Hello,
From my experience, in most (all?) cases, the "untrusted non-3GPP
access" model is used. In this scenario, the mobile phone establishes an
ipsec tunnel with a network element called "ePDG" (Evolved Packet Data
Gateway) to connect to the mobile core. See 3GPP TS 24.302 for details.
The address(es) of the ePDG are discovered using DNS: the phone will try
to resolve epdg.epc.mncXXX.mccYYY.pub.3gppnetwork.org, where XXX is your
operator's Mobile Network Code (for instance Swisscom is 001), and YYY
is your Mobile Country Code (228 for Switzerland).
So I guess a first test can be to look for these addresses and watch for
ipsec traffic.
Best regards,
Alexandre
On 2020-06-25 08:56, Christian 'wiwi' Wittenhorst wrote:
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
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