  In the context of networked control systems, event-triggered control (ETC)
has emerged as a major topic due to its alleged resource usage reduction
capabilities. However, this is mainly supported by numerical simulations, and
very little is formally known about the traffic generated by ETC. This work
devises a method to estimate, and in some cases to determine exactly, the
minimum average inter-sample time (MAIST) generated by periodic event-triggered
control (PETC) of linear systems. The method involves abstracting the traffic
model using a bisimulation refinement algorithm and finding the cycle of
minimum average length in the graph associated to it. This always gives a lower
bound to the actual MAIST. Moreover, if this cycle turns out to be related to a
periodic solution of the closed-loop PETC system, the performance metric is
exact.
