Applications use two primary mechanisms to send commands to IoT devices, cloud-to-device messaging and direct methods.

• Applications send cloud-to-device messages to device-specific message queues on the IoT platform for devices to read when they're connected. The devices decide when to read the messages.

• Applications invoke direct methods directly on connected devices, using a request-response pattern over dedicated IoT device endpoints.

This article discusses characteristics of cloud-to-device messaging and direct methods. The article also describes how to use direct methods with protocol gateways and connected standby devices.]

https://learn.microsoft.com/en-us/azure/architecture/example-scenario/iot/cloud-to-device