An efficient error recovery algorithm is essential for reliable multicast in large groups. Tree-based protocols group receivers into local regions and select a repair server for performing error recovery in each region. Hence a single server bears the entire responsibility of error recovery for a region. In addition, the deployment of repair servers requires topological information of the underlying multicast tree, which is generally not available at the transport layer.
RRMP is a randomized reliable multicast protocol that improves the robustness of tree-based protocols by diffusing the responsibility of error recovery among all members in a group. It is developed as part of my thesis work at Cornell University. The protocol works well within the existing IP multicast framework and does not require additional support from routers. It uses an innovative two-phase buffering algorithm, which explicitly addresses variations in delivery latency seen in large multicast groups. The algorithm effectively reduces buffer requirements by adaptively allocating buffer space to messages most needed in the system and by spreading the load of buffering across the group. Analysis and simulation results show that the performance penalty due to randomization is low and can be tuned according to application requirements.
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