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In: MissingRef
Network Working Group                                           A. Roach
Internet-Draft                                                   Mozilla
Intended status: Standards Track                           S. Nandakumar
Expires: December 23, 2016                                 Cisco Systems
                                                             P. Thatcher
                                                                  Google
                                                           June 21, 2016


            RTP Stream Identifier Source Description (SDES)
                        draft-ietf-avtext-rid-04

Abstract

   This document defines and registers two new RTCP SDES items.  One,
   named RtpStreamId, is used for unique identification of RTP streams.
   The other, RepairedRtpStreamId, can be used to identify which stream
   a redundancy RTP stream is to be used to repair.

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
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   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 23, 2016.

Copyright Notice

   Copyright (c) 2016 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
   (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



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   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.  Usage of RtpStreamId and RepairedRtpStreamId in RTP and RTCP    3
     3.1.  RTCP 'RtpStreamId' SDES Extension . . . . . . . . . . . .   4
     3.2.  RTCP 'RepairedRtpStreamId' SDES Extension . . . . . . . .   4
     3.3.  RTP 'RtpStreamId' and 'RepairedRtpStreamId' Header
           Extensions  . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  New RtpStreamId SDES item . . . . . . . . . . . . . . . .   5
     4.2.  New RepairRtpStreamId SDES item . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   RTP sessions frequently consist of multiple streams, each of which is
   identified at any given time by its SSRC; however, the SSRC
   associated with a stream is not guaranteed to be stable over its
   lifetime.  Within a session, these streams can be tagged with a
   number of identifiers, including CNAMEs and MSIDs
   [I-D.ietf-mmusic-msid].  Unfortunately, none of these have the proper
   ordinality to refer to an individual stream; all such identifiers can
   appear in more than one stream at a time.  While approaches that use
   unique Payload Types (PTs) per stream have been used in some
   applications, this is a semantic overloading of that field, and one
   for which its size is inadequate: in moderately complex systems that
   use PT to uniquely identify every potential combination of codec
   configuration and unique stream, it is possible to simply run out of
   values.

   To address this situation, we define a new RTCP SDES identifier,
   RtpStreamId, that uniquely identifies a single RTP stream.  A key
   motivator for defining this identifier is the ability to
   differentiate among different encodings of a single Source Stream
   that are sent simultaneously (i.e., simulcast).  This need for unique
   identification extends to dependent streams (e.g., where layers used
   by a layered codec are transmitted on separate streams).





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   At the same time, when redundancy RTP streams are in use, we also
   need an identifier that connects such streams to the RTP stream for
   which they are providing redundancy.  For this purpose, we define an
   additional SDES identifier, RepairedRtpStreamId.  This identifier can
   appear only in packets associated with a redundancy RTP stream.  They
   carry the same value as the RtpStreamId of the RTP stream that the
   redundant RTP stream is correcting.

2.  Terminology

   In this document, the terms "source stream", "encoded stream," "RTP
   stream", "source RTP stream", "dependent stream", "received RTP
   stream", and "redundancy RTP stream" are used as defined in
   [RFC7656].

3.  Usage of RtpStreamId and RepairedRtpStreamId in RTP and RTCP

   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; however, in some use cases, applications need
   further identifiers in order to effectively map the individual RTP
   Streams to their equivalent payload configurations in the SDP.

   This specification defines two new RTCP SDES items [RFC3550].  The
   first item is 'RtpStreamId', which is used to carry RTP stream
   identifiers within RTCP SDES packets.  This makes it possible for a
   receiver to associate received RTP packets (identifying the RTP
   stream) with a media description having the format constraint
   specified.  The second is 'RepairedRtpStreamId', which can be used in
   redundancy RTP streams to indicate the RTP stream repaired by a
   redundancy RTP stream.

   To be clear: the value carried in a RepairedRtpStreamId will always
   match the RtpStreamId value from another RTP stream in the same
   session.  For example, if a source RTP stream is identified by
   RtpStreamId "A", then any redundancy RTP stream that repairs that
   source RTP stream will contain a RepairedRtpStreamId of "A" (if this
   mechanism is being used to perform such correlation).  These
   redundant RTP streams may also contain their own unique RtpStreamId.

   This specification also uses the RTP header extension for RTCP SDES
   items [I-D.ietf-avtext-sdes-hdr-ext] to allow carrying RtpStreamId
   and RepairedRtpStreamId values in RTP packets.  This allows
   correlation at stream startup, or after stream changes where the use
   of RTCP may not be sufficiently responsive.






