Improving the performance of TCP in the presence of interacting UDP flows in ad hoc networks

In this paper, we study how fairness affects the performance of TCP over ad hoc networks with IEEE 802.11 at the MAC layer. The problem addressed is that the throughput of TCP flows degrades severely in the presence of heavily loaded UDP flows. Our contribution is twofold. First, we identify the factors affecting the TCP throughput by providing a micro-analysis of the performance at a level of detail that is not seen in previous studies. The intuition obtained from the first part leads us to our second contribution. We propose and study the use of per flow fairness through a mechanism we call backpressure. Backpressure improves the performance of TCP flows in the presence of heavy UDP flows. In fact, in some cases, this increased TCP throughput does not affect the throughput of UDP flows. We find that backpressure can increase the TCP throughput by as much as 95%. An advantage of backpressure is that it does not require any changes to the existing TCP or IEEE 802.11 protocols