MQTT

MQTT (Message Queuing Telemetry Transport, ISO/IEC 20922) is a lightweight publish/subscribe messaging protocol designed for constrained devices and unreliable networks. It is the dominant wire protocol for edge-to-cloud telemetry in IIoT and is the transport beneath many connected-product use cases that feed digital twins and product analytics.

What it covers

• Pub/sub topology with a broker decoupling producers from consumers.
• QoS levels 0–2 trading throughput for delivery guarantees (at-most-once, at-least-once, exactly-once).
• Retained messages and last-will/testament for durable state and offline awareness.
• Tiny wire footprint suited to battery- and bandwidth-constrained sensors.
• Sparkplug B and OPC UA PubSub profiles that layer typed payloads on top of raw MQTT.

Relationships (see sidebar)

• Dependency of the Industrial Connectivity, IoT Platform, and Digital Twin capabilities — telemetry into the digital thread typically rides MQTT.
• Supports the Manufacturing Execution and Service and Maintenance processes.
• Implemented by PTC ThingWorx, PTC Kepware, and Siemens Insights Hub.
• Frequently paired with OPC UA (OPC UA PubSub can run over MQTT).