Cyber Physical Security Solutions for Pervasive Health Monitoring Systems - E-Healthcare Systems and Wireless Communications - page 152

and (3) Actuation : This deals with executing the
actions determined during data processing phase.
Actuation can take many forms from changing the
behavior of the cyber element, to changing the
physical process itself. For example, delivery of
medicine and authorizing information access in
a PHM-CPS. This work-flow of CPS can execute
in one of three possible modes (see Figure 1):

• Active : In this mode, CPSs monitor its
constituent physical process and if some
property is not being satisfied they execute
a direct actuation by modifying the behav-
ior of the process to ensure the property
is satisfied, example, an HVAC (heating,
ventilating, and air conditioning) unit in a
building blowing cold air into the building
if the temperature goes beyond a certain
established limit. • Passive : In this mode, CPSs act as infor-

mation gathering platforms only and solely
monitor its constituent physical process,
process the data, e.g., medical devices such
as pulse oximeters
• Autonomic : In this mode, CPSs monitor
their constituent physical process and if
they see some property not being satis-
fied they execute an indirect actuation by
changing their own behavior (the cyber as-
pect) so that the property can be satisfied,
example, data centers performing smart
scheduling to minimize temperature rise at
specific spots

All CPSs need not implement all these modes
operation. Some may implement one or a particular
combination of modes. Many issues need to be
addressed in order to make each of these types of
CPS system types viable such as managing the
cyber and physical interactions, ensuring safety,
energy-efficiency, interoperability, sustainability.
One of the most important aspects that need to
be considered in this early development phase of
cyber-physical systems is security.

Figure 1. CPS Workflow and Operating Modes