Cross sim calling/backup calling reliability

stonefish1

Hi all,
I've recently had the pleasure of using Graphene's recently added feature of cross sim calling.
Fantastic for travel use with a dual sim setup where one is a travel esim for data, with home SIM calling out via the travel esim's data connection.

I notice something and thought it might be able to contribute to improved reliability of this feature.
I am using Pixel 7a

The only way I could get this feature working was if I did the following.
Assume that phone was rebooted and both SIMs are on.

Put phone in Flight Mode
Enable WiFi
Confirm that I cannot call on home SIM
Disable Flight Mode
Confirm that I can do a traditional WiFi call on home SIM
Disable WiFi
Cross sim calling (VoLTE) from the home SIM over the data connection of travel eSIM now works (as if it was the fallback option of WiFi calling when the WiFi is removed)

So it seems to me that we may have some problem with cross sim calling not working until it effectively becomes the fallback option of a instantiation of WiFi-calling?

Please let me know if I am doing something wrong.

For clarity, I could never get Cross Sim Calling working if I did not have a genuine WiFi connection available to start from. So if I rebooted the phone in an area without WiFi, then I would not be able to get Cross Sim Calling working again until I found a WiFi network. I believe this is not intended behaviour.

Thank you!

wizoatk

stonefish1

Enabling Wi-Fi shouldn't be necessary. More likely, Cross SIM Calling is not actually enabled.

To enable:

Go to Settings > Network and Internet > SIMs > Your primary SIMs
Set Calls and Texts to your Home SIM
Set Mobile data to your Travel SIM
Turn Automatic data switching Off and On (this is the important bit)

You should see Mobile Network: <name> Backup calling on your Home SIM settings page. If not, backup to the SIMs summary page and select your Home SIM again.

Assuming that works, you should be able to restart the phone and have Backup Calling working without any extra dance or fuss.

stonefish1

wizoatk

Thanks for your reply!
Cross SIM Calling was enabled. And I read somewhere that it was necessary to toggle, go back, and toggle again - so I did that too.

So I just trialled this. From a working state of Cross SIM calling, I did the following:

Switched Flight Mode on, then back off
Observe in About Phone --> SIM1 that it is not yet connected with Backup Calling, but is connected to the roaming provider's network
Confirmed that primary SIMs are set to Calls: home SIM, Texts: home SIM, Mobile data: travel SIM
Toggle automatic data switching off, then back on

Backup Calling does not come back after waiting a few minutes.

Turn WiFi on
Confirm that WiFi calling is still not available on home SIM
Toggle flight mode on, then off
Confirm that WiFi calling is now available on home SIM
Confirm that home SIM is still declaring roaming provider as Network (in About Phone)
Kill WiFi
about 0.5seconds after killing WiFi, observe that Network (in About Phone) switches to "<name> Backup calling"

Please let me know if you still think this is an operator problem. To me it seems that the phone doesn't see the Backup Calling (VoLTE?) as a viable option for an alternative path for voice calls until WiFi is activated and removed.

wizoatk

stonefish1

I don't think this is an operator problem. My working premise is that having Backup Calling automatically preempt roaming calling wasn't intented to work, and you've found an interesting work around. I'll give it some more thought.

If you've got the time and inclination, perhaps you can force a disconnect on your home SIM rather than having it roam? Perhaps one of the following:

If there is no 3G service available, try enabling 2G network protection and setting preferred network type to 3G
If there is no 5G SA service available, try enabling 5G Only. You might have to use Carrier Overrides to enable the 5G capabilities "Force NSA and SA" in order for "5G
Turn off the Automatically select network, and manually select a "(forbidden network)". Note that this is not reliable as the phone may go back to automatically select by itself.

See if things work easier and/or without having to tickle Wi-Fi on off. Please note that Vo4G and Wi-Fi Calling must be on in your Home SIM settings or Cross Sim Calling won't work at all.

stonefish1

wizoatk
Thanks wizoatk.

