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Versions: 00 01 02 03 04 05                                             
CLUE WG                                                          R. Even
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                          March 12, 2012
Expires: September 13, 2012


               Mapping RTP streams to CLUE media captures
                   draft-even-clue-rtp-mapping-01.txt

Abstract

   This document describes mechanisms and recommended practice for
   mapping RTP media streams defined in SDP to CLUE media captures.

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 September 13, 2012.

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Mapping CLUE Media Captures to RTP streams  . . . . . . . . . . 3
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 9







































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1.  Introduction

   Telepresence systems can send and receive multiple media streams.
   The CLUE framework [I-D.ietf-clue-framework] defines media captures
   as a source of Media, such as from one or more Capture Devices.  A
   Media Capture (MC) may be the source of one or more Media streams.  A
   Media Capture may also be constructed from other Media streams.  A
   middle box can express Media Captures that it constructs from Media
   streams it receives.

   SIP offer answer [RFC3264] uses SDP [RFC4566] to describe the
   RTP[RFC3550] media streams.  Each RTP stream has a payload type
   number and SSRC.  The content of the RTP stream is created by the
   encoder in the endpoint.  This may be an original content from a
   camera or a content created by an intermediary device like an MCU.

   The Telepresence systems MUST work in point to point calls and
   multipoint calls when there is a central multipoint Control unit
   (MCU).  They should work in the RTP topologies defined in [RFC5117].
   There may be some topologies that do not scale well with SIP offer
   answer like Topo-Translator.  The assumption here is that when
   handling the RTP streams the MCU works as an RTP mixer.

   The relation between the two SDP and CLUE descriptions is that the
   CLUE media capture defines adds some semantics that describing the
   content of an RTP stream and the relations between the streams not
   specified in SDP like spatial relation with regards to the conference
   room.

   This document discusses the relation between the CLUE media captures
   and the RTP streams and makes recommendations on how to co-relate
   between the two.  It tries to use SDP attribute when possible in
   order to not duplicate information.


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.


3.  Mapping CLUE Media Captures to RTP streams

   The SDP description of the RTP streams provides among others the
   information about the encoding and decoding capabilities of the media
   as well as transport addresses for receiving the RTP streams and some



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   channels capabilities like the maximum bandwidth available for the
   data.

   The CLUE MCs provide semantic information of the streams which may be
   its spatial information like left camera or on its content like
   loudest speaker.

   An RTP stream can have different content based on the MC description.
   For example one video capture from a camera may capture a third of
   the room while another from the same camera may provide a zoom
   version of the whole room.  These two media captures can be mapped to
   the same RTP stream and they are mutually exclusive using the same
   physical device.

   Using the video capture example from the framework document:

   o  VC0- (the camera-left camera stream, purpose=main, switched:no

   o  VC1- (the center camera stream, purpose=main, switched:no

   o  VC2- (the camera-right camera stream), purpose=main, switched:no

   o  VC3- (the loudest panel stream), purpose=main, switched:yes

   o  VC4- (the loudest panel stream with PiPs), purpose=main,
      composed=true; switched:yes

   o  VC5- (the zoomed out view of all people in the room),
      purpose=main, composed=no; switched:no

   o  VC6- (presentation stream), purpose=presentation, switched:no

   Note that the actual content of a mix or switched stream is define by
   the provider and the description in the parenthesis is an example.

   Where the physical simultaneity information is:

      {VC0, VC1, VC2, VC3, VC4, VC6}

      {VC0, VC2, VC5, VC6}

   To describe the MCs Media Captures we need 6 RTP streams since the
   first simultaneous entry defines 6 streams.  The RTP stream used for
   VC1 is also the RTP stream for VC5 coming from the same camera, it
   may even use the same RTP payload type number since the only
   difference between the two is the view port.  This will mean that the
   mapping from a Media capture to an RTP stream is fixed.  The number
   of RTP streams defined in the SDP depends on the maximum number of



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   captures in one capture set entry from the capture set.

   The offer answer exchange should work with systems that do not
   support CLUE protocol or multiple streams.  It should also allow both
   sides to learn if CLUE is supported.  One approach is to have two
   stage negotiation offering a single audio and maybe also a single
   video that will allow a connection with media to be established.
   This exchange will also enable both sides to learn if CLUE is
   supported and start a second exchange that will list the available
   media streams.

   Another approach is to use the same logic specified in the
   [I-D.ietf-mmusic-sdp-bundle-negotiation] which uses a new grouping
   attribute and allows offering of multiple media lines in the first
   offer.

   The proposal bellow can be used as the initial offer if using the
   bundle approach or for the second exchange.  It provides all the
   individual encoding information and specify the mapping between the
   SDP media lines and the different CLUE media captures.

   The example bellow uses a separate UDP port for each m-line but
   multiplexing grouping as specified in
   [I-D.ietf-mmusic-sdp-bundle-negotiation] can be applied here.

   This mapping can be done by defining a new [RFC5888] grouping
   attribute CaptureId and a new CLUE MC attribute RTP-id.

