Registration issues with Telit modem LE910C4 and modem manager 1.18.8

[Félix R.]

Hi,

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.

*Félix-Antoine Robert*
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