Nail Akar Nihat Cem Oguz Khosrow Sohraby Matrix-geometric solutions of M/G/1-type Markov chains: a unifying generalized state-space approach. 626-639 1998 16 IEEE J. Sel. Areas Commun. 5 https://doi.org/10.1109/49.700901 db/journals/jsac/jsac16.html#AkarOS98