Large-Scale RTCP Feedback Optimization

Nowadays, multimedia streaming is a common service on the Internet including both fixed and mobile networks. The RTP protocol is usually used to transfer the media. The RTCP protocol is an accompanying protocol for the RTP and it is used for feedback transmission in order to control multimedia session behaviour. The issue is the bandwidth dedicated for the RTCP protocol. As defined in the RTP specification, it is limited to 5 % of the total allowed bandwidth. This is a limiting factor for large-scale media streaming services based on Source-Specific Multicast (SSM) since the RTCP bandwidth is shared among all the receivers. It causes large delays in sending feedback data from each receiver. For the purpose of solving this issue, a hierarchical structure of receivers with summarisation nodes has been proposed. The paper introduces an optimization of this hierarchical structure in order to achieve the lowest feedback transmission intervals. The proposal is supported by a simulation in Matlab environment. Furthermore, the paper deals with a design of a new protocol called Tree Transmission Protocol (TTP) that was proposed to organize session nodes into a hierarchical tree structure.