1. Gross, D. and Harris, C.M., Fundamentals of Queueing Theory, 2nd edn. Wiley, New York, 1985.
2. Feller, W., an Introduction to Probability Theory and its Applications, Vol. 1, 3rd edn. Wiley, New York, 1968.
3. The productivity of several machines under the care of one operator;Ashcroft;Journal of the Royal Statistical Society B,1950
4. The productivity of machines requiring attention at random interval;Benson;Journal of the Royal Statistical Society B,1951
5. The M/Ek/R machine interference model: steady state equations and numerical solutions;Maritas;European Journal of Operational Research,1977