OPC UA or MQTT: which protocol to connect industrial data?

Before any AI or predictive maintenance project, data has to get out of the machines. Two protocols dominate this integration today: OPC UA and MQTT. The right question is not which to choose, but where to use each.

OPC UA: describing the machine

OPC UA (IEC 62541) is an industrial standard that carries values and their context: an information model describes the machine, its variables, their units and relationships. It includes authentication and encryption, and many recent PLCs expose it natively. It is historically client/server, with a publish/subscribe extension.

Strengths: semantics, cross-vendor interoperability, built-in security. Limits: heavier to implement, less suited to broadcasting to many consumers.

MQTT: distributing the data

MQTT is a very lightweight publish/subscribe messaging protocol: devices publish to a broker, applications subscribe to the topics they need. It is simple, bandwidth-efficient and decouples producers from consumers.

Strengths: lightweight, scalable, suited to constrained networks. Limits: it does not define data structure; conventions such as Sparkplug B or a Unified Namespace fill that gap.

The most common architecture

• Close to the machines, an edge gateway reads PLCs (OPC UA, Modbus, proprietary protocols) without modifying their programs.
• The gateway publishes contextualised data over MQTT to a broker.
• Historians, dashboards and analytics models consume the data, on site or on a sovereign platform.

Security by design

Every new connection is an attack surface: integration must fit OT network segmentation (outbound flows only, broker in an intermediate zone, encryption, device authentication). That is why our industrial data integration service is designed together with OT cybersecurity, and starts with a one-line pilot.