Risk based design, referred to as failure more and effects management - FMEA in manufacturing, provides an excellent basis for critical network design.

FMEA in network design considers the levels of communication described by the OSI 7 Layer model (link).

An FMEA approach to automation network design considers:

The environment, power, location

Level 1 - physical

Media selection (copper, fibre, wireless), resilience, cable routing and containment.

Level 2 - data link

Error detection, flow control, resilience, switching, segmentation.

Level 3 - network layer

Network addressing, routing, switching, fire walling

Level 4 - transport layer

End to end connectivity, error control and fire walling.

System monitoring and management

SNMP, Syslog, SIEM (security information and event management), IDS/IPS (intrusion detection and prevention).

It is the consideration of these factors that differentiates one automation network design & implementation from another.