PDP settings for LTE only network

[Aleksander Morgado]

Hey,

On Tue, Jun 14, 2022 at 9:53 AM Brendan Simon <Brendan at brendansimon.com> wrote:
>
> Hello,
>
> I have a number of embedded linux boxes with Quectel EC21 4G modems, connected to various cellular networks (AT&T, Verizon, ...).
>
> AT&T are removing 3G from some areas and the modems are not reconnecting.  My devices are vanishing off the face of the Internet.
>
> Quectel have provided some assistance and guidance and advised to configure some settings for AT&T Sunsetting.  The UE Usage Setting was changed to configure the device as Data Centric (i.e. no voice), however it did not resolve the issue.
>
> AT&T provided some assistance - apparently the APN was wrong.  Seems like some generic APNs are being used and not the APN specified in the NetworkManager configuration.  This all worked ok when 3G was available.
>
> AT&G also suggested the PDP settings of the modem are the issue.
> Changing the default PDP context (#!) from an APN of "" to the provided APN seems to have resolved the connection issue.
>
> I have used `mmcli -m N --command="..." to modify the PDP context for testing.
>
> I feel this is hacky and shouldn't be required.
>
> Is there a better (more elegant and generic method) to set the PDP contexts so modems (preferably any brand) will work on 4G only networks?
>

The way to elegantly change the APN settings for the initial EPS
default bearer would be using e.g.:
$ mmcli --3gpp-set-initial-eps-bearer-settings='apn=something'

In QMI-based modems as the EC21, this would internally change the
profile associated to the initial bearer.

> NOTE: we are using Debian Buster with ModemManager 1.10.0.
>
> Would upgrading MM help?  Buster-Backports has 1.14.0 available, which would be easy to build/install on the existing OS.
>

The QMI-based initial EPS bearer settings update was implemented in
commit 5613215db8 (November 2020), which was released with
ModemManager 1.16.0. The latest update in the 1.16.x series is
1.16.10, but the series is now fully unsupported; the latest supported
series is 1.18.x.

-- 
Aleksander
https://aleksander.es