Linear stability of TCP/RED and a scalable control
We demonstrate that the dynamic behavior of queue and average window is determined predominantly by the stability of TCP/RED, not by AIMD probing nor noise traffic. We develop a general multi-link multi-source model for TCP/RED and derive a local stability condition in the case of a single link with heterogeneous sources. We validate our model with simulations and illustrate the stability region of TCP/RED. These results suggest that TCP/RED becomes unstable when delay increases, or more strikingly, when link capacity increases. The analysis illustrates the difficulty of setting RED parameters to stabilize TCP: they can be tuned to improve stability, but only at the cost of large queues even when they are dynamically adjusted. Finally, we present a simple distributed congestion control algorithm that maintains stability for arbitrary network delay, capacity, load and topology.
© 2003 Elsevier B.V. Received 7 April 2003, Accepted 25 April 2003, Available online 10 July 2003. We acknowledge the supports of NSF through grants ANI-0113425, ANI-0230967 and ECS-9875056 and AFOSR through grant F49620-03-1-0119.