draft-ietf-mmusic-msid-13.txt   draft-ietf-mmusic-msid-14.txt 
Network Working Group H. Alvestrand Network Working Group H. Alvestrand
Internet-Draft Google Internet-Draft Google
Intended status: Standards Track April 5, 2016 Intended status: Standards Track June 6, 2016
Expires: October 7, 2016 Expires: December 8, 2016
WebRTC MediaStream Identification in the Session Description Protocol WebRTC MediaStream Identification in the Session Description Protocol
draft-ietf-mmusic-msid-13 draft-ietf-mmusic-msid-14
Abstract Abstract
This document specifies a Session Description Protocol (SDP) Grouping This document specifies a Session Description Protocol (SDP) Grouping
mechanism for RTP media streams that can be used to specify relations mechanism for RTP media streams that can be used to specify relations
between media streams. between media streams.
This mechanism is used to signal the association between the SDP This mechanism is used to signal the association between the SDP
concept of "media description" and the WebRTC concept of concept of "media description" and the WebRTC concept of
"MediaStream" / "MediaStreamTrack" using SDP signaling. "MediaStream" / "MediaStreamTrack" using SDP signaling.
skipping to change at page 1, line 45 skipping to change at page 1, line 45
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-
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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 October 7, 2016. This Internet-Draft will expire on December 8, 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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3.2.3. Generating the answer . . . . . . . . . . . . . . . . 8 3.2.3. Generating the answer . . . . . . . . . . . . . . . . 8
3.2.4. Offerer processing of the answer . . . . . . . . . . 9 3.2.4. Offerer processing of the answer . . . . . . . . . . 9
3.2.5. Modifying the session . . . . . . . . . . . . . . . . 9 3.2.5. Modifying the session . . . . . . . . . . . . . . . . 9
3.3. Example SDP description . . . . . . . . . . . . . . . . . 9 3.3. Example SDP description . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
4.1. Attribute registration in existing registries . . . . . . 10 4.1. Attribute registration in existing registries . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 11 7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 11 7.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Design considerations, rejected alternatives . . . . 12 Appendix A. Design considerations, rejected alternatives . . . . 12
Appendix B. Change log . . . . . . . . . . . . . . . . . . . . . 12 Appendix B. Change log . . . . . . . . . . . . . . . . . . . . . 12
B.1. Changes from alvestrand-rtcweb-msid-00 to -01 . . . . . . 12 B.1. Changes from alvestrand-rtcweb-msid-00 to -01 . . . . . . 13
B.2. Changes from alvestrand-rtcweb-msid-01 to -02 . . . . . . 13 B.2. Changes from alvestrand-rtcweb-msid-01 to -02 . . . . . . 13
B.3. Changes from alvestrand-rtcweb-msid-02 to mmusic-msid-00 13 B.3. Changes from alvestrand-rtcweb-msid-02 to mmusic-msid-00 13
B.4. Changes from alvestrand-mmusic-msid-00 to -01 . . . . . . 13 B.4. Changes from alvestrand-mmusic-msid-00 to -01 . . . . . . 13
B.5. Changes from alvestrand-mmusic-msid-01 to -02 . . . . . . 13 B.5. Changes from alvestrand-mmusic-msid-01 to -02 . . . . . . 13
B.6. Changes from alvestrand-mmusic-msid-02 to ietf-mmusic-00 13 B.6. Changes from alvestrand-mmusic-msid-02 to ietf-mmusic-00 14
B.7. Changes from mmusic-msid-00 to -01 . . . . . . . . . . . 14 B.7. Changes from mmusic-msid-00 to -01 . . . . . . . . . . . 14
B.8. Changes from mmusic-msid-01 to -02 . . . . . . . . . . . 14 B.8. Changes from mmusic-msid-01 to -02 . . . . . . . . . . . 14
B.9. Changes from mmusic-msid-02 to -03 . . . . . . . . . . . 14 B.9. Changes from mmusic-msid-02 to -03 . . . . . . . . . . . 14
B.10. Changes from mmusic-msid-03 to -04 . . . . . . . . . . . 14 B.10. Changes from mmusic-msid-03 to -04 . . . . . . . . . . . 14
B.11. Changes from -04 to -05 . . . . . . . . . . . . . . . . . 14 B.11. Changes from -04 to -05 . . . . . . . . . . . . . . . . . 15
