Two Different Models of FAST TCP and Their Stable and Efficient Modification

In this paper, we introduce two different models of FAST TCP. One is from the original FAST TCP model, and the other is from the ns-2 implementation of FAST TCP. Interestingly, these two models show significantly different dynamic performance and stability characteristics. That is, while the latter model is always globally exponentially stable, the former model is faster than the latter model and possible to go unstable. Motivated from these two models, we suggest a modified congestion control algorithm. By tuning the gain of the terms caused by the difference of the two models, the modified algorithm can be made to become globally asymptotically stable and more responsive than the ns-2 implementation model of FAST TCP. The stability condition of the modified algorithm is decoupled from the network parameters and does not change the equilibrium state.