Improving TCP performance for asymmetric networks

Abstract

This paper proposes a new TCP variation called Formosa that significantly improves TCP end-to-end performance in terms of high connection throughput and high degree of fairness in resource sharing among multiple competing connections in asymmetric networks. Existing TCP implementations are based on ACK-clock, which clocks out a single data packet on receipt of an ACK. Formosa TCP pushes the frequency of ACKs per round trip time (RTT) to the lowest limit, using an ACK to cumulatively acknowledge a window's worth of data packets. The congestion window is updated to reflect the available bandwidth estimated on the forward channel, without the aids of the intermediate routers. As a result, the number of ACK packets is significantly reduced, while the principle of "conservation of packets" is still maintained. Based on "an ACK per window," Formosa estimates forward delay and implements the additive increase and multiplicative decrease algorithm for better congestion avoidance. In addition, it employs the negative acknowledgement mechanism for better congestion control during loss recovery. As compared to existing implementations, TCP Formosa demonstrates the best performance in terms of high connection throughput, high degree of fairness among connections and robustness in the face of two-way, transfers in asymmetric networks.