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Wireless local area nerworks (WLANs) are increasingly finding applications that include real time traffic like voice over IP (VoIP). Medium access coordination function for WLANs in IEEE 802.11 basically implements medium access control (MAC) by employing distributed coordination function (DCF). IEEE 802.11 WLANs provide limited support for quality of service (QoS). A new standard, namely IEEE 802.11e, defines MAC procedure to support QoS requirements of applications. IEEE 802.11e introduces the hybrid coordination function (HCF), which specifies distributed contention-based access scheme, called as enhanced distributed channel access (EDCA), to access the shared wireless media . This paper is focused on the performance evaluations of EDCA for various access categories (ACs)  on mobile ad-hoc and infrastructure based wireless networks. It has been shown through simulation studies that performance of wireless network is improved in IEEE 802.11e, as compared to that in IEEE 802.11, in terms of high average throughout, lower mean delay and reduced probability of packet loss.