Analysis of unreliable BMAP/PH/N type queue with Markovian flow of breakdowns

Abstract

Unreliability of components is the inherent feature of many real world systems and its account is vital for correct prediction of performance measures of the system. Multi-server queueing model considered in this paper allows to evaluate characteristics of the systems under much more general assumptions about the probabilistic distributions describing behavior of the system than models known in existing literature. We analyse the multi-server queue with infinite buffer and the Batch Markovian Arrival Process (BMAP) of customers. The servers are identical and independent of each other. Service time of a customer has phase-type (PH) distribution. Servers are subject to breakdowns and repairs. Breakdowns occurrence moments are defined by the Markovian Arrival Process (MAP). The breakdown causes a failure of any server, which is not under repair. When a server fails the repair period starts immediately. The duration of this period has PH distribution. A customer whose service is interrupted occupies an idle server, if any, and continues his/her service. If he/she does not see an idle server, the customer goes to the buffer with some probability and permanently leaves the system with the complementary probability. We derive the constructive ergodicity condition and calculate the stationary distribution and the main performance characteristics of the system. Illustrative numerical examples are presented.