Rapid Synchronisation of RTP Flows
RFC 6051
Document | Type |
RFC - Proposed Standard
(November 2010; No errata)
Updates RFC 3550
|
|
---|---|---|---|
Last updated | 2018-12-20 | ||
Replaces | draft-perkins-avt-rapid-rtp-sync | ||
Stream | IETF | ||
Formats | plain text pdf html bibtex | ||
Reviews | |||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 6051 (Proposed Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Robert Sparks | ||
Send notices to | (None) |
Internet Engineering Task Force (IETF) C. Perkins Request for Comments: 6051 University of Glasgow Updates: 3550 T. Schierl Category: Standards Track Fraunhofer HHI ISSN: 2070-1721 November 2010 Rapid Synchronisation of RTP Flows Abstract This memo outlines how RTP sessions are synchronised, and discusses how rapidly such synchronisation can occur. We show that most RTP sessions can be synchronised immediately, but that the use of video switching multipoint conference units (MCUs) or large source-specific multicast (SSM) groups can greatly increase the synchronisation delay. This increase in delay can be unacceptable to some applications that use layered and/or multi-description codecs. This memo introduces three mechanisms to reduce the synchronisation delay for such sessions. First, it updates the RTP Control Protocol (RTCP) timing rules to reduce the initial synchronisation delay for SSM sessions. Second, a new feedback packet is defined for use with the extended RTP profile for RTCP-based feedback (RTP/AVPF), allowing video switching MCUs to rapidly request resynchronisation. Finally, new RTP header extensions are defined to allow rapid synchronisation of late joiners, and guarantee correct timestamp-based decoding order recovery for layered codecs in the presence of clock skew. 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/rfc6051. Perkins & Schierl Standards Track [Page 1] RFC 6051 RTP Synchronisation November 2010 Copyright Notice Copyright (c) 2010 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. Table of Contents 1. Introduction ....................................................3 2. Synchronisation of RTP Flows ....................................4 2.1. Initial Synchronisation Delay ..............................5 2.1.1. Unicast Sessions ....................................5 2.1.2. Source-Specific Multicast (SSM) Sessions ............6 2.1.3. Any-Source Multicast (ASM) Sessions .................7 2.1.4. Discussion ..........................................8 2.2. Synchronisation for Late Joiners ...........................9 3. Reducing RTP Synchronisation Delays ............................10 3.1. Reduced Initial RTCP Interval for SSM Senders .............10 3.2. Rapid Resynchronisation Request ...........................10 3.3. In-Band Delivery of Synchronisation Metadata ..............11 4. Application to Decoding Order Recovery in Layered Codecs .......14 4.1. In-Band Synchronisation for Decoding Order Recovery .......14 4.2. Timestamp-Based Decoding Order Recovery ...................15 4.3. Example ...................................................16 5. Security Considerations ........................................18 6. IANA Considerations ............................................19 7. Acknowledgements ...............................................19 8. References .....................................................20 8.1. Normative References ......................................20 8.2. Informative References ....................................20 Perkins & Schierl Standards Track [Page 2] RFC 6051 RTP Synchronisation November 2010 1. Introduction When using RTP to deliver multimedia content it's often necessary to synchronise playout of audio and video components of a presentation. This is achieved using information contained in RTP Control ProtocolShow full document text