Differentiated Services: A New Direction for Distinguishing Congestion Losses from Wireless Losses

Currently, a TCP sender considers all losses as congestion signals and reacts to them by throttling the sending rate. With Internet becoming more heterogeneous with wireless error-prone links, a TCP connection may unduly throttle its sending rate and experience a poor performance over non congested paths. A closed form expression is developed for the expected improvement of TCP throughput if TCP can differentiate congestion losses and react appropriately. Differentiated Services (Diffserv) offer a new opportunity to enable a TCP sender to identify accurately wireless losses and react appropriately. A technique based on Diffserv is proposed to accurately differentiate congestion losses from other types of losses. This technique is supported by a simple probablistic argument and evaluated through simulations. Congestion losses are identified with an accuracy of 95%. Wireless losses are identified with an accuracy higher than 70%. We propose TCP-Casablanca which is TCP-Newreno endowed with our discriminator. With TCP-Casablanca, an improvement of up to 150% is observed on paths lightly congested with mild wireless error rates.