Performance Analysis of HighSpeed TCP and its Improvement for High Throughput and Fairness against TCP Reno Connections

Among Internet services that have recently been initiated, including data GRID network and storage area network (SAN), the server machines have gigabit-level network interfaces such as Gigabit Ethernet, and directly connect to high-speed network to deliver gigabyte/terabyte data to other hosts. Although these services require a large amount of network bandwidth and disk storage, such services will emerge increasingly in the future Internet since their costs are rapidly decreasing. When the TCP Reno version, which is the most popular version of TCP included in the current OSs, is used for such high-speed data transmissions, it cannot achieve enough throughput because of the essential nature of TCP’s congestion control mechanism. HighSpeed TCP has recently been proposed as one of the possible ways to improve the throughput by modifying the congestion control mechanism. However, the performance of HighSpeed TCP has not been fully investigated. Especially, fairness issues between HighSpeed TCP and TCP Reno have not been considered. In this paper, we first investigate the throughput and fairness properties of HighSpeed TCP through mathematical analysis and simulation studies. We show that HighSpeed TCP can provide larger throughput than TCP Reno, but it cannot fully utilize the link bandwidth because of bursty packet losses at the router buffer. We also demonstrate that HighSpeed TCP degrades the throughput of TCP Reno when they share the bottleneck link. We then propose Gentle HighSpeed TCP, which has new congestion control mechanisms of TCP that improve the throughput of HighSpeed TCP. One of the major features in Gentle HighSpeed TCP is that it has two modes in the congestion avoidance phase, each of which uses different algorithms in changing window size. It also has a new mechanism to avoid throughput degradation in the initial slow start phase. We confirm the effectiveness of Gentle HighSpeed TCP by simulation experiments. We observe from the simulation results that the throughput of Gentle HighSpeed TCP becomes larger than that of the original HighSpeed TCP by up to 30%. Furthermore, Gentle HighSpeed TCP can greatly improve the data transmission performance without degrading the throughput of competing TCP Reno connections. That is, Gentle HighSpeed TCP outperform the original HighSpeed TCP in both terms of the throughput and the fairness with TCP Reno.