📡 IoT · Sequence
MQTT Publish/Subscribe Messaging
How MQTT messaging works between devices, a broker and applications: connect, subscribe, publish with QoS, retained messages and last will.
Drawing diagram…
What this diagram shows
- Devices and apps only talk to the broker, never to each other
- QoS 1 messages are acknowledged and resent if lost
- Last will tells subscribers when a device drops off
Prompt used
MQTT sequence: a sensor connects to the broker with a last-will message 'offline', a dashboard app subscribes to building/+/temperature, the sensor publishes a temperature reading with QoS 1 and the retained flag, the broker acknowledges (PUBACK) and forwards it to subscribers, a new subscriber immediately receives the retained last value, and when the sensor's connection drops the broker publishes its last will.
Mermaid code
sequenceDiagram participant S as Sensor participant B as MQTT Broker participant D as Dashboard App participant N as New Subscriber S->>B: CONNECT (last will: offline) B-->>S: CONNACK D->>B: SUBSCRIBE building/+/temperature B-->>D: SUBACK S->>B: PUBLISH building/a/temperature 26.4 (QoS 1, retained) B-->>S: PUBACK B->>D: 26.4 N->>B: SUBSCRIBE building/a/temperature B->>N: Retained value 26.4 Note over S,B: Connection lost B->>D: Last will: sensor offline
Related templates
IoT Telemetry Data Pipeline
How sensor readings travel from devices to dashboards and alerts: MQTT ingestion, stream processing, time-series storage and anomaly detection.
IoT Device Provisioning Sequence
How a new device joins the platform securely: claiming by the owner, certificate issue and its first connection to the MQTT broker.
IoT Platform Reference Architecture
A general-purpose IoT platform: device connectivity, device management, data processing, rules and the apps built on top.
IoT Edge Computing Deployment
Where processing happens in an edge IoT setup: devices, an on-site edge server running containers, and the cloud for fleet management and long-term storage.
Smart Home Automation Flow
How a smart home reacts to events: motion, door and temperature triggers run rules for lights, locks, AC and alerts.
IoT Device Lifecycle
Every state an IoT device goes through, from manufacture to decommissioning, including updates, faults and replacement.