MQTT vs OPC UA: getting machine data into IT systems

How MQTT and OPC UA differ in communication model, data description and security, and which ICP DAS devices support each protocol.

Udgivet 28. oktober 2026

MQTT vs OPC UA: getting machine data into IT systems — Foto: Brian Kostiuk · CC0 · Wikimedia Commons

Most automation projects eventually have to deliver machine data to systems outside the control network: a SCADA server, an MES, a database or a cloud platform. Two protocols dominate that task. This article compares MQTT vs OPC UA in practical terms: how each one communicates, how data is described and secured, and which systems typically receive it. It ends with an overview of ICP DAS devices that support one or both protocols.

Two different communication models

MQTT is a publish/subscribe protocol. Devices connect as clients to a central broker and publish messages to topics such as site1/line2/press4/temperature. Applications that subscribe to a topic receive its messages. Publishers and subscribers do not need to know about each other. The default ports are 1883 for plain TCP and 8883 for MQTT over TLS.

OPC UA is mostly used as client/server. The device or gateway runs an OPC UA server, and a client such as a SCADA system connects to it, browses the address space, reads and writes values and subscribes to changes. The default port is 4840. The specification also defines a publish/subscribe mode, but most installed servers and clients use client/server.

This matters for network design. With MQTT the field device opens the connection, which suits sites behind NAT or a firewall that only allows outgoing traffic. With OPC UA client/server, the client must be able to reach the server, so both are usually on the same network or connected through a VPN.

Information model versus payload

MQTT transports bytes. The protocol does not define what a message contains, so topic structure, payload format (often JSON), units and timestamps must be agreed between sender and receiver. Conventions such as Sparkplug B add a defined payload, but only if both sides support them.

OPC UA includes an information model. Each value is a node with a data type, a timestamp, a status code and optional attributes such as engineering unit and description. A client can browse the server to find out what is available, without a separate register list.

In practice, MQTT is quick to set up and flexible, but documenting topics and payloads is your job. OPC UA takes more configuration on both sides, but the data describes itself.

Security

MQTT relies on TLS for encryption, user name and password or client certificates for authentication, and access rules in the broker that control who may publish or subscribe to which topics. OPC UA has security built into the protocol: application certificates, the security modes None, Sign and SignAndEncrypt, and user authentication. In both cases the protection only works when it is configured. A broker on port 1883 without authentication, or an OPC UA endpoint with security mode None, is open to anyone who can reach it.

MQTT vs OPC UA at a glance

	MQTT	OPC UA
Model	Publish/subscribe through a broker	Client/server (PubSub optional)
Connection direction	Device connects out to the broker	Client connects to the server in the device
Default ports	1883, 8883 (TLS)	4840
Data description	Topics and payload defined by the user	Information model with types, units, timestamps and status
Delivery options	QoS 0, 1 and 2, retained messages, last will	Subscriptions with sampling and publishing intervals
Typical receivers	Brokers, cloud IoT services, databases, IT applications	SCADA, MES, historians, HMIs with an OPC UA client

Choosing for your project

Choose MQTT when many distributed devices send data to a central or cloud system, when sites connect over 4G or the Internet, or when IT already runs a broker.
Choose OPC UA when a SCADA, MES or historian on the plant network should read structured data through its OPC UA client.
Use both when the same data is needed on the plant floor and in IT. A communication server can serve OPC UA to SCADA and publish the same values to a broker.

Check what the receiving system supports before choosing field hardware. The receiver usually decides the protocol.

ICP DAS devices with MQTT and OPC UA

Both protocols in one device

The UA series communication servers (UA-2241M, UA-2841M, UA-5231M and UA-7231M) read data over Modbus TCP, Modbus RTU/ASCII, MQTT and EtherNet/IP and provide it through an OPC UA server, MQTT and SNMP at the same time. They include an MQTT broker, write data to databases such as MS SQL, MySQL and MariaDB with offline data recovery, and support HTTPS, an OpenVPN client and IP whitelists.

ICP DAS OPC UA I/O modules such as the U-7526M (AI, AO, DI and DO) and U-7544M (8 DI and 8 DO), combine built-in I/O with an OPC UA server and client, an MQTT client and a RESTful API that can run simultaneously. They have a two-port Ethernet switch, can be powered over PoE and support IF-THEN-ELSE rules.

MQTT at device level

WISE edge controllers such as WISE-5231M and WISE-2841M: MQTT client with publish, subscribe and SSL, plus Modbus TCP/RTU and SNMP.
WISE-75xxM I/O modules such as WISE-7526M: MQTT client (non-SSL) and Modbus TCP.
ET-2200 Ethernet I/O such as ET-2217: publishes I/O status, subscribes to topics and reconnects automatically.
ETS-7200 cybersecurity I/O such as ETS-7255: MQTT with optional TLS, Modbus TCP/TLS and HTTPS.
MQ-7200M modules such as MQ-7244M: MQTT 3.1 and Modbus TCP.
CL-200 data loggers such as CL-202-E for CO2, temperature and humidity: Modbus TCP and MQTT over Ethernet.

On the receiving side, BRK-2841M is a dedicated MQTT broker for MQTT 3.1, 3.1.1 and 5.0 with QoS, retained messages, last will, authentication, encryption and bridging. It writes to databases such as MySQL and buffers data on microSD during outages.

OPC UA in controllers

Win-GRAF PACs such as XP-9188-IoT and RPAC-2658M run IEC 61131-3 programs and include an OPC UA server, so control and data access are handled in one device.

Send us a description of your data sources and the receiving system, and our technical sales team will suggest a suitable combination.

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