Limitations of Fixed Timers for Wireless Links

Traditional reliable link layer protocols set their fixed retransmission timers under the assumption that they operate in isolation over the link. Emerging wireless networks however allow multiple link layer sessions to dynamically share the link. To assess the impact of this development, we examine the performance of Web Browsing over a Selective Repeat protocol with fixed retransmission timers, showing that the optimal retransmission timer values depend on the level of contention. We therefore propose an adaptive Selective Repeat protocol that modifies its retransmission timers based on prevailing conditions. Our measurements show that this adaptive scheme provides excellent Web Browsing performance regardless of the level of contention, under two very different wireless error models.