BG95-M5 gets "rejected" during eMTC attachment after reset

IoT Modules LTE Standard Module
1

Hi,

We’re using the EG95-M5 modem in our development and currently facing an issue where the device gets “CEREG: 3 Registration denied” from the LTE-M/eMTC network when it tries to re-attach.

We can reproduce the error with more than one device and this happens when:

  1. We are connected to the LTE-M/eMTC network for some time (this is stable)
  2. Modem is turned of / reset.
  3. Modem is turned off (this time can be anything from 10 seconds to 48 hours)
  4. When device starts next time and tries to attach to network it gets: CEREG: 3 Registration denied
  5. Modem start searching for GSM network and gets attached to GSM with success
  6. Modem never goes back to LTE-M/eMTC (can be on for hours)

We would have expected that the modem can re-connect to LTE-M/eMTC network, even if it has to go through a new network-scan process, or at least that after some time it tries again.

I have checked the eMM cause we get after rejection which states: EMM_15.
My network provider could see that the network respond like this due to that the device is “passive”.
We did not set up any eDRX or PSM.
Running FW: BG95M5LAR02A03_01.200.01.200

I would appreciate any help or ideas that you could bring to this.
In our application, it is expected that the modem may loose power at some time. (disconnected)
Do we need to configure something to perform a clean start ?

Thank you in advance,
Best Regards,
Niklas Pettersson

2

Check whether the APN is correctly configured?
Or as you frequently restart and re-register, the network will deny the terminal access again, you can try to change the location (change the base station)

3

Could you solve the problem? I think there is something similar with the bg600 and SIMs from 1NCE.
Maybe I found an explanation: https://support.emnify.com/hc/en-us/articles/7116269647260-Network-Attachment-with-NB-IoT-networks

4

Please confirm with 1NCE again whether the SIM card you are using supports NB-IoT. Perhaps its current APN only supports GSM and catm

5

The Problem seems to be a protocol variance from local providers. Eg. with ‘KPN’ in the Netherlands it happens sometimes, but rare, whereas Vodafone or Telekom-de as Provider never. I also found a hint in a u-Blox AppNote to ignore the first few “Net denied” for e.g 20 seconds. Since now, it seems to work for us.