Retrial Queues with Unreliable Servers and Delayed Feedback

In this paper, models of unreliable multi-server retrial queues with delayed feedback are examined. The Bernoulli is allowed upon the arrival both primary (from outside) and customers orbit), as well that may occur after each service in system. Servers can break down during when they idle. If a server breaks customer, then interrupted accordance scheme, decides either to leave system or join common orbit customers. An approximate method, based on space merging approach three-dimensional Markov chains, proposed for calculation steady-state probabilities, performance measures results numerical experiments demonstrated.