RTP Control Protocol (RTCP) Extension for a Third-Party Loss Report
RFC 6642

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Internet Engineering Task Force (IETF)                        Q. Wu, Ed.
Request for Comments: 6642                                        F. Xia
Category: Standards Track                                        R. Even
ISSN: 2070-1721                                                   Huawei
                                                               June 2012

  RTP Control Protocol (RTCP) Extension for a Third-Party Loss Report

Abstract

   In a large RTP session using the RTP Control Protocol (RTCP) feedback
   mechanism defined in RFC 4585, a feedback target may experience
   transient overload if some event causes a large number of receivers
   to send feedback at once.  This overload is usually avoided by
   ensuring that feedback reports are forwarded to all receivers,
   allowing them to avoid sending duplicate feedback reports.  However,
   there are cases where it is not recommended to forward feedback
   reports, and this may allow feedback implosion.  This memo discusses
   these cases and defines a new RTCP Third-Party Loss Report that can
   be used to inform receivers that the feedback target is aware of some
   loss event, allowing them to suppress feedback.  Associated Session
   Description Protocol (SDP) signaling is also defined.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6642.

Wu, et al.                   Standards Track                    [Page 1]
RFC 6642                 Third-Party Loss Report               June 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
   (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
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   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 ....................................................3
   2. Terminology .....................................................3
      2.1. Requirements Notation ......................................3
      2.2. Glossary ...................................................4
   3. Example Use Cases ...............................................4
      3.1. Source-Specific Multicast (SSM) Use Case ...................4
      3.2. Unicast-Based Rapid Acquisition of Multicast Stream
           (RAMS) Use Case ............................................5
      3.3. RTP Transport Translator Use Case ..........................5
      3.4. Multipoint Control Unit (MCU) Use Case .....................6
      3.5. Mixer Use Case .............................................6
   4. Protocol Overview ...............................................6
   5. Format of RTCP Feedback Messages ................................7
      5.1. Transport-Layer Feedback: Third-Party Loss Report (TPLR) ...8
      5.2. Payload-Specific Feedback:  Third-Party Loss Report (TPLR) .8
   6. SDP Signaling ...................................................9
   7. Security Considerations ........................................10
   8. IANA Considerations ............................................11
   9. Acknowledgments ................................................11
   10. References ....................................................12
      10.1. Normative References .....................................12
      10.2. Informative References ...................................12

Wu, et al.                   Standards Track                    [Page 2]
RFC 6642                 Third-Party Loss Report               June 2012

1.  Introduction

   The RTP Control Protocol (RTCP) feedback messages [RFC4585] allow the
   receivers in an RTP session to report events and ask for action from
   the media source (or a delegated feedback target when using unicast
   RTCP feedback with Source-Specific Multicast (SSM) [RFC5760]).  There
   are cases where multiple receivers may initiate the same, or an
   equivalent, message towards the same media source or the same
   feedback target.  When the receiver count is large, this behavior may