Local error recovery in SRM: comparison of two approaches

Scalable reliable multicast (SRM) is a framework for reliable multicast delivery. In order to maximize the collaboration among the group members in error recovery, both retransmission requests and replies are multicast to the entire group. While SRM effectively uses random timers to suppress duplicate requests and replies, the global nature of the request and replies means that every packet loss results in at least one request and reply message sent to the entire group. To further improve the scalability of SRM, one must localize the scope of error recovery traffic. In this paper, we present two approaches to local recovery: hop-based scope control and use of local recovery groups. The first approach uses hop count to limit the distribution of requests and replies whereas the second approach confines error recovery traffic using separately addressed local recovery groups. The local recovery groups and hop count settings are automatically created and dynamically adjusted based on observed loss patterns. The use simulation experiments to examine the performance of both approaches.