1. Introduction
In these days wireless services such as WLAN, Bluetooth, WiBro and home network are getting popular all around the world. Because of its already well organized network architecture, IEEE 802.11 WLAN services are most successful and becoming important. Furthermore the integration of WLAN and mobile networks, such as Global System for Mobile Communications/General Packet Radio Service (GSMIGPRS), Universal Mobile Telecommunications System (UMTS), Code Division Multiple Access 2000 (CDMA2000), and WiBro offers the possibility of achieving anytime and anywhere Internet access. Given the complementary characteristics of WLAN with faster short-distance access and mobile networks with slower long-distance access, it is compelling to combine them to bring a cost-effective system capable of providing ubiquitous data services and high data rate services [1], [2].