Performance of two TCP implementations in mobile computing environments

The error recovery algorithm in TCP has been designed for congestion control in wired networks. However, the packet losses in wireless networks are mostly caused by outages due to connection interruptions such as fading, channel preemptions, and handoffs. We investigate the performance of two TCP implementations in mobile computing environments. We consider simplified versions of two TCP implementations (referred to as Protocol I & II). Protocol I is a variation of the TCP Tahoe which uses a fine-grained timer. Protocol II is a simplified version of the TCP Vegas. We first describe an interesting observed phenomena with these two timer-based protocols when the wireless channel is periodically taken away from the end/end connections. Next, we show the robustness of Protocol II and quantify its improvement over Protocol I in terms of achievable goodputs. We also discuss better goodputs can be achieved by setting the RTO differently to account for a higher variability in delays caused by the wireless channel. Finally, we describe how a bigger TCP segment size helps to improve goodputs when these TCP segments are transported over the wireless channel.