Two-moment analysis of alternative tool models with random breakdowns

In this paper a two-station, single-server queuing system with random breakdowns is investigated. Two classes of customers arrive at the system with finite buffers where one server is dedicated to only one customer class while the second server can process both types of customers. Interarrival and service times are exponentially distributed while failure and repair times follow the generalized exponential distribution. Motivated by the application of alternative tools in semiconductor manufacturing two different control schemes are considered that trigger processing of customers of the second class on the server that is usually dedicated to customers of the first class. The first two moments of customer flow times for both control schemes are calculated