How Industrial Systems Communicate: A Field Guide to OT Protocols and Vendors

Industrial plants do not run on one network protocol. A single facility typically speaks several at once, each serving a different layer of the operation: field devices exchanging real-time signals with controllers, engineering stations programming those controllers, supervisory systems collecting data from them, and cloud platforms receiving it all. Public discussion of OT security often blurs these layers together, which makes it hard to reason about what any given protocol actually does or where any given product actually sits. This briefing is a reference map. It explains, in plain terms, how the layers of an industrial system communicate, which protocols dominate each layer, who the major controller vendors are, and how vendors and protocols relate to each other. It is informational by design: it argues no thesis and evaluates no product.