Statistical bandwidth sharing: A study of congestion at flow level

In this paper we study the statistics of the realized throughput of elastic document transfers, accounting for the way network bandwidth is shared dyn amically between the randomly varying number of concurrent flows. We first discuss the way TCP realizes statistical bandwidth sharing, illustrating es sential properties by means of packet level simulations. Mathematical flow level models based on the theory of stochastic networks are then proposed t o explain the observed behavior. A notable result is that first order perfo rmance (e.g., mean throughput) is insensitive with respect both to the flow size distribution and the flow arrival process, as long as "sessions" arri ve according to a Poisson process. Perceived performance is shown to depend most significantly on whether demand at flow level is less than or greater than available capacity. The models provide a key to understanding the eff ectiveness of techniques for congestion management and service differentiat ion.