A computer network has a collection of resources shared by multiple users. The capacity of the resources is limited, and if the user demands exceed the capacity, the network becomes ’congested’. The congestion causes a degradation in system performance. In interconnected networks there are two classes of traffic within a network. One class is the local traffic that is generated and transmitted within the network. The other class is the internetwork traffic transmitted to or from other networks. In this thesis, the effect of internetwork traffic on the performance of a network is investigated. Computer simulation of an interconnected network model is provided in order to evaluate the effectiveness of a window-based congestion control mechanism on preventing congestion in gateways and in attached networks caused by the overload of internetwork traffic. Also two dynamic window congestion control algorithms are provided and studied. These algorithms provide further control to window mechanism by adjusting the window size in accordance with the availability of the network resources at the destination. Dynamic algorithms are evaluated comparing them with static window control.