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Today's IEEE 802.11 wireless local area network (WLAN) is an excellent solution for the broadband wireless networking. However, the legacy protocol lacks the capability to support real-time services such as Voice over IP (VoIP) properly because it depends on the best effort service. New IEEE 802.11e protocol can support QoS. This paper presents the VoIP stations capacity in IEEE 802.11 WLAN and IEEE 802.11e WLAN via computer simulation. Additionally new access category parameter is suggested to enhance the VoIP capacity in 802.11e WLAN. I -IntroductionVoice over Internet Protocol (VoIP) is one of the fastest growing Internet applications today. It has two fundamental benefits compared with voice over traditional telephone networks. First, by exploiting advanced voicecompression techniques and bandwidth sharing in packet-switched networks, VoIP can dramatically improve bandwidth efficiency. Second, it facilitates the creation of new services that combine voice communication with other media and data applications such as video, white boarding, and file sharing. At the same time, driven by huge demands for portable access, WLAN market is increasing quickly, due to its mobility, and high-speed access, so, it is believed that VoIP over WLAN is poised to become an important Internet application [1]. In WLAN the IEEE 802.11 standard is being accepted widely and rapidly for many different environments today. The main characteristics of the WLAN 802.11 networks are their simplicity and robustness against failures. Using the ISM band at 2.4 GHz, the 802.11b version provides data rates of up to 11 Mbit/s. Now, the new 802.11a version can achieve data rates of up to 54 Mbit/s using the OFDM modulation technique in the unlicensed 5 GHz band. Today, 802.11 WLAN can be considered as a wireless version of Ethernet, which supports best-effort service [2]. QoS is not supported by IEEE 802.11 protocol, because it does not assure delay limits for time sensitive applications like voice and video. The 802.11 Working Group E established an activity to enhance the current 802.11 standard to support applications with QoS requirements, the new protocol called IEEE 802.11e [2]. The main idea in the new QoS protocol is to make traffic differentiation and assign different access parameters for every traffic category, and hence give the delay sensitive applications priority over other applications. Generally the main problem in WLAN VoIP networks is that the system capacity can be quite low. In this paper a new access category parameter is suggested which can decrease the access delay for VoIP traffic and hence increases the VoIP WLAN capacity. It is focused here on Distributed Coordination Function (DCF) and enhanced distribution channel access (EDCA) access methods in 802.11 and 802.11e respectively. The rest of the paper is organized as follows. In section II, IEEE 802.11 MAC is briefly reviewed, and the VoIP capacity will be calculated. In Section III, IEEE 802.11e description is presented and VoIP capacity will be calculated. Section IV ...

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In this paper some WiMAX MAC layer parameters will be optimized to improve applications performance. The study is aimed to show, via simulation, the effect of Automatic Repeat Request (ARQ) parameters on the WiMAX performance. Also, it is aimed to verify the effectiveness of

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