G. Ayyappan, and S. Karpagam. “An $M^{[X]}/G(a,b)/1$ Queueing System With Breakdown and Second Optional Repair, Stand-by Server, Balking, Variant Arrival Rate and Multiple Vacation”. International Journal of Mathematics And Its Applications, vol. 6, no. 2 - A, May 2018, pp. 145-56, https://ijmaa.in/index.php/ijmaa/article/view/657.