Analysis of dynamic behaviors of many TCP connections sharing tail-drop/RED routers

Appropriate control parameters are important for the successful deployment of RED (Random Early Detection) routers, especially when many TCP connections share the bottleneck link. In this paper, we first describe a new simple analysis method for determining the window size distribution of many TCP connections sharing a bottleneck router. We consider two kinds of buffering disciplines: TD (Tail Drop) and RED. We model the window size evolution of TCP connections by using a Markov process whose state is represented by a set of the current window size and the ssthreth value. The state transition matrix is then calculated by considering the characteristics of TD and RED routers. We show numerical results demonstrating the accuracy of our analysis and we discuss the fairness of TD and RED. We confirm that RED does not help improve the router´s throughput even when appropriate control parameters are chosen but that it is still useful to provide the fairness among many competing TCP connections