TCP over WiMAX: A Measurement Study

We present active measurement results from a commercial IEEE 802.16/WiMAX-based network, with primary focus on TCP performance. We compare four TCP variants, namely New Reno, Cubic, Vegas and Veno, using throughput, round-trip time (RTT), and retransmission rate metrics. While all TCP variants achieve similar throughput, they do so in different ways, with different impacts on the network performance. We identify adverse effects of TCP window auto-tuning in this environment and demonstrate that on the downlink, congestion losses dominate wireless transmission errors. We reveal several issues for this WiMAX-based network, including limited bandwidth for TCP, high RTT and jitter, and unfairness during bidirectional transfers. Such a network environment may be challenging for many wireless Internet applications, such as remote login, VoIP, and video streaming.