A Compound TCP Approach for High-speed and Long Distance Networks

Many applications require fast data transfer over high speed and long distance networks. However, standard TCP fails to fully utilize the network capacity due to the limitation in its conser-vative congestion control (CC) algorithm. Some works have been proposed to improve the connection’s throughput by adopting more aggressive loss-based CC algorithms. These algorithms, although can effectively improve the link utilization, have the weakness of poor RTT fairness. Further, they may severely de-crease the performance of regular TCP flows that traverse the same network path. On the other hand, pure delay-based ap-proaches that improve the throughput in high-speed networks may not work well in an environment, where the background traffic is mixed with both delay-based and greedy loss-based flows. In this paper, we propose a novel Compound TCP (CTCP) approach, which is a synergy of delay-based and loss-based approach. In CTCP, we add a scalable delay-based component into the standard TCP Reno congestion avoidance algorithm (i.e., the loss-based component). The sending rate of CTCP is controlled by both com-ponents. This new delay-based component can rapidly increase sending rate when network path is under utilized, but gracefully retreat in a busy network when bottleneck queue is built. Aug-mented with this delay-based component, CTCP provides very good bandwidth scalability with improved RTT fairness, and at the same time achieves good TCP-fairness, irrelevant to the win-dows size. We developed an analytical model of CTCP and imple-mented it on the Windows operating system. Our analysis and experiment results verify the properties of CTCP.