PLC’s for short, are used extensively in SCADA networks for meter readings and equipment status reports, which are then sent over an IP network (using IEC61850, DNP3, MODBUS, etc) to the Supervisory Station. PLC’s run both a piece of software to report back up to the station while simultaneously controlling physical entities like electric motors, pneumatic or hydraulic cylinders, magnetic relays, etc. You can see where I’m going with this: There are two alternate universes here and they should not affect each other. On the measurement/controlling side, responses have to be sent back within certain time bounds or things will break leading to physical and collateral damage. On the IP side, the inherent unreliability of IP networks has to be handled. This is very similar to how routing vendors [try and] isolate the control and forwarding planes, except the forwarding plane here controls and measures physical entities.

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