Registration issues with Telit modem LE910C4 and modem manager 1.18.8

[Aleksander Morgado]

Hey

> I hope someone can help shed some light onto this issue as I am at a loss.
>
> I am investigating an issue that is occurring in a few IoT devices where either the modem has trouble registering to the network or it is being rejected shortly after a data connection is established. I'm trying to get a better understanding of the error messages reported in the modem manager logs.
>
> In the case where the modem is not able to register to the network, the logs will show:
>
>  <warn>  [modem25] network reject indication received
> <warn>  [modem25]   service domain: cs-ps
> <warn>  [modem25]   radio interface: lte
> <warn>  [modem25]   reject cause: no-suitable-cells-in-location-area
> <warn>  [modem25] network reject indication received
> <warn>  [modem25]   service domain: cs-ps
> <warn>  [modem25]   radio interface: lte
> <warn>  [modem25]   reject cause: plmn-not-allowed
>
> My first thought was that the sim card was not properly provisioned, however deactivated sims show a different error message. I've contacted my service provider for some insight, but they don't see any network issues on their end: neither with the cell equipment or my sim cards.
>
> The odd thing is that after some time, the device is able to register to the network and will then easily connect before being rejected again, this time with the following error message:
>
> <warn>  [modem2] network reject indication received
> <warn>  [modem2]   service domain: ps
> <warn>  [modem2]   radio interface: lte
> <warn>  [modem2]   reject cause: implicitly-detached
>
> I'm interested in what the reject causes above may mean as that might provide some insight on possible fixes on the device side of the connection.
>
> I am using the Telit LE910C4 modem with modem manager 1.18.8 in tandem with network manager.  The modem is mounted within a custom made IoT device.
>

Not exactly sure what leads to these problems, but something you can
check is whether the operator you're using expects to use a specific
set of APN settings **during network attach**. In LTE, the network
registration flow involves agreeing on APN settings to use, to
establish the initial default EPS bearer.

You can see the current configured settings in the "mmcli -m a" output
in the 3GPP section. If the section is empty, you don't have explicit
settings (and you may need them).

Changing these settings can be done with mmcli, e.g.:
$ mmcli -m a --3gpp-set-initial-eps-bearer-settings="apn=internet,ip-type=ipv4v6"

See https://modemmanager.org/docs/modemmanager/ip-connectivity-setup-in-lte-modems/
for some context


-- 
Aleksander