Extending equation-based congestion control to multicast applications

In this paper we introduce TFMCC, an equation-based multicast congestion co ntrol mechanism that extends the TCP-friendly TFRC protocol from the unicas t to the multicast domain. The key challenges in the design of TFMCC lie in scalable round-trip time measurements, appropriate feedback suppression, a nd in ensuring that feedback delays in the control loop do not adversely af fect fairness towards competing flows. A major contribution is the feedback mechanism, the key component of end-to-end multicast congestion control sc hemes. We improve upon the well-known approach of using exponentially weigh ted random timers by biasing feedback in favor of low-rate receivers while still preventing a response implosion. We evaluate the design using simulat ion, and demonstrate that TFMCC is both TCP-friendly and scales well to mul ticast groups with thousands of receivers. We also investigate TFMCC's weak nesses and scaling limits to provide guidance as to application domains for which it is well suited.