Transmission control protocol (TCP) is known to suffer from performance degradation in mobile wireless environments. This is because such environments are prone to packet losses due to high bit error rates and mobility induced disconnections. TCP interprets packet losses as an indication of congestion and inappropriately invokes congestion control mechanisms, leading to degraded performance. While there are several proposals to optimize TCP in the presence of high bit error rates and mobility, they focus mainly on scenarios where the TCP sender is a fixed host. In this paper we propose ATCP, an approach which mitigates the degrading effect of host mobility on TCP performance for two-way data transfers, i.e. scenarios where the TCP sender is a mobile host, in addition to scenarios where the TCP sender is a fixed host. ATCP uses network layer feedback in terms of disconnection and connection signals, to modify the congestion control mechanisms of TCP, thereby achieving enhanced throughput in mobile wireless environments. We have compared ATCP with 3-dupacks (3DA), Freeze TCP and TCP Reno, by simulations using ns-2. We show that ATCP achieves an improvement of up to 40% over TCP Reno in WLAN environments and up to 150% in WWAN environments in both directions of data transfer.
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