  A networked control system (NCS) consisting of cascaded two-port
communication channels between the plant and controller is modeled and
analyzed. Towards this end, the robust stability of a standard closed-loop
system in the presence of conelike perturbations on the system graphs is
investigated. The underlying geometric insights are then exploited to analyze
the two-port NCS. It is shown that the robust stability of the two-port NCS can
be guaranteed when the nonlinear uncertainties in the transmission matrices are
sufficiently small in norm. The stability condition, given in the form of
"arcsin" of the uncertainty bounds, is both necessary and sufficient.
