Simulation Study of TCP in Overload

We study through simulations the transient performance deterioration on an overloaded link and compare the results with the processor sharing model. We find many similarities. The performance depends essentially on the load and on the distribution of flow sizes. Moreover the distribution of sizes observed on public networks leads to a very slow degradation. The number of active flows and the sojourn times increase linearly. We also observe that the link capacities has a small impact. These results are independent of usual TCP releases and they are due to the relatively fair bandwidth sharing between connections. This may allow acceptable waiting times for short transfers during overloads lasting many tens of minutes. We however notice some differences. The arrival process has a low but non negligible influence on TCP simulations. More important are the worse performance and the slow convergence of the dispersion of sojourn times