Reliable multicast: where to use FEX

The MBONE provides an infrastructure for multicast communication on the internet based on IP. Several proposals have been made to create reliable multicast transport on top of the MBONE structure. Nearly all research on reliable multicast protocols for the MBONE focuses on ARQ error recovery. The counterpart of ARQ, FEC, does not guarantee 100% reliability but increases the reliability. The aim of this paper is to determine the best place in a multicast tree for the use of FEC. We develop a framework that allows us to model analytically the impact of FEC on the average number of transmissions necessary to transmit a packet to all members of the multicast group. We look on di erent multicast tree topologies, di erent degrees of correlated loss in the multicast tree, di erent multicast group sizes and show the e ect of FEC in terms of transmissions needed to achieve 100% reliability. We nd that the shared part of the multicast tree is not always the best part to employ FEC.