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WebRTC MediaStream Identification in the Session Description Protocol
draft-ietf-mmusic-msid-12

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8830.
Author Harald T. Alvestrand
Last updated 2016-03-18
Replaces draft-alvestrand-mmusic-msid
RFC stream Internet Engineering Task Force (IETF)
Formats
Reviews
Additional resources Mailing list discussion
Stream WG state WG Consensus: Waiting for Write-Up
Document shepherd Flemming Andreasen
IESG IESG state Became RFC 8830 (Proposed Standard)
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD (None)
Send notices to (None)
draft-ietf-mmusic-msid-12
", draft-ietf-rtcweb-jsep-08
              (work in progress), October 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [W3C.WD-webrtc-20150210]
              Bergkvist, A., Burnett, D., Jennings, C., and A.
              Narayanan, "WebRTC 1.0: Real-time Communication Between
              Browsers", World Wide Web Consortium WD WD-
              webrtc-20150210, February 2015,
              <http://www.w3.org/TR/2015/WD-webrtc-20150210>.

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7.2.  Informative References

   [I-D.ietf-mmusic-sdp-bundle-negotiation]
              Holmberg, C., Alvestrand, H., and C. Jennings,
              "Negotiating Media Multiplexing Using the Session
              Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
              negotiation-07 (work in progress), April 2014.

   [I-D.ietf-rtcweb-overview]
              Alvestrand, H., "Overview: Real Time Protocols for
              Browser-based Applications", draft-ietf-rtcweb-overview-13
              (work in progress), November 2014.

   [RFC5761]  Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
              Control Packets on a Single Port", RFC 5761, April 2010.

   [RFC5888]  Camarillo, G. and H. Schulzrinne, "The Session Description
              Protocol (SDP) Grouping Framework", RFC 5888, June 2010.

Appendix A.  Design considerations, rejected alternatives

   One suggested mechanism has been to use CNAME instead of a new
   attribute.  This was abandoned because CNAME identifies a
   synchronization context; one can imagine both wanting to have tracks
   from the same synchronization context in multiple MediaStreams and
   wanting to have tracks from multiple synchronization contexts within
   one MediaStream (but the latter is impossible, since a MediaStream is
   defined to impose synchronization on its members).

   Another suggestion has been to put the msid value within an attribute
   of RTCP SR (sender report) packets.  This doesn't offer the ability
   to know that you have seen all the tracks currently configured for a
   media stream.

   A suggestion that survived for a number of drafts was to define
   "msid" as a generic mechanism, where the particular semantics of this
   usage of the mechanism would be defined by an "a=wms-semantic"
   attribute.  This was removed in April 2015.

Appendix B.  Change log

   This appendix should be deleted before publication as an RFC.

B.1.  Changes from alvestrand-rtcweb-msid-00 to -01

   Added track identifier.

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   Added inclusion-by-reference of draft-lennox-mmusic-source-selection
   for track muting.

   Some rewording.

B.2.  Changes from alvestrand-rtcweb-msid-01 to -02

   Split document into sections describing a generic grouping mechanism
   and sections describing the application of this grouping mechanism to
   the WebRTC MediaStream concept.

   Removed the mechanism for muting tracks, since this is not central to
   the MSID mechanism.

B.3.  Changes from alvestrand-rtcweb-msid-02 to mmusic-msid-00

   Changed the draft name according to the wishes of the MMUSIC group
   chairs.

   Added text indicting cases where it's appropriate to have the same
   appdata for multiple SSRCs.

   Minor textual updates.

B.4.  Changes from alvestrand-mmusic-msid-00 to -01

   Increased the amount of explanatory text, much based on a review by
   Miguel Garcia.

   Removed references to BUNDLE, since that spec is under active
   discussion.

   Removed distinguished values of the MSID identifier.

B.5.  Changes from alvestrand-mmusic-msid-01 to -02

   Changed the order of the "msid-semantic: " attribute's value fields
   and allowed multiple identifiers.  This makes the attribute useful as
   a marker for "I understand this semantic".

