Performance analysis of TCP with RIO routers

We present an approach to analyzing the performance characteristics of TCP sessions in the presence of network routers which deploy the random early detection (RED) mechanism with two in-and-out drop probability functions (RIO). We consider the case with a large number of TCP sessions which use token buckets for marking in and out packets at the entrance of the network. Under some simplifying assumptions, we derive a set of equations that govern the evolution of these TCP sessions and the routers under consideration. The equations are solved numerically using a fixed point method. Our analysis can capture characteristics of both RED and tail drop (TD) mechanisms in the RIO router. Our model is validated through simulations which show that less than 5% error is achieved in most cases. Various performance analyses are carried out using this approach to study the impact of the RIO parameters on the performance characteristics of TCP sessions. The results show that the loss probability threshold of out packets has a significant effect on the TCP throughput and on the average queue length. Setting this parameter consists of trading off between network utilization and fairness among TCP connections. The results also show that the tail drop mechanism is particularly suitable for use in packets to satisfy various QoS constraints.