References
- Feller , W. 1966 . An Introduction to Probability Theory and its Applications , Vol. 2 , New York : John Wiley and Sons, Inc. .
- Parzen , E. 1962 . Stochastic Processes , San Francisco : Holden-Day, Inc. .
- Takacs , L. 1962 . An Introduction to the Theory of Queues , New York : Oxford University Press .