6.2. The main performance measures
(i) Utilizations
Utilizations can now be considered for individual servers or for the system as a whole. The process (X(t), t ≥ 0) is assumed to be in equilibrium. Considering the system as the whole, it will be empty only when there are no requests at the service facility and will be busy at other times. As usual, using renewaltheoretic arguments for the system utilization, that is the long-run fraction of time when at least one server is busy, we have