B.12. Changes from -05 to -06 . . . . . . . . . . . . . . . . . 14 B.12. Changes from -05 to -06 . . . . . . . . . . . . . . . . . 15
B.13. Changes from -06 to -07 . . . . . . . . . . . . . . . . . 15 B.13. Changes from -06 to -07 . . . . . . . . . . . . . . . . . 15
B.14. Changes from -07 to -08 . . . . . . . . . . . . . . . . . 15 B.14. Changes from -07 to -08 . . . . . . . . . . . . . . . . . 15
B.15. Changes from -08 to -09 . . . . . . . . . . . . . . . . . 15 B.15. Changes from -08 to -09 . . . . . . . . . . . . . . . . . 16
B.16. Changes from -09 to -10 . . . . . . . . . . . . . . . . . 16 B.16. Changes from -09 to -10 . . . . . . . . . . . . . . . . . 16
B.17. Changes from -10 to -11 . . . . . . . . . . . . . . . . . 16 B.17. Changes from -10 to -11 . . . . . . . . . . . . . . . . . 16
B.18. Changes from -11 to -12 . . . . . . . . . . . . . . . . . 16 B.18. Changes from -11 to -12 . . . . . . . . . . . . . . . . . 16
B.19. Changes from -12 to -13 . . . . . . . . . . . . . . . . . 16 B.19. Changes from -12 to -13 . . . . . . . . . . . . . . . . . 16
B.20. Changes from -13 to -14 . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
1.1. Structure Of This Document 1.1. Structure Of This Document
This document adds a new Session Description Protocol (SDP) [RFC4566] This document adds a new Session Description Protocol (SDP) [RFC4566]
mechanism that can associate application layer identifiers with the mechanism that can associate application layer identifiers with the
binding between media streams, attaching identifiers to the media binding between media streams, attaching identifiers to the media
streams and attaching identifiers to the groupings they form. It is streams and attaching identifiers to the groupings they form. It is
designed for use with WebRTC[I-D.ietf-rtcweb-overview] . designed for use with WebRTC[I-D.ietf-rtcweb-overview] .
Section 1.2 gives the background on why a new mechanism is needed. Section 1.2 gives the background on why a new mechanism is needed.
Section 2 gives the definition of the new mechanism. Section 2 gives the definition of the new mechanism.
Section 3 gives the necessary semantic information and procedures for Section 3 gives the necessary semantic information and procedures for
using the msid attribute to signal the association of using the msid attribute to signal the association of
MediaStreamTracks to MediaStreams in support of the WebRTC API MediaStreamTracks to MediaStreams in support of the WebRTC API
[W3C.WD-webrtc-20150210]. [W3C.WD-webrtc-20160531].
1.2. Why A New Mechanism Is Needed 1.2. Why A New Mechanism Is Needed
When media is carried by RTP [RFC3550], each RTP media stream is When media is carried by RTP [RFC3550], each RTP media stream is
distinguished inside an RTP session by its SSRC; each RTP session is distinguished inside an RTP session by its SSRC; each RTP session is
distinguished from all other RTP sessions by being on a different distinguished from all other RTP sessions by being on a different
transport association (strictly speaking, 2 transport associations, transport association (strictly speaking, 2 transport associations,
one used for RTP and one used for RTCP, unless RTP/RTCP multiplexing one used for RTP and one used for RTCP, unless RTP/RTCP multiplexing
[RFC5761] is used). [RFC5761] is used).
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media source is carried in its own RTP session. media source is carried in its own RTP session.
The SDP grouping framework [RFC5888] can be used to group media The SDP grouping framework [RFC5888] can be used to group media
descriptions. However, for the use case of WebRTC, there is the need descriptions. However, for the use case of WebRTC, there is the need
for an application to specify some application-level information for an application to specify some application-level information
about the association between the media description and the group. about the association between the media description and the group.
This is not possible using the SDP grouping framework. This is not possible using the SDP grouping framework.
