AbstractEven though tree‐based reliable multicast protocols are known to be most scalable for one‐to‐many sessions, there is still an open question as to whether these protocols are also scalable for many‐to‐many sessions. In this paper, we analyze and compare two promising multicast protocols—the receiver‐initiated protocol with NACK suppression and the tree‐based protocol—using a new spatial loss model. The proposed model considers the correlation of packet loss events for more realistic analysis unlike the previous work. The analysis results show that the tree‐based protocol achieves much higher throughput than the receiver‐initiated protocol for a many‐to‐many session as the number of participants in the session becomes larger. Copyright © 2004 John Wiley & Sons, Ltd.