draft-ietf-mmusic-sdp-simulcast-04.txt   draft-ietf-mmusic-sdp-simulcast-05.txt 
Network Working Group B. Burman Network Working Group B. Burman
Internet-Draft M. Westerlund Internet-Draft M. Westerlund
Intended status: Standards Track Ericsson Intended status: Standards Track Ericsson
Expires: August 6, 2016 S. Nandakumar Expires: December 31, 2016 S. Nandakumar
M. Zanaty M. Zanaty
Cisco Cisco
February 3, 2016 June 29, 2016
Using Simulcast in SDP and RTP Sessions Using Simulcast in SDP and RTP Sessions
draft-ietf-mmusic-sdp-simulcast-04 draft-ietf-mmusic-sdp-simulcast-05
Abstract Abstract
In some application scenarios it may be desirable to send multiple In some application scenarios it may be desirable to send multiple
differently encoded versions of the same media source in different differently encoded versions of the same media source in different
RTP streams. This is called simulcast. This document describes how RTP streams. This is called simulcast. This document describes how
to accomplish simulcast in RTP and how to signal it in SDP. The to accomplish simulcast in RTP and how to signal it in SDP. The
described solution uses an RTP/RTCP identification method to identify described solution uses an RTP/RTCP identification method to identify
RTP streams belonging to the same media source, and makes an RTP streams belonging to the same media source, and makes an
extension to SDP to relate those RTP streams as being different extension to SDP to relate those RTP streams as being different
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 6, 2016. This Internet-Draft will expire on December 31, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4 2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Reaching a Diverse Set of Receivers . . . . . . . . . . . 5 3.1. Reaching a Diverse Set of Receivers . . . . . . . . . . . 5
3.2. Application Specific Media Source Handling . . . . . . . 6 3.2. Application Specific Media Source Handling . . . . . . . 6
3.3. Receiver Media Source Preferences . . . . . . . . . . . . 7 3.3. Receiver Media Source Preferences . . . . . . . . . . . . 7
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Detailed Description . . . . . . . . . . . . . . . . . . . . 9 6. Detailed Description . . . . . . . . . . . . . . . . . . . . 9
6.1. Simulcast Attribute . . . . . . . . . . . . . . . . . . . 9 6.1. Simulcast Attribute . . . . . . . . . . . . . . . . . . . 9
6.2. Simulcast Capability . . . . . . . . . . . . . . . . . . 11 6.2. Simulcast Capability . . . . . . . . . . . . . . . . . . 11
6.2.1. Declarative Use . . . . . . . . . . . . . . . . . . . 13 6.3. Offer/Answer Use . . . . . . . . . . . . . . . . . . . . 13
6.2.2. Offer/Answer Use . . . . . . . . . . . . . . . . . . 13 6.3.1. Generating the Initial SDP Offer . . . . . . . . . . 13
6.3. Relating Simulcast Streams . . . . . . . . . . . . . . . 15 6.3.2. Creating the SDP Answer . . . . . . . . . . . . . . . 13
6.4. Signaling Examples . . . . . . . . . . . . . . . . . . . 15 6.3.3. Offerer Processing the SDP Answer . . . . . . . . . . 14
6.4.1. Single-Source Client . . . . . . . . . . . . . . . . 16 6.3.4. Modifying the Session . . . . . . . . . . . . . . . . 15
6.4.2. Multi-Source Client . . . . . . . . . . . . . . . . . 17 6.4. Declarative Use . . . . . . . . . . . . . . . . . . . . . 15
7. Network Aspects . . . . . . . . . . . . . . . . . . . . . . . 20 6.5. Relating Simulcast Streams . . . . . . . . . . . . . . . 15
7.1. Bitrate Adaptation . . . . . . . . . . . . . . . . . . . 20 6.6. Signaling Examples . . . . . . . . . . . . . . . . . . . 16
8. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 21 6.6.1. Single-Source Client . . . . . . . . . . . . . . . . 16
8.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 21 6.6.2. Multi-Source Client . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 7. Network Aspects . . . . . . . . . . . . . . . . . . . . . . . 21
10. Security Considerations . . . . . . . . . . . . . . . . . . . 21 7.1. Bitrate Adaptation . . . . . . . . . . . . . . . . . . . 21
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22 8. Limitation . . . . . . . . . . . . . . . . . . . . . . . . . 22
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 10. Security Considerations . . . . . . . . . . . . . . . . . . . 23
13.1. Normative References . . . . . . . . . . . . . . . . . . 22 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 23
13.2. Informative References . . . . . . . . . . . . . . . . . 23 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23
Appendix A. Changes From Earlier Versions . . . . . . . . . . . 25 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
A.1. Modifications Between WG Version -03 and -04 . . . . . . 25 13.1. Normative References . . . . . . . . . . . . . . . . . . 23
A.2. Modifications Between WG Version -02 and -03 . . . . . . 26 13.2. Informative References . . . . . . . . . . . . . . . . . 25
A.3. Modifications Between WG Version -01 and -02 . . . . . . 26 Appendix A. Changes From Earlier Versions . . . . . . . . . . . 26
A.4. Modifications Between WG Version -00 and -01 . . . . . . 26 A.1. Modifications Between WG Version -04 and -05 . . . . . . 26
A.5. Modifications Between Individual Version -00 and WG A.2. Modifications Between WG Version -03 and -04 . . . . . . 27
Version -00 . . . . . . . . . . . . . . . . . . . . . . . 26 A.3. Modifications Between WG Version -02 and -03 . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 A.4. Modifications Between WG Version -01 and -02 . . . . . . 28
A.5. Modifications Between WG Version -00 and -01 . . . . . . 28
A.6. Modifications Between Individual Version -00 and WG
Version -00 . . . . . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction 1. Introduction
Most of today's multiparty video conference solutions make use of Most of today's multiparty video conference solutions make use of
centralized servers to reduce the bandwidth and CPU consumption in centralized servers to reduce the bandwidth and CPU consumption in
the endpoints. Those servers receive RTP streams from each the endpoints. Those servers receive RTP streams from each
participant and send some suitable set of possibly modified RTP participant and send some suitable set of possibly modified RTP
streams to the rest of the participants, which usually have streams to the rest of the participants, which usually have
heterogeneous capabilities (screen size, CPU, bandwidth, codec, etc). heterogeneous capabilities (screen size, CPU, bandwidth, codec, etc).
One of the biggest issues is how to perform RTP stream adaptation to One of the biggest issues is how to perform RTP stream adaptation to
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[RFC7656], and RTP Topologies [RFC7667]. In addition, the following [RFC7656], and RTP Topologies [RFC7667]. In addition, the following
terms are used: terms are used:
RTP Mixer: An RTP middle node, defined in [RFC7667] (Section 3.6 to RTP Mixer: An RTP middle node, defined in [RFC7667] (Section 3.6 to
3.9). 3.9).
RTP Switch: A common short term for the terms "switching RTP mixer", RTP Switch: A common short term for the terms "switching RTP mixer",
"source projecting middlebox", and "video switching MCU" as "source projecting middlebox", and "video switching MCU" as
discussed in [RFC7667]. discussed in [RFC7667].
Simulcast Stream: One Encoded Stream or Dependent Stream from a set Simulcast Stream: One encoded stream or dependent stream from a set
of concurrently transmitted Encoded Streams and optional Dependent of concurrently transmitted encoded streams and optional dependent
Streams, all sharing a common Media Source, as defined in streams, all sharing a common media source, as defined in
[RFC7656]. Decoding a Dependent Stream also requires the related [RFC7656]. Decoding a dependent stream also requires the related
(Dependent and) Encoded Stream(s), but in the context of simulcast (dependent and) encoded stream(s), but in the context of simulcast
that is considered a property of the Dependent Stream constituting that is considered a property of the dependent stream constituting
the simulcast stream. For example, HD and thumbnail video the simulcast stream. For example, HD and thumbnail video
simulcast versions of a single Media Source sent concurrently as simulcast versions of a single media source sent concurrently as
separate RTP Streams. separate RTP Streams.
Simulcast Format: Different formats of a simulcast stream serve the Simulcast Format: Different formats of a simulcast stream serve the
same purpose as alternative RTP payload types in non-simulcast same purpose as alternative RTP payload types in non-simulcast
SDP, to allow multiple alternative media formats for a given RTP SDP, to allow multiple alternative media formats for a given RTP
Stream. As for multiple RTP payload types on the m-line, any one stream. As for multiple RTP payload types on the m-line in offer/
of the alternative formats can be used at a given point in time, answer [RFC3264], any one of the negotiated alternative formats
but not more than one (based on RTP timestamp), and what format is can be used in a single RTP stream at a given point in time, but
used can change dynamically from one RTP packet to another. For not more than one (based on RTP timestamp). What format is used
example, if all participants in a group video call can decode can change dynamically from one RTP packet to another.
