Research Of Flow Control Protocol In Wireless Local Area Networks

Wireless local area network (WLAN) is the product of combination between computer network and wireless communication technique. WLAN adopts the wireless method to connect with each other. Compared with wired ones, it's more complex. Nowadays, the hotspots and difficulties of WLAN research includes media access control (MAC) protocol, fairness assurance, efficiency assurance, transmission control protocol (TCP) and energy consumption, etc.Design of MAC protocols is one key problem in wireless local area networks. The major features of a MAC protocol are high throughput and good fairness. In this paper, we propose a new efficient contention-window (CW) resolution mechanism, called adaptive double increase double decrease algorithm (ADD), according to the IEEE 802.11 distributed coordination function (DCF), which improves the performance of original MAC protocol. The algorithm is developed as follows: each station will halve the contention window after n consecutive successful transmissions, and the value of n is adjusted adaptively according to the throughput of Access Point (AP) node. This algorithm can reduce the collision probability; meanwhile, it improves the fairness between different stations.Subsequently, the dissertation summarizes the difference of the fairness between WLANs and wired networks, and introduces the background of time-fairness and relative research work. On that basis, a new mechanism, Time-fairness Active Queue Management (TRED), is put forward. It uses the concept of Contention Overhead (CO) to compute the dropping probabilities of flows with different rate, and hence deals with these flows separately, i.e. limiting the media access time of the slow flow, and reach the goal of time-fairness. Through the simulation result, it's obvious that the algorithm satisfies the design demand, that is, good total system throughput, and the ratio of channel access time between flows is the same as the result analysed.