Performance of Different TCP Variants in IEEE 802.11 WLAN and the TCP-WOW Algorithm

摘要

There have been a number of TCP variants proposed in the literature to combat random packet losses in wireless networks. In this paper we first perform a simulation study on the performance of these TCP variants in the context of IEEE 802.11 WLAN with various channel conditions, generated using different wireless error models and show that none of the existing TCP variants has superior performance over the conventional TCP in such WLANs. We also observe that in IEEE 802.11 WLAN efficiency problem with TCP protocols only exists when the number of active wieless nodes is small and the channel condition is extremely bad. We further demonstrate that employing the delayed ACK mechanism and SACK option at the TCP receiver can generally improve the performance. With the option to modify the TCP implementation at the receivers we further propose TCP-WOW algorithm, which estimates the flow queue size on the forward path and further uses such estimates as quantitative indication of the congestion level to dynamically guide the congestion response. TCP-WOW is robust to reverse traffic interactions. TCP-WOW also shows a better RTT fairness and consistently good performance in our IEEE 802.11 WLAN simulations.