Effects of Applying High Speed Congestion Control Algorithms in the Internet

In recent years, many high speed congestion control algorithms have been proposed for utilizing network pipes with large bandwidth-delay product, and some of them have also been implemented in popular operating systems. Since the Internet is and tends to be lightly-loaded and there are many bandwidth-greedy applications, high speed congestion control algorithms may be used by many flows of the Internet. Considering that the Internet is now very important, it is necessary to make sure that applying high speed congestion control algorithms will not hurt the existing applications, especially the interactive World Wide Web and streaming applications, such as Voice over IP. In this paper, several influential high speed congestion control algorithms, HS-TCP, H-TCP, Cubic-TCP, and delaybased Compound-TCP, are evaluated with the focus on their effects to existing applications. Many simulations are carried out for answering whether it is safe to apply high speed congestion control algorithms in high speed wide area network and/or local area network of the Internet, and which algorithm performs the best. Through this study, we find that it is safe and profitable to apply Cubic-TCP inside high speed local area network. Network utilization ratio can be improved and the experience of users, that communicate with remote hosts of the Internet through existing applications, is not adversely affected. As for high speed wide area network, we find that with large amount of web traffics, routers should be provisioned with a large queue for accommodating their burstiness. With this prerequisite, all algorithms are not satisfying in high speed wide area network. Loss-based HS-TCP, H-TCP, and Cubic-TCP inevitably increase queue delay experienced by the existing applications, H-TCP also causes much higher packet loss rate, and these QoS (Quality of Service) degradation can be perceived by users. Delay-based CompoundTCP can well utilize the network without adversely affecting the existing applications only when congestion can be detected through queue delay. Considering that queue delay detection method of Compound-TCP is not scalable with the number of Compound-TCP flows, a new delay-based high speed congestion control algorithm, which is scalable with flow number, should be a promising solution for high speed wide area network of the Internet. ∗This work is supported by National University of Singapore under research grant R-252-000-203-112. Copyright is held by the author/owner(s). XXXXXX, XXXXXX. . Simulation results of this study also indicate that end hosts should be a little more intelligent and use different high speed congestion control algorithms on different network pipes of the heterogeneous Internet.