It is very important in many real-life systems to decide when the server sh
ould start his service because frequent setups inevitably make the operatin
g cost too high. Furthermore, today's systems are too intelligent for the i
nput to be assumed as a simple homogenous Poisson process. In this paper, a
n M/G/1 queue with general server setup time under a control policy is stud
ied. We consider the case when the arrival rate varies according to the ser
ver's status: idle, setup and busy states. We derive the distribution funct
ion of the steady-state queue length, as well as the Laplace-Stieltjes tran
sform of waiting time. For this model, the optimal N-value from which the s
erver starts his setup is found by minimizing the total operation cost of t
he system. We finally investigate the behavior of system operation cost and
the optimal N for various arrival rates by a numerical study. (C) 1999 Els
evier Science Inc. All rights reserved.