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3.1.  RTCP 'RtpStreamId' SDES Extension

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |RtpStreamId=TBD|     length    | RtpStreamId                 ...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The RtpStreamId payload is UTF-8 encoded and is not null-terminated.

      RFC EDITOR NOTE: Please replace TBD with the assigned SDES
      identifier value.

3.2.  RTCP 'RepairedRtpStreamId' SDES Extension

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Repaired...=TBD|     length    | RepairRtpStreamId           ...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The RepairedRtpStreamId payload is UTF-8 encoded and is not null-
   terminated.

      RFC EDITOR NOTE: Please replace TBD with the assigned SDES
      identifier value.

3.3.  RTP 'RtpStreamId' and 'RepairedRtpStreamId' Header Extensions

   Because recipients of RTP packets will typically need to know which
   streams they correspond to immediately upon receipt, this
   specification also defines a means of carrying RtpStreamId and
   RepairedRtpStreamId identifiers in RTP extension headers, using the
   technique described in [I-D.ietf-avtext-sdes-hdr-ext].

   As described in that document, the header extension element can be
   encoded using either the one-byte or two-byte header, and the
   identification-tag payload is UTF-8 encoded, as in SDP.

   As the identifier is included in an RTP header extension, there
   should be some consideration given to the packet expansion caused by
   the identifier.  To avoid Maximum Transmission Unit (MTU) issues for
   the RTP packets, the header extension's size needs to be taken into
   account when the encoding media.  Note that set of header extensions
   included in the packet needs to be padded to the next 32-bit boundary
   [RFC5285].





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   In many cases, a one-byte identifier will be sufficient to
   distinguish streams in a session; implementations are strongly
   encouraged to use the shortest identifier that fits their purposes.

4.  IANA Considerations

4.1.  New RtpStreamId SDES item

      RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of
      this document.

      RFC EDITOR NOTE: Please replace TBD with the assigned SDES
      identifier value.

   This document adds the RtpStreamId SDES item to the IANA "RTCP SDES
   item types" registry as follows:

              Value:          TBD
              Abbrev.:        RtpStreamId
              Name:           RTP Stream Identifier
              Reference:      RFCXXXX


4.2.  New RepairRtpStreamId SDES item

      RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of
      this document.

      RFC EDITOR NOTE: Please replace TBD with the assigned SDES
      identifier value.

   This document adds the RepairedRtpStreamId SDES item to the IANA
   "RTCP SDES item types" registry as follows:

              Value:          TBD
              Abbrev.:        RepairedRtpStreamId
              Name:           Repaired RTP Stream Identifier
              Reference:      RFCXXXX


5.  Security Considerations

   The actual identifiers used for RtpStreamIds (and therefore
   RepairedRtpStreamIds) are expected to be opaque.  As such, they are
   not expected to contain information that would be sensitive, were it
   observed by third-parties.





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6.  Acknowledgements

   Many thanks for review and input from Cullen Jennings, Magnus
   Westerlund, Colin Perkins, Peter Thatcher, Jonathan Lennox, and Paul
   Kyzivat.

7.  References

7.1.  Normative References

   [I-D.ietf-avtext-sdes-hdr-ext]
              Westerlund, M., Burman, B., Even, R., and M. Zanaty, "RTP
              Header Extension for RTCP Source Description Items",
              draft-ietf-avtext-sdes-hdr-ext-07 (work in progress), June
              2016.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <http://www.rfc-editor.org/info/rfc3550>.

   [RFC5285]  Singer, D. and H. Desineni, "A General Mechanism for RTP
              Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July
              2008, <http://www.rfc-editor.org/info/rfc5285>.

   [RFC7656]  Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
              B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
              for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
              DOI 10.17487/RFC7656, November 2015,
              <http://www.rfc-editor.org/info/rfc7656>.

7.2.  Informative References

   [I-D.ietf-mmusic-msid]
              Alvestrand, H., "WebRTC MediaStream Identification in the
              Session Description Protocol", draft-ietf-mmusic-msid-14
              (work in progress), June 2016.

Authors' Addresses

   Adam Roach
   Mozilla

   Email: adam@nostrum.com







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   Suhas Nandakumar
   Cisco Systems

   Email: snandaku@cisco.com


   Peter Thatcher
   Google

   Email: pthatcher@google.com









































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