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MMUSIC WG                                                        R. Even
Internet-Draft                                       Huawei Technologies
Intended status: Informational                                 J. Lennox
Expires: December 30, 2013                                         Vidyo
                                                                   Q. Wu
                                                     Huawei Technologies
                                                           June 28, 2013


   The Session Description Protocol (SDP) Application Token Attribute
               draft-even-mmusic-application-token-00.txt

Abstract

   The RTP fixed header includes the payload type number and the SSRC
   values of the RTP stream.  RTP defines how you de-multiplex streams
   within an RTP session, but in some use cases applications need
   further identifiers in order to identify the application semantics
   associated with particular streams within the session.

   This document defines a mechanism to provide the mapping between the
   SSRCs of RTP streams and the application semantics by defining
   extensions to RTP and RTCP messages.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 30, 2013.

Copyright Notice

   Copyright (c) 2013 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
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Proposal for an Application ID token  . . . . . . . . . . . .   4
     3.1.  RTCP SDES message . . . . . . . . . . . . . . . . . . . .   6
     3.2.  RTP Header Extension  . . . . . . . . . . . . . . . . . .   6
   4.  Using Application ID token  . . . . . . . . . . . . . . . . .   7
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The RTP [RFC3550] header includes the payload type number and the
   SSRC values of the RTP stream.  RTP defines how you de-multiplex
   streams within an RTP session, but in some use cases, applications
   need further identifiers in order to identify semantics associated
   with particular streams within the session.

   There is ongoing work to define how to support, using SDP [RFC4566],
   multiple RTP media streams in one or more m-lines that define a
   single RTP session (as specified in [RFC3550]).  The work is
   addressing the WebRTC architecture [I-D.ietf-rtcweb-overview], and
   some work will be needed when looking for a general solution in
   MMUSIC that can be used for non-WebRTC systems.

   RTCWEB Plan A [I-D.roach-rtcweb-plan-a] that an m-line in SDP
   represents a single RTP stream.  De-multiplexing is done by payload
   type (PT) number (which MUST be unique), and if unique PTs are not
   feasible, use SSRC information in the SDP to identify the RTP stream.

   RTCWEB Plan B [I-D.uberti-rtcweb-plan] takes a different approach,
   and creates a hierarchy within SDP; an m= line defines an "envelope",
   specifying codec and transport parameters, and [RFC5576] a=ssrc lines
   are used to describe individual media sources within that envelope.



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   Each m-line defines multiple RTP streams.  This requires that the
   SSRCs of all RTP streams in the session are declared before they
   appear as RTP streams.

   No plan [I-D.ivov-rtcweb-noplan]  proposes using a single m-line for
   each media type but does not require that all SSRCs will be declared
   in the SDP.  The de-multiplexing is done based on the unique PT
   numbers and the mapping of SSRC to the application usage may be done
   by application protocol.  In web application, for example, the
   application specific signaling may use something like { "leftSSRC":
   "1234", "rightSSRC": "5678" }.

   Some applications may require more information about the usage of the
   RTP streams.  For example, RTP streams from different cameras that
   need to be identified by the application in order to render them
   correctly, or a source that can send multiple versions of the same
   stream in different resolutions (Simulcast
   [I-D.westerlund-avtcore-rtp-simulcast]).

   SDP provides in [RFC4574] a "label" attribute that contains a token
   defined by an application and is used in its context.  "Label" can be
   attached to m-lines in multiple SDP documents allowing the
   application to logically identify the media streams across SDP
   sessions when necessary.  The "label" attribute is a token and does
   not provide any information about the content of the stream.
   [RFC4796] defines the "content" attribute providing information about
   the content of the stream, currently there is a small set of values
   for the content attribute.

   Both "label" and "content" attribute are SDP media-level attributes,
   so when an SDP m-line supports multiple RTP streams, this value is
   applicable to all sources described by the SDP m-line.

   There is a need to have a token that will allow the mapping between a
   single source (identified by an SSRC) in an m-line to the application
   logic (Source may be a single RTP stream identified by a unique
   SSRC).  For example, SSRC1 is the RTP stream from the left camera and
   SSRC2 is the RTP stream from the right camera both can be specified
   in a single SDP m-line and may have the same PT number.

2.  Terminology

   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 RFC2119[RFC2119] and
   indicate requirement levels for compliant RTP implementations.





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3.  Proposal for an Application ID token

   As we saw in the previous section, there are tokens defined that
   could be used for the mapping, but they have existing usages and
   semantics, and tend to apply at media-level rather than source-level.
   In order to avoid overload of existing attributes, it is better to
   have a new token attribute that can identify a specific source
   corresponding to the application.  This document defines such a new
   token, called "AppID".

   AppID is a general-purpose token associated with an RTP stream,
   allowing the semantics of the stream with a token to be defined by
   the application.  This token may be mapped, for example, to a CLUE
   media capture using CLUE protocol [I-D.ietf-clue-framework], or to a
   specific resolution in a simulcast application described in the SDP .

   The token is chosen by the sender, and represents the RTP stream that
   will be sent to the receiver.

