TCP Enhancement in IEEE 802.11e Wireless Networks

Wireless networks and multimedia applications are two rapidly emerging technological trends. The IEEE 802.11e protocol has been developed to support QoS for such delay-sensitive applications in wireless networks. This protocol has also been extensively studied in the literature over the past few years, and several mechanisms to improve its performance have been proposed concentrating on ways to reinforce QoS guarantees for delay-sensitive applications. While the Internet traffic is still dominated by TCP-based applications, the negative effects of IEEE 802.11e service differentiation scheme on the performance of TCP have not received enough attention. In this paper, we first, as an attempt to highlight these effects, evaluate the performance of TCP in 802.11e WLANs when competing with high priority VoIP traffic. We then evaluate the enhancement achievable by our proposed cross-layer schemes, IEDCA and RE-TCP, which exploit the TCP bidirectional nature to alleviate TCP starvation and consequently improving its performance. Our simulation results show significant improvements in terms of TCP goodput, retransmissions and segment delay (without any negative effect on the performance of delay-sensitive applications).