1.3. The WEBRTC MediaStream 1.3. The WEBRTC MediaStream
The W3C WebRTC API specification [W3C.WD-webrtc-20150210] specifies The W3C WebRTC API specification [W3C.WD-webrtc-20160531] specifies
that communication between WebRTC entities is done via MediaStreams, that communication between WebRTC entities is done via MediaStreams,
which contain MediaStreamTracks. A MediaStreamTrack is generally which contain MediaStreamTracks. A MediaStreamTrack is generally
carried using a single SSRC in an RTP session (forming an RTP media carried using a single SSRC in an RTP session (forming an RTP media
stream. The collision of terminology is unfortunate.) There might stream. The collision of terminology is unfortunate.) There might
possibly be additional SSRCs, possibly within additional RTP possibly be additional SSRCs, possibly within additional RTP
sessions, in order to support functionality like forward error sessions, in order to support functionality like forward error
correction or simulcast. This complication is ignored below. correction or simulcast. This complication is ignored below.
MediaStreamTracks are unidirectional; they carry media on one MediaStreamTracks are unidirectional; they carry media on one
direction only. direction only.
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MediaStream for each media description, which can be accomplished MediaStream for each media description, which can be accomplished
with a media-level SDP attribute. with a media-level SDP attribute.
This usage is described in Section 3. This usage is described in Section 3.
2. The Msid Mechanism 2. The Msid Mechanism
This document defines a new SDP [RFC4566] media-level "msid" This document defines a new SDP [RFC4566] media-level "msid"
attribute. This new attribute allows endpoints to associate RTP attribute. This new attribute allows endpoints to associate RTP
media streams that are described in different media descriptions with media streams that are described in different media descriptions with
the same MediaStreams as defined in [W3C.WD-webrtc-20150210]., and to the same MediaStreams as defined in [W3C.WD-webrtc-20160531], and to
carry an identifier for each MediaStreamTrack in its "appdata" field. carry an identifier for each MediaStreamTrack in its "appdata" field.
The value of the "msid" attribute consists of an identifier and an The value of the "msid" attribute consists of an identifier and an
optional "appdata" field. optional "appdata" field.
The name of the attribute is "msid". The name of the attribute is "msid".
The value of the attribute is specified by the following ABNF The value of the attribute is specified by the following ABNF
[RFC5234] grammar: [RFC5234] grammar:
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The msid attributes depend on the association of RTP media streams The msid attributes depend on the association of RTP media streams
with media descriptions, but does not depend on the association of with media descriptions, but does not depend on the association of
RTP media streams with RTP transports; therefore, its mux category is RTP media streams with RTP transports; therefore, its mux category is
NORMAL - the process of deciding on MSID attributes doesn't have to NORMAL - the process of deciding on MSID attributes doesn't have to
take into consideration whether the media streams are bundled or not. take into consideration whether the media streams are bundled or not.
3. Procedures 3. Procedures
This section describes the procedures for associating media This section describes the procedures for associating media
descriptions representing MediaStreamTracks within MediaStreams as descriptions representing MediaStreamTracks within MediaStreams as
defined in [W3C.WD-webrtc-20150210]. defined in [W3C.WD-webrtc-20160531].
In the Javascript API, each MediaStream and MediaStreamTrack has an In the Javascript API, each MediaStream and MediaStreamTrack has an
"id" attribute, which is a DOMString. "id" attribute, which is a DOMString.
The value of the "msid-id" field in the msid consists of the "id" The value of the "msid-id" field in the msid consists of the "id"
attribute of a MediaStream, as defined in its WebIDL specification. attribute of a MediaStream, as defined in its WebIDL specification.
The value of the "msid-appdata" field in the msid consists of the The value of the "msid-appdata" field in the msid consists of the
"id" attribute of a MediaStreamTrack, as defined in its WebIDL "id" attribute of a MediaStreamTrack, as defined in its WebIDL
specification. specification.
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The following is a high level description of the rules for handling The following is a high level description of the rules for handling
SDP updates. Detailed procedures are in Section 3.2. SDP updates. Detailed procedures are in Section 3.2.
o When a new msid "identifier" value occurs in a session o When a new msid "identifier" value occurs in a session
description, the recipient can signal to its application that a description, the recipient can signal to its application that a
new MediaStream has been added. new MediaStream has been added.
o When a session description is updated to have media descriptions o When a session description is updated to have media descriptions
with an msid "identifier" value, with one or more different with an msid "identifier" value, with one or more different
"appdata" values, the recipient can signal to its application that "appdata" values, the recipient can si2gnal to its application
new MediaStreamTracks have been added to the MediaStream. This is that new MediaStreamTracks have been added to the MediaStream.
done for each different msid "identifier" value. This is done for each different msid "identifier" value.
o When a session description is updated to no longer list any msid o When a session description is updated to no longer list any msid
attribute on a specific media description, the recipient can attribute on a specific media description, the recipient can
signal to its application that the corresponding MediaStreamTrack signal to its application that the corresponding MediaStreamTrack
has ended. has ended.
