Comparative throughput analysis of queueing networks with exponential and deterministic service times in the nodes

We consider a queueing network consisting of |M|m and |GI|∞ systems. Poisson arrivals are assumed (if the network is open). We show that the throughput characteristics are not degraded when the exponential service time in one or several |M|I systems is replaced with a deterministic service time with the same mean: if the network is open the total number of customers in the modified network is stochastically less than in the original network; if the network is closed, the average load coefficients of the systems in the modified network are not less than in the original network.