Performance analysis of TCP over WiMAX

The demand for fast transfer of large volumes of data, and the deployment of the network infrastructures is ever increasing. However, the dominant transport protocol of today, TCP, does not meet this demand because it favors reliability over timeliness and fails to fully utilize the network capacity due to limitations of its conservative congestion control algorithm. The slow response of TCP in fast long distance networks leaves sizeable unused bandwidth in such networks. A large variety of TCP variants have been proposed to improve the connection´s throughput by adopting more aggressive congestion control algorithms. Some of the flavors of TCP congestion control are loss-based, high-speed TCP congestion control algorithms that uses packet losses as an indication of congestion; delay-based TCP congestion control that emphasizes packet delay rather than packet loss as a signal to determine the rate at which to send packets. Following three TCP variants, namely Tahoe, New Reno and Vegas were compared using throughput, round-trip time (RTT) and packet loss ratio. While all the TCP variants achieve similar throughput, they do so in different ways, with different impacts on the network performance. The adverse effects of TCP window auto-tuning is identified in this environment and demonstrate that on the downlink, congestion losses dominate wireless transmission error. Several issues were revealing for this WiMAX-based networks, including limited bandwidth for TCP, high RTT and jitter, and unfairness during remote login, VoIP, and video streaming.