Policies utilizing tactical inventory for service-differentiated customers

We consider a manufacturer serving two customer classes where one wants the item immediately and the second receives a discount to accept a delay. We show that an (S,R,B)(S,R,B) base-stock policy is optimal under differentiation and non-differentiation where SS, RR, and BB are the order-up-to, reserve-up-to, and backlog-up-to amounts.