Rapid Synchronisation of RTP Flows
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From: The IESG <email@example.com> To: IETF-Announce <firstname.lastname@example.org> Cc: Internet Architecture Board <email@example.com>, RFC Editor <firstname.lastname@example.org>, avt mailing list <email@example.com>, avt chair <firstname.lastname@example.org> Subject: Protocol Action: 'Rapid Synchronisation of RTP Flows' to Proposed Standard The IESG has approved the following document: - 'Rapid Synchronisation of RTP Flows ' <draft-ietf-avt-rapid-rtp-sync-12.txt> as a Proposed Standard This document is the product of the Audio/Video Transport Working Group. The IESG contact persons are Robert Sparks and Gonzalo Camarillo. A URL of this Internet-Draft is: http://www.ietf.org/internet-drafts/draft-ietf-avt-rapid-rtp-sync-12.txt
Technical Summary 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 synchronization 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. Working Group Summary There is nothing specific to note. Document Quality This document explains and updates the timing consideration for RTCP in RFC 3550. It also defines new protocol that is referenced by other documents like payload specification for H.264 SVC http://tools.ietf.org/html/draft-ietf-avt-rtp-svc-21 Personnel Roni Even is the document shepherd. The responsible area director is Robert Sparks.