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.