H.264 and H.265 video, but only some can encode H.265, both H.264
and H.265 can be kept as alternative formats, and the format may Simulcast Stream Identifier (SCID): The identification value used to
dynamically switch between H.264 and H.265 as different refer to individual simulcast streams, identical to the "rid-id"
participants become active speaker. identification value for an RTP Constraint [I-D.ietf-mmusic-rid]
and the corresponding content of "RtpStreamId" RTCP SDES Item
[I-D.ietf-avtext-rid].
2.2. Requirements Language 2.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
3. Use Cases 3. Use Cases
Many use cases of simulcast as described in this document relate to a Many use cases of simulcast as described in this document relate to a
multi-party communication session where one or more central nodes are multi-party communication session where one or more central nodes are
used to adapt the view of the communication session towards used to adapt the view of the communication session towards
individual participants, and facilitate the media transport between individual participants, and facilitate the media transport between
participants. Thus, these cases targets the RTP Mixer type of participants. Thus, these cases target the RTP Mixer type of
topology. topology.
There are two principle approaches for an RTP Mixer to provide this There are two principle approaches for an RTP Mixer to provide this
adapted view of the communication session to each receiving adapted view of the communication session to each receiving
participant: participant:
o Transcoding (decoding and re-encoding) received RTP streams with o Transcoding (decoding and re-encoding) received RTP streams with
characteristics adapted to each receiving participant. This often characteristics adapted to each receiving participant. This often
include mixing or composition of media sources from multiple include mixing or composition of media sources from multiple
participants into a mixed media source originated by the RTP participants into a mixed media source originated by the RTP
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For example, assume for simplicity a set of receiving participants For example, assume for simplicity a set of receiving participants
that differ only in that some have support to receive Codec A, and that differ only in that some have support to receive Codec A, and
the others have support to receive Codec B. Further assume that the the others have support to receive Codec B. Further assume that the
sending participant can send both Codec A and B. It can then reach sending participant can send both Codec A and B. It can then reach
all receivers by creating two simulcasted RTP streams from each media all receivers by creating two simulcasted RTP streams from each media
source; one for Codec A and one for Codec B. source; one for Codec A and one for Codec B.
In another simple example, a set of receiving participants differ In another simple example, a set of receiving participants differ
only in screen resolution; some are able to display video with at only in screen resolution; some are able to display video with at
most 360p resolution and some support 720p resolution. A sending most 360p resolution and some support 720p resolution. A sending
participant can then reach all receivers by creating a simulcast of participant can then reach all receivers with best possible
RTP streams with 360p and 720p resolution for each sent video media resolution by creating a simulcast of RTP streams with 360p and 720p
source. resolution for each sent video media source.
In more elaborate cases, the receiving participants differ both in In more elaborate cases, the receiving participants differ both in
available sampling and bitrate, and maybe also codec, and it is up to available sampling and bitrate, and maybe also codec, and it is up to
the RTP switch to find a good trade-off in which simulcasted stream the RTP switch to find a good trade-off in which simulcasted stream
to choose for each intended receiver. It is also the responsibility to choose for each intended receiver. It is also the responsibility
of the RTP switch to negotiate a good fit of simulcast streams with of the RTP switch to negotiate a good fit of simulcast streams with
the sending participant. the sending participant.
The maximum number of simulcasted RTP streams that can be sent is The maximum number of simulcasted RTP streams that can be sent is
mainly limited by the amount of processing and uplink network mainly limited by the amount of processing and uplink network
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5. Overview 5. Overview
As an overview, the above requirements are met by signaling simulcast As an overview, the above requirements are met by signaling simulcast
capability and configurations in SDP [RFC4566]: capability and configurations in SDP [RFC4566]:
o An offer or answer can contain a number of simulcast streams, o An offer or answer can contain a number of simulcast streams,
separate for send and receive directions. separate for send and receive directions.
o An offer or answer can contain multiple, alternative simulcast o An offer or answer can contain multiple, alternative simulcast
stream formats in the same fashion as multiple, alternative codecs stream formats in the same fashion as multiple, alternative
can be offered in a media description. formats can be offered in a media description.
o A single media source per SDP media description is assumed, which o A single media source per SDP media description is assumed, which
is aligned with the concepts defined in [RFC7656] and will is aligned with the concepts defined in [RFC7656] and will
specifically work in a WebRTC context, both with and without specifically work in a WebRTC context, both with and without
BUNDLE [I-D.ietf-mmusic-sdp-bundle-negotiation] grouping. BUNDLE [I-D.ietf-mmusic-sdp-bundle-negotiation] grouping.
o The codec configuration for a simulcast stream is expressed o The codec configuration for a simulcast stream is expressed
through use of a separately specified RTP-level identification through use of separately specified RTP payload format constraints
mechanism [I-D.ietf-mmusic-rid][I-D.roach-avtext-rid], which [I-D.ietf-mmusic-rid] with an associated RTP-level identification
complements and effectively extends the available simulcast stream mechanism [I-D.ietf-avtext-rid] to identify which RTP payload
identification and configuration possibilities that could be format constraints an RTP stream adheres to. This complements and
provided by using only SDP formats. effectively extends simulcast stream identification and
configuration possibilities that could be provided by using only
SDP formats as identifier.
o It is possible, but not required to use source-specific signaling o It is possible, but not required to use source-specific signaling
[RFC5576] with the proposed solution. [RFC5576] with the proposed solution.
6. Detailed Description 6. Detailed Description
This section further details the overview above (Section 5). First, This section further details the overview above (Section 5). First,
formal syntax is provided (Section 6.1), followed by the rest of the formal syntax is provided (Section 6.1), followed by the rest of the
SDP attribute definition in Section 6.2. Relating Simulcast Streams SDP attribute definition in Section 6.2. Relating Simulcast Streams
(Section 6.3) provides the definition of the RTP/RTCP mechanisms (Section 6.5) provides the definition of the RTP/RTCP mechanisms
used. The section is concluded with a number of examples. used. The section is concluded with a number of examples.
6.1. Simulcast Attribute 6.1. Simulcast Attribute
Name: simulcast This document defines a new SDP media-level "a=simulcast" attribute
with the following ABNF [RFC5234] syntax:
Value: sc-value
Usage Level: media
Charset Dependent: no
Multiplex Category: NORMAL
Syntax [RFC5234]:
sc-attr = "a=simulcast:" sc-value sc-attr = "a=simulcast:" sc-value
sc-value = sc-str-list [SP sc-str-list] sc-value = sc-str-list [SP sc-str-list]
sc-str-list = sc-dir SP sc-alt-list *( ";" sc-alt-list ) sc-str-list = sc-dir SP sc-alt-list *( ";" sc-alt-list )
sc-dir = "send" / "recv" sc-dir = "send" / "recv"
sc-alt-list = sc-id *( "," sc-id ) sc-alt-list = sc-id *( "," sc-id )
sc-id-paused = "~" sc-id-paused = "~"
sc-id = [sc-id-paused] rid-identifier / token sc-id = [sc-id-paused] rid-identifier
; SP defined in [RFC5234] ; SP defined in [RFC5234]
; token defined in [RFC4566]
; rid-identifier defined in [I-D.ietf-mmusic-rid] ; rid-identifier defined in [I-D.ietf-mmusic-rid]
Figure 1: ABNF for Simulcast Figure 1: ABNF for Simulcast
The "a=simulcast" attribute has a parameter in the form of one or two The "a=simulcast" attribute has a parameter in the form of one or two
simulcast stream descriptions, each consisting of a direction ("send" simulcast stream descriptions, each consisting of a direction ("send"
or "recv"), followed by a list of one or more simulcast streams. or "recv"), followed by a list of one or more simulcast streams. The
Each simulcast stream in that list is separated by a semicolon (";"). simulcast stream identification (SCID) MUST be have the form of an
Each simulcast stream can in turn be offered in one or more RTP stream identifier, as described by RTP Payload Format Constraints
alternative formats, where each simulcast stream alternative is [I-D.ietf-mmusic-rid].
separated by a comma (","). The simulcast stream alternative MUST be
described in the form of a RID, as described by In the list of simulcast streams, each SCID is separated by a
[I-D.ietf-mmusic-rid]. Each simulcast stream can be initially paused semicolon (";"). Each simulcast stream can in turn be offered in one
[I-D.ietf-avtext-rtp-stream-pause], indicated by prepending a "~" to or more alternative formats, where each alternative SCID is separated
the simulcast stream. In case there are simulcast stream by a comma (","). Each simulcast stream can also be specified as
alternatives, pause can be specified individually for each initially paused [RFC7728], indicated by prepending a "~" to the
alternative. The reason to allow separate initial pause states for SCID. In case there are alternative SCID, pause can be specified
each simulcast stream alternative is that pause capability can be individually for each SCID. The reason to allow separate initial
specified individually for each RTP payload type referenced by a RID, pause states for each SCID is that pause capability can be specified
which makes it infeasible to pause RID where any of the related RTP individually for each RTP payload type referenced by an SCID. Since
pause capability specified via the "a=rtcp-fb" attribute and SCID
specified by "a=rid" can refer to common payload types, it is
unfeasible to pause streams with SCID where any of the related RTP
payload type(s) do not have pause capability. payload type(s) do not have pause capability.
