Sending Multiple RTP Streams in a Single RTP Session
RFC 8108

Document Type RFC - Proposed Standard (March 2017; No errata)
Last updated 2017-03-07
Replaces draft-lennox-avtcore-rtp-multi-stream
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IESG IESG state RFC 8108 (Proposed Standard)
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Internet Engineering Task Force (IETF)                         J. Lennox
Request for Comments: 8108                                         Vidyo
Updates: 3550, 4585                                        M. Westerlund
Category: Standards Track                                       Ericsson
ISSN: 2070-1721                                                    Q. Wu
                                                                  Huawei
                                                              C. Perkins
                                                   University of Glasgow
                                                              March 2017

          Sending Multiple RTP Streams in a Single RTP Session

Abstract

   This memo expands and clarifies the behavior of Real-time Transport
   Protocol (RTP) endpoints that use multiple synchronization sources
   (SSRCs).  This occurs, for example, when an endpoint sends multiple
   RTP streams in a single RTP session.  This memo updates RFC 3550 with
   regard to handling multiple SSRCs per endpoint in RTP sessions, with
   a particular focus on RTP Control Protocol (RTCP) behavior.  It also
   updates RFC 4585 to change and clarify the calculation of the timeout
   of SSRCs and the inclusion of feedback messages.

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
   http://www.rfc-editor.org/info/rfc8108.

Lennox, et al.               Standards Track                    [Page 1]
RFC 8108        Multiple Media Streams in an RTP Session      March 2017

Copyright Notice

   Copyright (c) 2017 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
   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.

Lennox, et al.               Standards Track                    [Page 2]
RFC 8108        Multiple Media Streams in an RTP Session      March 2017

Table of Contents

   1. Introduction ....................................................4
   2. Terminology .....................................................4
   3. Use Cases for Multi-Stream Endpoints ............................4
      3.1. Endpoints with Multiple Capture Devices ....................4
      3.2. Multiple Media Types in a Single RTP Session ...............5
      3.3. Multiple Stream Mixers .....................................5
      3.4. Multiple SSRCs for a Single Media Source ...................5
   4. Use of RTP by Endpoints That Send Multiple Media Streams ........6
   5. Use of RTCP by Endpoints That Send Multiple Media Streams .......6
      5.1. RTCP Reporting Requirement .................................7
      5.2. Initial Reporting Interval .................................7
      5.3. Aggregation of Reports into Compound RTCP Packets ..........8
           5.3.1. Maintaining AVG_RTCP_SIZE ...........................9
           5.3.2. Scheduling RTCP when Aggregating Multiple SSRCs ....10
      5.4. Use of RTP/AVPF or RTP/SAVPF Feedback .....................13
           5.4.1. Choice of SSRC for Feedback Packets ................13
           5.4.2. Scheduling an RTCP Feedback Packet .................14
   6. Adding and Removing SSRCs ......................................15
      6.1. Adding RTP Streams ........................................16
      6.2. Removing RTP Streams ......................................16
   7. RTCP Considerations for Streams with Disparate Rates ...........17
      7.1. Timing Out SSRCs ..........................................19
           7.1.1. Problems with the RTP/AVPF T_rr_interval
                  Parameter ..........................................19
           7.1.2. Avoiding Premature Timeout .........................20
           7.1.3. Interoperability between RTP/AVP and RTP/AVPF ......21
           7.1.4. Updated SSRC Timeout Rules .........................22
      7.2. Tuning RTCP Transmissions .................................22
           7.2.1. RTP/AVP and RTP/SAVP ...............................22
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