Marketplace:Device Access-customized Message Sending and Receiving

Devices that use the MQTT protocol to access the IoT platform communicate with the platform by publishing messages to and subscribing to topics. Topics are divided into system topics, object model topics, and custom topics, of which custom topics need to be defined by users in the console. This article introduces how devices use custom topics to communicate with the IoT platform for uplink and downlink messages, as well as the communication steps between the IoT platform and the business server.

Wi-Fi Smart Socket Case

In this example, a Wi-Fi smart socket product is used as an example. The device uses the MQTT protocol to access the IoT platform, receives instructions issued by the IoT platform by subscribing to a custom topic, and reports current, voltage, and power data by publishing messages to the custom topic. The IoT platform forwards the received data to the user's business server through AMQP or Kafka. The business server calls the northbound API provided by the IoT platform to publish messages to the custom topic. The device receives instructions through the subscribed topic to control the smart socket.

Console operation steps

1. Create a product

In the left navigation bar, select Product Development to enter the product list page, click the Create Product button in the upper right corner to enter the Create Product page, enter the product information, and generate a unique product ID, namely ProductID, hereinafter referred to as PID.

Enter the product name, select Directly connected device, One device and one password, Alibaba Cloud IoT customization, click the Create Product button below to create the product and generate a unique product ID, i.e. ProductID.

2. Custom product topics

In the left navigation bar, select Product Development, enter the product list page, select the corresponding product, click the Continue Development button on the right, and enter the product details.

On the Topic Management tab of the product details, click Custom Topic and click the Add Custom Topic button to add a Topic.

In this example, the following two Topic classes are defined：

• Device publish message Topic: /TbSCo****/${deviceName}/user/devmsg, permission is publish. Used by the device to send messages (data) to the IoT platform, the data format can be defined by the user.

• Device subscription message topic:/TbSCo****/${deviceName}/user/cloudmsg, with the permission of subscription. When developing on the device side, subscribe to this topic. When the cloud sends a message downward, the message is sent to the device through this topic.

3. Add a device

In the left navigation bar, click Device Management > Device List to enter the Device Management page, and click the Add Device button in the upper right corner.

4. Get the device MQTT connection parameters

In the left navigation bar, click Device Management > Device List to enter the device management page. Select the corresponding device and click View to enter the device details.

On the device details page, click Connection Parameters in the upper right corner to view the MQTT connection parameters.

5. Configure server subscription (optional)

If you need to monitor the data reported by the device, the device online status, etc. on your own server, You need to create a vpc peer connection and create a server subscription

Use Postman to simulate a device

1. Introduction to Postman

Postman is a powerful interface testing tool that is familiar to every developer. It is mainly used to test HTTP requests and supports various HTTP request methods, including GET, POST, PUT, DELETE, etc. It can help developers simulate various HTTP requests initiated by users and verify whether the response results meet expectations. As the MQTT protocol is gradually used in various applications, Postman now also supports debugging the MQTT protocol.

2. Postman MQTT configuration

Postman is mainly used for testing HTTP protocol interfaces. It now also supports debugging of WebSocket, Socket.io, GraphQL, gPRC, and MQTT protocols. When Postman is opened, the default is usually the HTTP protocol debugging page. Click the "protocol icon" in the upper left corner to switch to the MQTT protocol debugging page.

After switching to the Postman MQTT debugging page, configure the MQTT parameters according to the following figure to simulate the device to be connected. Note that there should be no spaces before and after.

3. Simulate device online

According to the introduction of Postman MQTT configuration in the previous step，fill in the obtained MQTT connection parameters into the input box as required and click Connect.

If Connected is displayed as shown in the figure, it means that a device has been simulated using Postman and connected to the IoT platform using the MQTT protocol. Refresh the device details page to see that the device is online and the online time is displayed.

4. Simulate the device to send data to the platform

4.1. Defines the protocol for sending data

The Wi-Fi smart socket reports voltage and current data to the IoT platform at regular intervals. This example does not use the object model to report data, but uses a custom data protocol format to report data. The custom protocol format is as follows:

4.2. Determine the topic that the device publishes

Send data 05 CC 60 02 49 F0 to the IoT platform through the custom topic /${ProductID}/${HardwareID}/user/devmsg in the custom product topic.

4.3. Postman simulates sending data

1. Prerequisites: According to the configuration in the simulated device online, first put the device online；

2. Switch to the Message tab of Postman, enter the message to be sent and the Topic to be sent, and click the Send button;

3. In the left navigation bar, select Log Service and refresh the page. If you can see the data just sent, it means that the data has been reported successfully.

5. The platform sends instructions to the simulated device

5.1. Define the platform's instruction protocol

The Wi-Fi smart socket needs to control the socket switch according to the platform instructions and query the voltage and current parameters according to the instructions. This example does not use the object model to report data, but uses a custom data protocol format to report data. The custom protocol format is as follows:

5.2. Determine the topic you need to subscribe to

Subscribe to the topic /${ProductID}/${HardwareID}/user/cloudmsg defined in the custom product topic to receive control instructions sent by the platform to the device.

5.3. Simulate device subscription topic

Switch to the Topics tab of Postman, enter the Topic you want to subscribe to, click the SUBSCRIBE switch on the right to start subscribing. If Subscibed appears below, it means that the subscription is successful. You can check it in the Topic list of platform device details.

In the left navigation bar, click Device List to find the corresponding device. Under the Device Details Topic List tab, if the Topic you just subscribed to appears, it means that the Topic subscription is successful. You can send instructions to the device through the Topic.

5.4. The platform sends instructions to the simulated device

After the device successfully subscribes to the Topic, you can find the corresponding Topic under the Topic List tab of the device details, click Publish Message, and enter the command to be sent in the pop-up dialog box: 01 01, which means turning on the smart socket.

On the Postman page, you can see the sent command message 01 01, indicating that the control command was sent successfully. If it is a real device, you can parse the corresponding command and execute the corresponding logic.