Adaptive timeout policies for wireless links

A considerable body of evidence indicates that the use of reliable link layer protocols over error prone wireless links dramatically improves the performance of Internet protocols and applications. While traditional link layer protocols set their timeout values assuming that they fully control the underlying link, some wireless networks allow multiple link layer sessions to co-exist over the same link. Since the optimal timeout values for a reliable link layer protocol depend on the available bandwidth, with dynamic link sharing such a protocol should ideally adapt its timeout values accordingly. We have thus designed an adaptive selective repeat protocol that modifies its timeout values based on the policy used by TCP. We compare the performance of Web browsing over selective repeat when using our adaptive timeout scheme with a range of parameters, against a manually tuned fixed timeout version. Our measurements show that these adaptive timeout policies outperform the fixed one, regardless of the level of contention, and that the best adaptive timeout policy in this setting is not the one used by TCP.