Waiting-Time Distributions for Application to a Series of Service Centers

The method described in this paper is a result of analyzing job shop production processes as a network of waiting lines at machine (production) centers. The waiting time distribution for a series of N work centers, P [(sum) j =1 j = N X j (le) (tau)], is derived as a function of the waiting-time distributions at the individual work centers, P [ X j (le) (tau)], j = 1, 2, ..., N , where the cumulative waiting-time probability distribution at each work center is of the form P [ X j (le) (tau)] = l - K j exp( C j (tau)), with C j and K j constant. The resulting formula for total waiting time is amenable to desk computation and may be useful in estimating job flow time distributions in production control applications for which the first-come, first-served, steady-state model described below is applicable. Also, the method of proof may suggest an approach for convolution in other waiting-line models.