  Filtered Smith predictors are well established for controlling linear plants
with constant time delays. Apart from this classical application scenario, they
are also employed within networked control loops, where the measurements are
sent in separate packets over a transmission channel that is subject to
time-varying delays. However, no stability guarantees can be given in this
case. The present paper illustrates that the time-varying delays as well as the
packetized character of the transmissions have to be taken into account for
stability analysis. Hence, three network protocols, which use different packet
selection and hold mechanisms, are considered. Criteria for robust stability of
the networked feedback loop are given. They are based on the small gain theorem
and allow a computationally inexpensive way to check stability for the case
with bounded packet delays. Simulation examples provide insight into the
presented approach and show why the inclusion of the time-varying packetized
character of the network transmissions is vital for stability analysis.
