Excess bandwidth distribution in DiffServ networks

The per-hop-behaviors (PHB) proposed for use within the DiffServ architecture are designed to meet the demands of diverse Internet applications. An important aspect of one such PHB, assured forwarding (AF), is the distribution of excess bandwidth among aggregates with different network parameters in an over-provisioned network. The lack of control over excess bandwidth distribution can be an impediment for successful adoption of AF PHB, particularly for applications built over congestion reactive transport protocols like TCP. This paper presents a model that helps understand the dependence of excess bandwidth distribution on different network parameters, including the number of flows per aggregate that has so far been ignored in previous studies. Furthermore, considering the dynamic behavior of a DiffServ controlled TCP aggregate we show that the mechanisms of DiffServ complicate TCP dynamics and changes its convergence properties. This knowledge can guide the design of networks and their various components such as meters and markers to achieve more control over the excess bandwidth distribution and make AF PHB more attractive. The model is validated through ns-2 simulation studies