Exact sampling of TCP window states

We demonstrate how to apply Coupling from the Past, a simulation technique for exact sampling, to Markov chains based on TCP variants. This approach provides a new, statistically sound paradigm for network simulations: instead of simulating a protocol over long times, or explicitly finding the stationary distribution of a Markov chain, use Coupling from the Past to quickly obtain samples from the stationary distribution. Coupling from the Past is most efficient when the underlying state space satisfies a partial order and certain monotonicity conditions. To efficiently apply this general paradigm to TCP, we demonstrate that the states of a simple TCP model possess a monotonic partial order; this order appears interesting in its own right. Preliminary simulation results indicate that this approach is quite efficient, and produces results which am similar to those obtained by simulating a TCP-Tahoe connection.