Examples: Examples:
a=simulcast:send 1,2,3;~4,~5 recv 1;~2,~5 a=simulcast:send 1,2,3;~4,~5 recv 6;~7,~8
a=simulcast:recv 1;4,5 send 1;2 a=simulcast:recv 1;4,5 send 6;7
Figure 2: Simulcast Examples Figure 2: Simulcast Examples
Above are two examples of different "a=simulcast" lines. Above are two examples of different "a=simulcast" lines.
The first line is an example offer to send two simulcast streams and The first line is an example offer to send two simulcast streams and
to receive two simulcast streams. The first simulcast stream in send to receive two simulcast streams. The first simulcast stream in send
direction can be sent as three different alternatives (1, 2, 3), and direction can be sent in three different alternative formats (SCID 1,
the second simulcast stream in send direction can be sent as two 2, 3), and the second simulcast stream in send direction can be sent
different alternatives (4, 5). All second stream send alternatives in two different alternative formats (SCID 4, 5). Both of the second
are offered as initially paused. The first simulcast stream in stream alternative formats in send direction are offered as initially
receive direction has no alternatives (only 1). The second simulcast paused. The first simulcast stream in receive direction has no
stream in receive direction has two alternatives (2, 5) that are both alternative formats (SCID 6). The second simulcast stream in receive
direction has two alternative formats (SCID 7, 8) that are both
offered as initially paused. offered as initially paused.
The second line is an example answer to the first line, accepting to The second line is an example answer to the first line, accepting to
send and receive the two offered simulcast streams, however send and send and receive the two offered simulcast streams, however send and
receive directions are specified in opposite order compared to the receive directions are specified in opposite order compared to the
first line, which lets the answer keep the same order of simulcast first line, which lets the answer keep the same order of simulcast
streams in the SDP as in the offer, even though directionality is streams in the SDP as in the offer, for convenience, even though
reversed. This example answer has removed all offered alternatives directionality is reversed. This example answer has removed all
for the first simulcast stream (keeping only 1), but kept alternative offered alternative formats for the first simulcast stream (keeping
formats for the second simulcast stream in receive direction (4, 5). only SCID 1), but kept alternative formats for the second simulcast
The answer accepts to send two simulcast streams, without stream in receive direction (4, 5). The answer accepts to send two
alternatives. The answer does not accept initial pause of any simulcast streams, without alternatives. The answer does not accept
simulcast streams, in either direction. More examples can be found initial pause of any simulcast streams, in either direction. More
in Section 6.4. examples can be found in Section 6.6.
6.2. Simulcast Capability 6.2. Simulcast Capability
Simulcast capability is expressed as a new media level SDP attribute, Simulcast capability is expressed through a new media level SDP
"a=simulcast" (Section 6.1), with multiplex category attribute, "a=simulcast" (Section 6.1). The meaning of the attribute
[I-D.ietf-mmusic-sdp-mux-attributes] NORMAL. on SDP session level is undefined and MUST NOT be used. The meaning
of including multiple "a=simulcast" lines in a single SDP media
description is undefined and MUST NOT be used.
For each desired direction (send/recv), the simulcast attribute For each desired direction (send/recv), the simulcast attribute
defines a list of simulcast streams (separated by semicolons), each defines a list of simulcast streams (separated by semicolons), each
of which is a list of simulcast formats (separated by commas). The of which is a list of alternate simulcast stream formats (separated
meaning of the attribute on SDP session level is undefined and MUST by commas). The different simulcast stream formats MUST be
NOT be used. identified through the RTP payload format constraints
[I-D.ietf-mmusic-rid] RTP-level identification mechanism
The meaning of including multiple "a=simulcast" lines in a single SDP [I-D.ietf-avtext-rid], here denoted SCID. Simulcast streams using
media description is undefined and MUST NOT be used. There are undefined SCID MUST NOT be used as valid simulcast streams by an RTP
separate and independent sets of parameters for simulcast in send and stream receiver.
receive directions. When listing multiple directions, each direction
MUST NOT occur more than once on the same line.
The different simulcast streams MUST be identified through the RTP-
level "RID" identification mechanism [I-D.ietf-mmusic-rid].
There are separate and independent sets of parameters for simulcast
in send and receive directions. When listing multiple directions,
each direction MUST NOT occur more than once on the same line.
Attribute parameters are grouped by direction and consist of a Attribute parameters are grouped by direction and consist of a
listing of simulcast stream identifications to be used. The number listing of SCID to be used. The direction for an SCID MUST be
of (non-alternative, see below) identifications in the list sets a aligned with the direction specified for the corresponding RTP stream
identifier on the "a=rid" line.
The number of (non-alternative, see above) SCID in the list sets a
limit to the number of supported simulcast streams in that direction. limit to the number of supported simulcast streams in that direction.
The order of the listed simulcast versions in the "send" direction The order of the listed SCID in the "send" direction suggests a
suggests a proposed order of preference, in decreasing order: the proposed order of preference, in decreasing order: the SCID listed
stream listed first is the most preferred Section 3.1, and subsequent first is the most preferred and subsequent streams have progressively
streams have progressively lower preference. The order of the listed lower preference. The order of the listed SCID in the "recv"
simulcast streams in the "recv" direction expresses a preference direction expresses a preference which simulcast streams that are
which simulcast streams that are preferred, with the leftmost being preferred, with the leftmost being most preferred. This can be of
most preferred. This can be of importance if the number of actually importance if the number of actually sent simulcast streams have to
sent simulcast streams have to be reduced for some reason. be reduced for some reason.
Formats that have explicit dependencies [RFC5583] SCID that have explicit dependencies [RFC5583] [I-D.ietf-mmusic-rid]
[I-D.ietf-mmusic-rid] to other formats (even in the same media to other SCID (even in the same media description) MAY be used.
description) MAY be listed as different simulcast streams.
Alternative simulcast formats MAY be specified as part of the Alternative SCID MAY be specified as part of the attribute parameters
attribute parameters by expressing each simulcast stream as a comma- by expressing each simulcast stream as a comma-separated list of
separated list of alternative format identifiers. In this case, it alternative SCID. In this case, it is not possible to align what
is not possible to align what alternative formats that are used alternative SCID that are used between different simulcast streams,
between different simulcast streams, like requiring all simulcast like requiring all simulcast streams to use SCID alternatives
streams to use alternatives with the same codec format. The order of referring to the same codec format. The order of the SCID
the format alternatives within a simulcast stream is significant; the alternatives within a simulcast stream is significant; the SCID
alternatives are listed from (left) most preferred to (right) least alternatives are listed from (left) most preferred to (right) least
preferred. For the use of simulcast, this overrides the normal codec preferred. For the use of simulcast, this overrides the normal codec
preference as expressed by format type ordering on the "m="-line, preference as expressed by format type ordering on the "m=" line,
using regular SDP rules. This is to enable a separation of general using regular SDP rules. This is to enable a separation of general
codec preferences and simulcast stream configuration preferences. codec preferences and simulcast stream configuration preferences.
A simulcast stream can use a codec defined such that the same RTP A simulcast stream can use a codec defined such that the same RTP
SSRC can change RTP payload type multiple times during a session, SSRC can change RTP payload type multiple times during a session,
possibly even on a per-packet basis. A typical example can be a possibly even on a per-packet basis. A typical example can be a
speech codec that makes use of Comfort Noise [RFC3389] and/or DTMF speech codec that makes use of Comfort Noise [RFC3389] and/or DTMF
[RFC4733] formats. In those cases, such "related" formats MUST NOT [RFC4733] formats. In those cases, such "related" formats MUST NOT
be listed explicitly in the attribute parameters, since they are not be defined as SCID and listed explicitly in the attribute parameters,
strictly simulcast streams of the media source, but rather a specific since they are not strictly simulcast streams of the media source,
way of generating the RTP stream of a single simulcast stream with but rather a specific way of generating the RTP stream of a single
varying RTP payload type. Instead, only a single simulcast stream simulcast stream with varying RTP payload type.
identification MUST be used per simulcast stream or alternative
simulcast format (if there are such) in the SDP.
