This paper presents an analytic model of a reliable multicast session protocol for collaborative continuous-feed applications. The protocol supports NxN group multicast communications at the session layer and runs on the top of existing reliable transport protocols (e.g., TCP). The protocol is portable as a network-layer-independent library that is suitable for both LAN and WAN environments. It multiplexes messages from different group members into transport packets to reduce the transport overhead per message. It requires only two transport-level connections per node, irrespective of the multicast group size, to reduce the overhead of acknowledgments and retransmissions per node. We compare the throughput of this protocol with the throughput of general sender-initiated and receiver-initiated reliable multicast transport protocols.