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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@csperkins.org,
ts@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.
[STANDARDS-TRACK]
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
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