Wireless communications is the fastest growing segment of the communications industry. Everyone wants the quality of services anytime & anywhere. Wireless networks can integrate various heterogeneous radio access technologies as GSM, WLAN, WiMAX etc. WiMAX is an IP based, wireless broadband access technology that provides performance similar to 802.11/Wi-Fi networks with the coverage and QOS (Quality Of Service) of cellular networks. WiMAX is also an acronym meaning Worldwide interoperability for Microwave Access (WiMAX). The main promise of interconnecting these heterogeneous networks is to provide high performance in achieving a high data rate and support real time applications.