WINTRAC: A TCP window adjustment scheme for bandwidth management

In TCP, congestion control as well as error recovery are implemented by a sliding 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 buffer overflows, reduced throughput, unfairness and underutilization. It is generally accepted that there is a limit to how much control can be accomplished from the congestion control mechanisms in the end systems. Some mechanisms are needed in the intermediate network elements to complement the endpoint 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 resources by modifying at an intermediate network element, the receiver's advertised window in TCP acknowledgments returning to the source. We show through simulations that the scheme can efficiently control TCP traffic to limit queue buildups and buffer requirements at the network nodes, resulting in significant improvements in delay, packet loss rates, fairness in the distribution of the maximum achievable window size, and link utilization.