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

[Aleksander Morgado]

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