I. Introduction
A Heterogeneous wireless network is a combination of several wireless networks which includes cellular networks, ad-hoc networks and wireless LAN's, connected to the Internet. Heterogeneous wireless networks provide a diverse wireless network access. Improving the communication throughput, extending the service coverage of the existing cellular and WLAN infrastructure, reducing packet transmission latency based on availability of different types of radio network in the roaming area are some of the advantages of Heterogeneous wireless networks.