MQTT (Message Queuing Telemetry Transport) has become the de facto protocol for Industrial IoT data collection. Originally designed for satellite communication in the 1990s, it is now the backbone of IIoT platforms from Ignition Edge to AWS IoT Core.

Why MQTT Fits IIoT

MQTT’s design choices align perfectly with industrial field conditions:

  • Lightweight: Fixed header of just 2 bytes. Minimal bandwidth on cellular or satellite links.
  • Publish/Subscribe: Devices publish to topics; subscribers receive data. Decouples producers from consumers.
  • QoS levels: Three guaranteed delivery options match application requirements.
  • Persistent sessions: Broker stores messages for offline subscribers.
  • Last Will and Testament (LWT): Broker publishes a predefined message when a client disconnects unexpectedly – instant fault detection.

QoS Levels Explained

  • QoS 0 – Fire and Forget: No acknowledgement. Fastest, lowest overhead. Use for high-frequency sensor data where occasional loss is acceptable.
  • QoS 1 – At Least Once: Acknowledged delivery. Message may arrive more than once. Use for alarm events and production counts.
  • QoS 2 – Exactly Once: Four-way handshake guarantees one delivery. Highest overhead. Use for financial transactions and safety-critical commands.

MQTT Sparkplug B

Raw MQTT has no standard message format – each vendor invents their own. Sparkplug B solves this with a standardized payload schema for SCADA and historian data:

  • Defined topic namespace: spBv1.0/Group/DDATA/Node/Device
  • Protobuf-encoded payloads with timestamps and data quality
  • Birth/death certificates for device state management
  • Used by Ignition, AVEVA, Inductive Automation, and most modern IIoT platforms

Security Considerations

Plain MQTT has no built-in security. In industrial deployments:

  • Always use MQTT over TLS (port 8883) in production
  • Implement client certificate authentication or username/password
  • Use an MQTT broker with ACL (Access Control Lists) to restrict topic access per device
  • Never expose an unauthenticated MQTT broker to the internet

Popular MQTT Brokers

  • Mosquitto: Open-source, lightweight, ideal for edge deployments
  • HiveMQ: Enterprise-grade, clustering, Sparkplug B native support
  • EMQX: High performance, cloud-native, supports millions of connections
  • AWS IoT Core / Azure IoT Hub: Cloud-managed, no broker to operate