ملخص
Abstract
Wireless local area networks (WLANs) have been rapidly developed in recent years. It is used for various applications. VoWLAN, which transmits VoIP data over WLANs, shows its amazing attraction and constitutes one of the most flourishing applications nowadays in WLANs. One of Wireless Local Area Networks (WLAN) main drawbacks, when compared to wired networks, is that WLANs are less predictable and efficient. Wireless physical medium is harder to be controlled than physical wire. WLAN medium is also unlicensed, and thus susceptible to interferences produced by other devices. Therefore, great effort is being done in order to obtain Quality of Service (QoS) in real-time voice communications using WLANs. This topic has opened plenty of new research lines to upgrade current WLAN standards. In this thesis, a study is carried out for the behavior of new Medium Access Control (MAC) protocols defined in IEEE 802.11e draft standard Enhanced Distributed coordination function EDCF as well as for its subsequent modified versions. The Adaptive Enhanced Distributed coordination function AEDCF, designed to support QoS when providing voice communication services between stations in WLAN. Also presents experimental results obtained from simulations, and compare our results with simulations made using IEEE 802.11 standard MAC. The simulation work was done using NS-2 simulator, with the addition of specific modules for 802.11e. A performance comparison is carried out between the modified MAC scheme and IEEE standard MAC scheme, using Experimental simulation models. It is found that the adaptive technique method not only increases the medium utilization ratio and lowers the collision rate by more than 50%, but also enhances vii the overall throughput by around 20% compared with the basic IEEE 802.11DCF technique.