  In this paper, we study a controllable tandem queueing system consisting of
two nodes and a controller, in which customers arrive according to a Poisson
process and must receive service at both nodes before leaving the system. A
decision maker dynamically allocates the number of service resource to each
node facility according to the number of customers in each node. In the model,
the objective is to minimize the long-run average costs. We cast these problems
as Markov decision problems by dynamic programming approach and derive the
monotonicity of the optimal allocation policy and the relationship between the
two nodes' optimal policy. Furthermore, we get the conditions under which the
optimal policy is unique and has the bang-bang control policy property.