If RTP stream pause/resume [I-D.ietf-avtext-rtp-stream-pause] is If RTP stream pause/resume [RFC7728] is supported, any SCID MAY be
supported, any simulcast stream identification MAY be prefixed by a prefixed by a "~" character to indicate that the corresponding
"~" character to indicate that the corresponding simulcast stream is simulcast stream is initially paused already from start of the RTP
initially paused already from start of the RTP session. In this session. In this case, support for RTP stream pause/resume MUST also
case, support for RTP stream pause/resume MUST also be included under be included under the same "m=" line where "a=simulcast" is included.
the same "m="-line listing "a=simulcast". If the simulcast stream is If the simulcast stream is specified as a list of alternative SCID,
specified as a list of alternative formats, the indication is each of which can be individually prefixed by the paused indication.
prepended to the first format of the list and applies to whatever All RTP payload types related to such initially paused simulcast
alternative that is eventually chosen. All RTP payload types related stream MUST be listed in the SDP as pause/resume capable as specified
to such initially paused simulcast stream MUST be listed in the SDP by [RFC7728], e.g. by using the "*" wildcard format for "a=rtcp-fb".
as pause/resume capable as specified by
[I-D.ietf-avtext-rtp-stream-pause].
An initially paused simulcast stream in "send" direction MUST be An initially paused simulcast stream in "send" direction MUST be
considered equivalent to an unsolicited locally paused stream, and be considered equivalent to an unsolicited locally paused stream, and be
handled accordingly. Initially paused simulcast streams are resumed handled accordingly. Initially paused simulcast streams are resumed
as described by the RTP pause/resume specification. An RTP stream as described by the RTP pause/resume specification. An RTP stream
receiver that wishes to resume an unsolicited locally paused stream receiver that wishes to resume an unsolicited locally paused stream
needs to know the SSRC of that stream. The SSRC of an initially needs to know the SSRC of that stream. The SSRC of an initially
paused simulcast stream can be obtained from an RTP stream sender paused simulcast stream can be obtained from an RTP stream sender
RTCP Sender Report (SR) including both the desired SSRC as "SSRC of RTCP Sender Report (SR) including both the desired SSRC as "SSRC of
sender", and the stream RID identification as an RID RTCP SDES item. sender", and the SCID value in an RtpStreamId RTCP SDES item
[I-D.ietf-avtext-rid].
Including an initially paused simulcast stream in "recv" direction in Including an initially paused simulcast stream in "recv" direction in
an SDP towards an RTP sender, SHOULD cause the remote RTP sender to an SDP towards an RTP sender, SHOULD cause the remote RTP sender to
put the stream as unsolicited locally paused, unless there are other put the stream as unsolicited locally paused, unless there are other
RTP stream receivers that do not mark the simulcast stream as RTP stream receivers that do not mark the simulcast stream as
initially paused. The reason to require an initially paused "recv" initially paused. The reason to require an initially paused "recv"
stream to be considered locally paused by the remote RTP sender, stream to be considered locally paused by the remote RTP sender,
instead of making it equivalent to implicitly sending a pause instead of making it equivalent to implicitly sending a pause
request, is because the pausing RTP sender cannot know which SSRC request, is because the pausing RTP sender cannot know which
owns the restriction when TMMBR/TMMBN are used for pause/resume receiving SSRC owns the restriction when TMMBR/TMMBN are used for
signaling since the RTP receiver's SSRC in send direction is not pause/resume signaling since the RTP receiver's SSRC in send
known yet. direction is sometimes not yet known.
Use of the redundant audio data [RFC2198] format could be seen as a Use of the redundant audio data [RFC2198] format could be seen as a
form of simulcast for loss protection purposes, but is not considered form of simulcast for loss protection purposes, but is not considered
conflicting with the mechanisms described in this memo and MAY conflicting with the mechanisms described in this memo and MAY
therefore be used as any other format. In this case the "red" therefore be used as any other format. In this case the "red"
format, rather than the carried formats, SHOULD be the one to list as format, rather than the carried formats, SHOULD be the one to list as
a simulcast stream on the "a=simulcast" line. a simulcast stream on the "a=simulcast" line.
The media formats and corresponding characteristics of simulcast The media formats and corresponding characteristics of simulcast
streams SHOULD be chosen such that they are different. If this streams SHOULD be chosen such that they are different, either as
different SDP formats with differing "a=rtpmap" and/or "a=fmtp"
lines, as differently defined RTP Constraints, or both. If this
difference is not required, RTP duplication [RFC7104] procedures difference is not required, RTP duplication [RFC7104] procedures
SHOULD be considered instead of simulcast. SHOULD be considered instead of simulcast.
6.2.1. Declarative Use 6.3. Offer/Answer Use
When used as a declarative media description, "a=simulcast" line
"recv" direction formats indicate the configured end point's required
capability to recognize and receive a specified set of RTP streams as
simulcast streams. In the same fashion, "a=simulcast" line "send"
direction requests the end point to send a specified set of RTP
streams as simulcast streams.
If multiple simulcast formats are listed, it means that the
configured end point MUST be prepared to receive any of the "recv"
formats, and MAY send any of the "send" formats for that simulcast
stream.
Editor's note: It may not be beneficial for declarative use to be Note: The inclusion of "a=simulcast" or the use of simulcast does
limited to a single media source per "m=" line, as elaborated not change any of the interpretation or Offer/Answer procedures
further in Section 8. for other SDP attributes, like "a=fmtp" or "a=rid".
6.2.2. Offer/Answer Use 6.3.1. Generating the Initial SDP Offer
An offerer wanting to use simulcast SHALL include the "a=simulcast" An offerer wanting to use simulcast SHALL include the "a=simulcast"
attribute in the offer. An offerer that receives an answer without attribute in the offer. An offerer listing a set of receive
"a=simulcast" MUST NOT use simulcast towards the answerer. An simulcast streams and/or alternative formats as SCID in the offer
offerer that receives an answer with "a=simulcast" without any MUST be prepared to receive RTP streams for any of those simulcast
simulcast stream identifications in a specified direction MUST NOT streams and/or alternative formats from the answerer.
use simulcast in that direction.
6.3.2. Creating the SDP Answer
An answerer that does not understand the concept of simulcast will An answerer that does not understand the concept of simulcast will
also not know the attribute and will remove it in the SDP answer, as also not know the attribute and will remove it in the SDP answer, as
defined in existing SDP Offer/Answer [RFC3264] procedures. defined in existing SDP Offer/Answer [RFC3264] procedures.
An answerer that does understand the attribute and that wants to An answerer that does understand the attribute and that wants to
support simulcast in an indicated direction SHALL reverse support simulcast in an indicated direction SHALL reverse
directionality of the unidirectional direction parameters; "send" directionality of the unidirectional direction parameters; "send"
becomes "recv" and vice versa, and include it in the answer. becomes "recv" and vice versa, and include it in the answer.
An offerer listing a set of receive simulcast streams and/or
alternative formats in the offer MUST be prepared to receive RTP
streams for any of those simulcast streams and/or alternative formats
from the answerer.
An answerer that receives an offer with simulcast containing an An answerer that receives an offer with simulcast containing an
"a=simulcast" attribute listing alternative formats for simulcast "a=simulcast" attribute listing alternative SCID MAY keep all the
streams MAY keep all the alternatives in the answer, but it MAY also alternative SCID in the answer, but it MAY also choose to remove any
choose to remove any non-desirable alternatives per simulcast stream non-desirable alternative SCID in the answer. The answerer MUST NOT
in the answer. The answerer MUST NOT add any alternatives that were add any alternative SCID that were not present in the offer. The
not present in the offer. answerer MUST be prepared to receive any of the receive direction
SCID alternatives, and MAY send any of the send direction
alternatives that are kept in the answer.
An answerer that receives an offer with simulcast that lists a number An answerer that receives an offer with simulcast that lists a number
of simulcast streams, MAY reduce the number of simulcast streams in of simulcast streams, MAY reduce the number of simulcast streams in
the answer, but MUST NOT add simulcast streams. the answer, but MUST NOT add simulcast streams.
An offerer that receives an answer where some simulcast formats are An answerer that receives an offer without RTP stream pause/resume
kept MUST be prepared to receive any of the kept send direction capability MUST NOT mark any simulcast streams as initially paused in
alternatives, and MAY send any of the kept receive direction the answer.
alternatives from the answer. Similarly, the answerer MUST be
prepared to receive any of the kept receive direction alternatives,
and MAY send any of the kept send direction alternatives in the
answer.