I did:

Set Home SIM preference to "5G only". It appears there is no 5G here so that resulted in "No service" on Home SIM.
Toggled Automatic Data Switching off, then on
Still "No service" on Home SIM. So I guess we can conclude here that forcing disconnect on Home SIM also does not produce intended result of Backup Calling?
-----------------------------------------
For curiousity - I enabled WiFi.
WiFi calling from Home SIM worked immediately. I know it was calling from Home SIM because travel eSIM does not have any calling functionality (data only). I also noticed that with WiFi enabled, in About Phone, Home SIM now shows Network: $real-network-provider, Mobile network state: Disconnected, Mobile data network type: IWLAN
Switching WiFi off - Home SIM reverted to No Service. This was interesting, I thought this would work now.
Revert original changes - by toggling off 2G network protection, and setting Preferred Network Type back to "5G (recommended)"
Home SIM reverts to the roaming provider for service. Backing Calling still unavailable. In About Phone--> Home SIM --> Mobile voice network type = 4G
Enable WiFi
Observe WiFi calling is still not available after 3mins
Confirm in About Phone --> Home SIM --> Mobile voice network type is still "4G"
Enable Flight Mode (note: now Flight Mode is on, and WiFi is still on)
Disable Flight Mode
Observe that WiFi calling is now working. (Does WiFi need to be available before the SIM first becomes active in order to get WiFi calling - is that a clue?).
Note that About Phone --> Home SIM --> Mobile voice network type = "4G" while WiFi calling is working
Switch WiFi off --> Home SIM immediately switches to "$home-network Backup calling"
Observe that Mobile voice network type is still "4G". I guess that doesn't change when Backup Calling is working. I thought it would.

Note: on Home SIM, carrier settings are (and were unchanged during this):
VoLTE/Vo4G: default available
VoNR/Vo5G: default available
5G: default NSA and SA
WiFi calling availability: default available
Cross SIM calling / backup calling availability: Default unavailable (but for travel eSIM it is Default available)

Edit: confirming (as per your last paragraph) that Vo4G and Wi-Fi Calling were always enabled on Home SIM. I guess this is indicated by the fact that Backup Calling does eventually work. It just needs the right sequence of events to work.

wizoatk

stonefish1

Thanks for the details. Since you've eliminated roaming as the cause, I should be able to replicate your behavior if I can figure out what on your phone is different from mine (other than model number). If I can't replicate then the next step would be to open an issue, assuming you haven't already.

https://github.com/GrapheneOS/os-issue-tracker

Please confirm what, if anything, you have done with carrier-overrides, adb, root, etc. that could possibly be affecting. Also, if you could provide SIM settings details for both of the SIMs.

It's a puzzle.

Edit: to be clear, what you're reporting is not intended behavior.

wizoatk

stonefish1

Can you provide what the "Wi-Fi Calling - Calling preference" of the Home SIM is set to? Should be either "Call over Wi-Fi" or "Call over mobile network". It's unlikely to affect Cross Sim Calling directly, but it would help explain some of your observations.

stonefish1

Thanks for reply @wizoatk
Appreciate your time looking into this.

Carrier overrides: nil for both SIMs.
No changes to GrapheneOS at all. Just stock.
Phone is Pixel 7a as you know.

SIM settings are as follows:
Home SIM (physical SIM)
Roaming (data): off
4G calling: on
Preferred network type: 4G only (originally was 5G recommended but switched today for battery)
Carrier settings overrides: none
Default carrier settings that are available: VoLTE/Vo4G, VoNR/Vo5G, 5G NSA and SA, Wi-Fi Calling
Wifi calling: on
Calling preference: Call over Wi-Fi
Roaming preference: Wi-Fi
Automatically select network: on
2G protection: off

Travel esim
Roaming (data): on
Preferred network type: LTE (but note: originally was 5G, I switched to try save battery)
Carrier setting overrides: none
Default carrier settings that are available: 5G NSA, Cross SIM calling/backup calling
Automatically select network: on
2G protection: off

Settings on SIMs page:
Both SIMs on
Mobile data: on
Auto data switching: on
Primary SIMS:
Calls: Home SIM
Texts: Home SIM
Mobile data: travel esim

Please let me know if I can help in any way.

