Distinguishing Congestion Losses from Wireless Transmission Losses : A Negative Result

TCP is a popular transport protocol used in present-day internet. When packet losses occur, TCP assumes that the packet losses are due to congestion, and responds by reducing its congestion window. When a TCP connection traverses a wireless link, a significant fraction of packet losses may occur due to transmission errors. TCP responds to such losses also by reducing congestion window. This results in unnecessary degradation in TCP performance. We define a class of functions named loss predictors which may be used by a TCP sender to guess the actual cause of a packet loss (congestion or transmission error) and take appropriate actions. These loss predictors use simple statistics on round-trip times and/or throughput, to determine the cause of a packet loss. We investigate their ability to determine the cause of a packet loss. Unfortunately, our simulation measurements suggest that the three loss predictors do not perform too well.