5. USER MOBILITY PATTERN BASED TCP FOR WIRELESS CELLULAR NETWORKS Ayhan EMRE, 2003

Keywords : Wireless Networks, Tethered Network, TCP, Handoff, User Mobility Pattern, U‑TCP, Location Management, Transport Layer, Middleware, Mobility, I-TCP, TCP-Peach

A wireless cellular network consists of cells (Base Stations) interconnected by a tethered network. TCP is a connection oriented, reliable transport layer protocol used in tethered and wireless networks. It performs well in tethered networks (TN) where packet losses happen mostly because of congestion. However, the users are mobile and packet losses are mainly due to higher bit error rates and mobility in wireless networks. When a mobile terminal (MT) moves from the coverage area of one cell to another, a handoff occurs and the access point to the TN changes. In this case a new TCP connection must be established and a new window advertisement and slow start (congestion window) process should be started. This reduces the throughput for the connection, wastes available bandwidth and introduces additional jitter. In this thesis, we introduce User Mobility Pattern based TCP (U-TCP), a middleware between application and transport layers that uses existing TCP protocols in the transport layer. The cells expected to be visited and the predicted cell entry times are given by the UMP based location management scheme. The window advertisement and slow start processes can be completed before the handoff by establishing warm-up TCP connections for the cells expected to be visited. Hence, the call termination rates, jitter and the impact of mobility on TCP connections are reduced.