WINTRAC: a TCP window adjustment scheme for bandwidth management

In TCP, congestion control as well as error recovery are implemented by a s liding window. The dynamics of TCP specifically, a mismatch between the TCP window and the bandwidth-delay product of the network can sometimes cause the network switches or routers to accumulate large queues, resulting in bu ffer overflows, reduced throughput, unfairness and underutilization. It is generally accepted that there is a limit to how much control can be accompl ished from the congestion control mechanisms in the end systems. Some mecha nisms are needed in the intermediate network elements to complement the end point congestion avoidance mechanisms. We describe in this paper, a new TCP rate control scheme based on a simple recursive algorithm. The idea behind the algorithm is to match the offered network load to the available resour ces by modifying at an intermediate network element, the receiver's adverti sed window in TCP acknowledgments returning to the source. We show through simulations that the scheme can efficiently control TCP traffic to limit qu eue buildups and buffer requirements at the network nodes, resulting in sig nificant improvements in delay, packet loss rates, fairness in the distribu tion of the maximum achievable window size, and link utilization. (C) 2001 Elsevier Science B.V. All rights reserved.