Glossary · Industrial communication
MQTT
Also known as: MQ Telemetry Transport
German: MQTT
In IIoT communication, MQTT is a lightweight publish-subscribe messaging protocol in which clients publish messages to topics on a broker, which forwards them to all clients that have subscribed to those topics. It is an OASIS standard; version 3.1.1 is also published as ISO/IEC 20922.
- Industrial communication
- Standards
In one sentence
MQTT is a lightweight publish-subscribe protocol where clients exchange messages on topics via a broker (OASIS standard, ISO/IEC 20922).
Example
Edge gateways publish machine states to the topic plant1/line3/filler/state on an MQTT broker, and the MES and a dashboard subscribe to it.
Explained in context
Context cards connect this term with others to answer one question. Also in British English and German.
How it applies
- Engineering: MQTT decouples producers and consumers: publishers don't know who subscribes. It works well over unreliable or low-bandwidth links and through firewalls, because clients open outbound connections to the broker.
- Design: MQTT defines three QoS levels (at most once, at least once, exactly once) and retained messages, but no payload format. Topic structure and payload schemas must be designed; Sparkplug B is one standardized convention.
- Security: TLS, client authentication and topic-level authorization have to be configured on the broker. An open broker lets anyone read and publish.
- Documentation: The documentation team documents the topic tree, payload schemas, QoS and retain settings, and the broker's access rules.
MQTT vs. OPC UA
MQTT is a transport for messages with no built-in information model. OPC Unified Architecture (OPC UA) provides a rich information model and services; OPC UA PubSub can use MQTT as a transport. Protocol vs. data model again: MQTT moves the bytes, the payload schema gives them meaning.