The offerer and answerer MUST NOT send more than a single alternative An RTP stream pause/resume capable answerer that receives an offer
format at a time (based on RTP timestamps) per simulcast stream, but with RTP stream pause/resume capability MAY mark any SCID that refer
MAY change format on a per-RTP packet basis. This corresponds to the to pause/resume capable formats as initially paused in the answer.
existing (non-simulcast) SDP offer/answer case when multiple formats
are included on the "m=" line in the SDP answer.
An offerer that receives an answer where some of the simulcast An answerer that receives indication in an offer of an SCID being
streams are removed MAY release the corresponding resources (codec, initially paused , SHOULD mark that SCID as initially paused also in
transport, etc) in its receive direction and MUST NOT send any RTP the answer, regardless of direction, unless it has good reason for
packets corresponding to the removed simulcast streams. the SCID not being initially paused. One such reason could for
example be that the answerer would otherwise initially not receive
any media of that type at all.
Simulcast streams or formats using undefined simulcast stream 6.3.3. Offerer Processing the SDP Answer
identifications MUST NOT be used as valid simulcast streams by an RTP
stream receiver.
An answerer that receives an offer without RTP stream pause/resume An offerer that receives an answer without "a=simulcast" MUST NOT use
capability MUST NOT mark any simulcast streams as initially paused in simulcast towards the answerer. An offerer that receives an answer
the answer. with "a=simulcast" without any SCID in a specified direction MUST NOT
use simulcast in that direction.
An answerer that receives an offer with RTP stream pause/resume An offerer that receives an answer where some SCID alternatives are
capability MAY mark any simulcast streams as initially paused in the kept MUST be prepared to receive any of the kept send direction SCID
answer. alternatives, and MAY send any of the kept receive direction SCID
alternatives.
An answerer that receives indication in an offer of a simulcast An offerer that receives an answer where some of the SCID are removed
stream being initially paused , SHOULD mark that simulcast stream as MAY release the corresponding resources (codec, transport, etc) in
initially paused also in the answer, regardless of direction, unless its receive direction and MUST NOT send any RTP packets corresponding
it has good reason for the stream not being initially paused. to the removed SCID.
An offerer that offered some of its simulcast streams as initially An offerer that offered some of its SCID as initially paused and that
paused and that receives an answer that does not indicate RTP stream receives an answer that does not indicate RTP stream pause/resume
pause/resume capability, MUST NOT intially pause any simulcast capability, MUST NOT initially pause any simulcast streams.
streams.
An offerer with RTP stream pause/resume capability that receives an An offerer with RTP stream pause/resume capability that receives an
answer where some simulcast streams are marked as initially paused, answer where some SCID are marked as initially paused, SHOULD
SHOULD initially pause them regardless if they were marked as initially pause those RTP streams regardless if they were marked as
initially paused also in the offer, unless it has good reason for initially paused also in the offer, unless it has good reason for
those streams not being initially paused. those RTP streams not being initially paused. One such reason could
for example be that the answerer would otherwise initially not
receive any media of that type at all.
Note: The inclusion of "a=simulcast" or the use of simulcast does 6.3.4. Modifying the Session
not change any of the interpretation or Offer/Answer procedures
for other SDP attributes, like "a=fmtp" or "a=rid".
6.3. Relating Simulcast Streams Offers and answers inside an existing session follow the rules for
initial session negotiation, with the additional restriction that any
SCID marked as initially paused in such offer or answer MUST already
be paused, thus a new offer/answer MUST NOT replace use of RTP stream
pause/resume [RFC7728] in the session. Session modification
restrictions in section 6.5 of "a=rid" [I-D.ietf-mmusic-rid] also
apply.
6.4. Declarative Use
When used as a declarative media description, "a=simulcast" line
"recv" direction formats indicate the configured end point's required
capability to recognize and receive a specified set of RTP streams as
simulcast streams. In the same fashion, "a=simulcast" line "send"
direction requests the end point to send a specified set of RTP
streams as simulcast streams.
If multiple alternative simulcast formats are listed, it means that
the configured end point MUST be prepared to receive any of the
"recv" formats, and MAY send any of the "send" formats for that
simulcast stream, which is aligned with the semantics of listing
multiple formats on the "m=" line.
It may not be beneficial for declarative use to be limited to a
single media source per "m=" line, as elaborated further in
Section 8.
6.5. Relating Simulcast Streams
Simulcast RTP streams MUST be related on RTP level through RID Simulcast RTP streams MUST be related on RTP level through RID
[I-D.roach-avtext-rid], as specified in the SDP "a=simulcast" [I-D.ietf-avtext-rid], as specified in the SDP "a=simulcast"
attribute (Section 6.2) parameters. This is sufficient as long as attribute (Section 6.2) parameters. This is sufficient as long as
there is only a single media source per SDP media description. When there is only a single media source per SDP media description. When
using BUNDLE [I-D.ietf-mmusic-sdp-bundle-negotiation], where multiple using BUNDLE [I-D.ietf-mmusic-sdp-bundle-negotiation], where multiple
SDP media descriptions jointly specify a single RTP session, the SDES SDP media descriptions jointly specify a single RTP session, the SDES
MID identification mechanism in BUNDLE allows relating RTP streams MID identification mechanism in BUNDLE allows relating RTP streams
back to individual media descriptions, after which the above back to individual media descriptions, after which the above
described RID relations can be used. Use of the RTP header extension described RID relations can be used. Use of the RTP header extension
[RFC5285] for both MID and RID identifications can be important to [RFC5285] for both MID and RID identifications can be important to
ensure rapid initial reception, required to correctly interpret and ensure rapid initial reception, required to correctly interpret and
process the RTP streams. Implementers of this specification MUST process the RTP streams. Implementers of this specification MUST
support RTCP source description (SDES) item and SHOULD support RTP support RTCP source description (SDES) item and SHOULD support RTP
header extension method to signal RID on RTP level. header extension method to signal RID on RTP level.
6.4. Signaling Examples RTP streams MUST only use a single alternative SCID at a time (based
on RTP timestamps), but MAY change format on a per-RTP packet basis.
This corresponds to the existing (non-simulcast) SDP offer/answer
case when multiple formats are included on the "m=" line in the SDP
answer.
6.6. Signaling Examples
These examples describe a client to video conference service, using a These examples describe a client to video conference service, using a
centralized media topology with an RTP mixer. centralized media topology with an RTP mixer.
+---+ +-----------+ +---+ +---+ +-----------+ +---+
| A |<---->| |<---->| B | | A |<---->| |<---->| B |
+---+ | | +---+ +---+ | | +---+
| Mixer | | Mixer |
+---+ | | +---+ +---+ | | +---+
| F |<---->| |<---->| J | | F |<---->| |<---->| J |
+---+ +-----------+ +---+ +---+ +-----------+ +---+
Figure 3: Four-party Mixer-based Conference Figure 3: Four-party Mixer-based Conference
6.4.1. Single-Source Client 6.6.1. Single-Source Client
Alice is calling in to the mixer with a simulcast-enabled client Alice is calling in to the mixer with a simulcast-enabled client
capable of a single media source per media type. The client can send capable of a single media source per media type. The client can send
a simulcast of 2 video resolutions and frame rates: HD 1280x720p a simulcast of 2 video resolutions and frame rates: HD 1280x720p
30fps and thumbnail 320x180p 15fps. This is defined below using the 30fps and thumbnail 320x180p 15fps. This is defined below using the
"imageattr" [RFC6236]. In this example, only the "pt" RID parameter "imageattr" [RFC6236]. In this example, only the "pt" RID parameter
is used, effectively achieving a 1:1 mapping between RID and media is used, effectively achieving a 1:1 mapping between RID and media
formats (RTP payload types), to describe simulcast stream formats. formats (RTP payload types), to describe simulcast stream formats.
Alice's Offer: Alice's Offer:
skipping to change at page 16, line 40 skipping to change at page 17, line 19
c=IN IP4 192.0.2.156 c=IN IP4 192.0.2.156
m=audio 49200 RTP/AVP 0 m=audio 49200 RTP/AVP 0
a=rtpmap:0 PCMU/8000 a=rtpmap:0 PCMU/8000
m=video 49300 RTP/AVP 97 98 m=video 49300 RTP/AVP 97 98
a=rtpmap:97 H264/90000 a=rtpmap:97 H264/90000
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:97 profile-level-id=42c01f; max-fs=3600; max-mbps=108000 a=fmtp:97 profile-level-id=42c01f; max-fs=3600; max-mbps=108000
a=fmtp:98 profile-level-id=42c00b; max-fs=240; max-mbps=3600 a=fmtp:98 profile-level-id=42c00b; max-fs=240; max-mbps=3600
a=imageattr:97 send [x=1280,y=720] recv [x=1280,y=720] a=imageattr:97 send [x=1280,y=720] recv [x=1280,y=720]
a=imageattr:98 send [x=320,y=180] recv [x=320,y=180] a=imageattr:98 send [x=320,y=180] recv [x=320,y=180]
a=rid:1 pt=97 a=rid:1 pt=97 send
a=rid:2 pt=98 a=rid:2 pt=98 send
a=simulcast:send 1;2 recv 1 a=rid:3 pt=97 recv
a=simulcast:send 1;2 recv 3
Figure 4: Single-Source Simulcast Offer Figure 4: Single-Source Simulcast Offer
The only thing in the SDP that indicates simulcast capability is the The only thing in the SDP that indicates simulcast capability is the
line in the video media description containing the "simulcast" line in the video media description containing the "simulcast"
attribute. The included format parameters indicates that sent attribute. The included "a=fmtp" and "a=imageattr" parameters
simulcast streams can differ in video resolution. indicates that sent simulcast streams can differ in video resolution.
