ModemManager RAT definitions, etc.

[Aleksander Morgado]

Hey!

>
> I'm working on integrating LPWA modem and I got a few questions mostly
> on conceptual level.
>

Nice!

> #1There is MMModemAccessTechnology which "Describes various access
> technologies that a device uses when registered with or connected to a
> network".
> In addition to 27.007, there is also 3GPP TS 29.274 which defines the
> following RAT Types: UTRAN, GERAN, WLAN, GAN, HSPA Evolution, EUTRAN
> (WB-E-UTRAN), Virtual, EUTRAN-NB-IoT, LTE-M, NR. While 5GNR is defined
> (however not sure if NSA and SA modes can be identified and stated),

Access tech is a bitmask, and right now we're assuming that if
LTE+5GNR are given at the same time in the bitmask, that's NSA; and if
only 5GNR is given, that's SA. We don't have a way to report whether
it's ENDC or NEDC though, in general it's safe to assume ENDC for now.

> can't see any reference to LPWA technologies like Cat-M and Cat-NB.
> This information could be easily acquired by +COPS? command (at least
> I tried two different module vendors using different chipset vendors).

What <Act> values are given in +COPS? for those?
This is the mapping we currently have in MM:
https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/blob/main/src/mm-modem-helpers.c#L1150

I assume you're saying we could have separate MMModemAccessTechnology
values for the COPS <Act> equivalents of numbers 8 (EC-GSM-IoT (A/Gb
mode)) and 9 (E-UTRAN (NB-S1)) at least?

> - How should LPWA modems be identified? (new LTE Categories enum,
> change existing, etc)
>

I don't know enough about the type of LPWA modems there are. Which
list of new AcTs would you add? Could you include in this discussion
the actual list of values given by the 3GPP specs?

> #2 Related to topic above, currently LPWA modem identified as HSPA
> (3G), however in reality 3G is not supported. Changing the way how RAT
> is identified, would most likely ruin support for old modems in
> plugin. Maybe some folks already faced a problem with command
> incompatibility among  different modems in the same plugin.
> - What approach would be preferable in solving AT command collision problem?
>

Can you describe with detail which is the actual collision? Is the
modem reporting a 3G AcT?


> #3 related to above. Approx 10 years ago AT*CNTI was introduced to
> check access tech in a generic code. it is a proprietary command not
> supported by a many modems.
> - Could it be moved to relevant plugins only? (especially in the light
> of 3G sunset)
>

Not sure I understand what your suggestion is. The truth is that we
don't care much about whether some operators are leaving 3G for good.
There will be operators out there in some country still using 3G for a
while (right?), so the usecase still exists. Same as for 2G.

> #4 Command "mmcli -m 0" in a segment "IP" states the following:
> "supported: ipv4, ipv6, ipv4v6"
> - Could someone clarify the meaning of it: is it "a list of supported
> PDP context types" or "type of currently active/main PDP context"?
>

List of supported PDP context types by the modem+MM combination.
Unrelated to the current ones. If you want to know the current
bearer/context type in the initial default LTE bearer (so, as agreed
with the network), you can check the initial 3GPP EPS bearer status
reported by MM in the bearer object given at the path in the "3GPP EPS
| initial bearer path".

> #5 Is there any particular reason that "build" directory is not
> included in MM .gitignore file?
>

The "build" directory is not part of the build process per se. A user
could choose to build using meson in a directory named "temp" and it
would be equally fine. Or users may even have different build settings
in different build directories, e.g. "build-default", "build-no-doc"
and such. That said, I don't really care much :) If  you want to add
build in .gitignore, please suggest it in a merge request! :D

> Just in case, when I read setup at
> https://modemmanager.org/docs/contribution-guidelines/using-gitlab/developer-setup/,
> I noticed that a text
> "ModemManager: https://gitlab.freedesktop.org/username/ModemManager"
> has hyperlink which actually points to docs page instead of git (I
> dunno if it was by intention).
>

Whatever fix you may have for the docs is greatly appreciated, just
fork and suggest a merge request to the docs repository:
https://gitlab.freedesktop.org/mobile-broadband/mobile-broadband.pages.freedesktop.org

Cheers!

-- 
Aleksander