Utilizing characteristics of last link to improve TCP performance

TCP, perhaps the most widely used transport protocol, was designed for wired links and stationary hosts. But more and more links with different characteristics are used to access the Internet. The variations in link characteristics present different problems to TCP and enhancement of TCP performance over these links remains an active area of research. Since the current core network of the Internet is composed mainly of optical fiber links and high speed routers, the characteristics of the access link (or the last link) usually dominate the characteristics of the end-to-end network path. As a result, if the client can acquire the characteristics of the access link (e.g. through measurement), the TCP server can utilize heuristics that exploit the access link's characteristics in order to improve the performance of TCP. In this paper, we propose and evaluate the performance of several heuristics that exploit knowledge of access link characteristics such as bandwidth and packet error rate. Simulation results show that these heuristics can indeed improve TCP performance significantly and demonstrate the potential benefits of using heuristics that adjust TCP congestion control behaviors to match the access link characteristics.