Codec-Layer Feedback for the Real-time Transport Control Protocol (RTCP)
draft-realvnc-rtcp-codec-00

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Internet Engineering Task Force                           N. Wilson, Ed.
Internet-Draft                                               RealVNC Ltd
Intended status: Informational                        September 24, 2018
Expires: March 28, 2019

Codec-Layer Feedback for the Real-time Transport Control Protocol (RTCP)
                      draft-realvnc-rtcp-codec-00

Abstract

   This document specifies an extension to the messages defined in the
   Audio-Visual Profile with Feedback (AVPF), allowing for an RTP codec
   to send codec-specific feedback via RTCP.  Currently, RTCP feedback
   messages have been defined only for generic capabilities which may be
   defined in the context of individual codecs, and some codecs have
   their own RTCP feedback messages.  There is a need for a feedback
   message at the codec-layer, allowing other codecs to send codec-
   specific feedback.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on March 28, 2019.

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Wilson                   Expires March 28, 2019                 [Page 1]
Internet-Draft        Codec-Layer Feedback for RTCP       September 2018

   include Simplified BSD License text as described in Section 4.e of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Format of RTCP Feedback Message . . . . . . . . . . . . . . .   5
   6.  Semantics of the RTCP Feedback Message  . . . . . . . . . . .   5
   7.  SDP Definition  . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Extension of the rtcp-fb attribute  . . . . . . . . . . .   6
     7.2.  Offer/Answer  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The Extended RTP Profile for RTCP-Based Feedback (RTP/AVPF,
   [RFC4585]) introduced the concept of feedback messages, which may be
   used by RTP peers to exchange information controlling an RTP stream.
   The framework provided by RTP/AVPF divides such feedback into
   Transport-Layer (RTPFB) and Payload-Specific feedback (PSFB)
   messages.  These include generic capabilities such as "Slice Loss
   Indication" (SLI), which are widely applicable to many different
   codecs, yet require interpretation in the context of each codec,
   since the notion of "slice" is codec-specific.  Since then, further
   Codec-Control messages have been defined in the same framework, which
   further expand the generic messages defined for the RTP/AVPF control
   layer, for example "Full Intra Request" from [RFC5104], which follows
   the same model as SLI.

   However, these generic messages do not enable truly codec-specific
   feedback to be exchanged.  There is currently no payload-specific
   feedback number assigned for codec-defined feedback which is not
   covered by the existing mechanisms (SLI, FIR, and others).  Some
   codecs have resorted to defining their own top-level feedback
   messages (such as the H.271 Video Back Channel Message, [RFC5104]),
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