Investigation Of IEEE 802.11e EDCA In WLAN

It is said by Friedrich Engels that if society has a technical need,it serves as a greater spur to the progress of science than do ten universities.Earlier WLANs equipped with IEEE 802.11 can just provide 'best-effort' service,without QoS support.In order to improve the quality of service,ISO developed IEEE std.802.11 e after a great deal of amendment on early 802.11 versions.802.11e introduces Enhanced Distributed Channel Access(EDCA) enhancing the legacy 802.11 medium access functions.In order to allow prioritized and separate handling of traffic,802.11e EDCA uses the eight IEEE 802.1D User Priorities(UPs).Arriving traffic of these eight Ups is mapped to four different Access Categories(ACs)—for Voice(AC_VO),Video (AC_VI),Best-Effort(AC_BE),and Background(AC_BK) traffic.Each Access Category is equipped with a single transmit queue.This paper presents an evaluation of IEEE 802.11e EDCA traffic priority mechanism performance based on its priority parameter values.Simulation was conducted using ns2(ns 2.29) platform.Simulation result shows that changes on the value of priority parameter(AIFS,CWmin,CWmax) affect traffic's throughput.High priority traffic(in this paper,priority 0 is the highest) is guaranteed to get more bandwidth resource than any other lower traffic priority.However,IEEE 802.11e can not guarantee that a traffic in WLAN will always get the same service all the time for its QoS requirements.This is due to the fact that the total bit rate from all other lower priority traffic in the WLAN will affect(reduce) higher priority traffic throughput.Pictures 55,tabels 9,references 19.