A single-queue model with group Poisson input and two service modes is
considered in which a certain period of time is required to switch fr
om one service mode to the other. Using a regenerative approach, it is
possible to estimate the mean number of customers (jobs) in the syste
m for a so-called hysteresis strategy. This also solves the problem of
finding a strategy for minimization of the mean number of customers i
n the system.