A retrial queue with redundancy and unreliable server

Retrial queues are useful in the stochastic modelling of computer and telecommunication systems amongst others. In this paper a version of the retrial queue with variable serivce is studied. Such a point of view gives another look at the unreliable retrial queueing problem which includes the redundancy model. By using the theory of piecewise Markovian processes, the analogue of the Pollaczek-Khintchine formula for such retrial queues is obtained, which is useful for operations researchers to obtain performance measures of interest.