LTE reconnection issue

[eguerard1]

Hello everyone,

I Have a LTE reconnection issue after LTE signal loss with SDK 1.3.6. I was doing some LTE connectivity tests by placing the board in a faraday box. After reopening the box the modem does not register back to network. (always cereg = 2). I've attached wireshark capture made with the cellular monitor tool. I also did the same test with SDK 2.5.2 and was not able to reproduce the problem.

Board: nRF9160DK

Modem firmware: 1.3.6

SDK: 2.6.1

Steps to reproduce:

1) Wait until the LTE is connected with the network

2) Close the faraday box and wait up to 1 minute

3) Open the box

Information on  the capture files:

Both capture files has been generated from reset and contains 1 connection loss action.

nRF9160_SDK2.6.1.pcapng

LTE connection loss at line 151 for around 1 minute

nrf9160_SDK2.5.2.pcapng

LTE connection loss at line 158 for around 1 minute

Can you help me to figure out why, in the case of SDK 2.6.1, is not able to reconnect to network at all ? Thanks for your help!

Eric

nRF9160_SDK2.6.1.pcapngnRF9160_SDK2.5.2.pcapng

[Øyvind]

Hello, 

Thank you for providing this information. Could you please provide modem trace? This provides more information on what is going on inside the modem. I will have a look at the wireshark traces as well. 

Kind regards,
Øyvind

[eguerard1]

Hello,

Do you mean all AT command sent to the modem ? If yes, they are part of the pcap files.

Best regards,

Eric

[Øyvind]

Hi Eirc, no the modem trace (.mtrace) includes more information that is only readable by our team. You collect it using Cellular Monitor found in our nRF Connect for Desktop. The wireshark traces provide a lot of info as well.

Kind regards,
Øyvind

[Øyvind]

From nRF9160_SDK2.6.1.pcapng I can see that your device is disconnected and receives two reject reasons

174 292.841370 AT 47 Rcvd AT Command: +CEREG: 2,"AD1D","0103EF81",9,0,9
188 293.481232 AT 48 Rcvd AT Command: +CEREG: 2,"AD1D","0103EF81",9,0,14

From 3GPP TS 24.301 Annex A we see that these are

Cause #9 – UE identity cannot be derived by the network.
This EMM cause is sent to the UE when the network cannot derive the UE's identity from the GUTI/S-TMSI/PTMSI
and RAI e.g. no matching identity/context in the network or failure to validate the UE's identity due to
integrity check failure of the received message.

Cause #14 – EPS services not allowed in this PLMN
This EMM cause is sent to the UE which requests service, or if the network initiates a detach request, in a PLMN
which does not offer roaming for EPS services to that UE.

Not sure what causes these, and with 2.6.1 only. Are you using the PDN library in your device? I.e. any special SIM settings ? I would reach out to your network provider for more information. As mentioned, the modem traces will provide us with more information on what causes this. 

What SIM are you using? Is this activated for both LTE-m and NB-IoT?

Kind regards,
Øyvind

[eguerard1]

Hi 0yvind,

To my knowkedge, we don't use any special settings. We are using BELL sim card. It is activated for LTE-M. We also use the PDN library in the device.

Best regards,

Eric

[eguerard1]

Hi 0yvind,

I finally found the problem. By doing your modem traces, I tried another SIM card manufacturer and found that the first time the device register on the network, it connects in LTE-M. When the device lost connection, it tries to reconnect in NB-IOT. The problem is NB-IOT is not widely support in Canada. The supported bearers changed from SDK 2.5.2 and version 2.6.2. I had to enforce to use the LTE-M bearer by adding these configuration options in the prj.conf.

CONFIG_LTE_NETWORK_MODE_LTE_M=y

CONFIG_LTE_NETWORK_MODE_LTE_M_NBIOT=n

 

I just want to thank you for the quick support you gave me!

Best regards,

Eric

[Øyvind]

Hi Eric, 

Happy to hear that you found the answer to your issue. Let us know if you have any further issues with the network connection. 

Kind regards,
Øyvind