Balancing Loss-Tolerance between Link and Transport Layers in Multi-Hop Wireless Networks

Broadband technologies have made multi-hop wireless communications a reality. Loss-prone multi-hop networks pose challenges to link and transport layer protocols. Wireless links need to export low link-latencies, high goodputs and low residual loss rates to effectively enable interactive applications. Current link protocols with high ARQ persistence incur high latencies that impair such applications. We propose LL-HARQ, a link protocol that meets these goals. However, under high and bursty loss rates even LL-HARQ exports a small residual loss rate that could accumulate over multiple hops. Since TCP-SACK cannot handle error rates greater than 5%, a transport protocol (LT-TCP) designed for loss tolerance can be used under such cases. We provide insights into the structuring of the building blocks and balance between error-protection functions at the two layers and examine the case for cross-layer co-operation. Finally, we demonstrate that the combination achieves improved end-end performance (delay, loss and goodput) over traditional approaches.