You can follow the instructions in the AT command manual for how to use the MQTT-SN Client. The SARA-R422 manual including the MQTT-SN details has not yet been released but the commands are the same on both modules. Some simple examples to get you up and running quickly are listed below.
For the fastest network registration on your Thingstream SIM, we suggest to set AT+URAT=9,7. This speeds up the network scan time by disabling NBIoT where there are very few available networks.
This needs to be a unique value for your Thingstream domain. We suggest using the Identity value of your SN Thing which you can find on the Thing Details page of the management console.
Set server IP address and port
Set connection duration (seconds)
Using the MQTT-SN Client
Once you have completed the MQTT client configuration, you will need to set up the packet switched data configuration to use the TSUDP APN and you can proceed with the MQTT-SN commands.
Register a topic
Before you can publish to a normal topic, you need to register with with the broker and get back a topic ID.
Expect +UUMQTTSNC: 2,1,1 as a response to confirm the registration. The final argument in the response is the topic ID to use when you publish.
Expect +UUMQTTSNC: 4,1 as a response to confirm the publish. You will also now see a new device originated message in the activity tab for your Thing in the management console.
To receive messages on your module, you need to subscribe to a topic.
Expect +UUMQTTSNC: 5,1,0,1 as a response to confirm you have subscribed. You will also now see a new subscription in the activity tab for your Thing in the management console.
Now if you publish a message to "my/subscribe/topic " you will see it arrive on the module. You can use the "Send Message" function in the management console to send a test message. Check out the guide here to see how.
Read a received message
When the message arrives, you'll see +UUMQTTSNC: 9,1 in the terminal. You can read the message with the following command.