In addition to signaling that the track is closed when its msid In addition to signaling that the track is closed when its msid
attribute disappears from the SDP, the track will also be signaled as attribute disappears from the SDP, the track will also be signaled as
being closed when all associated SSRCs have disappeared by the rules being closed when all associated SSRCs have disappeared by the rules
of [RFC3550] section 6.3.4 (BYE packet received) and 6.3.5 (timeout), of [RFC3550] section 6.3.4 (BYE packet received) and 6.3.5 (timeout),
skipping to change at page 7, line 14 skipping to change at page 7, line 14
3.1. Handling of non-signalled tracks 3.1. Handling of non-signalled tracks
Entities that do not use msid will not send msid. This means that Entities that do not use msid will not send msid. This means that
there will be some incoming RTP packets that the recipient has no there will be some incoming RTP packets that the recipient has no
predefined MediaStream id value for. predefined MediaStream id value for.
Note that this handling is triggered by incoming RTP packets, not by Note that this handling is triggered by incoming RTP packets, not by
SDP negotiation. SDP negotiation.
When MSID is used, the only time this can happen is when, at a time When MSID is used, the only time this can happen is when, after the
subsequent to the initial negotiation, a negotiation is performed initial negotiation, a negotiation is performed where the answerer
where the answerer adds a MediaStreamTrack to an already established adds a MediaStreamTrack to an already established connection and
connection and starts sending data before the answer is received by starts sending data before the answer is received by the offerer.
the offerer. For initial negotiation, packets won't flow until the For initial negotiation, packets won't flow until the ICE candidates
ICE candidates and fingerprints have been exchanged, so this is not and fingerprints have been exchanged, so this is not an issue.
an issue.
The recipient of those packets will perform the following steps: The recipient of those packets will perform the following steps:
o When RTP packets are initially received, it will create an o When RTP packets are initially received, it will create an
appropriate MediaStreamTrack based on the type of the media appropriate MediaStreamTrack based on the type of the media
(carried in PayloadType), and use the MID RTP header extension (carried in PayloadType), and use the MID RTP header extension
[I-D.ietf-mmusic-sdp-bundle-negotiation] (if present) to associate [I-D.ietf-mmusic-sdp-bundle-negotiation] (if present) to associate
the RTP packets with a specific media section. If the connection the RTP packets with a specific media section. If the connection
is not in the RTCSignalingState "stable", it will wait at this is not in the RTCSignalingState "stable", it will wait at this
point. point.
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o If there is no msid attribute, the identifier of the o If there is no msid attribute, the identifier of the
MediaStreamTrack will be set to a randomly generated string, and MediaStreamTrack will be set to a randomly generated string, and
it will be signalled as being part of a MediaStream with the it will be signalled as being part of a MediaStream with the
WebIDL "label" attribute set to "Non-WebRTC stream". WebIDL "label" attribute set to "Non-WebRTC stream".
o After deciding on the "id" field to be applied to the o After deciding on the "id" field to be applied to the
MediaStreamTrack, the track will be signalled to the user. MediaStreamTrack, the track will be signalled to the user.
The process above may involve a considerable amount of buffering The process above may involve a considerable amount of buffering
before the stable state is entered, If the implementation wishes to before the stable state is entered. If the implementation wishes to
limit this buffering, it MUST signal to the user that media has been limit this buffering, it MUST signal to the user that media has been
discarded. discarded.
It follows from the above that media stream tracks in the "default" It follows from the above that media stream tracks in the "default"
media stream cannot be closed by removing the msid attribute; the media stream cannot be closed by removing the msid attribute; the
application must instead signal these as closed when the SSRC application must instead signal these as closed when the SSRC
disappears according to the rules of RFC 3550 section 6.3.4 and 6.3.5 disappears according to the rules of RFC 3550 section 6.3.4 and 6.3.5
or by disabling the media description by setting its port to zero. or by disabling the media description by setting its port to zero.
