The M/G/1 queue with two service speeds

We consider an M/G/1 queue with the special feature that the speed of the s erver alternates between two constant values s(L) and s(H) > s(L). The high -speed periods are exponentially distributed, and the low-speed periods hav e a general distribution. Our main results are: (i) for the case that the d istribution of the low-speed periods has a rational Laplace-Stieltjes trans form, we obtain the joint distribution of the buffer content and the state of the server speed; (ii) for the case that the distribution of the low-spe ed periods and/or the service request distribution is regularly varying at infinity, we obtain explicit asymptotics for the tail of the buffer content distribution. The two cases in which the offered traffic load is smaller o r larger than the low service speed are shown to result in completely diffe rent asymptotics.