Codec Control Messages in the RTP Audio-Visual Profile with Feedback (AVPF)
RFC 5104

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Network Working Group                                          S. Wenger
Request for Comments: 5104                                    U. Chandra
Category: Standards Track                                          Nokia
                                                           M. Westerlund
                                                               B. Burman
                                                                Ericsson
                                                           February 2008

                     Codec Control Messages in the
             RTP Audio-Visual Profile with Feedback (AVPF)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document specifies a few extensions to the messages defined in
   the Audio-Visual Profile with Feedback (AVPF).  They are helpful
   primarily in conversational multimedia scenarios where centralized
   multipoint functionalities are in use.  However, some are also usable
   in smaller multicast environments and point-to-point calls.

   The extensions discussed are messages related to the ITU-T Rec. H.271
   Video Back Channel, Full Intra Request, Temporary Maximum Media
   Stream Bit Rate, and Temporal-Spatial Trade-off.

Wenger, et al.              Standards Track                     [Page 1]
RFC 5104             Codec Control Messages in AVPF        February 2008

Table of Contents

   1. Introduction ....................................................4
   2. Definitions .....................................................5
      2.1. Glossary ...................................................5
      2.2. Terminology ................................................5
      2.3. Topologies .................................................8
   3. Motivation ......................................................8
      3.1. Use Cases ..................................................9
      3.2. Using the Media Path ......................................11
      3.3. Using AVPF ................................................11
           3.3.1. Reliability ........................................12
      3.4. Multicast .................................................12
      3.5. Feedback Messages .........................................12
           3.5.1. Full Intra Request Command .........................12
                  3.5.1.1. Reliability ...............................13
           3.5.2. Temporal-Spatial Trade-off Request and
                  Notification .......................................14
                  3.5.2.1. Point-to-Point ............................15
                  3.5.2.2. Point-to-Multipoint Using
                           Multicast or Translators ..................15
                  3.5.2.3. Point-to-Multipoint Using RTP Mixer .......15
                  3.5.2.4. Reliability ...............................16
           3.5.3. H.271 Video Back Channel Message ...................16
                  3.5.3.1. Reliability ...............................19
           3.5.4. Temporary Maximum Media Stream Bit Rate
                  Request and Notification ...........................19
                  3.5.4.1. Behavior for Media Receivers Using TMMBR ..21
                  3.5.4.2. Algorithm for Establishing Current
                           Limitations ...............................23
                  3.5.4.3. Use of TMMBR in a Mixer-Based
                           Multipoint Operation ......................29
                  3.5.4.4. Use of TMMBR in Point-to-Multipoint Using
                           Multicast or Translators ..................30
                  3.5.4.5. Use of TMMBR in Point-to-Point Operation ..31
                  3.5.4.6. Reliability ...............................31
   4. RTCP Receiver Report Extensions ................................32
      4.1. Design Principles of the Extension Mechanism ..............32
      4.2. Transport Layer Feedback Messages .........................33
           4.2.1. Temporary Maximum Media Stream Bit Rate
                  Request (TMMBR) ....................................34
                  4.2.1.1. Message Format ............................34
                  4.2.1.2. Semantics .................................35
                  4.2.1.3. Timing Rules ..............................39
                  4.2.1.4. Handling in Translators and Mixers ........39
           4.2.2. Temporary Maximum Media Stream Bit Rate
                  Notification (TMMBN) ...............................39
                  4.2.2.1. Message Format ............................39

Wenger, et al.              Standards Track                     [Page 2]