Current Internet multicast conferencing tools treat all sources with equal importance in that they either statically allocate a fixed bandwidth to each source in a session, or they automatically adapt each source's transmission rate independently of all other sources. But not all sources are of equal interest to all receivers. We believe that to effectively support human to human communication, this disparity in receiver interest should be reflected in the rate-adaptation process. To this end, we propose a protocol called "SCUBA" that enables media sources to intelligently account for receiver interest in their rate-adjustment algorithms. SCUBA is orthogonal to and complements existing rate-adaptation schemes and can interoperate with either sender- or receiver-directed control systems. To scale the SCUBA protocol with multicast session size, we decouple the receiver-feedback process from the session size through sampling. This approach introduces a "tunable" tradeoff between convergence time and sampling accuracy that for large sessions is solely dependent on the control traffic bandwidth. In addition to its applicability in video conferencing, our control scheme can be combined with media transcoders to intelligently manage a bottleneck link at a well-known and fixed location in the network. We implemented SCUBA within our video conferencing tool vic and our media gateway rtpgw and feedback from their preliminary deployment indicates that the efficacy of the overall multimedia communication system has been greatly enhanced.
