PERFORMANCE EVALUATION OF CLOSED TANDEM QUEUING-NETWORKS WITH FINITE BUFFERS

In this paper we propose a new approximation method for the analysis o f closed tandem queueing networks with general service times and block ing-after-service. The principle of the method is to decompose the ori ginal network consisting of M servers into a set of M subsystems, each subsystem consisting of two servers separated by a finite buffer. In order to determine the distributions of the service times of the two s ervers of each subsystem, we express relationships among distributions pertaining to the different subsystems. We then propose to use a two- moment approximation. The population constraint of the closed network is taken into account by prescribing that the sum of the average buffe r sizes of the subsystems is equal to the number of the customers of t he network. We end up with a set of equations that characterize the un known parameters of the service time distributions of the servers of t he subsystems. An iterative procedure is then used to determine these unknown parameters. Numerical results show that the new method is quit e accurate.