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

[Dan Williams]

On Fri, 2025-02-28 at 15:05 +0100, Robert Marko wrote:
> 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

Robert,

Overall logic looks good, just a couple nits here and there; I'll leave
the real comments in the merge request.

Thanks again!

Dan

> 
> Regards,
> Robert
> > 
> > Dan
> > 
> 
>