Extending equation-based congestion control to multicast applications

In this paper we introduce TFMCC, an equation-based multicast congestion control mechanism that extends the TCPfriendly TFRC protocol from the unicast to the multicast domain. The key challenges in the design of TFMCC lie in scalable round-trip time measurements, appropriate feedback suppression, and in ensuring that feedback delays in the control loop do not adversely affect fairness towards competing flows. A major contribution is the feedback mechanism, the key component of end-to-end multicast congestion control schemes. We improve upon the well-known approach of using exponentially weighted random timers by biasing feedback in favor of low-rate receivers while still preventing a response implosion. We evaluate the design using simulation, and demonstrate that TFMCC is both TCP-friendly and scales well to multicast groups with thousands of receivers. We also investigate TFMCC’s weaknesses and scaling limits to provide guidance as to application domains for which it is well suited. Keywords: congestion control, multicast, single-rate, TCPfriendliness, feedback suppressio