Possible reasons for nRF9160 reporting EMM Cause #255

[stso]

Hi, we are investigating some devices in field, and have limited logs to work with. From time to time, we see EMM reports with cause 255. According to nRF9160 AT Commands, this is an unspecified error.

Can this error originate from the network, modem firmware, or both?

Which situations can lead to this occurring?

Is it an indication that something is severely wrong, or is this expected in normal operation?

[Håkon Alseth]

Hi,

 

Cause codes are sent from the eNB to the UE, ie. nRF only acts as a messenger in that case. This is sent by the network.

You can see the complete list here in chapter 9.2:

https://www.etsi.org/deliver/etsi_ts/127000_127099/127007/18.06.00_60/ts_127007v180600p.pdf

 

255 is not defined, as you also mention.

Is this repeatable on your end? If yes, could you please share a modem trace showing the issue?

 

Kind regards,

Håkon

[stso]

Thanks, so we can rule out that this is caused by any internal behavior in the modem, and conclude that the network is actually sending cause 255.

It is unfortunately not something we have been able to reproduce, we see it in logs from devices in field from time to time.

[Håkon Alseth]

Hi,

 

Have you asked the network provider about this behaviour, especially in your area?

Let me know if you are able to isolate the issue and reproduce the behaviour.

 

Kind regards,

Håkon