Difference between "Usage preference" "voice-centric" or "data-centric"?

[Robert Marko]

On Tue, Feb 18, 2025 at 3:21 AM Dan Williams <dan at ioncontrol.co> wrote:
>
>
>
> > On Feb 17, 2025, at 4:18 PM, Aleksander Morgado <aleksander.morgado at gmail.com> wrote:
> >
> > Hey
> >
> >>
> >>>
> >>> when using this command:
> >>>
> >>> # qmicli -p -d /dev/cdc-wdm0 --nas-get-system-selection-preference
> >>> [/dev/cdc-wdm0] Successfully got system selection preference
> >>>         Emergency mode: 'no'
> >>>         Mode preference: '5gnr'
> >>>         Disabled modes: 'none'
> >>>         Band preference: 'wcdma-2100, wcdma-pcs-1900, wcdma-1700-us,
> >>> wcdma-850-us, wcdma-900, wcdma-850-japan'
> >>>         LTE band preference: '1, 2, 3, 4, 5, 7, 8, 12, 13, 14, 17,
> >>> 18,
> >>> 19, 20, 25, 26, 28, 29, 30, 32, 34, 38, 39, 40, 41, 42, 43'
> >>>         LTE band preference (extended): '1, 2, 3, 4, 5, 7, 8, 12,
> >>> 13,
> >>> 14, 17, 18, 19, 20, 25, 26, 28, 29, 30, 32, 34, 38, 39, 40, 41, 42,
> >>> 43,
> >>> 46, 48, 66, 71'
> >>>         NR5G SA band preference: '1, 2, 3, 5, 7, 8, 12, 13, 14, 18,
> >>> 20,
> >>> 25, 26, 28, 29, 30, 38, 40, 41, 48, 66, 70, 71, 75, 76, 77, 78, 79'
> >>>         NR5G NSA band preference: '1, 2, 3, 5, 7, 8, 12, 13, 14, 18,
> >>> 20, 25, 26, 28, 29, 30, 38, 40, 41, 48, 66, 70, 71, 75, 76, 77, 78,
> >>> 79'
> >>>         TD-SCDMA band preference: 'a, b, c, d, e, f'
> >>>         Roaming preference: 'any'
> >>>         Network selection preference: 'automatic'
> >>>         Service domain preference: 'cs-ps'
> >>>         GSM/WCDMA acquisition order preference: 'automatic'
> >>>         Usage preference: 'data-centric'
> >>>         Voice domain preference: 'ps-preferred'
> >>>         Registration restriction: 'unrestricted'
> >>>         Acquisition order preference: '5gnr, lte, umts'
> >>> #
> >>>
> >>> there is "Usage preference", which can be "voice-centric" or "data-
> >>> centric".
> >>>
> >>> In Quectel RM520N-GL there is an AT command, where I can choose
> >>> between
> >>> the two modes.
> >>>
> >>> What is the difference between them?
> >>>
> >>> What does the module do different when choosing the one or the other?
> >>>
> >>> Could it be (with voice centric) that it builds up a connection to
> >>> somewhere, for voice calls,
> >>> which could influence my data calls (especially when choosing APN/IP-
> >>> Type)?
> >>
> >> I'm not 100% sure, but I believe if voice-centric is selected then the
> >> device should try as hard as it can to only attach to networks that
> >> provide voice services. That might mean detaching from 5G and re-
> >> attaching to LTE automatically if the 5G network doesn't provide voice
> >> services that the device wants or is capable of using.
> >>
> >> I would say that unless you care about voice calls, keeping the usage
> >> preference as data-centric is probably best.
> >>
> >
> > It's exactly that, yes. I had issues with this setting years ago in
> > China Mobile with a 2G+4G modem; if configured in voice-centric mode
> > the modem would prefer 2G by default instead of 4G as there was no
> > VoLTE support.
> >
> > The SetEpsUeModeOperation() allows changing this setting for modems
> > supporting AT+CEMODE. See
> > https://www.freedesktop.org/software/ModemManager/doc/latest/ModemManager/gdbus-org.freedesktop.ModemManager1.Modem.Modem3gpp.html#gdbus-method-org-freedesktop-ModemManager1-Modem-Modem3gpp.SetEpsUeModeOperation
> > and https://www.freedesktop.org/software/ModemManager/doc/latest/ModemManager/ModemManager-Flags-and-Enumerations.html#MMModem3gppEpsUeModeOperation
>
> I found we don't implement this for QMI. We should probably just grab the value from System Selection Preference and set it via SSP too.
>
> This would be pretty low-hanging fruit for any contributor. Hint hint!

Here is my attempt at it, since I need this anyway on RM520N.
Do note that I have barely used GLib before dealing with ModemManager.

https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_requests/1302

Regards,
Robert
>
> Dan
>


-- 
Robert Marko
Staff Embedded Linux Engineer
Sartura d.d.
Lendavska ulica 16a
10000 Zagreb, Croatia
Email: robert.marko at sartura.hr
Web: www.sartura.hr