3.2. Detailed Offer/Answer Procedures 3.2. Detailed Offer/Answer Procedures
skipping to change at page 11, line 16 skipping to change at page 11, line 16
Ted Hardie, Adam Roach, Magnus Westerlund and Paul Kyzivat for their Ted Hardie, Adam Roach, Magnus Westerlund and Paul Kyzivat for their
work in reviewing this draft, with many specific language work in reviewing this draft, with many specific language
suggestions. suggestions.
7. References 7. References
7.1. Normative References 7.1. Normative References
[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-02 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-12
(work in progress), July 2014. (work in progress), January 2016.
[I-D.ietf-rtcweb-jsep] [I-D.ietf-rtcweb-jsep]
Uberti, J., Jennings, C., and E. Rescorla, "Javascript Uberti, J., Jennings, C., and E. Rescorla, "Javascript
Session Establishment Protocol", draft-ietf-rtcweb-jsep-07 Session Establishment Protocol", draft-ietf-rtcweb-jsep-14
(work in progress), July 2014. (work in progress), March 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, March 1997. Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<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, July 2003. Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <http://www.rfc-editor.org/info/rfc3550>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <http://www.rfc-editor.org/info/rfc4566>.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/
RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[W3C.WD-webrtc-20150210] [W3C.WD-webrtc-20160531]
Bergkvist, A., Burnett, D., Jennings, C., and A. Wilson, C. and J. Kalliokoski, "WebRTC 1.0: Real-time
Narayanan, "WebRTC 1.0: Real-time Communication Between Communication Between Browsers", World Wide Web Consortium
Browsers", World Wide Web Consortium WD WD- WD WD-webrtc-20160531, May 2016,
webrtc-20150210, February 2015, <http://www.w3.org/TR/2016/WD-webrtc-20160531>.
<http://www.w3.org/TR/2015/WD-webrtc-20150210>.
7.2. Informative References 7.2. Informative References
[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-07 (work in progress), April 2014. negotiation-29 (work in progress), April 2016.
[I-D.ietf-rtcweb-overview] [I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-10 Browser-based Applications", draft-ietf-rtcweb-overview-15
(work in progress), June 2014. (work in progress), January 2016.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
Control Packets on a Single Port", RFC 5761, April 2010. Control Packets on a Single Port", RFC 5761, DOI 10.17487/
RFC5761, April 2010,
<http://www.rfc-editor.org/info/rfc5761>.
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description
Protocol (SDP) Grouping Framework", RFC 5888, June 2010. Protocol (SDP) Grouping Framework", RFC 5888, DOI
10.17487/RFC5888, June 2010,
<http://www.rfc-editor.org/info/rfc5888>.
Appendix A. Design considerations, rejected alternatives Appendix A. Design considerations, rejected alternatives
One suggested mechanism has been to use CNAME instead of a new One suggested mechanism has been to use CNAME instead of a new
attribute. This was abandoned because CNAME identifies a attribute. This was abandoned because CNAME identifies a
synchronization context; one can imagine both wanting to have tracks synchronization context; one can imagine both wanting to have tracks
from the same synchronization context in multiple MediaStreams and from the same synchronization context in multiple MediaStreams and
wanting to have tracks from multiple synchronization contexts within wanting to have tracks from multiple synchronization contexts within
one MediaStream (but the latter is impossible, since a MediaStream is one MediaStream (but the latter is impossible, since a MediaStream is
defined to impose synchronization on its members). defined to impose synchronization on its members).
skipping to change at page 16, line 30 skipping to change at page 16, line 41
same msid (id and appdata identical). same msid (id and appdata identical).
B.18. Changes from -11 to -12 B.18. Changes from -11 to -12
Added mux-category to the IANA considerations section. Added mux-category to the IANA considerations section.
B.19. Changes from -12 to -13 B.19. Changes from -12 to -13
Modified registration description to delete dependency on -4566-bis Modified registration description to delete dependency on -4566-bis
Author's Address B.20. Changes from -13 to -14
Addressed nits found in Gen-ART review
Author's Address
Harald Alvestrand Harald Alvestrand
Google Google
Kungsbron 2 Kungsbron 2
Stockholm 11122 Stockholm 11122
Sweden Sweden
Email: harald@alvestrand.no Email: harald@alvestrand.no
 End of changes. 29 change blocks. 
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