Wi-Fi Calling on EE problem, is it worth trying one of these ROMs?


PhilipL

Members
Nov 7, 2021
6
13
I've just purchased a 11T Pro, great phone. The only issue I have is on Wi-Fi calling on the EE network. The connection drops every 50 minutes exactly, by that I mean if I monitor in my router diagnostic page I can see the keepalives being sent every 20s to port 4500 (the VPN that is created to connect back to EE), and at 50 minutes the connection is dropped and remade. Pixel phones don't exhibit this behaviour, they remain happily connected. Of course if on a call at the time the call is dropped.

Xiaomi phones are not offered on EE, so I'm suspecting there is some carrier settings baked in that are perhaps wrong (one could be the esp timeout which on my Pixel devices are set to 3000 seconds (so that's 50 minutes so is a bit of coincidence), so perhaps that value is set too high on the Xiaomi.

Would these carrier settings be different in the EU roms making it worth trying? Is there a way I can look at the carrier settings (Github maybe) that is in the source to see where the issue might be to help feed this back to Xiaomi.

Thanks for any help.
 

PhilipL

Members
Nov 7, 2021
6
13
I can confirm the Wi-Fi calling bug exists in:

EEA ROM
Global ROM
This ROM (seems to be based of Global)

Feedback has been sent to Xiaomi months ago but no response. Got a few weeks still in my return window so will be sending this phone back. Can't recommend the 11T Pro for the UK on EE (or any thing that runs over EE) if you would like to make use of reliable Wi-Fi calling.
 

PhilipL

Members
Nov 7, 2021
6
13
So I've been doing some diagnostics on the issue with Wi-Fi calling on EE in the UK. Possibly going all they way back to Qualcomm default supplied modem configurations, it seems that most, if not all Xiaomi and possibly other makes do not work correctly with EE in the UK with Wi-Fi calling. The symptoms of this are unreliable Wi-Fi calls where no call can last longer than 50 minutes, but may also drop much sooner depending on when you make or answer a call during the 50 minute cycle. If there is a VoLTE signal, it is possible the call will hand over okay, but if that signal is borderline it will give rise to further issues.

The problem is in the modem configuration settings. There is a rekey timer set to 3000 seconds, so every 50 minutes the established connection to EE's servers wants to get new security keys, but the information on how to negotiate and obtain those new keys is missing from the configuration. The result of this missing configuration is the negotiation fails at 50 minutes and the connection drops, a few seconds later the connection is re-established and the 50 minute count down to new keys starts again, and the cycle repeats.

I've been able to debug (via Qualcomm PST/EFS tools) and get a corrected configuration file (this compiles into the mdm_sw.mbn modem driver for EE) which resolves the problem, and keys are recreated all okay now and the connection no longer drops, and it would be great if this could be bundled into the EU ROMs. I'm trying to feed this back directly to Xiaomi but getting anyone's contact details who would take any notice is hard work.

If a dev wants to include this fix in the EU ROM or can give me the name of someone at Xiaomi I can contact, then please PM me.