I'm using SER on a Public IP, do IPv4 and IPv6 Conversion, Nathelper Module and RTPProxy. Both parties are behind NAT and gateways/routers arranged to forward 5060 UDP and TCP ports to LAN IP's of the ATA's on both side. There are 3 Registered Users, 8334454556 can call 8334843600, everything is okay, each party talks, the quality of voice is great. But when 8334843600 calls 8334454556, there's no ringing tone, nothing happens. When i check wih serctl util, i realized one thing like ; Contact : 'sip:8334454556@81.215.239.231:5060' Call-ID : &#39;13491B1111341212(a)81.215.239.231&#39; <<< This is Public IP Contact : 'sip:8334843600@85.96.192.140:5060' Call-ID : &#39;1360D1B911761212(a)192.168.0.101&#39; <<< This is LAN IP What may be wrong with SER or ATA's. root@sipproxy~> serctl ul show Dumping all contacts may take long: are you sure you want to proceed? [Y|N] y ===Domain list=== ---Domain--- name : 'location_inet6' size : 512 table: 0x422b80f8 d_ll { n : 0 first: (nil) last : (nil) } ---/Domain--- ---Domain--- name : 'location_inet4' size : 512 table: 0x422b6090 d_ll { n : 3 first: 0x422ba1f8 last : 0x422ba100 } ...Record(0x422ba1f8)... domain: 'location_inet4' aor : '103201' ~~~Contact(0x422ba328)~~~ domain : 'location_inet4' aor : '103201' Contact : 'sip:103201@212.156.169.125:5060' Expires : 1491 q : 0.00 Call-ID : &#39;7320E5ADBA8E1526(a)212.156.169.125&#39; CSeq : 70 replic : 0 User-Agent: 'Unknown' State : CS_NEW Flags : 0 next : (nil) prev : (nil) ~~~/Contact~~~~ .../Record... ...Record(0x422ba2e0)... domain: 'location_inet4' aor : '8334454556' ~~~Contact(0x422ba238)~~~ domain : 'location_inet4' aor : '8334454556' Contact : 'sip:8334454556@81.215.239.231:5060' Expires : 56 q : 0.00 Call-ID : &#39;13491B1111341212(a)81.215.239.231&#39; CSeq : 128 replic : 0 User-Agent: 'Unknown' State : CS_NEW Flags : 0 next : (nil) prev : (nil) ~~~/Contact~~~~ .../Record... ...Record(0x422ba100)... domain: 'location_inet4' aor : '8334843600' ~~~Contact(0x422ba148)~~~ domain : 'location_inet4' aor : '8334843600' Contact : 'sip:8334843600@85.96.192.140:5060' Expires : 32 q : 0.00 Call-ID : &#39;1360D1B911761212(a)192.168.0.101&#39; CSeq : 8 replic : 0 User-Agent: 'Unknown' State : CS_NEW Flags : 0 next : (nil) prev : (nil) ~~~/Contact~~~~ .../Record... ---/Domain--- ===/Domain list=== root@sipproxy~> --