Novalissoide

stonefish1 Is Developer options turned ON, or OFF?

stonefish1

Novalissoide
I never turned Developer Options on, so it is presumably OFF (if OFF by default)

stonefish1

wizoatk
Sorry - I did put this in my reply yesterday, but I see now that my indented formatting did not work to show child settings.

Home SIM:
Use WiFi Calling: on
...Calling preference: Call over Wi-Fi
...Roaming preference: Wi-Fi

I have had that setting the whole time.
It's a good point that perhaps this is causing a problem with Cross Sim Calling only working after WiFi calling works then fails.

So I tested this.
From a state of working WiFi calling, I changed to:
WiFi Calling: on
...Calling preference: call over mobile network
...Roaming preference: mobile

But the outcome was the same. The Home SIM switched network to roaming provider. No Backup Calling available. I believe I read on Github that one of the requirements is that WiFi calling is on for Backup Calling to work.

I also switched WiFi Calling off completely and confirm the expected result - Home SIM still just uses roaming provider network. No Backup Calling.

Then I reverted all of the following settings:
WiFi Calling: on
Calling Preference: WiFi
Roaming Preference: WiFi
Result: Home SIM still stays on roaming network, no Backup Calling.

Toggled Auto Data Switching off then on and result is same.

Toggle WiFi to on. Wi-Fi calling does not enable. Confirm by trying to make call. Confirm by checking Home SIM status in About Phone: Network: roaming provider, Mobile voice network type: 4G, Mobile data network type: 4G, Roaming: Roaming

Toggle Flight Mode to on (with WiFi still on)
Toggle Flight Mode to off
Now Home SIM immediately takes on WiFi Calling. About Phone --> Home SIM Status says:
Network: $home_network, Mobile voice network type: 4G, Mobile data network type: IWLAN, Roaming: Roaming
So is there where our first problem is? That WiFi calling will not take effect unless WiFi connection precedes attempt to establish Home SIM network connection?

Then disable WiFi.
Home SIM's Mobile data network type immediately switches to 4G, and 2 seconds later Network switches to $home-network Backup Calling

I am a little more convinced that our problem might be that WiFi Calling will not activate unless WiFi precedes initial Home SIM network connection. Once WiFi Calling is working, it appears seamless to switch from WiFi Calling to Cross Sim Calling. I recall that one of the conditions for Cross Sim Calling is that WiFi Calling is enabled. So could this be where the condition is failing which is preventing Backup Calling from firing?

wizoatk

stonefish1 I am a little more convinced that our problem might be that WiFi Calling will not activate unless WiFi precedes initial Home SIM network connection.

That doesn't feel quite right to me. You've provided enough detail. I've been able to reproduce some, but not all of your observations. I'll likely be able to tell what is actually going on when I put a test unit (with a debug build) on the bench and look at some logs. Likely some time in the near future.

Freek

stonefish1 are you tried VPN with WiFi calling?
Me also looking for a solution to avoid roaming charges.

I never went into real roaming places but here what I did to create the roaming environment.

A physical router (rooted mobile) with VPN and able to tunnel all the hotspot (WiFi clients) traffic through VPN, then WiFi calling detecting iam in roaming places. VPN server i connected to different countrie.

I am tried to help some roaming friends but I don't know whats the issues, they are unable to use WiFi calling when VPN connected in rooted mobile. Without VPN they are able to connect but it's roaming 😄 .
There is a skill issue too .
Note no vpn using in the device that we are enabling WIFi calling.