributes. (Section 6.12) and "a=sdplang:" (Section 6.11) attributes.
* Removed some references to SAP because it is no longer in * Removed some references to SAP because it is no longer in
widespread use. widespread use.
* Changed the way <fmt> values for UDP transport are registered * Changed the way <fmt> values for UDP transport are registered
(Section 8.2.3). (Section 8.2.3).
* Changed the mechanism and documentation required for registering * Changed the mechanism and documentation required for registering
new attributes (Section 8.2.4.1). new attributes (Section 8.2.4.1).
* Tightened up IANA registration procedures for extensions. Removed * Tightened up IANA registration procedures for extensions. Removed
phone number and long-form name (Section 8.2). phone number and long-form name (Section 8.2).
* Expanded the IANA nettype registry to identify valid addrtypes * Expanded the IANA <nettype> registry to identify valid <addrtype>
(Section 8.2.6). subfields (Section 8.2.6).
* Reorganized the several IANA att-field registries into a single * Reorganized the several IANA "att-field" registries into a single
registry (Section 8.2.4). <attribute-name> registry (Section 8.2.4).
* Revised ABNF syntax (Section 9) for clarity. Backward * Revised ABNF syntax (Section 9) for clarity and for alignment with
compatibility is maintained with a few exceptions: text. Backward compatibility is maintained with a few exceptions.
Of particular note:
- Revised the syntax of time descriptions ("t=", "r=", "z=") to - Revised the syntax of time descriptions ("t=", "r=", "z=") to
remove ambiguities. Clarified that "z=" only modifies the remove ambiguities. Clarified that "z=" only modifies the
immediately preceding "r=" lines. Made "z=" without a immediately preceding "r=" lines. Made "z=" without a
preceding "r=" a syntax error (Section 5.11). (This is preceding "r=" a syntax error (Section 5.11). (This is
incompatible with certain aberrant usage.) incompatible with certain aberrant usage.)
- Updated the "IP6-address" and "IP6-multicast" rules, consistent - Updated the "IP6-address" and "IP6-multicast" rules, consistent
with the syntax in [RFC3986], mirroring a bug fix made to with the syntax in [RFC3986], mirroring a bug fix made to
[RFC3261] by [RFC5954]. Removed rules that were unused as a [RFC3261] by [RFC5954]. Removed rules that were unused as a
result of this change. result of this change.
- The "att-field" rule has been renamed "attribute-name" because
elsewhere "*-field" always refers to a complete line. However,
the rulename "att-field" remains defined as a synonym for
backward compatibility with references from other RFCs.
- The "att-value" rule has been renamed "attribute-value".
* Revised normative statements that were redundant with ABNF syntax, * Revised normative statements that were redundant with ABNF syntax,
making the text non-normative. making the text non-normative.
* Revised IPv4 unicast and multicast addresses in the example SDP * Revised IPv4 unicast and multicast addresses in the example SDP
descriptions per [RFC5735] and [RFC5771]. descriptions per [RFC5735] and [RFC5771].
* Changed some examples to use IPv6 addresses, and added additional * Changed some examples to use IPv6 addresses, and added additional
examples using IPv6. examples using IPv6.
* Incorporated case-insensitivity rules from [RFC4855]. * Incorporated case-insensitivity rules from [RFC4855].
* Revised sections that incorrectly referenced NTP (Section 5.2, * Revised sections that incorrectly referenced NTP (Section 5.2,
Section 5.9, Section 5.10, and Section 5.11). Section 5.9, Section 5.10, and Section 5.11).
* Clarified the explanation of the impact and use of "a=charset" * Clarified the explanation of the impact and use of the
(Section 6.10). "a=charset:" attribute (Section 6.10).
* Revised the description of "a=type" to remove implication that it * Revised the description of the "a=type:" attribute to remove
sometimes changes the default media direction to something other implication that it sometimes changes the default media direction
than sendrecv (Section 6.9). to something other than "a=sendrecv" (Section 6.9).
11. References 11. References
11.1. Normative References 11.1. Normative References
[E164] International Telecommunication Union, "E.164 : The [E164] International Telecommunication Union, "E.164 : The
international public telecommunication numbering plan", international public telecommunication numbering plan",
ITU Recommendation E.164, November 2010, ITU Recommendation E.164, November 2010,
<https://www.itu.int/rec/T-REC-E.164-201011-I/en>. <https://www.itu.int/rec/T-REC-E.164-201011-I/en>.
skipping to change at line 2767 skipping to change at line 2796
<https://www.rfc-editor.org/rfc/rfc8864>. <https://www.rfc-editor.org/rfc/rfc8864>.
11.2. Informative References 11.2. Informative References
[ITU.H332.1998] [ITU.H332.1998]
International Telecommunication Union, "H.332 : H.323 International Telecommunication Union, "H.332 : H.323
extended for loosely coupled conferences", ITU extended for loosely coupled conferences", ITU
Recommendation H.332, September 1998, Recommendation H.332, September 1998,
<https://www.itu.int/rec/T-REC-H.332-199809-I/en>. <https://www.itu.int/rec/T-REC-H.332-199809-I/en>.
[MSRP-DATACHANNEL]
Recio, J. and C. Holmberg, "MSRP over Data Channels", Work
in Progress, Internet-Draft, draft-ietf-mmusic-msrp-usage-
data-channel-20, 30 June 2020,
<https://tools.ietf.org/html/draft-ietf-mmusic-msrp-usage-
data-channel-20>.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996, Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>. <https://www.rfc-editor.org/info/rfc2045>.
[RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description [RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, DOI 10.17487/RFC2327, April 1998, Protocol", RFC 2327, DOI 10.17487/RFC2327, April 1998,
<https://www.rfc-editor.org/info/rfc2327>. <https://www.rfc-editor.org/info/rfc2327>.
[RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session [RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session
skipping to change at line 2834 skipping to change at line 2856
"Indicating User Agent Capabilities in the Session "Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, Initiation Protocol (SIP)", RFC 3840,
DOI 10.17487/RFC3840, August 2004, DOI 10.17487/RFC3840, August 2004,
<https://www.rfc-editor.org/info/rfc3840>. <https://www.rfc-editor.org/info/rfc3840>.
[RFC3890] Westerlund, M., "A Transport Independent Bandwidth [RFC3890] Westerlund, M., "A Transport Independent Bandwidth
Modifier for the Session Description Protocol (SDP)", Modifier for the Session Description Protocol (SDP)",
RFC 3890, DOI 10.17487/RFC3890, September 2004, RFC 3890, DOI 10.17487/RFC3890, September 2004,
<https://www.rfc-editor.org/info/rfc3890>. <https://www.rfc-editor.org/info/rfc3890>.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145,
DOI 10.17487/RFC4145, September 2005,
<https://www.rfc-editor.org/info/rfc4145>.
[RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session
Description Protocol (SDP) Security Descriptions for Media Description Protocol (SDP) Security Descriptions for Media
Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006, Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006,
<https://www.rfc-editor.org/info/rfc4568>. <https://www.rfc-editor.org/info/rfc4568>.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload [RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007, Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007,
<https://www.rfc-editor.org/info/rfc4855>. <https://www.rfc-editor.org/info/rfc4855>.
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for
Real-time Transport Control Protocol (RTCP)-Based Feedback
(RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February
2008, <https://www.rfc-editor.org/info/rfc5124>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008, DOI 10.17487/RFC5322, October 2008,
<https://www.rfc-editor.org/info/rfc5322>. <https://www.rfc-editor.org/info/rfc5322>.
[RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses", [RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
RFC 5735, DOI 10.17487/RFC5735, January 2010, RFC 5735, DOI 10.17487/RFC5735, January 2010,
<https://www.rfc-editor.org/info/rfc5735>. <https://www.rfc-editor.org/info/rfc5735>.
[RFC5771] Cotton, M., Vegoda, L., and D. Meyer, "IANA Guidelines for [RFC5771] Cotton, M., Vegoda, L., and D. Meyer, "IANA Guidelines for
IPv4 Multicast Address Assignments", BCP 51, RFC 5771, IPv4 Multicast Address Assignments", BCP 51, RFC 5771,
skipping to change at line 2871 skipping to change at line 2893
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description
Protocol (SDP) Grouping Framework", RFC 5888, Protocol (SDP) Grouping Framework", RFC 5888,
DOI 10.17487/RFC5888, June 2010, DOI 10.17487/RFC5888, June 2010,
<https://www.rfc-editor.org/info/rfc5888>. <https://www.rfc-editor.org/info/rfc5888>.
[RFC5954] Gurbani, V., Ed., Carpenter, B., Ed., and B. Tate, Ed., [RFC5954] Gurbani, V., Ed., Carpenter, B., Ed., and B. Tate, Ed.,
"Essential Correction for IPv6 ABNF and URI Comparison in "Essential Correction for IPv6 ABNF and URI Comparison in
RFC 3261", RFC 5954, DOI 10.17487/RFC5954, August 2010, RFC 3261", RFC 5954, DOI 10.17487/RFC5954, August 2010,
<https://www.rfc-editor.org/info/rfc5954>. <https://www.rfc-editor.org/info/rfc5954>.
[RFC6135] Holmberg, C. and S. Blau, "An Alternative Connection Model
for the Message Session Relay Protocol (MSRP)", RFC 6135,
DOI 10.17487/RFC6135, February 2011,
<https://www.rfc-editor.org/info/rfc6135>.
[RFC6466] Salgueiro, G., "IANA Registration of the 'image' Media [RFC6466] Salgueiro, G., "IANA Registration of the 'image' Media
Type for the Session Description Protocol (SDP)", Type for the Session Description Protocol (SDP)",
RFC 6466, DOI 10.17487/RFC6466, December 2011, RFC 6466, DOI 10.17487/RFC6466, December 2011,
<https://www.rfc-editor.org/info/rfc6466>. <https://www.rfc-editor.org/info/rfc6466>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013, RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>. <https://www.rfc-editor.org/info/rfc6838>.
skipping to change at line 2956 skipping to change at line 2973
Email: ali.begen@networked.media Email: ali.begen@networked.media
Paul Kyzivat Paul Kyzivat
United States of America United States of America
Email: pkyzivat@alum.mit.edu Email: pkyzivat@alum.mit.edu
Colin Perkins Colin Perkins
University of Glasgow University of Glasgow
School of Computing Science School of Computing Science
University of Glasgow
Glasgow Glasgow
G12 8QQ G12 8QQ
United Kingdom United Kingdom
Email: csp@csperkins.org Email: csp@csperkins.org
Mark Handley Mark Handley
University College London University College London
Department of Computer Science Department of Computer Science
London London
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