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Comparative call Capacity analysis of VOIP in IEEE802.11b WLAN Environment

In recent years, Voice over Internet Protocol (VoIP) is growing very fast and is providing a cost effective alternative for Voice communication. VoIP over WLAN is poised to become an important Internet application. Since numbers of VoIP client over WLAN is increasing at a fast pace, the number of simultaneous VoIP streams supported by IEEE WLAN standard is an important area of study. With each VoIP stream typically requiring less than 10kbps, an IEEE802.11b WLAN operated at 11Mbps could in principle support 550 VoIP sessions, but in practice it provides very few VoIP sessions, typically 8 to 10. IEEE 802.11b standard operates in two modes i.e. Distributed Co-ordination Function (DCF) and Point Co-ordination Function (PCF). Although, both modes of operation could work for any type of traffic (Data traffic, Real-time Traffic, Video traffic), but PCF is more suitable real time traffic (Voice). The reason for low capacity is the small packet size of VoIP packets and a large overhead at MAC layer. Many schemes, such as PCF, Modified PCF, CSSR, ICF and MICF have been proposed to reduce polling overhead to enhance call capacity. In this paper call capacity performance of PCF, Modified PCF, CSSR, ICF and MICF have been evaluated and compared using MATLAB simulation.