Explanation IoT Hub provides three options for device apps to expose functionality to a back-end app: * 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. * 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. * Cloud-to-device messages for one-way notifications to the device app. Reference: https://docs.microsoft.com/en-us/azure/iot-hub/iot-hub-devguide-c2d-guidance