LTE attach settings

[Aleksander Morgado]

Hey Giacinto!

>
> I need to set up the default LTE bearer settings: APN, type of APN,
> authentication parameters, in the Cinterion plugin.
>
> And for this, I am going to add the two methods:
>     void     (* set_initial_eps_bearer_settings)
> (MMIfaceModem3gpp     *self, ..
>     gboolean (* set_initial_eps_bearer_settings_finish)
> (MMIfaceModem3gpp     *self, ..
>
> Is this the right way to do it? I see that nobody implemented it so
> far. Is this called for mbim or qmi?
>

This is currently implemented for MBIM devices, because in MBIM
devices there are explicit APIs to set them without needing to worry
about what specific CID number we're touching.

> I will have to run the following sequence:
> -        go in AT+CFUN=4 (airplane mode with SIM connected). This is
> necessary because the CID might be locked or not taken into account
> immediately (in case there is an attach attempt ongoing).
> -        set AT+CGDCONT for the right CID (normally 1)
> -        set AT^SGAUTH for the same CID
> -        go back to AT+CFUN=1.
>
> Is this ok to you?

The requirement to run CFUN=4 before and CFUN=1 after seems very
generic to me; at the end we're changing the APN settings used during
LTE registration, so it is assumed the device needs to re-register. I
say this because it may make sense to move that logic "up" to the
Modem3gpp interface, so that the interface itself puts the modem in
low-power mode before the change and puts it back into full-power mode
after the change. But don't worry about that, this can be done later,
if you do the CFUN=4/1 yourself in the cinterion plugin for now it's
ok.

>
> Instead of CFUN=4/1 also COPS=2/0 could be used, but I prefer the former.
>

The only issue I see is the selection of the "right CID" in CGDCONT.
As you said, it is normally 1, but as we've already found in the past
it may be operator dependent; e.g. wasn't it CID=4 for Verizon?

I believe that other vendors use other approaches, even with separate
APIs, e.g. the u-blox TOBY-L2 had specific commands for this IIRC.

At this point, and given that it is everyday more common to have the
requirement to change the initial LTE bearer settings, I wouldn't mind
to have this logic with the "far from perfect" initial default of
reconfiguring CID=1. I just got this very same requirement just
yesterday debugging connectivity with an Orange Morocco SIM, so I'm
sure there are users out there also requiring this kind of
configuration.

-- 
Aleksander
https://aleksander.es