The IEEE 802.11e task group has reached a stable consensus on two basic can. tention-based priority mechanisms to promote for standardization: usage of different arbitration interframe spaces and usage of different minimum/maximum contention windows, The goal of this article is to provide a thorough understanding of the principles behind their operation. To this purpose, rather than limit our investigation to high-level (e.g. throughput and delay) performance figures, we take a closer look at their detailed operation, also in terms of low-level performance metrics (e.g., the probability of accessing specific channel slots), Our investigation on one hand confirms that AIFS differentiation provides superior and more robust operation than contention window differentiation. On the other hand, it highlights performance issues related to the coexistence between 802.11e contention-based stations with legacy 802.11 stations, and provides guidelines for the 802.11e parameter settings when such a coexistence is the goal

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In this paper we propose PiggyCode, a networkcoding based scheme specifically designed to enhance TCP performance over IEEE 802.11 multi-hop wireless networks. The root of this approach is a network coding module operating between the Network and the MAC layer. Each node running PiggyCode encodes, whenever it is possible, TCP-DATA and TCP-ACK packets belonging to the same information flow. The coding approach is conceptually analogous to piggyback the TCP-ACK packet within the TCP-DATA packet, with the substantial difference that, by performing network coding operations, the actual packet size remains unchanged. The proposed scheme is simple and effective. It leverages the benefits of network coding in the wireless environment, to jointly reduce the overall number of transmissions on the channel and speed up the delivery process of TCP-ACK packets, thus achieving significant improvements in terms of TCP performance 1 .