[ublox] A problem with the network connection over LTE on TOBY-L2

[Ulrich Mohr]

Hey,

Am 05.11.2018 um 10:51 schrieb Aleksander Morgado:
> Hey,
>>> Upon connection from e.g. NM, MM will check whether the requested settings (APN, ip-type...) match the ones from the default LTE attach bearer, and if they do, MM will report that the modem is connected right away without trying to create and connect a different context. This is already more or less what the u-blox plugin does. And when disconnecting the connection, if it was the initial default LTE bearer, we'll just report disconnection without touching the actual bearer in the modem (as that would probably return an error). This procedure is IIRC what Microsoft suggests in the MBIM extensions that allow this kind of management, see:
>>> https://docs.microsoft.com/en-us/windows-hardware/drivers/network/mb-lte-attach-operations
>> Ok, that approach more or less matches the implementation I test at the
>> moment, except that I set the default bearer upon first connection
>> establishment with that APN (lacking other possibilities to do so).
>>
>> That leads me directly to the one open point: How will the use case
>> works when using Network Manger with your new API?
>> The user will enter the APN information to set up the connection
>> information (in my case, that will be a device configuration UI). That
>> will result in a new (or changed) Network manager connection
>> configuration. Now, the Network manager will have to bring the modem to
>> low power and set the default LTE bearer and then bring the modem back
>> to full power. How will this be done?
>>
> I am actually not expecting NetworkManager changes at this point. The
> fact that someone needs to change the initial default LTE bearer
> manually is not a common use case. If the device doesn't have an
> explicit config for the SIM card in use, the network provides some
> default values (if I'm not mistaken), and that is usually more than
> enough in most cases.
I suspect you are wrong here: Without the default LTE bearer, there is 
no LTE connection possible at all using TOBY with specific providers 
(Telekom.de, Telekom.cz), since the network provides default values, but 
these values are not suitable to get a functional LTE connection. 
Instead you get routed to a non-functional APN ('nodata.telekom.de'). (I 
am not sure why the do it that way, it seems they want to force the user 
to specify the APN settings explicitely, e.g. to provide several APNs 
with different services using the same SIM card? Just guessing ...)
These cards are not special SIM cards, these are the normal LTE SIM 
cards every customer gets (and the they are the biggest provider in 
Germany). None of these cards can be used with ModemManager at the 
moment with the TOBY modem.

>  From my point of view, this setting could be a modem-wide setting, to
> be treated in the same way as e.g. the allowed/preferred access
> technology modes, and so this could be managed in the System Settings
> panel, not directly associated to any given connection profile in
> NetworkManager. NetworkManager won't do any automagic to change the
> default initial LTE bearer settings in the device.
Unless I know any other method to make LTE work with the telekom SIM 
cards, I suspect the network manager has to change the LTE default 
bearer somehow.
> So, if a user does require to change the default initial LTE bearer
> settings, two steps would be required: change the settings in the
> modem (e.g. via System settings or mmcli) and then setup a
> NetworkManager connection profile with those same settings.
>
> Does this make sense?
This does makes sense when we assume that the default LTE bearer is only 
needed in rare cases, which apparently isn't true for the SIM cards we 
are talking about.

-- 
Best regards / Mit freundlichen Grüßen / Salutations distinguées

Ulrich Mohr

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