Enhancement of TCP in 802.11e Wireless Local Area Networks

In order to guarantee the QoS requirements in IEEE 802.11 WLANs, the IEEE 802.11e standard for MAC enhancement has been proposed to support delay-sensitive applications. The IEEE 802.11e enhanced distributed coordination function (EDCF) provides traffic differentiation based on a set of static Access Category (AC) MAC parameters which guarantee prioritization of real-time flows with strict bandwidth and delay requirements. This reduces the network capacity available for best-effort flows in heterogeneous traffic environments. While today´s Internet traffic is still dominated by TCP based applications, the negative effects of IEEE 802.11e service differentiation scheme on TCP performance have not been extensively explored. In this paper, the performance of TCP in 802.11e WLAN competing with high priority traffic is evaluated. A simple TCP-based scheme, called Prioritized Adaptive EDCF, is proposed to improve the existing IEEE 802.11e EDCF mechanism by assigning the highest priority to TCP control packets and adjusting MAC parameters accordingly. The results demonstrate that the proposed scheme improves TCP performance in terms of traffic efficiency, throughput and delay.