A versatile model for asymmetric TCP sources

In the literature it is quite common to model TCP sources as Additive-Increase Multiplicative-Decrease sources. Within this framework we develop a Markov chain model that captures the interaction between the source and buffer processes. This approach permits to investigate a number of TCP related phenomena that are inherently stochastic. In the first place we evaluate two popular loss models: one in which sources react in a synchronized manner to loss, the other in which just one source reduces its window after loss epochs with a probability that is proportional to the source window. A comparison with a simulation in ns2 shows that the real loss process is somewhere in between the two loss models. Secondly, we show that the celebrated 'root p' law is still valid when the loss process is strictly dependent on the source state instead of an autonomous process, and the roundtrip times are stochastic instead of constant. Finally, we analyze the impact of source on/off behavior when the source on-times depend on momentary source transmission rates, as is the case in practice.