Device Management and OTA System Overview

1. System Overview

This system supports real-time communication between each IoT device (e.g., sensors, controllers, etc.) and the central server. This communication is done via a protocol called MQTT, where devices periodically report status information and the server can send commands to devices as needed.

2. Key Concepts and Terms

• MQTT: A lightweight and fast messaging protocol for communication between devices and the server.
• link_id: A unique ID for identifying a device.
• Topic: The address structure used to deliver messages.

3. MQTT Topic Hierarchy

• l/{link_id}/h: Heartbeat
• l/{link_id}/s/{sensor_id}: Sensor data report
• l/{link_id}/s/{status_type}: Device status report
• l/{link_id}/e/{event_id}: Event report
• l/{link_id}/c/{command_id}/req: Server → Device command request
• l/{link_id}/c/{command_id}/res: Device → Server command response

4. Heartbeat

The device periodically notifies the server that it is operating normally.

• Format: l/{link_id}/h

• Payload:

  {
    "uptime": 1234567
  }

  • uptime: Elapsed time since the system booted (in milliseconds)

5. Sensor Data Report

The device sends measured sensor data to the server.

• Format: l/{link_id}/s/{sensor_id}

• Payload Example:

  • Number:

    23.5

  • JSON:

    {
      "value": 23.5,
      "unit": "C",
      "timestamp": 1621234567890
    }

6. Status Report

The device reports its operational or configuration status to the server.

• Format: l/{link_id}/s/{status_type}
• Example: Current mode, operational status, etc.

7. Event Report

The device sends specific events that occur to the server.

• Format: l/{link_id}/e/{event_id}
• Example: Button press, warning triggered, sensor error, etc.

8. Command Request and Response

8.1 Command Request (Server → Device)

• Format: l/{link_id}/c/{command_id}/req
• Example: Request to change settings, request to restart device, etc.

8.2 Command Response (Device → Server)

• Format: l/{link_id}/c/{command_id}/res

• Payload Format:

  {responseStatus}|{body}

  • Example:

    OK|{"message": "Completed"}

8.3 Possible Response Statuses

• OK: Command processed successfully
• UNPROCESSABLE: Unknown command
• ERROR: Error occurred during processing
• TIMEOUT: Timeout
• UNKNOWN: Other unknown error