Configuration for Quectel 3G and 4G modem

[Dan Williams]

On Mon, 2018-10-15 at 17:28 +1100, Brendan Simon (eTRIX) wrote:
> I have a linux filesystem (Debian based) for an embedded board which
> uses a Quectel UC20 3G modem via NetworkManager/ModemManager.
> 
> I want to upgrade to use a Quectel EC21 4G modem and want to know if
> I
> can use the same "system-connections" configuration file for both
> modems.  e.g. so that same software can run on new and old hardware -
> or
> do I have to have separate config/connection files for each modem?

This connection file looks fine for both modems. NetworkManager allows
the file to apply to any device of the type unless it is explicitly
restricted to a specific device, which this one is not because it
doesn't have the 'device-id' and/or 'sim-id' keys in the [gsm] section.

> > My 3G configuration looks like this:
> 
>     id=telstra-mobile-broadband-1
>     uuid=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
>     type=gsm
>     permissions=user:root:;
>     autoconnect=true
> 
>     [gsm]
>     number=*99#
>     password-flags=1
>     apn-telstra.extranet
> 
>     [ipv4]
>     method=auto
> 
>     [serial]
>     baud=115200
> 
> 
> Should this same config file work with a 4G modem (EC21) ?

Yes.

> Can I have the one configuation file that will work on 4G and 3G
> (e.g.
> if only 3G is available).  I'm *assuming* yes.  If so, how to
> configure it.

This file should work on both 3G & 4G, because the modem will actually
determine which of the two access technologies it wants to use and when
it wants to switch between them based on coverage and signal. You
almost never need to bother thinking about specific access
technologies.

> And 3G fallback also.  Is there anything special I need to do in
> configuration, or will ModemManager just wield its magic.

That's actually all done inside the modem itself and mostly transparent
to ModemManager and NetworkManager.

(yes, you can tell the modem to prefer a specific access technology,
but that's an unusual case and very few need to do that.)

Dan