Systems Integration, Networks, and Digital/Data Infrastructure
Integration work spans protocols, networks, and data infrastructure. Understand the Purdue/ISA-95 hierarchy from field devices through control, supervisory, operations, enterprise, and external zones; segmentation and conduits protect control systems. Know common protocols: Modbus is simple and has no built-in security; EtherNet/IP, PROFINET, and PROFIBUS differ in determinism and diagnostics; HART is a field-device digital signal over the analog loop; OPC Classic relies on DCOM, while OPC UA provides platform-independent, secure client/server and information modeling. SCADA, DCS, PLC, historian, and MES roles must be distinguished. IP addressing, subnetting, VLANs, firewalls, DMZs, time synchronization, redundancy, and backup/restore belong in the design. Latency, jitter, and determinism matter for control traffic; not every Ethernet network is suitable for every control loop.
Traps include assuming VLANs alone provide security, placing historians or engineering workstations directly on the control network, treating Modbus as authenticated, confusing OPC UA with OPC DA, and ignoring time sync when correlating alarms.
Worked example: a /24 IPv4 subnet has 256 addresses; two are reserved for network and broadcast, leaving 254 usable host addresses. For a small control VLAN that is ample, but a flat /24 spanning PLCs, HMIs, and engineering laptops is a segmentation failure. Rule of thumb: put a DMZ between OT and IT, allow only required bidirectional flows, and keep time sources consistent.