Jointly coordinating ECN and TCP for rapid adaptation to varying bandwidth

The introduction of service differentiation in the Internet implies that the residual bandwidth available to best-effort traffic becomes highly variable. We explore the design of a rapidly-reactive congestion control framework, where the ECN-aware best-effort flows aggressively go after any unused capacity. By making routers mark packets in a much more aggressive manner, we are able to achieve fast backoff in the network without resorting to the TCP's current drastic step of halving the congestion window. Simulations indicate that our ECN-mod protocol is better than ECN-NewReno in exploiting rapid variations in the available bandwidth. Moreover, the milder backoff policy of ECN-mod also makes the link utilization less dependent on the exact values of the parameters in the router marking function.