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In this paper, we consider downward and upward vertical handovers in integrated wireless LAN and cellular networks and address wireless-profiled Transmission Control Protocol premature timeouts due to step increase of round-trip time (RTT) and false fast retransmit due to packet reordering. Specifically, we develop a mobile-receiver centric loosely coupled cross-layer design, which is easy to implement and deploy, backward compatible with the Wireless Application Protocol version 2 architecture, and robust in the absence of perfect cross-layer information. We propose two proactive schemes, called RTT Inflation and RTT Equalization. The RTT Inflation scheme suppresses premature timeouts by carefully inflating retransmission timeout time, and the RTT Equalization scheme prevents false fast retransmit by equalizing the round-trip delay experienced by all packets. We conduct extensive simulations to evaluate the performance in downward and upward vertical handovers. It is demonstrated that the proposed schemes significantly improve the performance in a wide range of network conditions.
Date of Publication: Nov. 2007