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SOC for OT

Glossary

Purdue model

Also known as: Purdue Enterprise Reference Architecture, PERA

The Purdue model is a reference architecture that divides industrial networks into levels, from the physical process (level 0) up to enterprise IT (levels 4–5), with an industrial DMZ in between.

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The model originated in the Purdue Enterprise Reference Architecture of the 1990s and is still the common language for describing OT networks:

  • Level 0 — physical process: sensors, actuators, drives
  • Level 1 — basic control: PLCs, RTUs, safety controllers
  • Level 2 — supervisory control: HMIs, engineering workstations
  • Level 3 — site operations: historians, SCADA servers
  • Level 3.5 — industrial DMZ
  • Levels 4–5 — enterprise IT

Modern architectures (cloud, IIoT) blur the levels, but the model remains useful for segmentation and for deciding where an OT SOC places its passive sensors.

Purdue model with typical OT SOC monitoring pointsLevels 0 to 5 of the Purdue reference model, with the industrial DMZ at level 3.5 and passive network sensors between levels 1–2, 2–3 and at the IDMZ, feeding the SOC.L5Enterprise networkInternet access, e-mail, cloudL4Business planning & logisticsERP, MES interfaces, IT servicesL3.5Industrial DMZJump hosts, patch & AV relays, data brokersL3Site operationsHistorian, SCADA servers, OT domainL2Supervisory controlHMI, engineering workstationsL1Basic controlPLC, RTU, safety controllers (SIS)L0Physical processSensors, actuators, drivesSOC
Passive sensor (SPAN/TAP) — Purdue model with typical OT SOC monitoring points

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