RTP Stream Identifier Source Description (SDES)
RFC 8852

Document Type RFC - Proposed Standard (January 2021; No errata)
Authors Adam Roach  , Suhas Nandakumar  , Peter Thatcher 
Last updated 2021-01-19
Replaces draft-roach-avtext-rid
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IESG IESG state RFC 8852 (Proposed Standard)
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Internet Engineering Task Force (IETF)                        A.B. Roach
Request for Comments: 8852                                       Mozilla
Category: Standards Track                                  S. Nandakumar
ISSN: 2070-1721                                            Cisco Systems
                                                             P. Thatcher
                                                            January 2021

            RTP Stream Identifier Source Description (SDES)


   This document defines and registers two new Real-time Transport
   Control Protocol (RTCP) Stream Identifier Source Description (SDES)
   items.  One, named RtpStreamId, is used for unique identification of
   RTP streams.  The other, RepairedRtpStreamId, can be used to identify
   which stream is to be repaired using a redundancy RTP stream.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2021 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
   (https://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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Usage of RtpStreamId and RepairedRtpStreamId in RTP and RTCP
     3.1.  RTCP "RtpStreamId" SDES Extension
     3.2.  RTCP "RepairedRtpStreamId" SDES Extension
     3.3.  RTP "RtpStreamId" and "RepairedRtpStreamId" Header
   4.  IANA Considerations
     4.1.  New RtpStreamId SDES Item
     4.2.  New RepairRtpStreamId SDES Item
     4.3.  New RtpStreamId Header Extension URI
     4.4.  New RepairRtpStreamId Header Extension URI
   5.  Security Considerations
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Authors' Addresses

1.  Introduction

   RTP sessions frequently consist of multiple streams, each of which is
   identified at any given time by its synchronization source (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 MediaStream
   Identification (MSID) [RFC8830].  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 Stream Identifier
   Source Description (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).

   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", "RTP stream", "source
   RTP stream", "dependent stream", "received RTP stream", and
   "redundancy RTP stream" are used as defined in [RFC7656].
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