V-TCP: A Novel TCP Enhancement Technique for Wireless Mobile Environments

Abstract

Transmission Control Protocol (TCP) is a reliable transport protocol tuned to perform well in habitual networks made up of links with low bit-error rates. TCP was originally designed for wired networks, where packet loss is assumed to be due to congestion. In wireless links, packet losses are due to high error rates and the disconnections induced are due to mobility. TCP responds to these packet losses in the same way as wired links. It reduces the window size before packet retransmission, initiates congestion control avoidance mechanism and resets its transmission timer. This adjustment results in unnecessary reduction of the bandwidth utilization causing significant degraded end-to-end performance. A number of approaches have been proposed to improve the efficiency of TCP in an unreliable wireless network. But researches only focus on scenarios where TCP sender is a fixed host. In this paper we propose a novel protocol called V-TCP (versatile TCP), an approach that mitigates the degrading effect of host mobility on TCP performance. In addition to scenarios where TCP sender is fixed host, we also analyze the scenario where TCP sender is a mobile host. V-TCP modifies the congestion control mechanism of TCP by simply using the network layer feedback in terms of disconnection and connection signals, thereby enhancing the throughput in wireless mobile environments. Several experiments were performed using NS-2 simulator and the results were compared to the performance of V-TCP with Freeze-TCP [1], TCP Reno and with 3-dupacks [2]. Performance results show an improvement of up to 50% over TCP Reno in WLAN environments and up to 150% in WWAN environments in both directions of data transfer.