  The paper introduces a class of zero-sum games between the adversary and
controller as a scenario for a `denial of service' in a networked control
system. The communication link is modeled as a set of transmission regimes
controlled by a strategic jammer whose intention is to wage an attack on the
plant by choosing a most damaging regime-switching strategy. We demonstrate
that even in the one-step case, the introduced games admit a saddle-point
equilibrium, at which the jammer's optimal policy is to randomize in a region
of the plant's state space, thus requiring the controller to undertake a
nontrivial response which is different from what one would expect in a standard
stochastic control problem over a packet dropping link. The paper derives
conditions for the introduced games to have such a saddle-point equilibrium.
Furthermore, we show that in more general multi-stage games, these conditions
provide `greedy' jamming strategies for the adversary.
