Cloud-to-device communications guidance

IoT Hub provides three options for device apps to expose functionality to a back-end app:

  • Direct methods for communications that require immediate confirmation of the result. Direct methods are often used for interactive control of devices such as turning on a fan.
  • Twin's desired properties for long-running commands intended to put the device into a certain desired state. For example, set the telemetry send interval to 30 minutes.
  • Cloud-to-device messages for one-way notifications to the device app.

Here is a detailed comparison of the various cloud-to-device communication options.

Direct methods Twin's desired properties Cloud-to-device messages
Scenario Commands that require immediate confirmation, such as turning on a fan. Long-running commands intended to put the device into a certain desired state. For example, set the telemetry send interval to 30 minutes. One-way notifications to the device app.
Data flow Two-way. The device app can respond to the method right away. The solution back end receives the outcome contextually to the request. One-way. The device app receives a notification with the property change. One-way. The device app receives the message
Durability Disconnected devices are not contacted. The solution back end is notified that the device is not connected. Property values are preserved in the device twin. Device will read it at next reconnection. Property values are retrievable with the IoT Hub query language. Messages can be retained by IoT Hub for up to 48 hours.
Targets Single device using deviceId, or multiple devices using jobs. Single device using deviceId, or multiple devices using jobs. Single device by deviceId.
Size Up to 8 KB requests and 8 KB responses. Maximum desired properties size is 8 KB. Up to 64 KB messages.
Frequency High. For more information, see IoT Hub limits. Medium. For more information, see IoT Hub limits. Low. For more information, see IoT Hub limits.
Protocol Available using MQTT or AMQP. Available using MQTT or AMQP. Available on all protocols. Device must poll when using HTTPS.

Learn how to use direct methods, desired properties, and cloud-to-device messages in the following tutorials: