MQTT integration

Where it is used

Industrial gateways publish PLC tags, building controllers forward BACnet points, BLE and LoRaWAN gateways forward sensor readings, and fleet telematics units send position and CAN data. Brokers such as Eclipse Mosquitto, EMQX, HiveMQ or cloud IoT services sit in the middle. The integration uses MQTT 3.1.1 or 5.0 depending on broker capabilities.

Transport and security

Connections should use TLS, typically on port 8883, with server certificate validation. Clients authenticate with username and password or with client certificates, and broker access control lists restrict the integration to read-only subscriptions on specific topic filters. Plain port 1883 is only appropriate inside a closed test network.

Prerequisites

• Broker host, port, protocol version and TLS details.
• A dedicated client identity with subscribe-only permissions.
• The topic hierarchy, for example site/area/asset/measurement, and the payload schema for each topic.
• A decision on QoS level and whether persistent sessions should be used.

Payload meaning

Payloads may be JSON objects, Sparkplug B protobuf messages, or plain values. For JSON, the mapping identifies the value field, unit, and the device timestamp field if one exists. Sparkplug B adds birth and death certificates, metric names, datatypes and sequence numbers, which help detect missed messages and offline nodes. Retained messages provide the last known value on subscription but are old data, so their source time is preserved rather than replaced with the receive time.

Delivery and limitations

• QoS 1 gives at-least-once delivery, so duplicates are possible and are handled by identity and timestamp.
• If the platform database is unavailable while messages arrive, messages can be lost unless the broker retains them in a persistent session; recovery behaviour is checked during validation.
• Wildcard subscriptions on busy brokers can produce far more traffic than intended.
• MQTT carries no units or semantics; an undocumented payload cannot be interpreted reliably.
• Broker interoperability is confirmed per product during the project, not assumed from the catalogue.

Related

Read the MQTT guides for broker design, and compare with OPC UA where a direct server connection is available.

Further reading

• What is mqtt guide
• Mqtt protocol guide
• Mqtt broker guide
• All resources
• Connector catalogue
• Industries
• Products

Catalogue listings describe possible integration paths. Implementation and validation status is confirmed for each source during project scoping; no certification, service level or price is implied by this page.