Registration issues with Telit modem LE910C4 and modem manager 1.18.8

[Félix R.]

Hi Aleksander,

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
>

I was setting the bearer into the modem using a call to qmicli
--wds-create-profile="{*my info*}".

I've changed the code to use the mmcli call as suggested and included a
periodical clear of the FPLMN list that's saved on the modem, as per Telit
documentation recommendation (missed it on the first read).
These changes seem to have improved registration performances on my test
device.

Hopefully I'll also see an improvement on my devices out in the field once
I roll out the changes.

Thank you for the help!

*Félix-Antoine Robert*
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