HSRM: a hierarchical scalable reliable multicast model for conferencing control over Internet

A number of reliable multicast (RM) protocols have been proposed previously. However, when used in conferencing control over the Internet, they are all faced with challenges of poor scalability and robustness, or too much redundant packets and abuse of network bandwidth, especially with the growth of group size and scope. We present a new RM protocol named HSRM (hierarchical scalable reliable multicast) for distributed conferencing control over the Internet. We group hosts into subgroups according to their packet loss characteristics. Consequently, the heterogeneity of the hosts is reduced in each subgroup, and then the number of retransmission is decreased efficiently. Furthermore, since feedback and recovery packets are restricted to subgroups, they will never be spread to the whole multicast group. This is very advantageous to conferencing control, which always contains thousands of hosts distributed in a large area. We then present a mechanism to construct and maintain an adaptive hierarchical structure dynamically. The numeric analysis demonstrates that HSRM can improve the performance of RM compared with SRM, in the sense of redundant packets and the number of retransmissions. It is also shown that HSRM is much better than other hierarchical RM protocols in scalability and robustness.