Signalling Media Stream ID in the Session Description Protocol
draft-alvestrand-rtcweb-msid-01

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Last updated 2012-01-25 (latest revision 2012-01-11)
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Network Working Group                                      H. Alvestrand
Internet-Draft                                                    Google
Intended status: Standards Track                        January 25, 2012
Expires: July 28, 2012

     Signalling Media Stream ID in the Session Description Protocol
                    draft-alvestrand-rtcweb-msid-01

Abstract

   This document specifies how the association between the RTP concept
   of SSRC and the WebRTC concept of "media stream" / "media stream
   track" is carried using SDP signalling.

   This document is an input document for discussion.  It should be
   discussed in the RTCWEB WG list, rtcweb@ietf.org.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 28, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Basic mechanism . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Signalling muted and non-desired tracks . . . . . . . . . . . . 5
   4.  Handling of non-signalled tracks  . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Appendix A.  Design considerations, open questions and and
                alternatives . . . . . . . . . . . . . . . . . . . . . 8
   Appendix B.  Change log . . . . . . . . . . . . . . . . . . . . . . 8
     B.1.  Changes from -00 to -01 . . . . . . . . . . . . . . . . . . 9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 9

Alvestrand                Expires July 28, 2012                 [Page 2]
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1.  Introduction

   The W3C WebRTC API specification [W3C.WD-webrtc-20111027] specifies
   that communication between WebRTC entities is done via MediaStreams,
   which contain MediaStreamTracks.  A MediaStreamTrack is generally
   carried using a single SSRC in an RTP session.  There might possibly
   with additional SSRCs, possibly within additional RTP sessions, in
   order to support functionality like forward error correction or
   simulcast.  This complication is ignored below.

   One SSRC may utilize multiple codecs, such as an audio track
   switching between audio, comfort noise and DTMF.  An SSRC MUST NOT
   switch between media types (no switching between audio and video, for
   instance)

   In the RTP specification, media streams are identified using the SSRC
   field.  Streams are grouped into RTP Sessions, and also carry a
   CNAME.  Neither CNAME nor RTP session correspond to a MediaStream.
   Therefore, the association of an RTP media stream to MediaStreams
   need to be explicitly signalled.

   The marking needs to be on a per-SSRC basis, since one RTP session
   can carry media from multiple MediaStreams, and one MediaStream can
   have media in multiple RTP sessions.  This means that the [RFC4574]
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