We propose an optimal schedule for multiple classes of arrivals in a queuei
ng system consisting of queues in tandem. The arrival process for each clas
s is Poisson with different rates, and the service times are constant. A th
eoretical result is presented by Linear Programming of sample-path argument
s, together with duality theory. The approach shows a powerful analytical t
ool which facilities the procedure in analysis of optimization in queueing
control problems and a possibility of future study in other similar problem
s.