Enhancing network performance with TCP rate control

Abstract

In TCP (transmission control protocol), 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 as to how much control can be accomplished from the congestion control mechanisms in the end systems. Some mechanisms are thus needed in the intermediate network elements to complement the endpoint congestion avoidance mechanisms. Network layer enhancements such as scheduling mechanisms and packet drop policies have been proposed which are aimed at improving fairness and throughput of the competing endpoint applications. We describe a new TCP rate control scheme based on a simple recursive algorithm. The idea behind the algorithm is to match the network load to the available resources by modifying at an intermediate network element, the receiver's advertised window in TCP acknowledgments returning to the sources. The scheme can be implemented in a router or switch for bandwidth management and does not require knowledge of network delays or maintenance of the per-flow state.