OT Networks and Segmentation

Physical layer, addressing, segmentation and the security boundary between plant and enterprise. The layer blamed for everything and instrumented for nothing.

Where this sits

This is ISA-95 Level 3-4. Naming the layer matters, because the most expensive mistakes in modernization come from solving a problem at the wrong level of the stack.

What we actually do here

• Assess what is installed, what version it is on, and what depends on it
• Decide what to modernize, in what order, and what to deliberately leave alone
• Write scope and acceptance criteria that a vendor cannot quietly reinterpret
• Review design and code before commissioning, not after
• Make sure the plant can support the result once the project team has gone

Device-level networks

Below the plant network sits the device level, and in a lot of plants that still means a fieldbus installed twenty years ago. Those segments are usually working, usually undocumented, and usually the thing that blocks a project the moment somebody needs data off them.

• DeviceNet, the CAN-based device-level fieldbus behind a large North American installed base. How it works, the cable rules that cap its speed, what fails in the field, and how to decide whether to migrate or hold

Platform position

Vendor-independent, but not opinion-neutral. When one platform is clearly better for a given situation, we will say which and why. When the honest answer is that the existing system is fine and the money is better spent elsewhere, that is the recommendation.