A Distributed Rendezvous Point Source (RPS) for Congestion Control in a Reliable Hybrid Multicast Protocol (RHMP)

Multicast protocols can be classified as either reliable or unreliable both uses a best effort method of setting up, maintaining and tearing down the multicast distribution tree. Pragmatic General Multicast (PGM), Reliable Hybrid Multicast Protocol (RHMP) and Elastic Reliable Multicast (ERM) are examples of reliable multicast protocols. PGM and ERM sends flood messages to the Rendezvous Point source (RPS) from the source node towards the stub nodes which then forward it to leaf nodes, leaf nodes that are not interested sends a prune message while any leaf node that misses a packet sends a message to the RPS through the stub node requesting for the missed multicast packet. A repair multicast packet is then forwarded to all leaf nodes that requested for it. For a large distribution tree congestion might occur in the RPS if there is much failure and the leaf node keeps requesting for repair data. In a distributed RPS such as the reliable hybrid multicast protocol (RHMP) the stub nodes originates the flood message to the leaf and uninterested leaf sends prune message, any stub that has one or more interested leaf sends a join message to the RPS. If a leaf node in the multicast distribution misses a multicast packet it requests a repair packet its stub node sends the repair data. A simulation model was developed to mimic the behaviour of PGM, ERM and RHMP in different network size using hierarchical network and the control bandwidth overhead (CBO) for each of the multicast protocols was calculated at the source node, stud node and leaf nodes, CBO was use as the cost metric. The result shows that the RHMP uses less CBO than PGM and ERM in a sparsely and densely populated network at the source and leaf nodes but more CBO is used at the stub nodes but since more than one stub nodes act as the RPS to the leafs connected to it, RHMP was found out to be better than the PGM or ERM.