The Answer from the server indicates that it too is simulcast The Answer from the server indicates that it too is simulcast
capable. Should it not have been simulcast capable, the capable. Should it not have been simulcast capable, the
"a=simulcast" line would not have been present and communication "a=simulcast" line would not have been present and communication
would have started with the media negotiated in the SDP. would have started with the media negotiated in the SDP.
v=0 v=0
o=server 823479283 1209384938 IN IP4 192.0.2.2 o=server 823479283 1209384938 IN IP4 192.0.2.2
s=Answer to Simulcast Enabled Client s=Answer to Simulcast Enabled Client
t=0 0 t=0 0
c=IN IP4 192.0.2.43 c=IN IP4 192.0.2.43
m=audio 49672 RTP/AVP 0 m=audio 49672 RTP/AVP 0
a=rtpmap:0 PCMU/8000 a=rtpmap:0 PCMU/8000
m=video 49674 RTP/AVP 97 98 m=video 49674 RTP/AVP 97 98
a=rtpmap:97 H264/90000 a=rtpmap:97 H264/90000
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:97 profile-level-id=42c01f; max-fs=3600; max-mbps=108000 a=fmtp:97 profile-level-id=42c01f; max-fs=3600; max-mbps=108000
a=fmtp:98 profile-level-id=42c00b; max-fs=240; max-mbps=3600 a=fmtp:98 profile-level-id=42c00b; max-fs=240; max-mbps=3600
a=imageattr:97 send [x=1280,y=720] recv [x=1280,y=720] a=imageattr:97 send [x=1280,y=720] recv [x=1280,y=720]
a=imageattr:98 send [x=320,y=180] recv [x=320,y=180] a=imageattr:98 send [x=320,y=180] recv [x=320,y=180]
a=rid:1 pt=97 a=rid:1 pt=97 recv
a=rid:2 pt=98 a=rid:2 pt=98 recv
a=simulcast:recv 1;2 send 1 a=rid:3 pt=97 send
a=simulcast:recv 1;2 send 3
Figure 5: Single-Source Simulcast Answer Figure 5: Single-Source Simulcast Answer
Since the server is the simulcast media receiver, it reverses the Since the server is the simulcast media receiver, it reverses the
direction of the "simulcast" attribute parameters. direction of the "simulcast" and "rid" attribute parameters.
6.4.2. Multi-Source Client 6.6.2. Multi-Source Client
Fred is calling in to the same conference as in the example above Fred is calling in to the same conference as in the example above
with a two-camera, two-display system, thus capable of handling two with a two-camera, two-display system, thus capable of handling two
separate media sources in each direction, where each media source is separate media sources in each direction, where each media source is
simulcast-enabled in the send direction. Fred's client is restricted simulcast-enabled in the send direction. Fred's client is restricted
to a single media source per media description. to a single media source per media description.
The first two simulcast streams for the first media source use The first two simulcast streams for the first media source use
different codecs, H264-SVC [RFC6190] and H264 [RFC6184]. These two different codecs, H264-SVC [RFC6190] and H264 [RFC6184]. These two
simulcast streams also have a temporal dependency. Two different simulcast streams also have a temporal dependency. Two different
video codecs, VP8 [I-D.ietf-payload-vp8] and H264, are offered as video codecs, VP8 [RFC7741] and H264, are offered as alternatives for
alternatives for the third simulcast stream for the first media the third simulcast stream for the first media source. Only the
source. Only the highest fidelity simulcast stream are sent from highest fidelity simulcast stream are sent from start, the lower
start, the lower fidelity streams being initially paused. fidelity streams being initially paused.
The second media source is offered with three different simulcast The second media source is offered with three different simulcast
streams. All video streams of this second media source are loss streams. All video streams of this second media source are loss
protected by RTP retransmission [RFC4588]. Also here, all but the protected by RTP retransmission [RFC4588]. Also here, all but the
highest fidelity simulcast stream are initially paused. highest fidelity simulcast stream are initially paused.
Fred's client is also using BUNDLE to send all RTP streams from all Fred's client is also using BUNDLE to send all RTP streams from all
media descriptions in the same RTP session on a single media media descriptions in the same RTP session on a single media
transport. Although using many different simulcast streams in this transport. Although using many different simulcast streams in this
example, the use of RID as simulcast stream identification enables example, the use of RID as simulcast stream identification enables
use of a low number of RTP payload types. Note that the use of both use of a low number of RTP payload types. Note that the use of both
BUNDLE and RID recommends using the RTP header extension [RFC5285] BUNDLE [I-D.ietf-mmusic-sdp-bundle-negotiation] and RID
for carrying these fields, which is consequently also included in the [I-D.ietf-mmusic-rid] recommends using the RTP header extension
SDP. [RFC5285] for carrying these RTP stream identification fields, which
is consequently also included in the SDP. Note also that for RID,
the corresponding SDES attribute is named RtpStreamId
[I-D.ietf-avtext-rid].
v=0 v=0
o=fred 238947129 823479223 IN IP4 192.0.2.125 o=fred 238947129 823479223 IN IP6 2001:db8::c000:27d
s=Offer from Simulcast Enabled Multi-Source Client s=Offer from Simulcast Enabled Multi-Source Client
t=0 0 t=0 0
c=IN IP4 192.0.2.125 c=IN IP6 2001:db8::c000:27d
a=group:BUNDLE foo bar zen a=group:BUNDLE foo bar zen
m=audio 49200 RTP/AVP 99 m=audio 49200 RTP/AVP 99
a=mid:foo a=mid:foo
a=rtpmap:99 G722/8000 a=rtpmap:99 G722/8000
m=video 49600 RTP/AVPF 100 101 103 m=video 49600 RTP/AVPF 100 101 103
a=mid:bar a=mid:bar
a=rtpmap:100 H264-SVC/90000 a=rtpmap:100 H264-SVC/90000
a=rtpmap:101 H264/90000 a=rtpmap:101 H264/90000
a=rtpmap:103 VP8/90000 a=rtpmap:103 VP8/90000
a=fmtp:100 profile-level-id=42400d; max-fs=3600; max-mbps=108000; \ a=fmtp:100 profile-level-id=42400d; max-fs=3600; max-mbps=108000; \
mst-mode=NI-TC mst-mode=NI-TC
a=fmtp:101 profile-level-id=42c00d; max-fs=3600; max-mbps=54000 a=fmtp:101 profile-level-id=42c00d; max-fs=3600; max-mbps=54000
a=fmtp:103 max-fs=900; max-fr=30 a=fmtp:103 max-fs=900; max-fr=30
a=rid:1 send pt=100;max-width=1280;max-height=720;max-fr=60;depend=2 a=rid:1 send pt=100;max-width=1280;max-height=720;max-fps=60;depend=2
a=rid:2 send pt=101;max-width=1280;max-height=720;max-fr=30 a=rid:2 send pt=101;max-width=1280;max-height=720;max-fps=30
a=rid:3 send pt=101;max-width=640;max-height=360 a=rid:3 send pt=101;max-width=640;max-height=360
a=rid:4 send pt=103;max-width=640;max-height=360 a=rid:4 send pt=103;max-width=640;max-height=360
a=depend:100 lay bar:101 a=depend:100 lay bar:101
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:2 urn:ietf:params:rtp-hdrext:sdes:rid a=extmap:2 urn:ietf:params:rtp-hdrext:sdes:RtpStreamId
a=rtcp-fb:* ccm pause nowait a=rtcp-fb:* ccm pause nowait
a=simulcast:send 1;2;~4,3 a=simulcast:send 1;2;~4,3
m=video 49602 RTP/AVPF 96 104 m=video 49602 RTP/AVPF 96 104
a=mid:zen a=mid:zen
a=rtpmap:96 VP8/90000 a=rtpmap:96 VP8/90000
a=fmtp:96 max-fs=3600; max-fr=30 a=fmtp:96 max-fs=3600; max-fr=30
a=rtpmap:104 rtx/90000 a=rtpmap:104 rtx/90000
a=fmtp:104 apt=96;rtx-time=200 a=fmtp:104 apt=96;rtx-time=200
a=rid:5 send pt=96;max-fs=921600;max-fr=30 a=rid:5 send pt=96;max-fs=921600;max-fps=30
a=rid:6 send pt=96;max-fs=614400;max-fr=15 a=rid:6 send pt=96;max-fs=614400;max-fps=15
a=rid:7 send pt=96;max-fs=230400;max-fr=30 a=rid:7 send pt=96;max-fs=230400;max-fps=30
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:2 urn:ietf:params:rtp-hdrext:sdes:rid a=extmap:2 urn:ietf:params:rtp-hdrext:sdes:RtpStreamId
a=rtcp-fb:* ccm pause nowait a=rtcp-fb:* ccm pause nowait
a=simulcast:send 5;~6;~7 a=simulcast:send 5;~6;~7
Figure 6: Fred's Multi-Source Simulcast Offer Figure 6: Fred's Multi-Source Simulcast Offer
Note: Empty lines in the SDP above are added only for readability Note: Empty lines in the SDP above are added only for readability
and would not be present in an actual SDP. and would not be present in an actual SDP.
