Scalable Feedback for Large Groups

We investigate the scalability of feedback in multicast communication and propose a new method of probalistic feedback based on exponentially distributed timers. By analysis and simulation for up to 10 sup 6 receivers, we show that feedback implosion is avoided while feedback latency is low. The mechanism is robust against the loss of feedback messages and works well in case of homogeneous and heterogeneous delays. We apply the feedback mechanism to reliable multicast and compare it to existing timerbased feedback schemes. Our mechanism achieves lower NAK latency for the same performance in terms of NAK suppression. No topological information of the network is used and data delivery is the only support required from the network. The mechanism adapts to a dynamic number of receivers and leads to a stable performance for implosion avoidance and feedback latency.