Applications requiring the reliable distribution of data to groups of clients would be supported perfectly by reliable multicast protocols. In many cases, the problem of congestion control (a major research issue otherwise) does not exist because downlink bandwidth is "owned" or can be preallocated to a particular server by independent means, but the problems of insuring reliable data delivery to larcre groups, and adaptability to heterogeneous clients, still remain. These problems can be solved at once with the use of FEC techniques. In this paper we show the design of a Reliable Multicast data Distribution Protocol (RMDP) that we have built using these techniques, and discuss the implementation tradeoffs. Experimental results show that, albeit somewhat expensive, doing encoding/decoding in software is affordable for speeds in the Mbit/s range even on low-end PCs. Slower machines can still receive at high speed, thus optimizing network usage, by taking advantage of the fact that decoding needs not to be done in real time. Finally, our RMDP can work even without any feedback from the receivers, thus making it well suited to mobile/wireless systems.
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