An alternating service problem

TL;DR

This paper analyzes the waiting time distribution of a server alternating between two points with preparation phases, using Lindley-type equations, and compares it to the machine repair problem, providing new insights into these queueing models.

Contribution

It derives the waiting time distribution for an alternating service system with phase-type preparation times and compares it to the machine repair problem, which has not been studied before.

Findings

Server waiting time is smaller in the machine repair model.

Waiting times are not stochastically ordered between models.

The analysis uses Lindley-type equations for phase-type distributions.

Abstract

We consider a system consisting of a server alternating between two service points. At both service points there is an infinite queue of customers that have to undergo a preparation phase before being served. We are interested in the waiting time of the server. The waiting time of the server satisfies an equation very similar to Lindley's equation for the waiting time in the GI/G/1 queue. We will analyse this Lindley-type equation under the assumptions that the preparation phase follows a phase-type distribution while the service times have a general distribution. If we relax the condition that the server alternates between the service points, then the model turns out to be the machine repair problem. Although the latter is a well-known problem, the distribution of the waiting time of the server has not been studied yet. We shall derive this distribution under the same setting and we shall compare the two models numerically. As expected, the waiting time of the server is on average smaller in the machine repair problem than in the alternating service system, but they are not stochastically ordered.