YezhovI. I., and KadankovV. F. “Main Probability Characteristics of the Queuing System $G^k|G|1$”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 53, no. 10, Oct. 2001, pp. 1343-57, https://umj.imath.kiev.ua/index.php/umj/article/view/4354.