   The above example will have the following SDP

         b=AS:10000

         a=group:captureId 1 2 3 4 5 6

         m=video 49170 RTP/AVP 96

         a=rtpmap:96 H264/90000

         a=fmtp:96 profile-level-id=42A01E; //Baseline profile, Level
         3.0

         mid=1

         b=TIAS:2000000

         m=video 49172 RTP/AVP 96





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         a=rtpmap:96 H264/90000

         a=fmtp:96 profile-level-id=42A01E; //Baseline profile, Level
         3.0

         mid=2

         b=TIAS:2000000

         m=video 49174 RTP/AVP 96

         a=rtpmap:96 H264/90000

         a=fmtp:96 profile-level-id=42A01E; //Baseline profile, Level
         3.0

         mid=3

         b=TIAS:2000000

         m=video 49176 RTP/AVP 96

         a=rtpmap:96 H264/90000

         a=fmtp:96 profile-level-id=42A01E; //Baseline profile, Level
         3.0

         mid=4

         b=TIAS:2000000

         m=video 49178 RTP/AVP 96

         a=rtpmap:96 H264/90000

         a=fmtp:96 profile-level-id=42A01E; //Baseline profile, Level
         3.0

         mid=5

         b=TIAS:2000000

         m=video 49180 RTP/AVP 96

         a=rtpmap:96 H264/90000

         a=fmtp:96 profile-level-id=42A01E; //Baseline profile, Level
         3.0



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         mid=6

         b=TIAS:2000000

   There is a need for a new MC attribute RTPid which will have the mid
   of the related RTP stream

   o  VC0- (the camera-left camera stream, purpose=main, switched:no,
      RTPid=1

   o  VC1- (the center camera stream, purpose=main, switched:no, RTPid=2

   o  VC2- (the camera-right camera stream), purpose=main, switched:no,
      RTPid=3

   o  VC3- (the loudest panel stream), purpose=main, switched:yes,
      RTPid=4

   o  VC4- (the loudest panel stream with PiPs), purpose=main,
      composed=true; switched:yes, RTPid=5

   o  VC5- (the zoomed out view of all people in the room),
      purpose=main, composed=no; switched:no, RTPid=2

   o  VC6- (presentation stream), purpose=presentation, switched:no,
      RTPid=6

   There was a concern about the size of SDP or CLUE messages if the MCU
   will advertise the roster information.  This is not the current
   approach defined in IETF work.  The assumption is that the MCU decide
   what to advertise and the roster information is provided by other
   means like XCON conference event package enabling the conference
   participants to use this information to select a new source.  Still
   the assumption is that the MCU acting as an RTP mixer will create the
   RTP stream using his own SSRC.  Note that for the video switch MCU
   the SDP SSRC attribute can be used to provide the information about
   the different sources, an example is in [RFC6184] section 8.3, this
   solution does not scale when there are many participants since the
   SDP may grow big and it will be better in this case to use the XCON
   conference event package that supports partial updates.

   The offer is for H.264 [RFC6184] profile level 3.  The level ID
   specifies the maximum encoding and decoding capabilities of the H.264
   codec like the max macroblocks process rate, max frame size.  The
   max-mbps, max-smbps, max-fs, max-cpb, max-dpb, and max-br parameters
   are used to signal the receiver implementation.  The level ID is used
   to convey also the maximum encoding capability.  [RFC6184] does not
   provide the means to override specific level parameters for the



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   encoder side; it only allows the decoder to ask for a specific
   configuration.

   [RFC6236] a generic session setup attribute that make it possible to
   negotiate the image attributes like frame size and aspect ratio.

   The bandwidth parameters can be used to specify the maximum session
   bandwidth as well as the maximum bandwidth for individual streams.


4.  Acknowledgements

   place holder


5.  IANA Considerations

   TBD


6.  Security Considerations

   TBD.


7.  References

7.1.  Normative References

   [I-D.ietf-clue-framework]
              Romanow, A., Duckworth, M., Pepperell, A., and B. Baldino,
              "Framework for Telepresence Multi-Streams",
              draft-ietf-clue-framework-03 (work in progress),
              February 2012.

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

7.2.  Informative References

   [I-D.ietf-mmusic-sdp-bundle-negotiation]
              Holmberg, C. and H. Alvestrand, "Multiplexing Negotiation
              Using Session Description Protocol (SDP) Port Numbers",
              draft-ietf-mmusic-sdp-bundle-negotiation-00 (work in
              progress), February 2012.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,



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              June 2002.

   [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.

   [RFC5117]  Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117,
              January 2008.

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

   [RFC6184]  Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP
              Payload Format for H.264 Video", RFC 6184, May 2011.

   [RFC6236]  Johansson, I. and K. Jung, "Negotiation of Generic Image
              Attributes in the Session Description Protocol (SDP)",
              RFC 6236, May 2011.


Author's Address

   Roni Even
   Huawei Technologies
   Tel Aviv,
   Israel

   Email: even.roni@huawei.com




















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