The authors develop a simple model for window flow control in homogeneous local area networks (LANs) interconnected by a media-access-layer bridge. Analysis of the model demonstrates that for each set of parameters values there is an optimal window that maximises the good throughput of virtual circuits interconnected via the bridge. Using this model the authors develop an adaptive window flow control algorithm that gives significantly better performance than an algorithm that is being considered for standardisation for interconnected token ring LANs