Initial EPS bearer on u-blox TOBY-L210

[Aleksander Morgado]

>> Ideally, and I'm going to work on that in the following weeks, we
>> should have an API to allow configuring that default LTE attach APN,
>> and of course that requires the device to be fully unregistered from
>> the network (so the CFUN=4 comment above makes sense). This should be
>> some API that is totally independent from the connection process I
>> think. See e.g. what Microsoft defines in this regard for MBIM
>> devices:
>> https://docs.microsoft.com/en-us/windows-hardware/drivers/network/mb-lte-attach-operations.
>> If the device allows managing the default bearer settings, we should
>> expose the ability to manage them in DBus. For the case of the
>> TOBY-L2, this would be done with UCGDFLT as you showed.
>>
> That would be a good idea, but will (as far as I understand as of today) not
> solve the problem I am facing with the Telekom SIM card. But when using the
> +UIPROUTE command works, there is not need for me to set the default bearer
> to make the Telekom SIM card work....
>

Using the TOBY with multiple connected contexts right now is not
possible with the current ModemManager API, because as you said the
TOBY wouldn't know how to route or what to route inside.

That said... I have a working custom implementation of ModemManager
working with a TOBY-L4 (similar to the TOBY-L2, as it actually only
works in router mode) connecting a default bearer plus a secondary
bearer, all working together, and allowing to setup custom routes for
each based on external rules. In this use case we have a dedicated APN
that requires some custom private network routes, plus another APN for
public internet. Routes are managed internally with UIPROUTE in the
TOBY for this setup. This is being used in real cars out there right
now, and I should definitely clean that branch up and put it in the
upstream git repo as soon as I find some time. But I will not want to
integrate that work in upstream ModemManager as it is right now,
because the implemented logic assumes a lot of things that are
particular to that use case...

Ideally, the TOBY-L4 and TOBY-L2 in router mode should allow creating
"multiple bearer objects" in the MM API associated to a single network
interface (this is currently not possible in MM), and managing the
connection to all of them via the Bearer API, and additionally we
would allow configuring custom routes for each bearer inside the
modem. This way of work is very particular to the u-blox as far as I
can see, because all other manufacturers will leave all routing work
to the host (e.g. by exposing multiple WWAN interfaces that may be
connected at the same time to multiple APNs, much easier!!), instead
of having one single WWAN interface that requires custom routes inside
the Linux running in the module.

-- 
Aleksander
https://aleksander.es