Hi,
This is a question for the more advanced telecom users out there: do you have an idea what the Zyxel 870HN (that is a Swisscom modem/router) has special to allow for the VoIP connection to go through (see image)? Maybe it’s something it doesn’t have (some new age protections)?
Here is an interesting error message in the “VoIP gateway”: Reason for error: DNS error.
