Custom Topic Communications

Introduction

IoTDA uses topics to communicate with devices connected using MQTT. There are custom topics and system topics. System topics are basic communication topics preconfigured on the platform. You can also customize topics on the platform based on service requirements.

Scenarios

• Devices publish messages to a custom topic, from which an application receives the messages using the data forwarding function.
• An application calls the API for delivering a message to a device to publish messages to a specified custom topic. Devices subscribe to this topic to receive messages from the server.

Topic Categories

Constraints

• You can define a maximum of 50 custom topics for a product model.
• Custom topics are only available for message communications.
• Max. length of a custom MQTT topic: 128 bytes.

Procedure

1. Access the IoTDA service page and click Access Console.
2. Select an MQTT product. On the product details page, click the Topic Management tab, select Custom Topic, and click Add Topic.
   Figure 1 Adding a custom topic
   

3. In the displayed dialog box, select device operation permissions and enter the topic name.
   Figure 2 Custom topic
   

   Table 2 Parameters

   Parameter	Description
   Name	The topic prefix is fixed at $oc/devices/{device_id}/user/. Replace {device_id} with the actual device ID during publishing and subscription. A custom topic must be in a slash-separated format. The value can contain 1 to 64 characters. Only digits, letters, underscores (_), and non-consecutive slashes (/) are allowed. Note: Custom topics do not support custom variables. For example, {type} in $oc/devices/{device_id}/user/setting/{type} is a variable and is not supported.
   Device Operation Permissions	Publish: Devices can report messages using this topic. A topic is carried in a device message during data transfer for better classification. Subscribe: Applications can specify a topic to deliver messages to devices. Publish and subscription: Devices can report and receive messages using this topic.
   Description	Provide a description of the topic.

4. Click OK.

   After the topic is added, you can modify or delete it in the custom topic list.

For details about how to use custom topics, see Using a Custom Topic for Communication. If a topic prefixed with $oc/devices/{device_id}/user/ cannot be used, you need to customize a topic. For details, see Migrating a Custom Topic to the Cloud.