Yealink Telekom-Cloud-Telephone problems

Hi at all,
I have a problem with a new Telekom cloud telephone solution (Yealink) - it rings but you can’t hear the other person.

Do any of you have a Telekom cloud telephone system (yealink) running behind an IPfire? What did you set on IPfire to make it work?

Everything works when connected to a LANCOM router - so it must be a matter of settings for the IPFire. All needed ports according to the manufacturer (tcp/udp) are configured but there is still the problem.

Thanks for any idea. Ralph

hi
i had a similar problem with my voip provider solved by checking the stun server ports