Hi at the moment I have the setup Internal.xml ext-rtp-ip = auto-nat ext-sip-ip = auto-nat External.xml ext-rtp-ip = “my_local_freeswitch_ip” ext-sip-ip = auto-nat RTP ports (only) are begin opened by UPNP and SIP via TCP is being keep open with “expire-seconds=600” and “register=true” (Is there an alternative for the expire-seconds ? nat-options-ping is only for endpoints registering to freeswitch, right?) The reason why I am doing this is, that I dont want to open up a SIP Port in the Firewall. But this setup up doesn’t seem right. Audio is working, inbound and outbound, both ways. But the echo application is not. When I change External.xml ext-rtp-ip = “auto-nat” I get one-way audio for inbound calls for the callee. The caller can be heard. I tried to analyses it in wireshark, but I don’t understand it. The sip provider keeps sending INVITE messages while freeswitch is confirming it with OK but keeps going on until the connection breaks. Thank you for your help