We consider control policies for perishable inventory systems with
random input whose purpose is to mitigate the effects of unavailability.
In the basic uncontrolled system, the arrival times of the items to be
stored and the ones of the demands for those items form independent
Poisson processes. The shelf lifetime of every item is finite and
deterministic. Every demand is for a single item and is satisfied by the
oldest item on the shelf, if available. The first controlled model
excludes the possibility of unsatisfied demands by introducing a second
source of fresh items that is completely reliable and delivers without
delay whenever the system becomes empty. In the second model, there is no
additional ordering option by outsourcing. However, to avoid the most
adverse effects of unavailability, the demands are classified into
different categories of urgency. An incoming demand is satisfied or not
according to its category and the current state of the system. For both
models, we determine the steady-state distribution of the virtual
outdating process, which is then used to derive the relevant cost
functionals: the steady-state distribution and expected value of the
number of items in the system, the rate of outdatings, as well as, for
model 1, the rate of special orders from the external source and, for
model 2, the rate of unsatisfied demands.