Handoff Mechanism in Universal Network

With the development of Internet technology, People's demand for mobile access is growing. The Wi-Fi technology, based on the IEEE 802.11 standards, is rapidly becoming a main stream for mobile access, as a result of extensive implant laptops, mobile phones, game consoles, and other personal portable lectronic equipment. However, traditional Internet is designed for providing the fixed, cable interconnection services to users, and it's not fit to mobility. The Universal Network theory, proposes a new Internet architecture based on Identifiers Separating and Mapping Scheme, which is able to better support mobility. Therefore, research on the access and handoff of Wi-Fi terminal in Universal Network becomes more important.In this thesis, we mainly focus on the design and implement of Wi-Fi terminal automatically handoff mechanism in the Universal Network. Firstly, we briefly introduce the access and authentication process, as well as the access steps involved in the wireless environment; Secondly, based on the analysis of the Wi-Fi terminal's general handoff process, we propose the design objectives of the automatic handoff mechanism, and also design the improved handoff process in the link layer( prescan handoff algorithm) and the "network layer" for fast handoff, and a mechanism of Automatic Handoff Fanite State Machine (AHFSM) to achieve automatically handoff control; Thirdly, we implement these in Linux OS.The traits of the implementation are shown as follows: 1) With the Linux thread library, we implement AHFSM mechanism, including the event-triggered control, timer control, network read/write control units, etc.; 2) With the Linux wireless libraries for IEEE 802.11, we modify it to implement link layer functions; 3) We uses data structure of two-way linked list to store the wireless APs information, and sort these based on RSSI value for link layer handoff; 4) With Linux routing operation library, we modify it to implement routeing operation in "network layer"; 5) We use the UNIX UDP socket to implement message interaction of handoff and authentication process in "network layer"; 5) With the Linux GTK graphics library, we implement the user interface, for users operating and viewing, as well as to meet the demand for the use and debuging.With installing the Wi-Fi terminal program in the prototype system of Universal Network, we test AHFSM mechanism and prescan handoff algorithm. Tests show that with control of the automatically handoff mechanism, the Wi-Fi terminal can not only support automatically access and prescan automatically handoff, but also manually access and handoff mode and manual operation in automatic handoff procedure, and It also can avoid "Pingpang" effect. Tests also show that manual handoff mode and automatic handoff mode are both meet the general needs of real-time business.