Semaphore queues: modeling multilayered window flow control mechanisms

We present an open queueing network for analysing multi-layered window flow control mechanisms consisting of different subnetworks. The number of customers in each subnetwork is controlled bya semaphore queue. The queueing network is analysed approximately using decomposition and aggregation. The approximation was validated against exact numerical and simulation data, and it was found to have an acceptable relative error. The queueing model is easy to implement and it can be included in a software package. Using this queueing network, we present a case study involving the modelling and analysis of the ISO X25 flow control mechanism.