Recently, networks have increased rapidly both in scale and speed. Problems related to the control and management are of increasing interest. The average throughput and end-to-end delay of a network flow are important design factors. However, there is no satisfactory tool to obtain such parameters. The traditional packet-by-packet event driven simulation is slow when the network speed is high. The time driven simulation faces the difficulty of choosing the right time interval when simulating packetswitched networks. As Transmission Control Protocol (TCP) is the most widely used transport layer protocol, and it uses window based flow control mechanism, classic queuing theories involving Markov Chain assumptions are not applicable. This paper describes a model for window based flow control packetswitched networks. The model attempts to provide a way to obtain the steady state results for large and high speed networks using TCP. In this paper, we discuss in detail the construction, implem...