Gateway and sub-device
Tips
In IoT systems, a gateway connects devices that cannot directly access the cloud platform. The gateway forwards data and performs protocol conversion.
Communication between a gateway and the cloud platform includes:
- Communication between the gateway device itself and the cloud platform, such as reporting gateway status and properties or receiving control commands from the cloud.
- Communication between gateway sub-devices and the cloud platform. For example, a Zigbee temperature and humidity sensor reports data through the gateway, or an RS485/Modbus eight-channel relay receives real-time commands through the gateway. These sub-device messages are forwarded by the gateway.
1. Terms
1.1 Device types under a product
Direct device
A device with an IP address that can connect directly to the IoT platform. It usually has its own network module, such as Wi-Fi or 4G, and can access the cloud through the Internet.
Gateway sub-device
Also called a slave device. It does not connect to the IoT platform directly. Instead, it accesses the platform through a gateway device.
Gateway device
A direct device that can mount sub-devices. The gateway has a sub-device management module, maintains topology relationships, and synchronizes the gateway-sub-device topology to the cloud.
Device communication mode
The physical communication mode used by the device, such as Wi-Fi, 2G/3G/4G/5G, BLE, Zigbee, LoRa, RS485, or Ethernet.
Sub-device number
Also called the sub-device address. It identifies a sub-device so the cloud platform and gateway can distinguish different sub-devices. The sub-device address must be unique under the same gateway.
Examples:
- A Modbus sub-device address is the slave station number.
- A BLE sub-device usually uses the module chip UUID.
- An OPC UA sub-device can use the MAC number.
- A Zigbee sub-device can use a custom number.
1.2 Gateway and sub-device protocol combinations
The protocols listed below are device-layer protocols, not transport protocols such as MQTT or TCP. For example, an OPC UA sub-device communicates with the gateway through OPC UA, and the gateway converts OPC UA to MQTT for cloud communication.
- Custom: the sub-device and gateway use another standard or private protocol.
- Modbus: the communication protocol between the sub-device and gateway is Modbus.
- OPC UA: the communication protocol between the sub-device and gateway is OPC UA.
- Zigbee: the communication protocol between the sub-device and gateway is Zigbee.
- BLE: the communication protocol between the sub-device and gateway is BLE.
2. Products
Gateways and sub-devices are both devices. Their difference is the product type they belong to:
- A gateway device must belong to a gateway product.
- A gateway sub-device must belong to a gateway sub-device product.
Configuration options
Direct access
When creating the product, select direct device as the device type. Define the thing model and configure Modbus parameters for this product.
Gateway with sub-devices
Create the gateway product first and select gateway device as the device type. The gateway product can omit thing model and Modbus configuration if the gateway itself does not collect additional data.
Then create the sub-device product, select gateway sub-device as the device type, and configure the thing model and Modbus parameters for the sub-device product.
After both products are created, create the gateway device and sub-devices. Bind the sub-devices on the gateway device page and set the sub-device slave addresses.
Tips
For both direct access and gateway sub-device access, if polling is selected, configure polling tasks on the direct device or gateway sub-device detail page.
Create a sub-device product
Configure the thing model
Configure Modbus parameters
Configure Modbus IO registers
Configure Modbus data registers
Create a sub-device
3. Create a gateway product
Optional: configure the gateway product thing model
If the gateway has additional properties to collect, configure them in the gateway product thing model.
Create a gateway device
Bind sub-devices
The gateway and sub-device topology is now established.