Modeling the Effects of Variable Bandwidth on TCP Throughput

Links of an end-to-end long lived TCP connection may provide bandwidth with significant variance. In this work, we model and study the effects of variable bandwidth on TCP throughput, taking into account various influencing factors such as random loss of links, buffer size and characteristics of the variable bandwidth in the bottleneck link. Result shows that the variance of bandwidth can severely deteriorate TCP throughput, even making it less than one thirds of the one without bandwidth variance in many cases and arbitrarily low if situations are bad enough, and that under the circumstance of variable bandwidth, a buffer size larger than the traditional recommended bandwidth delay product can greatly improve the throughput. Under the circumstance of variable bandwidth, our model can accurately model the TCP throughput, with an average error around 5%, and a maximum error less than 15%, while traditional formula based TCP throughput prediction can be significantly inaccurate, even with an error larger than 200%.