How bad is reliable multicast without local recovery?

We examine the impact of the loss recovery mechanisms on the performance of a reliable multicast protocol. Approaches to reliable multicast can be divided into two major classes: source-based recovery, and distributed recovery. For both classes we consider the state of the art: for source-based recovery, a type 2 hybrid ARQ scheme with parity retransmission; for distributed recovery, a scheme with local multicast retransmission and local feedback processing. We further show the benefits of combining the two approaches and consider a type 2 hybrid ARQ scheme with local retransmission. The schemes are compared for up to 10⁶ receivers under different loss scenarios with respect to network bandwidth usage and completion time of a reliable transfer. We show that the protocol based on local retransmissions via type 2 hybrid ARQ performs best for bandwidth and latency. For networks, where local retransmission is not possible, we show that a protocol based on type 2 hybrid ARQ comes close to the performance of a protocol with local retransmissions