Fluid-based analysis of a network of AQM routers supporting TCP flows withan application to RED

In this paper we use jump process driven Stochastic Differential Equations to model the interactions of a set of TCP flows and Active Queue Management routers in a network setting. We show how the SDEs can be transformed into a set of Ordinary Differential Equations which can be easily solved numeri cally. Our solution methodology scales well to a large number of flows. As an application, we model and solve a system where RED is the AQM policy. Ou r results show excellent agreement with those of similar networks simulated using the well known ns simulator. Our model enables us to get an in-depth understanding of the RED algorithm. Using the tools developed in this pape r, we present a critical analysis of the RED algorithm. We explain the role played by the RED configuration parameters on the behavior of the algorith m in a network. We point out a flaw in the RED averaging mechanism which we believe is a cause of tuning problems for RED. We believe this modeling/so lution methodology has a great potential in analyzing and understanding var ious network congestion control algorithms.