MQTT Connection keeps getting disconnected/closed while publishing or subscribing to topics using LTE Modem

Question

- I'm using Quectel modem BG95 with a host MCU to connect to AWS IoT core and publish to topics and subscribe to topics as well.
- I used to get an error occasionally that closed the MQTT connection exactly while doing pub/sub operations and connection had to be re-established , but that was very rare.
- However, since the last few days I have been running tests on multiple devices (using same IoT core endpoint) and have  been getting this MQTT dis-connection on each pub or sub operation. I am attaching a log for review.
- To me it seems a server side issue since I have tried it with multiple modems and previous versions of firmware.

```
[While publishing to topic]

;2022-05-08T02:29:41Z;28;-966233403;462863960;;RAK000121|-45,RAKTEST|-56

AT+QIDEACT=1
OK[ 2022-05-08T02:29:41Z ] [FARM_IP][INFO] MDM_SET_DEACTIVATE_PDP-else

AT+QIACT=1
OK
AT+QMTOPEN=0,"a5u9klmd2viw3z-ats.iot.us-west-1.amazonaws.com",8883
OK

+QMTOPEN: 0,0		           --- [Opening MQTT Connection]
[ 2022-05-08T02:29:41Z ] [FARM_IP][INFO] Mqtt opened
AT+QMTCONN=0,"0123qwer786"
OK

+QMTCONN: 0,0,0                            --- [MQTT client connected]
AT+QMTPUB=0,1,1,0,"fm/1011",72        --- [Publishing to the MQTT Topic]

> ;2022-05-08T02:29:41Z;28;-966233403;462863960;;RAK000121|-45,RAKTEST|-56
OK

+QMTSTAT: 0,1    			 --- [MQTT Connection Closed]
```

```
[While Subscribing to topic]

AT+QMTSUB=0,1,"imei/get_logs",0			--- [Subscribing to the MQTT Topic]
OK

+QMTSTAT: 0,1					--- [MQTT Connection Closed]
[  ] [FARM_IP][INFO] Starting timer
AT+QMTSUB=0,1,"imei/get_logs",0			--- [Subscribing to the MQTT Topic]
OK
	
+QMTSTAT: 0,1					--- [MQTT Connection Closed]	
```

Answer

When you client is disconnected while publishing or subscribing the reason might be the IoT policy that is used. If you are not allowed to publish or subscribe to a topic your client is being disconnected.

You can use CloudWatch logs to drill down this error further. If the IoT policy is the reason you will find an authorization error in CloudWatch logs.

KR,

Philipp

Answer

Not sure if you are still running into this problem but I was just faced with something similar. I spun up a second device and whenever one contacted AWS the other disconnected. I was sure I had made a mistake with credentials or something but actually I had overlooked an AT command from the MQTT Operation Example. When you send AT+QMTCONN=<client_idx>,<clientID>[,<username>[,<password>]] your clientID needs to be unique for each individual device. Changed clientID to be my thingName and everything has been smooth sailing since.

Hope it helps.

hans

Hope it helps.

hans

MQTT Connection keeps getting disconnected/closed while publishing or subscribing to topics using LTE Modem

相关内容