   Changed the syntax for "identifier" and "appdata" to be "token".

   Changed the registry for the "msid-semantic" attribute values to be a
   new registry, based on advice given in Atlanta.

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B.6.  Changes from alvestrand-mmusic-msid-02 to ietf-mmusic-00

   Updated terminology to refer to m-lines rather than RTP sessions when
   discussing SDP formats and the ability of other linking mechanisms to
   refer to SSRCs.

   Changed the "default" mechanism to return independent streams after
   considering the synchronization problem.

   Removed the space from between "msid-semantic" and its value, to be
   consistent with RFC 5576.

B.7.  Changes from mmusic-msid-00 to -01

   Reworked msid mechanism to be a per-m-line attribute, to align with
   draft-roach-mmusic-unified-plan.

B.8.  Changes from mmusic-msid-01 to -02

   Corrected several missed cases where the word "ssrc" was not changed
   to "M-line".

   Added pointer to unified-plan (which should be moved to point to
   -jsep)

   Removed suggestion that ssrc-group attributes can be used with "msid-
   semantic", it is now only the msid-semantic registry.

B.9.  Changes from mmusic-msid-02 to -03

   Corrected even more cases where the word "ssrc" was not changed to
   "M-line".

   Added the functionality of using an asterisk (*) in the msid-semantic
   line, in order to remove the need for listing all msids in the msid-
   semantic line whne only one msid-semantic is in use.

   Removed some now-unnecessary text.

B.10.  Changes from mmusic-msid-03 to -04

   Changed title to reflect focus on WebRTC MediaStreams

   Added a section on receiver-side media stream control, using the
   "msid-control" attribute.

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B.11.  Changes from -04 to -05

   Removed the msid-control section after WG discussion.

   Removed some text that seemed only to pertain to resolved issues.

B.12.  Changes from -05 to -06

   Addressed issues found in Fleming Andreassen's review

   Referenced JSEP rather than unified-plan for the M-line mapping model

   Relaxed MSID definition to allow "token-char" in values rather than
   a-z 0-9 hyphen; tightened ABNF by adding length description to it.

   Deleted discussion of abandoned alternatives, as part of preparing
   for publication.

   Added a "detailed procedures" section to the WMS semantics
   description.

   Added IANA registration of the "msid-semantic" attribute.

B.13.  Changes from -06 to -07

   Changed terminology from referring to "WebRTC device" to referring to
   "entities that implement the WMS semantic".

   Changed names for ABNF constructions based on a proposal by Paul
   Kyzivat.

   Included a section on generic offer/answer semantics.

B.14.  Changes from -07 to -08

   Removed Appendix B that described the (now obsolete) ssrc-specific
   usage of MSID.

   Adopted a restructuring of the IANA section based on a suggestion
   from Martin Thomson.

   A number of text and ABNF clarifications based on suggestions from
   Ted Hardie, Paul Kyzivat and Adam Roach.

   Changed the "non-signalled track handling" to create a single stream
   with multiple tracks again, according to discussions at TPAC in
   November 2014

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B.15.  Changes from -08 to -09

   Removed "wms-semantic" and all mention of multiple semantics for
   msid, as agreed at the Dallas IETF, March 2015.

   Addressed a number of review comments from Fleming Andresen and
   others.

   Changed the term "m-line" to "media description", since that is the
   term used in RFC 4566.

   Tried to make sure this document does not describe the API to the
   application.

B.16.  Changes from -09 to -10

   Addressed review comments from Paul Kyzivat.

B.17.  Changes from -10 to -11

   Defined the semantics of multiple MSIDs in a media section to be a
   MediaStreamTrack present in multiple MediaStreams.

   Made an explicit note that MediaStreamTracks are unidirectional.

   Disallowed the option of sending multiple media sections with the
   same msid (id and appdata identical).

B.18.  Changes from -11 to -12

   Added mux-category to the IANA considerations section.

Author's Address

   Harald Alvestrand
   Google
   Kungsbron 2
   Stockholm  11122
   Sweden

   Email: harald@alvestrand.no

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