Rapid Synchronisation of RTP Flows
RFC 6051
| Document | Type |
RFC - Proposed Standard
(November 2010; No errata)
Updates RFC 3550
|
|
|---|---|---|---|
| Last updated | 2015-10-14 | ||
| Replaces | draft-perkins-avt-rapid-rtp-sync | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| 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
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