Hi our FS is on public ip but the voip server to which trunk is made (SFB) is behind NAT. So the issue is that in SDP is private ip and FS sends RTP to this private ip, it does not change to src ip from which sip request was received. Remote SDP: 2016-04-21 08:04:00.954752 [DEBUG] sofia.c:5614 Remote SDP: v=0 o=- 46176 1 IN IP4 172.16.2.3 s=session c=IN IP4 172.16.2.3 b=CT:1000 t=0 0 m=audio 31200 RTP/AVP 8 101 13 c=IN IP4 172.16.2.3 a=rtpmap:8 PCMA/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-16 a=rtpmap:13 CN/8000 a=rtcp:31201 a=label:Audio And then: xxx.xxx.xxx.xxx (FS public ip) port 17094 -> 172.16.2.3 port 31200 codec: 8 ms: 30 I tried with: <param name="NDLB-force-rport" value="true"/> <param name="aggressive-nat-detection" value="true"/> on internal profile and on trunk profile but the same. tnx for help! Miha