Quectel EC25 bug - interaction between generic/3GPP and QMI connection methods

[Paul Bartell]

Tim,

On Thu, Apr 16, 2020 at 1:29 PM Tim Small <tim at seoss.co.uk> wrote:
>
> Hi Paul,
>
> Thanks for your response...
>
> On 16/04/2020 18:38, Paul Bartell wrote:
> > Alternatively, you can clear these settings each time a new SIM is
> > inserted with qmi WDS Modify Profile.
> > Setting the APN of profile 1 to an empty string will cause the modem
> > to use the network provided default apn for IMS / default bearer
> > purposes. Profile #1 always corresponds to the default bearer.
>
>
> The current model that NetworkManager and ModemManager use is that all
> state is defined in the nm connection settings, so from what you say I
> think that mm should probably (at least by default) remove configured
> settings to get the modem to a consistent state, irrespective of
> previous configurations that mm has installed on the modem in the past?
>

It's really about configuring the initial EPS bearer. The
SetInitialEpsBearerSettings api exposed by MM in the Modem3gpp
interface seems like a good way to expose this setting to MM client
apps.
So far it has only been implemented for mbim modems. EC25 modems in
mbim mode do not support this feature though. I'm not sure if this
gets set in the NetworkManager world.

In most cases, the apn setting that is hardcoded in the carrier config
mbn is correct.
For AT&T in the US, the default eps bearer apn changes depending on
the rate plan. Most other US carriers use a common default EPS bearer
apn for all of their rate plans.

I've seen a similar quirk when using other MDM9x07 modems (Telit LE910C4-NF).

> Regards.
>
> Tim.
>
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