The stationary waiting time and other variables in single-server queues with specialities at the beginning of a busy period G. Siegel — 1973 Applicationes Mathematicae
On Kingman's integral inequalities for approximations of the waiting time distribution in the queuing model GI/G/1 with and without warming-up time H. J. Rossberg; G. Siegel — 1974 Applicationes Mathematicae