7. Network Aspects 7. Network Aspects
skipping to change at page 21, line 5 skipping to change at page 22, line 5
varies during an RTP session such that it does not match what is varies during an RTP session such that it does not match what is
negotiated in SDP, the bitrate used by the different simulcast negotiated in SDP, the bitrate used by the different simulcast
streams may have to be reduced dynamically. What simulcast streams streams may have to be reduced dynamically. What simulcast streams
to prioritize when allocating available bitrate among the simulcast to prioritize when allocating available bitrate among the simulcast
streams in such adaptation SHOULD be taken from the simulcast stream streams in such adaptation SHOULD be taken from the simulcast stream
order on the "a=simulcast" line. Simulcast streams that have pause/ order on the "a=simulcast" line. Simulcast streams that have pause/
resume capability and that would be given such low bitrate by the resume capability and that would be given such low bitrate by the
adaptation process that they are considered not really useful can be adaptation process that they are considered not really useful can be
temporarily paused until the limiting condition clears. temporarily paused until the limiting condition clears.
8. Limitations 8. Limitation
The chosen approach has a few limitations that are described in this
section. The only one currently described relates to the use of a
single RTP session for all simulcast formats of a media source.
8.1. Single RTP Session
The limitations in this section come from sending all simulcast The chosen approach has a limitation that relates to the use of a
streams related to a media source under the same SDP media single RTP session for all simulcast formats of a media source, which
description, which also means they are sent in the same RTP session. comes from sending all simulcast streams related to a media source
under the same SDP media description.
It is not possible to use different simulcast streams on different It is not possible to use different simulcast streams on different
media transports, limiting the possibilities to apply different QoS media transports, limiting the possibilities to apply different QoS
to different simulcast streams. When using unicast, QoS mechanisms to different simulcast streams. When using unicast, QoS mechanisms
based on individual packet marking are feasible, since they do not based on individual packet marking are feasible, since they do not
require separation of simulcast streams into different RTP sessions require separation of simulcast streams into different RTP sessions
to apply different QoS. to apply different QoS.
It is not possible to separate different simulcast streams into It is also not possible to separate different simulcast streams into
different multicast groups to allow a multicast receiver to pick the different multicast groups to allow a multicast receiver to pick the
stream it wants, rather than receive all of them. In this case, the stream it wants, rather than receive all of them. In this case, the
only reasonable implementation is to use different RTP sessions for only reasonable implementation is to use different RTP sessions for
each multicast group so that reporting and other RTCP functions each multicast group so that reporting and other RTCP functions
operate as intended. operate as intended.
9. IANA Considerations 9. IANA Considerations
This document requests to register a new SDP attribute, simulcast, as This document requests to register a new media-level SDP attribute,
defined in Section 6.1. "simulcast", in the "att-field (media level only)" registry within
the SDP parameters registry, according to the procedures of [RFC4566]
and [I-D.ietf-mmusic-sdp-mux-attributes].
Contact name, email: IETF, contacted via mmusic@ietf.org, or a
successor address designated by IESG
Attribute name: simulcast
Long-form attribute name: Simulcast stream description
Charset dependent: No
Attribute value: See Section 6.1 of RFC XXXX.
Purpose: Signals simulcast capability for a set of RTP streams
MUX category: NORMAL
Note to RFC Editor: Please replace "RFC XXXX" with the assigned
number of this RFC.
10. Security Considerations 10. Security Considerations
The simulcast capability, configuration attributes, and parameters The simulcast capability, configuration attributes, and parameters
are vulnerable to attacks in signaling. are vulnerable to attacks in signaling.
A false inclusion of the "a=simulcast" attribute may result in A false inclusion of the "a=simulcast" attribute may result in
simultaneous transmission of multiple RTP streams that would simultaneous transmission of multiple RTP streams that would
otherwise not be generated. The impact is limited by the media otherwise not be generated. The impact is limited by the media
description joint bandwidth, shared by all simulcast streams description joint bandwidth, shared by all simulcast streams
skipping to change at page 22, line 10 skipping to change at page 23, line 26
allocated for the originally wanted RTP stream. allocated for the originally wanted RTP stream.
A hostile removal of the "a=simulcast" attribute will result in A hostile removal of the "a=simulcast" attribute will result in
simulcast not being used. simulcast not being used.
Neither of the above will likely have any major consequences and can Neither of the above will likely have any major consequences and can
be mitigated by signaling that is at least integrity and source be mitigated by signaling that is at least integrity and source
authenticated to prevent an attacker to change it. authenticated to prevent an attacker to change it.
Security considerations related to the use of RID is covered in Security considerations related to the use of RID is covered in
[I-D.ietf-mmusic-rid] and [I-D.roach-avtext-rid]. There are no [I-D.ietf-mmusic-rid] and [I-D.ietf-avtext-rid]. There are no
additional security concerns related to its use in this additional security concerns related to their use in this
specification. specification.
11. Contributors 11. Contributors
Morgan Lindqvist and Fredrik Jansson, both from Ericsson, have Morgan Lindqvist and Fredrik Jansson, both from Ericsson, have
contributed with important material to the first versions of this contributed with important material to the first versions of this
document. Robert Hansen and Cullen Jennings, from Cisco, Peter document. Robert Hansen and Cullen Jennings, from Cisco, Peter
Thatcher, from Google, and Adam Roach, from Mozilla, contributed Thatcher, from Google, and Adam Roach, from Mozilla, contributed
significantly to subsequent versions. significantly to subsequent versions.
12. Acknowledgements 12. Acknowledgements
13. References 13. References
13.1. Normative References 13.1. Normative References
[I-D.ietf-avtext-rtp-stream-pause] [I-D.ietf-avtext-rid]
Burman, B., Akram, A., Even, R., and M. Westerlund, "RTP Roach, A., Nandakumar, S., and P. Thatcher, "RTP Stream
Stream Pause and Resume", draft-ietf-avtext-rtp-stream- Identifier Source Description (SDES)", draft-ietf-avtext-
pause-10 (work in progress), September 2015. rid-04 (work in progress), June 2016.
[I-D.ietf-mmusic-rid] [I-D.ietf-mmusic-rid]
Thatcher, P., Zanaty, M., Nandakumar, S., Burman, B., Thatcher, P., Zanaty, M., Nandakumar, S., Burman, B.,
Roach, A., and B. Campen, "RTP Payload Format Roach, A., and B. Campen, "RTP Payload Format
Constraints", draft-ietf-mmusic-rid-01 (work in progress), Constraints", draft-ietf-mmusic-rid-05 (work in progress),
February 2016. March 2016.
[I-D.ietf-mmusic-sdp-mux-attributes] [I-D.ietf-mmusic-sdp-mux-attributes]
Nandakumar, S., "A Framework for SDP Attributes when Nandakumar, S., "A Framework for SDP Attributes when
Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-12 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-13
(work in progress), January 2016. (work in progress), June 2016.
[I-D.roach-avtext-rid]
Roach, A., Nandakumar, S., and P. Thatcher, "RTP Payload
Format Constraints", draft-roach-avtext-rid-01 (work in
progress), February 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <http://www.rfc-editor.org/info/rfc3550>. July 2003, <http://www.rfc-editor.org/info/rfc3550>.
skipping to change at page 23, line 28 skipping to change at page 24, line 44
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>. <http://www.rfc-editor.org/info/rfc5234>.
