Tree Structure for Specific-Source Multicast with Feedback Aggregation

The real time protocol (RTP) and its accompanying real time control protocol (RTCP) are employed in multicast applications. The RTCP protocol is used to distribute feedback on multimedia transmission among session members. The feedback is reported by sending, among others, RR (receiver report) and SR (sender report) packets. With the specific-source multicast, the hierarchical aggregation is used as a method of feedback distribution. The hierarchical aggregation allows a significant reduction of the feedback transmission delay in case of large-scale sessions such as IPTV broadcasting. This paper deals with a tree structure of session members for the feedback distribution with the hierarchical aggregation used. The tree concerned consists of end nodes and summarization nodes. A summarization node aggregates feedback produced from end nodes, which are situated on the lowest tree level only. The tree is applied to an IPTV broadcasting multicast session. The video format used is SD-DVB (standard definition-digital video broadcasting) with the MPEG-2 standard. Also, bandwidth requirements for the feedback distribution in case of the IPTV application described are discussed.