General AIMD congestion control

Instead of the increase-by-one decrease-to-half strategy used in TCP for congestion window adjustment, we consider the general case such that the increase value and decrease ratio are parameters. That is, in the congestion avoidance state, the window size is increased by α per window of packets acknowledged and it is decreased to β of the current value when there is congestion indication. We refer to this window adjustment strategy as general additive increase multiplicative decrease (GAIMD). We present the (mean) sending rate of a GAIMD flow as a function of α, β, loss rate, mean round-trip time, mean timeout value, and the number of packets acknowledged by each ACK. We conducted extensive experiments to validate this sending rate formula. We found the formula to be quite accurate for a loss rate of up to 20%. We also present a simple relationship between α and β for a GAIMD flow to be TCP-friendly, that is, for the GAIMD flow to have approximately the same sending rate as a TCP flow under the same path conditions. We present results from simulations in which TCP-friendly GAIMD flows (α=0.31, β=7/8) compete for bandwidth with TCP Reno flows and with TCP SACK flows, on a DropTail link as well as on a RED link. We found that the GAIMD flows were highly, TCP-friendly. Furthermore, with β at 7/8 instead of 1/2, these GAIMD flows have reduced rate fluctuations compared to TCP flows