A Scalability Scheme for the Real-time Control Protocol

Recently, some problems related to using the Real-time Control Protocol (RTCP) in very large dynamic groups have arisen. Some of these problems are: feedback delay, increasing storage state at every member, and ineffective RTCP bandwidth usage, especially for receivers that obtain incoming RTCP reports through low bandwidth links. In addition, the functionality of some fields (e.g. packet loss fraction) in the Receiver Reports (RRs) becomes questionable as, currently, an increasing number of real-time adaptive applications are using receiver-based rate adaptive schemes instead of rate adaptation schemes based on the sender. This paper presents the design of a scalable RTCP (S-RTCP) scheme. S-RTCP is based on a hierarchical structure in which members are grouped into local regions. For every region, there is an Aggregator (AG) which receives the RRs sent by its local members. The AG extracts and summarises important information in the RRs, derives some statistics, and sends them to a Manager. The Manager performs additional statistical analysis to monitor the transmission quality and to estimate regions which are suffering massively from congestion. We believe that our S-RTCP alleviates some of the RTCP scalability problems encountered in very large dynamic groups and makes effective use of RRs with regard to the current changing requirements of real-time adaptive applications in the Internet today.