| title | description | services | documentationcenter | author | manager | editor | ms.assetid | ms.service | ms.devlang | ms.topic | ms.tgt_pltfrm | ms.workload | ms.date | ms.author |
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Azure IoT Hub cloud to device communications guidance | Microsoft Docs |
Azure IoT Hub developer guide - guidance on when to use direct methods, device twin's desired properties, or cloud-to-device messages. |
iot-hub |
fsautomata |
timlt |
1ac90923-1edf-4134-bbd4-77fee9b68d24 |
iot-hub |
multiple |
article |
na |
na |
11/09/2016 |
elioda |
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 their result, usually interactive control of the device, e.g. turn 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 (C2D) 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 | C2D messages | |
|---|---|---|---|
| Scenario | Commands that require immediate confirmation, e.g. turn 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. 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 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 8KB requests and 8KB responses. | Maximum desired properties size is 8KB. | Up to 256KB messages. |
| Frequency | High. Refer to IoT Hub limits for more information. | Medium. Refer to IoT Hub limits for more information. | Low. Refer to IoT Hub limits for more information. |
| Protocol | Available on MQTT and AMQP. | Currently available only when using MQTT. | Available on all protocol. Device has to poll when using HTTP. |
Learn how to use direct methods, desired properties, and cloud-to-device messages in the following tutorials:
- Use direct methods, for direct methods;
- Use desired properties to configure devices, for twin's desired properties;
- Send cloud-to-device messages, for cloud-to-device messages.