The effect of variability in the GI/G/s queue

In 1969 H. and D. Stoyan showed that the stationary waiting-time distribution in a GI/G/ 1 queue increases in the ordering determined by the expected value of all non-decreasing convex functions when the interarrival-time and service-time distributions become more variable, as expressed in the ordering determined by the expected value of all convex functions. Ross (1978) and Wolff (1977) showed by counterexample that this conclusion does not extend to all GI/G/s queues. Here it is shown that this conclusion does hold for all GI/G/s queues for several other measures of congestion which coincide with the waiting time in single-server systems. One such alternate measure of congestion is the clearing time, the time required after the arrival epoch of the n th customer for the system to serve all customers in the system at that time, excluding the n th customer. The stochastic comparisons also imply an ordering for the expected waiting times in M/G/s queues.