We consider a queueing system with Poisson arrivals and exponentially distributed service time and FCFS service discipline. The service of a customer is started at the moment of arrival (in case of free system) or at moments differing from it by the multiples of a given cycle time T (in case of occupied server or waiting queue). The waiting time is always the multiple of cycle time T, one finds its generating function and mean value. The characteristics of service are illustrated by numerical examples. If we measure the waiting time by means of number of cycles, we can optimize the cycle time T.