TCP Dynamics in 802.11 Wireless Local Area Networks

In 802.11 wireless links with disabled MAC retries, data and ACK packets within a TCP session collide resulting in packet losses. We show in this paper that in this situation, certain popular optimizations of TCP (fast-recovery) worsen the performance by causing deadlocks that terminate with timeouts. We compare the performance of optimized TCP versions (Reno and NewReno) with an earlier version of TCP (Tahoe) and demonstrate the degradation during fast-recovery. TCP-Tahoe gains 80% in throughput over TCP-Reno and more moderately over TCP-NewReno. A key contribution of this paper is the visualization of TCP dynamics to capture MAC layer collisions between DATA and ACK packets of a TCP session, and the differences in the behavior of protocols in that situation. This case of poor TCP performance due to self-inflicted losses, makes a sound case for decoupling error and flow control algorithms for transport over 802.11 wireless networks.