BG96 with known good Vodafone SIM fails registration on Cat-NB1 network

IoT Modules LPWA Module
1

I have several SIM cards enabled for NB-IoT network that correctly operate on some BG96 modems, but fail to register on one particular BG96 (same firmware as the other ones).
AT+CEREG alway ends up with status 3 = registration denied on this particular modem.

Is it possible that specific IMEI is “banned” or locked out from the network provider? I read somewhere that wrong configuration of the modem can lead to that IMEI+SIM combination to be blocked.
What could be the reason of such a permanent block?

All the modems have been configured the same way with “nwscanmode”=3, “iotopmode”=1 and specific LTE Band B20.
When manually setting AT+COPS=1,2,“22210”,9 I receive +CME ERROR: 13 or 30.
The other modems work just fine with the default +COPS=0 (auto).

2

for NB need APN from provider

3

I normally set the APN after +CEREG: 1 or 5 and this sequence works well with other BG96 modems.

It seems a problem with a specific unit, which is always denied registration. Sometimes I can see the network with AT+QENG=“servingcell”, but still registration fails after a few minutes.

4

more of the problems are a weak signal… if frequency is 1800
after CEREG? after CEREG you are connected to cell

5

Vodafone NB-IoT is using LTE Band B20 (800 MHz) and I set AT+QCFG=“band” accordingly to speed up network scan.

Also, the same unit that fails to register under LTE NB1 is working fine with another Vodafone SIM when I set the modem to use the GSM network only (“nwscanmode”=1).

1 Like
6

set NB
set/store APN
ACT
wait CEREG
?

try update firmware

7

Thanks for the help, it seems the issue resolved itself (or the APN did it):

AT+CEREG?
+CEREG: 0,2
OK

AT+QNWINFO
+QNWINFO: No Service
OK

AT+QENG=“servingcell”
+QENG: “servingcell”,“SEARCH”
OK

AT+CSQ
+CSQ: 99,99
OK

AT+QCSQ
+QCSQ: “NOSERVICE”
OK

After a few minutes:

AT+QENG=“servingcell”
+QENG: “servingcell”,“NOCONN”,“CAT-NB”,“FDD”,222,10,EA5F71,137,6353,20,0,0,90E8,-92,-10,-82,18,36
OK

AT+QNWINFO
+QNWINFO: “CAT-NB1”,“22210”,“LTE BAND 20”,6353
OK

AT+QCSQ
+QCSQ: “CAT-NB1”,-80,-91,189,-7
OK

AT+CSQ
+CSQ: 17,99
OK

AT+CEREG?
+CEREG: 0,5
OK

I checked places where I previously had set the APN and there it is, even after power cycles:

AT+CGDCONT?
+CGDCONT: 1,“IP”,“ep.inetd.gdsp”,“0.0.0.0”,0,0,0,0
OK

AT+QICSGP=1
+QICSGP: 1,“ep.inetd.gdsp”,"","",0
OK

Since last power on I have not set the APN, so either it was remembered from previous sessions, or set auto-magically (I doubt it).

I will do more tests by swapping SIM card and network mode to 2G and NB-IoT back and forth to see what happens again.

I found that using a non-NB enabled SIM does reset “nwscanmode” from 3 to 0. Maybe using different SIM and network settings might leave the modem in some weird status.

8

//Set APN
AT+CGDCONT=1,“IP”,“smartsites.t-mobile”

9

Just some follow up on this issue…

I removed the APN and immediately got disconnected from the network:

AT+QICSGP=1
+QICSGP: 1,“ep.inetd.gdsp”,"","",0
OK

AT+CGDCONT?
+CGDCONT: 1,“IP”,“ep.inetd.gdsp”,“0.0.0.0”,0,0,0,0
OK

AT+CGDCONT=1,“IP”,""
OK

AT+CGDCONT?
+CGDCONT: 1,“IP”,"",“0.0.0.0”,0,0,0,0
OK

AT+CEREG?
+CEREG: 0,3
OK

AT+QICSGP=1
+QICSGP: 1,"","","",0
OK

AT+CGATT?
+CGATT: 0
OK

I did also these commands:

AT+COPS=0
OK

AT+CEREG?
+CEREG: 0,2
OK

AT+QENG=“servingcell”
+QENG: “servingcell”,“SEARCH”
OK

Then verified “nwscanmode”, that had been reset to 0=auto (default), and set it to 3=LTE Only and also verified it was still configured for Cat-NB1 only:

AT+QCFG=“nwscanmode”
+QCFG: “nwscanmode”,0
OK

AT+QCFG=“nwscanmode”,3
OK

AT+QCFG=“iotopmode”
+QCFG: “iotopmode”,1
OK

Then I performed a soft-reset with AT+CFUN=1,1 and the module was back to usual behavior. It registered on the LTE Cat-NB1 network straight away without any APN stored.

I suspect the issue I had was because the module had been previously used in GSM mode only with another SIM/APN already set. If the APN setting is persistent, then when I switched to Cat-NB1 only, the modem tried to use the wrong APN and the network eventually kicked it out with +CEREG: 0,3 (denied).

But why is the modem using the APN before I send AT+QIACT? I thought it was not used until I activate the data connection.

Anyway, good to know…

2 Likes
10

in NVDM exist “valid” APN … just store once your and connection will be auto

11

Thank you for posting your findings, we have a similar issue with SIM7000G (same silicon) and this gives us good good areas to explore.