Second SIM only GSM?

[Webaschtl]

Hey there,

do you know that you can use via your SIM2 card only GSM?
German (Dual-SIM-Handy – Wikipedia):

Viele Dual-SIM-Geräte besitzen eine Hauptkarte, über welche LTE/UMTS-Datenverbindungen aufgebaut und auch UMTS-Gespräche geführt werden können, sowie eine Nebenkarte, die sich nur über GSM/Edge ins Netz einwählen kann und eventuell für Daten gesperrt ist.

I didn’t know this since 5 minutes… Using from the beginning (FP1, too) both slots, but at the moment not having a signal via SIM1

Bye, webaschtl

[werner_noebauer]

Hi,

many dual sim phones support 3G (and 4G/LT) only with one SIM card, so you have to decide which SIM should be “the one”.

Normally you choose the SIM card which is used for data traffic as “the one”.

[Webaschtl]

By chance I decided to have “the one” as SIM 1 – but I have not known this before. Thought both cards/slots are equal. Maybe technical reasons? Strange world…

[TobiasF]

You can actually decide which SIM slot should have the 3G/4G support. You only have to switch the other SIM card to “2G only” before, after that you can switch your preferred SIM card to 3G/4G. So I have 3G/4G on SIM 2 (because I use mobile data with SIM2).

As this behaviour is confusing, I filed a feature request for an easier change option. Like at the feature request = vote.

[Webaschtl]

Ah, thanks for your hint!

I searched, found & changed the setting:

[Johannes]

@Webaschtl

Maybe technical reasons?

Yes. As far as I understand, the SoC only has a single modem. In Dual SIM Dual Standby only one SIM is active at the same time. For 2G this usually means there’s some form of time multiplexing to keep both SIMs reachable (and as a result, the other SIM is not reachable when making a call). 3G/4G seems to work differently, more like an always-on connection, which precludes time multiplexing - although I’ve never found a decent explanation, so I could have gotten the wrong end of the stick.

Dual SIM Dual Active phones usually have two modems (though I’m guessing this doesn’t necessarily mean both are 4G capable!), but also use more power as a result.

[werner_noebauer]

Here is a pretty good overview on dual sim types:

Dual SIM