MAC-layer adaptation to improve TCP flow performance in 802.11 wireless networks

In this paper, we are interested in improving TCP flow performance when a short loss of 802.11 signal leads to lose segments. A short analytical study and a set of simulations in common wireless environments with signal losses due to distance or interferences are made to highlight the distinct MAC and TCP loss-recovery levels and the lack of interactions between them. This study shows the interest, in case of signal failure, to adapt one of the MAC parameters, the Retry Limit (RL), to reduce the drop in performance due to the inappropriate triggering of TCP congestion control mechanisms. Starting from this, a MAC-layer LDA (Loss Differentiation Algorithm) is proposed. This LDA scheme is based on the adaptation of the RL parameter depending on the quality of the 802.11 wireless channel. The evaluation of the proposed scheme shows the important gain in performance obtained compared to the case where the RL is configured statically.