Dear Community.
We have a problem (tm): At some sites, WiFi Calling works, at others it does not. Sometimes it's dependent on the provider, e.g. Sunrise&Salt works, Swisscom does not. At another place, Salt&Swisscom works, but not Sunrise.
Does anyone know when a mobile devices decides that WiFi calling is possible? Which ports/protocols/... are used? What are the addresses of the endpoints? How do the probes work? Are there any specific, other requirements, such as: geolocation, RIPE DB entries, ...? Does anyone know of a decent technical spec?
I've seem some IPSEC tunnels and read draft-pularikkal. But there seems to be much more.
The issues are not device dependent, the used device (and subscriptions) do support WiFi Calling, and are able to use WiFi calling at "some" places.
Best regards
wiwi