Architecture & tech
OPC UA vs Modbus vs MQTT: Choosing Industrial Protocols in Plain Language
What each protocol is good at, where it struggles, and how they work together in one plant.
Trikaan Research & Engineering4 min read
KEY TAKEAWAYS
- Modbus is simple and everywhere, but carries little meaning.
- OPC UA offers structured data and built-in security.
- MQTT is a lightweight publish-subscribe transport, ideal from edge to cloud.
- Most plants use more than one, joined at an edge gateway.
Anyone connecting machines soon meets an alphabet of protocols. The choice affects cost, security and how much useful data you get.
Here is what the three most common options do, in plain language.
At a glance
| Protocol | Strengths | Limits | Typical use |
|---|---|---|---|
| Modbus (RTU/TCP) | Simple, widely supported, older devices | No data model, little security | Meters, drives, legacy PLCs |
| OPC UA | Structured data, security, discovery | More complex setup | Modern PLCs, SCADA, MES |
| MQTT | Lightweight, publish-subscribe, scales well | Transport only; needs a data convention | Edge to cloud, sensors |
Modbus
Modbus reads registers — numbers at addresses. You need a register map to know that address 40021 is motor current in tenths of an amp. It is reliable and supported by almost every device, but security must be provided by the network around it.
OPC UA
OPC UA exposes structured information with names, types and relationships, and supports encryption and authentication. It is the preferred choice for modern equipment where available.
MQTT
MQTT is a messaging protocol: devices publish messages to topics and subscribers receive them via a broker. It is efficient over unreliable networks and works well from edge gateways to cloud platforms. Pair it with a clear topic and payload convention.
How they work together
A common pattern: the edge gateway reads Modbus from older devices and OPC UA from modern PLCs, normalises names and units, buffers the data and publishes it over MQTT or HTTPS to the cloud — outbound only.
Frequently asked questions
Which protocol is most secure?
OPC UA has built-in security features; Modbus relies on network controls; MQTT should run over TLS with authentication.
Can we use MQTT directly from PLCs?
Some modern PLCs support it; often an edge gateway handles the conversion.
Is OPC UA always better?
It is richer, but older devices may only support Modbus. Use what each device supports.
Do we need a broker for MQTT?
Yes — publishers and subscribers communicate through a broker.
- #OPC UA vs MQTT
- #Modbus vs OPC UA
- #industrial communication protocols
- #IIoT protocols
- #PLC data protocols
Trikaan Research & Engineering
Trikaan
Written by the researchers and engineers who build Anvaya, ASTR and Seed Track, with input from Trikaan's delivery and engineering teams.
