Optimal Multicast Feedback

We investigate the scalability of feedback in multicast communication and propose a new method of probabilistic feedback based on exponentially distributed timers. By analysis and simulation for up to 106 receivers we show that feedback implosion is avoided with good latency performance obtained. The mechanism is robust against the loss of feedback messages and robust against 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 NAK suppression. It is scalable, the amount of state at every group member is independent of the number of receivers. No topological information of the network is used and data delivery is the only support required from the network. It adapts to the number of receivers and leads therefore to a constant performance for implosion avoidance and feedback latency.