Add info to use MQTT-WS if MQTT port is blocked. GH issue 45893 and 39536

Author: JimacoMS3

articles/iot-hub/iot-hub-mqtt-support.md

@@ -28,6 +28,24 @@ A device can use the MQTT protocol to connect to an IoT hub using any of the fol
 * Libraries in the [Azure IoT SDKs](https://github.com/Azure/azure-iot-sdks).
 * The MQTT protocol directly.
 
+MQTT protocol uses port 8883. This port is blocked in many corporate and educational networking environments. If you can't open port 8883 in your firewall, we recommend using MQTT over Web Sockets. MQTT over Web Sockets communicates over port 443, which is almost always open in networking environments. When using the Azure IoT SDKs, you typically specify the transport or protocol type in the call to create a client as in the following examples.
+
+```csharp
+private static TransportType s_transportType = TransportType.Mqtt_WebSocket_Only;
+DeviceClient deviceClient = DeviceClient.CreateFromConnectionString(s_deviceConnectionString, s_transportType);
+```
+
+```node.js
+var Client = require('azure-iot-device').Client;
+var Protocol = require('azure-iot-device-mqtt').MqttWs;
+var client = Client.fromConnectionString(deviceConnectionString, Protocol);
+```
+
+```python
+from azure.iot.device.aio import IoTHubDeviceClient
+device_client = IoTHubDeviceClient.create_from_connection_string(conn_str, websockets=True)
+```
+
 ## Using the device SDKs
 
 [Device SDKs](https://github.com/Azure/azure-iot-sdks) that support the MQTT protocol are available for Java, Node.js, C, C#, and Python. The device SDKs use the standard IoT Hub connection string to establish a connection to an IoT hub. To use the MQTT protocol, the client protocol parameter must be set to **MQTT**. By default, the device SDKs connect to an IoT Hub with the **CleanSession** flag set to **0** and use **QoS 1** for message exchange with the IoT hub.

articles/iot-hub/quickstart-send-telemetry-dotnet.md

@@ -45,6 +45,8 @@ az extension add --name azure-cli-iot-ext
 
 Download the Azure IoT C# samples from https://github.com/Azure-Samples/azure-iot-samples-csharp/archive/master.zip and extract the ZIP archive.
 
+Make sure that port 8883 is open in your firewall. The sample in this quickstart uses MQTT protocol, which communicates over port 8883. This port may be blocked in some corporate and educational network environments. For more information and ways to work-around this issue, see [Connecting to IoT Hub (MQTT)](iot-hub-mqtt-support.md#connecting-to-iot-hub).
+
 ## Create an IoT hub
 
 [!INCLUDE [iot-hub-include-create-hub](../../includes/iot-hub-include-create-hub.md)]