MQTT gateway devices communicate with IoT Platform through custom topics. IoT Platform passes through all upstream and downstream device data.
Topics
IoT Platform communicates with gateway devices through MQTT topics. You must define custom topics that comply with the standard MQTT protocol specifications. For more information, see What is a topic.
A device uses the same custom topic for both sending upstream data and receiving downstream data.
The following table compares topics on IoT Platform with those in the standard MQTT protocol.
|
Item |
IoT Platform |
Standard MQTT protocol |
|
Length |
The topic must be 1 to 128 characters in length. |
The topic can be up to 65,535 characters in length. |
|
Character set |
The topic can contain only letters, digits, and underscores (_). |
The topic can contain UTF-8 characters. No other limits exist. |
Limits
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An MQTT gateway device can subscribe to up to 100 topics.
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If you set the Device Operation Authorizations parameter of a topic category to Subscribe, you can specify the
plus sign (+)andnumber sign (#)wildcard characters in the topic category to allow devices to subscribe to multiple topics at the same time. For more information about how to use wildcard characters, see Custom topics with one or more wildcard characters.
Upstream communication: devices to IoT Platform
A device publishes messages to a custom topic. IoT Platform receives the messages through an AMQP server-side subscription or the data forwarding feature.
When you configure data forwarding rules, note the following items:
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Only the new version of the data forwarding feature supports gateway devices. For more information, see Configure a data forwarding parser.
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Messages cannot be forwarded between IoT Platform gateway products and devices and IoT Platform common products and devices.
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When you forward the data of a gateway device to another topic, you must configure the deviceName parameter. For more information, see Functions to forward data to data destinations.
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To specify a source topic for data forwarding, enter the topic name. For more information, see Add a data source.
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Server-side subscriptions support only the Device Upstream Notification, Device Status Change Notification, and Device Changes Throughout Lifecycle message types. For more information, see Configure AMQP server-side subscription.
Downstream communication: IoT Platform to devices
IoT Platform calls the Pub operation to publish messages to a custom topic. Devices receive the messages by subscribing to the topic.