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.