[rfc-dist] RFC 6051 on Rapid Synchronisation of RTP Flows

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Sun Nov 7 21:49:49 PST 2010

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        RFC 6051

        Title:      Rapid Synchronisation of RTP Flows 
        Author:     C. Perkins, T. Schierl
        Status:     Standards Track
        Stream:     IETF
        Date:       November 2010
        Mailbox:    csp at csperkins.org, 
                    ts at thomas-schierl.de
        Pages:      22
        Characters: 53503
        Updates:    RFC3550

        I-D Tag:    draft-ietf-avt-rapid-rtp-sync-12.txt

        URL:        http://www.rfc-editor.org/rfc/rfc6051.txt

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.  

This document is a product of the Audio/Video Transport Working Group of the IETF.

This is now a Proposed Standard Protocol.

STANDARDS TRACK: This document specifies an Internet standards track
protocol for the Internet community,and requests discussion and suggestions
for improvements.  Please refer to the current edition of the Internet
Official Protocol Standards (STD 1) for the standardization state and
status of this protocol.  Distribution of this memo is unlimited.

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