NB-IoT post data using AT Commands and MQTT to ThingSpeak

[gav_ncl]

I would like to evaluate the use of NB-IoT in the UK which Wireless Logic SIM included with nrf9151DK provides. Using the following sequence of AT commands I can send data over LTE-M to thingspeak but if I try the same sequence with NB-IoT as the mode and preference (i.e. AT%XSYSTEMMODE=0,1,0,2) i get ERROR response when i try to connect using AT#XMQTTCON instead of OK when using LTE-M. Can you advise where I may be going wrong please? I am using the Serial LTE Modem application in nrfConnect. 

• AT#XRESET
• AT%XSYSTEMMODE=1,1,0,1
• AT+CFUN=1
• AT+CEREG=5
• AT+CSCON=1
• AT+CGDCONT=1,"IP","APN HERE"
• AT+CESQ=0
• AT#XMQTTCFG="CLIENT ID HERE",300,1
• AT#XMQTTCON=1,"USER NAME HERE","PASSWORD HERE","mqtt3.thingspeak.com",1883
• AT#XMQTTPUB="TOPIC HERE","DATA HERE"

[Hakon]

Hello,

are you running the SLM sample as it is, or have you made any modifications in the code?

[gav_ncl]

Hi Hakon,

No modifications to the SLM code. Only interraction is using AT commands. I have since confirmed with the SIM provider that TCP using NB-IoT is supported. What information did the trace I attached for Jonathan show?

Thanks

Gavin

[Hakon]

gav_ncl said:

What information did the trace I attached for Jonathan show?

From the information you provided I would think that the error is related somehow to the AT handler, and that the error would likely not show up in the modem logs at all. If you give me some time I will try to reproduce the error.

[gav_ncl]

Ok no problem. Seems strange that LTE-M works no problem with the AT commands above and changing only AT%XSYSTEMMODE to NB-IoT is enough to stop it working. Using the above set of AT commands with AT%XSYSTEMMODE=0,1,0,2 can you send data using MQTT over NB-IoT with the SLM sample?

Thanks

Gavin

[Hakon]

I have not been able to use the same setup as you, but just testing with basic public brokers works just fine;

at#xmqttcon=1,"","","test.mosquitto.org",1883

OK

#XMQTTEVT: 0,0

+CEREG: 5,"A879","014A0303",9,,,"11100000","11100000"

at%xsystemmode?

%XSYSTEMMODE: 0,1,0,2

I would assume this basic test should also work for you. If it does, then maybe I can try to replicate your setup more closely. If necessary, we can make the ticket private, so you can share more details.

[gav_ncl]

Can you include all of your setup AT commands so that I can try to respoduce your result? This cant be everything as you need to turn the modem on.

Thanks

Gavin

[Hakon]

It is pretty much exactly what you did, setting AT%XSYSTEMMODE=0,1,0,2. So setting something like

AT%XSYSTEMMODE=0,1,0,2

at+cfun=1

at#xmqttcfg="something123",300,1

at#xmqttcon=1,"","","test.mosquitto.org",1883

OK

#XMQTTEVT: 0,0

+CEREG: 5,"A879","014A0303",9,,,"11100000","11100000"

at%xsystemmode?

%XSYSTEMMODE: 0,1,0,2

The broker seems to be down at the moment, but it was up and working when I was testing it earlier.

[gav_ncl]

Hi Hakon,

I have tried your AT commands and similar to your second attempt it wont connect and produces ERROR. It would be good if it said something more than just ERROR.

Does the latest firmware mfw_nrf91x1_2.0.2 support MQTT for NB-IoT using AT Commands?

After trying for some time I have still been unable to send a single message via NB-IoT using MQTT yet LTE-M works perfect.

Do you have any further advice to get this working?

Thanks again,

Gavin

[Hakon]

gav_ncl said:

I have tried your AT commands and similar to your second attempt it wont connect and produces ERROR. It would be good if it said something more than just ERROR.

Does it time out, or is it an instant error? If it times out, then you should try a different broker.

gav_ncl said:

Does the latest firmware mfw_nrf91x1_2.0.2 support MQTT for NB-IoT using AT Commands?

It should be supported as far as I know.

[gav_ncl]

Hi Hakon,

It is an instant error. I have tried multiple brokers including the one in your example. LTE-M works on every broker but I have not been able to connect to a broker using NB-IoT.

Do you have any idea what I may be doing wrong? I can see that the unit is connected via NB-IoT no problem but for whatever reason it will not connect to an MQTT broker.

Thanks

Gavin

[Hakon]

You can request the following notification Set command (AT%XPCO=1) and if received Notification is empty → NB-IoT ePCO is not supported in the SIM provider Packet Gateway element.

Set command AT%XEPCO=0 should fix this situation with Serial Modem application.