Compact equation of TCP throughput estimation at upgrading bottleneck link speed

This paper considers a network in which one of the links is the bottleneck of communication, and the speed of that link is upgraded. A simple method of calculation is proposed for the effect of the upgrading on the throughput of the TCP communication passing through the link. As the first step, a formula for the TCP communication throughput is proposed, which is a function of the mean window size of the TCP flow control, the round-trip time, and the loss ratio of the packet. The waiting time in the router, which is the major factor determining the round-trip time, is approximated by the M/M/1/m queue. By combining those two expressions, the change of the throughput by upgrading the link speed is calculated. In order to verify the validity of the throughput calculation and the router model, the change of the TCP communication throughput in upgrading the speed of the bottleneck link is calculated, and the result is compared to the result of actual measurement in the experimental network composed of PPP and Ethernet. It is seen that the model proposed in this paper agrees well with the actual measurement although it is simple. The method is applied to the network between Mie University and SINET. The effect of the link speed upgrading on TCP throughput is examined and verified. The result obtained in this paper is expected to be useful in the network design, in estimating the link speed required in dissolving the bottleneck. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(1): 65–73, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1147