   The proposed token can be sent using SDP, RTCP SDES messages
   [RFC3550], or an RTP header extension [RFC5285]

   The SSRC mapping may be available to the receiver when receiving the
   RTP stream through the RTP header extension, but may also be
   available ahead of time via an RTCP SDES message conveyed before the
   source started sending, even if the receiver has not seen any RTP
   packets from this source like in a multipoint conference or in the
   SDP description.

   The receiver can receive new sources that may be of two kinds.

   o  A new RTP stream replacing an existing RTP stream, in which case
      the AppID of the replaced RTP stream will be assigned to the new
      SSRC.

   o  A new RTP stream requiring a different AppID, for example, when
      adding a presentation stream to an existing call with two video
      cameras from a room.

   The solution should support a RTP session as described using SDP.
   The RTP session may be specified using a single SDP m-line, or using
   Bundle [I-D.ietf-mmusic-sdp-bundle-negotiation], using more than one
   m-line.  In the latter case, if the SSRCs of all RTP streams are not
   known in advance, the AppIDs associated with each m-line need to be
   available to the receiver in order to map each SSRC to a specific
   m-line configuration.





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   To support these cases the document defines a new SDP media level
   attribute a=appID that can be used to list all the appIDs that an
   application may use.

   The appID syntax provides a token identifier and optional SDP
   attributes that describe the application usage if exists in SDP.
   Application usage in SDP may be, for example, an image attribute
   describing a simulcast application usage
   [I-D.westerlund-avtcore-rtp-simulcast].

   Each value of the AppID maps to one SSRC at a time.  When a new SSRC
   is mapped to an existing AppID using an RTP header extension or SDES
   message, it replaces the previous RTP stream for this application
   usage.

   The formal representation of the appID token is:

      appid-attribute = "appID:" tokenlist [SP attribute]

      tokenlist = token *("," token)

      ; The base definition of "attribute" is in [RFC4566].

      ; (It is the content of "a=" lines.)

   Examples:

   The SSRCs of the streams are not known when the SDP offer is sent,
   two appID are specified and can be used for mapping to specific SSRCs
   in the application.

      m=video 49200 RTP/AVP 99

      a=rtpmap:99 H264/90000

      a=appID:2,3

   The second example is when the application usage of the RTP steam is
   specified using SDP to provide different image resolutions.

      m=video 49200 RTP/AVP 98, 99

      a=rtpmap:98 H264/90000

      a=rtpmap:99 H264/90000

      a=appID:2 imageattr:98 send [x=480,y=320]  recv *




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      a=appID:3 imageattr:99 send [x=800,y=640]  recv *

3.1.  RTCP SDES message

   The document specify a new RTCP SDES message

   0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    AppID = XXX    |     length    |AppID token
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   ....


   This AppID is the same token as defined in the new SDP attribute and
   will also be used in the RTP header extension.

   This SDES message MAY be sent in a compound RTCP packet based on the
   application need.

3.2.  RTP Header Extension

   The Application ID could be carried within the RTP header extension
   field, using [RFC5285] two bytes header extension.

   This is negotiated within the SDP i.e.

   a=extmap:1 urn:ietf:params:rtp-hdrext:App-ID

   Packets tagged by the sender with the AppID will then contain a
   header extension as shown below

   0                      1                   2                   3
          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |  ID=1            |   Len-1              |    AppID
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |  AppID   ..............       |
         +-+-+-+-+-+-+-+-+


   To add or modify the AppID by an intermediary can be an expensive
   operation, particularly if SRTP is used to authenticate the packet.
   Modification to the contents of the RTP header requires a re-
   authentication of the complete packet, and this could prove to be a
   limiting factor in the throughput of a multipoint device.





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   There is no need to send the AppID header extension with all RTP
   packets.  Senders MAY choose to send it only when a new SSRC is sent,
   or when an SSRC changes its association to an AppID.  If such a mode
   is being used, the header extension SHOULD be sent in the first few
   RTP packets to reduce the risk of losing it due to packet loss.  For
   codecs with decoder refresh points (such as I-Frames in video
   codecs), senders also SHOULD send the AppID header extension along
   with the packets carrying the decoder refresh.

4.  Using Application ID token

   The usage of mapping may depend on the de-multiplexing of the RTP
   streams in the SDP m-lines.  Currently we have three options
   discussed based on input from the RTCweb WG.

   For plan A [I-D.roach-rtcweb-plan-a], since each RTP stream is
   described by a specific m-line it will be enough to have a media
   level token for mapping the sent stream.

