Guide · Communication

MQTT & OPC UA — how machines exchange data.

Two protocols define industrial IoT: the lightweight MQTT and the data-rich OPC UA. They complement each other more than they compete.

Discuss a data project

MQTT — lightweight and scalable

MQTT is a lightweight publish/subscribe protocol: devices (publishers) send to a central broker (e.g. Mosquitto, HiveMQ); recipients (subscribers) subscribe only to the topics that interest them. Publishers and subscribers never communicate directly — which makes the model highly scalable.

Three delivery guarantees (QoS)

QoS 0 — at most once (fire and forget)
QoS 1 — at least once (with acknowledgement, retransmitted if needed)
QoS 2 — exactly once

OPC UA — data-rich and secure

OPC UA (OPC Foundation) is an industrial client/server protocol with a rich information model and built-in security — strong wherever interoperability and semantically described data matter.

Often the best solution: both

A proven combination uses OPC UA for the semantically rich, secure environment within the plant and MQTT as an efficient, scalable transport to the cloud — analysis, storage, visualization. For how this fits into the overall chain, see the IoT architecture.

Frequently Asked Questions

Which QoS should I choose?

QoS 0 for non-critical, frequent readings (where loss is acceptable), QoS 1 for important events (duplication possible), QoS 2 for cases where every message must arrive exactly once. Higher QoS costs latency and overhead.

MQTT or OPC UA?

It depends on the task — and often the answer is both. OPC UA for rich, secure machine data on site, MQTT for lightweight transport to the cloud. We choose the stack to suit the system.

Sources: HiveMQ — OPC UA vs. MQTT Sparkplug, EMQ — IIoT Protocols Compared.