Handoff in hybrid mobile data networks

With the emergence of a variety of mobile data services with variable cover age, bandwidth, and handoff strategies, and the need for mobile terminals t o roam among these networks, handoff in hybrid data networks has attracted tremendous attention. This article presents an overview of issues related t o handoff with particular emphasis on hybrid mobile data networks. Issues a re logically divided into architectural and handoff decision lime algorithm s. The handoff architectures in high-speed local coverage IEEE 802.11 wirel ess LANs, and low-speed wide area coverage CDPD and GPRS mobile data networks are described and compared. A survey of traditional algorithms and an example of an advanced algorithm using neural networks for HO decision time in homogeneous networks are presented. The H O architectural issues related to hybrid networks are discussed through an example of a hybrid network that employs GPRS and IEEE 802.11. Five archite ctures for the example hybrid network, based on emulation of GPRS entities within the WLAN, mobile IP, a virtual access point, and a mobility gateway (proxy), are described and compared. The mobility gateway and mobile IP app roaches are selected for more detailed discussion. The differences in apply ing a complex algorithm for HO decision time in a homogeneous and a hybrid network are shown through an example.