Unicast-Based Rapid Acquisition of Multicast RTP Sessions

Abstract

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, and 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 RTP Control Protocol (RTCP) machinery that reduces the acquisition delay. In this method, an auxiliary unicast RTP session carrying the Reference Information to the receiver precedes or 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, this method can also be used in other types of multicast applications where the acquisition delay is long enough to be a problem.

Peer-Assisted Content Delivery to Reduce the Bandwidth of TSTV Service in IPTV System

“…After joining the new channel and receiving the first multicast packet, the STB informs the FCC to stop sending the unicast stream [17][18][19]. Figure 3 shows the working mechanism of this technique.…”

“…In case there is some packet loss during the stream delivery, the STB R can demand the missing RTP packet from the STB S by reporting the sequence number of this packet [18].…”

A Novel Approach to Reduce the Unicast Bandwidth of an IPTV System in a High-Speed Access Network

“…If the STB changes the channel during the FCC period, the STB (receiver) will request the FCCC to resume the stream delivery by reporting the last RTP sequence number to the FCCC [20].…”

RTP Topologies

“…Shortcut name: Topo-SSM-RAMS "Unicast-Based Rapid Acquisition of Multicast RTP Sessions" [RFC6285] results in additional extensions to SSM topology. The rapid acquisition extension allows an endpoint joining an SSM multicast session to request media starting with the last sync point (from where media can be decoded without requiring context established by the decoding of prior packets) to be sent at high speed until such time where, after the decoding of these burstdelivered media packets, the correct media timing is established, i.e., media packets are received within adequate buffer intervals for this application.…”