N. R. D. Vedala, Y. Saritha, A. A. Rao, and G. Sridhar "Study of MX/M/1 Queueing System with Vacation, Two kinds of Repair facilities and Server Timeout", Advances in Science, Technology and Engineering Systems Journal, vol. 4, no. 6, pp. 339–342, 2019, doi: 10.25046/aj040643.