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

[Dan Williams]

> 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!

Dan