A simple mechanism for improving the throughput of reliable multicast

Single-rate reliable multicast protocols are known to have scalability problems in the presence of a large number of receivers because the sender cannot distinguish independent packet losses at different receivers from multiple packet losses at the same receiver. In the presence of a large number of receivers, the sender may perceive a large aggregate packet loss even if no individual receiver is highly congested. Consequently, the multicast session progresses at a much slower rate than its desired sending rate. In order to solve this problem, we argue for decoupling of the mechanisms to achieve congestion control and reliability in reliable multicast protocols, and present a very simple "loss notification"-based multicast congestion control mechanism that can be used to augment both ACK-based and NAK-based reliable multicast protocols and solve the independent packet loss problem. We illustrate the efficacy of our approach via simulations using the ns2 simulator.