Unicast-Based Rapid Acquisition of Multicast RTP Sessions
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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: 'Unicast-Based Rapid Acquisition of Multicast RTP Sessions' to Proposed Standard (draft-ietf-avt-rapid-acquisition-for-rtp-17.txt) The IESG has approved the following document: - 'Unicast-Based Rapid Acquisition of Multicast RTP Sessions' (draft-ietf-avt-rapid-acquisition-for-rtp-17.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://datatracker.ietf.org/doc/draft-ietf-avt-rapid-acquisition-for-rtp/
Technical summary. When an RTP receiver joins a multicast session, it may need to acquire and parse certain Reference Information before it can process any data sent in the multicast session. Depending on the join time, length of the Reference Information repetition (or appearance) interval, size of the Reference Information as well as the application and transport properties, the time lag before an RTP receiver can usefully consume the multicast data, which we refer to as the Acquisition Delay, varies and can be large. This is an undesirable phenomenon for receivers that frequently switch among different multicast sessions, such as video broadcasts. In this document, we describe a method using the existing RTP and RTCP protocol machinery that reduces the acquisition delay. In this method, an auxiliary unicast RTP session carrying the Reference Information to the receiver precedes/accompanies the multicast stream. This unicast RTP flow can be transmitted at a faster than natural bitrate to further accelerate the acquisition. The motivating use case for this capability is multicast applications that carry real-time compressed audio and video. However, the proposed method can also be used in other types of multicast applications where the acquisition delay is long enough to be a problem. Working group summary The document is a product of the AVT working group. The document has working group consensus. Document quality It is understood that there are existing implementations of the specification from a number of vendors. Extensive reviews were received from multiple working group participants. Personnel Keith Drage is the document shepherd. Robert Sparks is the responsible AD.