On large-scale reliable multicast protocols

We examine the impact of widely spread multicast groups on the performance of reliable multicast protocols. We show that transmission cost for reliable multicast increases rapidly with the distance between retransmitting and receiving hosts. Since this distance is not considered by existing protocols, which are based on retransmissions originated at the sender or receiver, the performance often is rather poor and a new error recovery concept has to be developed. Our approach, the scalable and reliable multicast transport protocol (SRMT), allows retransmissions by extended multicast routers to limit the path length for error recovery. Moreover, the retransmission load can be further reduced by an XOR combination of packets. The SRMT is defined as an overlay network model and therefore can be applied to any existing multicast protocol.