   Only need for example:

      m=video 49200 RTP/AVP 99

      a=rtpmap:99 H264/90000

      a=appID 2

   For plan B [I-D.uberti-rtcweb-plan] which adds another level of RTP
   stream description, the mapping of SSRC to the application will need
   to be at the SSRC level base on [RFC5576] since all SSRCs are
   specified in the m-line.  The document addresses the mapping of SSRCs
   using the SSRC attribute but uses the msid [I-D.ietf-mmusic-msid]
   that defines a specific semantics for each SSRC.  The following offer
   example is using RFC5576 to provide source specific attribute
   identifier.

      m=video 49200 RTP/AVP

      a=rtpmap:99 H264/90000

      a=max-send-ssrc:{*:3}

      a=max-recv-ssrc:{*:3}

      a=ssrc:11111 AppID:1

      a=ssrc:22222 AppID:2




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      a=ssrc:33333 AppID:3

   When using noplan [I-D.ivov-rtcweb-noplan] in MMUSIC, not all SSRCs
   will be known ahead of time.  For example, in the following SDP the
   offer offers either two streams with the same resolution (for example
   two cameras) or two streams with different resolutions.

      m=video 5002 RTP/SAVPF 98

      a=rtpmap:98 H264/90000

      a= appID 1,2 imageattr:98 send [x=800,y=640,sar=1.1,q=0.6]  recv *

      a= appID 3,4 imageattr:98 send [x=480,y=320]  recv *

      a=max-send-ssrc:{*:2}

   In the CLUE WG case the mapping is from an RTP stream to a CLUE media
   capture specified in the CLUE framework [I-D.ietf-clue-framework].
   The SSRCs of all streams may be known like in PLAN B but there are
   cases where the SDP may not be available so a pre-announce is
   recommended like in the following example.

      m=video 49200 RTP/AVP

      a=rtpmap:99 H264/90000

      a=max-send-ssrc:{*:5}

      a=max-recv-ssrc:{*:3}

      a=ssrc:11111 AppID:1

      a=ssrc:22222 AppID:2

      a=ssrc:33333 AppID:3

      a=appID 4, 5

   The pre-announce is needed since the new RTCP SDES message includes
   only the SSRC and the appID but not the PT.  A receiver of the SDES
   message will be able to map the SSRC to a codec configuration based
   on the SDP pre-announced tokens.

5.  Acknowledgements

   Place Holder




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6.  IANA Considerations

   TBD

7.  Security Considerations

   TBD.

8.  References

8.1.  Normative References

   [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.

   [RFC5285]  Singer, D. and H. Desineni, "A General Mechanism for RTP
              Header Extensions", RFC 5285, July 2008.

8.2.  Informative References

   [I-D.ietf-clue-framework]
              Duckworth, M., Pepperell, A., and S. Wenger, "Framework
              for Telepresence Multi-Streams", draft-ietf-clue-
              framework-10 (work in progress), May 2013.

   [I-D.ietf-mmusic-msid]
              Alvestrand, H., "Cross Session Stream Identification in
              the Session Description Protocol", draft-ietf-mmusic-
              msid-00 (work in progress), February 2013.

   [I-D.ietf-mmusic-sdp-bundle-negotiation]
              Holmberg, C., Alvestrand, H., and C. Jennings,
              "Multiplexing Negotiation Using Session Description
              Protocol (SDP) Port Numbers", draft-ietf-mmusic-sdp-
              bundle-negotiation-04 (work in progress), June 2013.

   [I-D.ietf-rtcweb-overview]
              Alvestrand, H., "Overview: Real Time Protocols for Brower-
              based Applications", draft-ietf-rtcweb-overview-06 (work
              in progress), February 2013.

   [I-D.ivov-rtcweb-noplan]
              Ivov, E., Marocco, E., and P. Thatcher, "No Plan:
              Economical Use of the Offer/Answer Model in WebRTC



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              Sessions with Multiple Media Sources", draft-ivov-rtcweb-
              noplan-01 (work in progress), June 2013.

   [I-D.roach-rtcweb-plan-a]
              Roach, A. and M. Thomson, "Using SDP with Large Numbers of
              Media Flows", draft-roach-rtcweb-plan-a-00 (work in
              progress), May 2013.

   [I-D.uberti-rtcweb-plan]
              Uberti, J., "Plan B: a proposal for signaling multiple
              media sources in WebRTC.", draft-uberti-rtcweb-plan-00
              (work in progress), May 2013.

   [I-D.westerlund-avtcore-rtp-simulcast]
              Westerlund, M., Lindqvist, M., and F. Jansson, "Using
              Simulcast in RTP Sessions", draft-westerlund-avtcore-rtp-
              simulcast-02 (work in progress), February 2013.

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

   [RFC4574]  Levin, O. and G. Camarillo, "The Session Description
              Protocol (SDP) Label Attribute", RFC 4574, August 2006.

   [RFC4575]  Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session
              Initiation Protocol (SIP) Event Package for Conference
              State", RFC 4575, August 2006.

   [RFC4796]  Hautakorpi, J. and G. Camarillo, "The Session Description
              Protocol (SDP) Content Attribute", RFC 4796, February
              2007.

   [RFC5576]  Lennox, J., Ott, J., and T. Schierl, "Source-Specific
              Media Attributes in the Session Description Protocol
              (SDP)", RFC 5576, June 2009.

Authors' Addresses

   Roni Even
   Huawei Technologies
   Tel Aviv
   Israel

   Email: roni.even@mail01.huawei.com







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   Jonathan Lennox
   Vidyo, Inc.
   433 Hackensack Avenue
   Seventh Floor
   Hackensack, NJ  07601
   US

   Email: jonathan@vidyo.com


   Qin Wu
   Huawei Technologies

   Email: bill.wu@huawei.com





































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