title	description	author	ms.service	services	ms.topic	ms.date	ms.author
Azure IoT Hub cloud-to-device options \| Microsoft Docs	Developer guide - guidance on when to use direct methods, device twin's desired properties, or cloud-to-device messages for cloud-to-device communications.	fsautomata	iot-hub	iot-hub	conceptual	01/29/2018	elioda

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	Maximum direct method payload size is 128 KB.	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:

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