When Should a Roving Server Be Patient?

Abstract

When polling systems are used to model real-world systems, it is typically assumed that the server switches continuously (“roves”) even when there are no waiting jobs in the system. However, requiring the server to be patient, instead of having it rove, might be more realistic. Furthermore, operational control of these systems can be improved by knowing answers to questions like “under what circumstances should be roving server be patient?” and “at which stations?”. This paper analyzes the patient server model and provides explicit expressions for the waiting time distributions, the mean waiting times and the pseudo-conservation law. Several variants of the patient server model are considered. We show that while the patient server mechanism is generally better than the roving server mechanism in the work-in-process (WIP) reduction sense, there do exist cases where roving is better. Counter-intuitive examples where reducing switchover time can increase WIP are also reported.