{"draft":"draft-ietf-avt-rapid-rtp-sync-12","doc_id":"RFC6051","title":"Rapid Synchronisation of RTP Flows","authors":["C. Perkins","T. Schierl"],"format":["ASCII","HTML"],"page_count":"22","pub_status":"PROPOSED STANDARD","status":"PROPOSED STANDARD","source":"Audio\/Video Transport","abstract":"This memo outlines how RTP sessions are synchronised, and discusses\r\nhow rapidly such synchronisation can occur.  We show that most RTP\r\nsessions can be synchronised immediately, but that the use of video\r\nswitching multipoint conference units (MCUs) or large source-specific\r\nmulticast (SSM) groups can greatly increase the synchronisation\r\ndelay.  This increase in delay can be unacceptable to some\r\napplications that use layered and\/or multi-description codecs.\r\n\r\nThis memo introduces three mechanisms to reduce the synchronisation\r\ndelay for such sessions.  First, it updates the RTP Control Protocol\r\n(RTCP) timing rules to reduce the initial synchronisation delay for\r\nSSM sessions.  Second, a new feedback packet is defined for use with\r\nthe extended RTP profile for RTCP-based feedback (RTP\/AVPF), allowing\r\nvideo switching MCUs to rapidly request resynchronisation.  Finally,\r\nnew RTP header extensions are defined to allow rapid synchronisation\r\nof late joiners, and guarantee correct timestamp-based decoding order\r\nrecovery for layered codecs in the presence of clock skew.  \r\n[STANDARDS-TRACK]","pub_date":"November 2010","keywords":["[--------]","rtcp","rtp control protocol","mcu","multipoint conference units","ssm","source-specific multicast"],"obsoletes":[],"obsoleted_by":[],"updates":["RFC3550"],"updated_by":[],"see_also":[],"doi":"10.17487\/RFC6051","errata_url":null}