[RFC7104] Begen, A., Cai, Y., and H. Ou, "Duplication Grouping [RFC7104] Begen, A., Cai, Y., and H. Ou, "Duplication Grouping
Semantics in the Session Description Protocol", RFC 7104, Semantics in the Session Description Protocol", RFC 7104,
DOI 10.17487/RFC7104, January 2014, DOI 10.17487/RFC7104, January 2014,
<http://www.rfc-editor.org/info/rfc7104>. <http://www.rfc-editor.org/info/rfc7104>.
[RFC7728] Burman, B., Akram, A., Even, R., and M. Westerlund, "RTP
Stream Pause and Resume", RFC 7728, DOI 10.17487/RFC7728,
February 2016, <http://www.rfc-editor.org/info/rfc7728>.
[RFC7741] Westin, P., Lundin, H., Glover, M., Uberti, J., and F.
Galligan, "RTP Payload Format for VP8 Video", RFC 7741,
DOI 10.17487/RFC7741, March 2016,
<http://www.rfc-editor.org/info/rfc7741>.
13.2. Informative References 13.2. Informative References
[I-D.ietf-avtcore-multiplex-guidelines] [I-D.ietf-avtcore-multiplex-guidelines]
Westerlund, M., Perkins, C., and H. Alvestrand, Westerlund, M., Perkins, C., and H. Alvestrand,
"Guidelines for using the Multiplexing Features of RTP to "Guidelines for using the Multiplexing Features of RTP to
Support Multiple Media Streams", draft-ietf-avtcore- Support Multiple Media Streams", draft-ietf-avtcore-
multiplex-guidelines-03 (work in progress), October 2014. multiplex-guidelines-03 (work in progress), October 2014.
[I-D.ietf-avtcore-rtp-multi-stream] [I-D.ietf-avtcore-rtp-multi-stream]
Lennox, J., Westerlund, M., Wu, Q., and C. Perkins, Lennox, J., Westerlund, M., Wu, Q., and C. Perkins,
"Sending Multiple RTP Streams in a Single RTP Session", "Sending Multiple RTP Streams in a Single RTP Session",
draft-ietf-avtcore-rtp-multi-stream-11 (work in progress), draft-ietf-avtcore-rtp-multi-stream-11 (work in progress),
December 2015. December 2015.
[I-D.ietf-mmusic-sdp-bundle-negotiation] [I-D.ietf-mmusic-sdp-bundle-negotiation]
Holmberg, C., Alvestrand, H., and C. Jennings, Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session "Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle- Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
negotiation-25 (work in progress), January 2016. negotiation-31 (work in progress), June 2016.
[I-D.ietf-payload-flexible-fec-scheme]
Singh, V., Begen, A., Zanaty, M., and G. Mandyam, "RTP
Payload Format for Flexible Forward Error Correction
(FEC)", draft-ietf-payload-flexible-fec-scheme-01 (work in
progress), October 2015.
[I-D.ietf-payload-vp8]
Westin, P., Lundin, H., Glover, M., Uberti, J., and F.
Galligan, "RTP Payload Format for VP8 Video", draft-ietf-
payload-vp8-17 (work in progress), September 2015.
[RFC2198] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V., [RFC2198] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V.,
Handley, M., Bolot, J., Vega-Garcia, A., and S. Fosse- Handley, M., Bolot, J., Vega-Garcia, A., and S. Fosse-
Parisis, "RTP Payload for Redundant Audio Data", RFC 2198, Parisis, "RTP Payload for Redundant Audio Data", RFC 2198,
DOI 10.17487/RFC2198, September 1997, DOI 10.17487/RFC2198, September 1997,
<http://www.rfc-editor.org/info/rfc2198>. <http://www.rfc-editor.org/info/rfc2198>.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002, DOI 10.17487/RFC3264, June 2002,
skipping to change at page 25, line 29 skipping to change at page 26, line 44
<http://www.rfc-editor.org/info/rfc7656>. <http://www.rfc-editor.org/info/rfc7656>.
[RFC7667] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667, [RFC7667] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667,
DOI 10.17487/RFC7667, November 2015, DOI 10.17487/RFC7667, November 2015,
<http://www.rfc-editor.org/info/rfc7667>. <http://www.rfc-editor.org/info/rfc7667>.
Appendix A. Changes From Earlier Versions Appendix A. Changes From Earlier Versions
NOTE TO RFC EDITOR: Please remove this section prior to publication. NOTE TO RFC EDITOR: Please remove this section prior to publication.
A.1. Modifications Between WG Version -03 and -04 A.1. Modifications Between WG Version -04 and -05
o Aligned with recent changes in draft-ietf-mmusic-rid and draft-
ietf-avtext-rid.
o Modified the SDP offer/answer section to follow the generally
accepted structure, also adding a brief text on modifying the
session that is aligned with draft-ietf-mmusic-rid.
o Improved text around simulcast stream identification (as opposed
to the simulcast stream itself) to consistently use the acronym
SCID and defined that in the Terminology section.
o Changed references for RTP-level pause/resume and VP8 payload
format that are now published as RFC.
o Improved IANA registration text.
o Removed unused reference to draft-ietf-payload-flexible-fec-
scheme.
o Editorial improvements and corrections.
A.2. Modifications Between WG Version -03 and -04
o Changed to only use RID identification, as was consensus during o Changed to only use RID identification, as was consensus during
IETF 94. IETF 94.
o ABNF improvements. o ABNF improvements.
o Clarified offer-answer rules for initially paused streams. o Clarified offer-answer rules for initially paused streams.
o Changed references for RTP topologies and RTP taxonomy documents o Changed references for RTP topologies and RTP taxonomy documents
that are now published as RFC. that are now published as RFC.
o Added reference to the new RID draft in AVTEXT. o Added reference to the new RID draft in AVTEXT.
o Re-structured section 6 to provide an easy reference by the o Re-structured section 6 to provide an easy reference by the
updated IANA section. updated IANA section.
o Added a sub-section 7.1 with a discussion of bitrate adaptation. o Added a sub-section 7.1 with a discussion of bitrate adaptation.
o Editorial improvements. o Editorial improvements.
A.2. Modifications Between WG Version -02 and -03 A.3. Modifications Between WG Version -02 and -03
o Removed text on multicast / broadcast from use cases, since it is o Removed text on multicast / broadcast from use cases, since it is
not supported by the solution. not supported by the solution.
o Removed explicit references to unified plan draft. o Removed explicit references to unified plan draft.
o Added possibility to initiate simulcast streams in paused mode. o Added possibility to initiate simulcast streams in paused mode.
o Enabled an offerer to offer multiple stream identification (pt or o Enabled an offerer to offer multiple stream identification (pt or
rid) methods and have the answerer choose which to use. rid) methods and have the answerer choose which to use.
o Added a preference indication also in send direction offers. o Added a preference indication also in send direction offers.
o Added a section on limitations of the current proposal, including o Added a section on limitations of the current proposal, including
identification method specific limitations. identification method specific limitations.
A.3. Modifications Between WG Version -01 and -02 A.4. Modifications Between WG Version -01 and -02
o Relying on the new RID solution for codec constraints and o Relying on the new RID solution for codec constraints and
configuration identification. This has resulted in changes in configuration identification. This has resulted in changes in
syntax to identify if pt or RID is used to describe the simulcast syntax to identify if pt or RID is used to describe the simulcast
stream. stream.
o Renamed simulcast version and simulcast version alternative to o Renamed simulcast version and simulcast version alternative to
simulcast stream and simulcast format respectively, and improved simulcast stream and simulcast format respectively, and improved
definitions for them. definitions for them.
o Clarification that it is possible to switch between simulcast o Clarification that it is possible to switch between simulcast
version alternatives, but that only a single one be used at any version alternatives, but that only a single one be used at any
point in time. point in time.
o Changed the definition so that ordering of simulcast formats for a o Changed the definition so that ordering of simulcast formats for a
specific simulcast stream do have a preference order. specific simulcast stream do have a preference order.
A.4. Modifications Between WG Version -00 and -01 A.5. Modifications Between WG Version -00 and -01
o No changes. Only preventing expiry. o No changes. Only preventing expiry.
A.5. Modifications Between Individual Version -00 and WG Version -00 A.6. Modifications Between Individual Version -00 and WG Version -00
o Added this appendix. o Added this appendix.
Authors' Addresses Authors' Addresses
Bo Burman Bo Burman
Ericsson Ericsson
Kistavagen 25 Gronlandsgatan 31
SE-164 80 Stockholm SE-164 80 Stockholm
Sweden Sweden
Email: bo.burman@ericsson.com Email: bo.burman@ericsson.com
Magnus Westerlund Magnus Westerlund
Ericsson Ericsson
Farogatan 2 Farogatan 2
SE-164 80 Stockholm SE-164 80 Stockholm
Sweden Sweden
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