A cell/area zone is a functional area within a plant or facility. It can be an individual production line or part of a production line.

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In general, most plants have multiple cell/area zones that are defined as a grouping of ICS devices, all working toward a common goal like producing a product or assembling a part of the product. The devices in a cell/area zone are allowed to communicate unhindered and in real time, but traffic leaving or entering the cell/area zone is subject to inspection. Properly defined cell/area zones add security to the ICS network by containing cell/area zone specific traffic in the zone and allowing strict control and inspection between cell/area zones.

A typical cell/area zone includes three levels of activity between related ICS devices, such as PLCs, HMIs, sensors, actuators, and the networking equipment used to communicate: