Hi! I have a very weird trouble here... I've been watching using a sniffer the messages exchange between 2 UA and SER .... and I can see very clear that the Caller UA never reply with an ACK message after it has received the 200 OK message from the Callee UA. It just open the rtp port and start sending out rtp streams... I have tried this either using ATA and Sipuras, but always the same result... because of this the caller never received audio streams from the callee due this last one is waiting for the ACK message after it sent out the 200 OK message... I have no clue why they are no sending this message to the callee.. I need help please!!! Any help or clue or hint...or whatever will be really appreciate!!! Thanks in advance! Armando Marrero Cti, Miami, FL Here is a Copy of a ngrep session. This ngrep session is in the attached file too. Bob using Real IP , Armando Private IP behind NAT.... rtpproxy is enforced. Call 1 = From Bob -> Armando = Success Call 2 = From Armando -> Bob = Failed because Armando UA never reply with ACK after 200 Ok Message ############ Call 1 caller: Bob , Callee : Armando.... Successfull Call Setup U Armando -> SER SIP/2.0 200 OK..Via: SIP/2.0/UDP 10.1.90.116;branch=z9hG4bK1ba9.f6fe0847.0 .Via: SIP/2.0/UDP 66.231.238.215:5060..Record- Route: <sip:3056034425@10.1.90.116;ftag=1564176202;lr=on>..From: <sip:1234@10.1.90.116;user=phone>;tag=1564176202..To: <s ip:3056034425@10.1.90.116;user=phone>;tag=642782702..Call-ID: 2352639743@66.231.238.215..CSeq: 1 INVITE..Contact: <sip:30 56034425@192.168.0.103:5061;user=phone;transport=udp>..Server: Cisco ATA 186 v2.16 ata18x (030509a)..Content-Length: 203 ..Content-Type: application/sdp....v=0..o=3056034425 62077 62077 IN IP4 192.168.0.103..s=ATA186 Call..c=IN IP4 192.168.0. 103..t=0 0..m=audio 16384 RTP/AVP 0 101..a=rtpmap:0 PCMU/8000/1. a=rtpmap:101 telephone-event/8000..a=fmtp:101 0-15.. # U SER -> Bob SIP/2.0 200 OK..Via: SIP/2.0/UDP 66.231.238.215:5060..Record-Route: <sip:3056034425@10.1.90.116;ftag=1564176202;lr=on>..F rom: <sip:1234@10.1.90.116;user=phone>;tag=1564176202..To: <sip:3056034425@10.1.90.116;user=phone>;tag=642782702..Call-ID : 2352639743@66.231.238.215..CSeq: 1 INVITE..Contact: <sip:3056034425@66 176.127.120:5061;user=phone;transport=udp>..Serv er: Cisco ATA 186 v2.16 ata18x (030509a)..Content-Length: 242. Content-Type: application/sdp....v=0..o=3056034425 62077 62077 IN IP4 192.168.0.103..s=ATA186 Call..c=IN IP4 66.231.238.115..t=0 0. m=audio 35118 RTP/AVP 0 101..a=rtpmap:0 PCMU/8 000/1..a=rtpmap:101 telephone-event/8000..a=fmtp:101 0-15. a=direction:active..a=nortpproxy:yes.. # U Bob -> SER ACK sip:3056034425@10.1.90.116 SIP/2.0..Route: <sip:3056034425@66.176.127 120:5061;user=phone;transport=udp>..Via: SIP/2. 0/UDP 66.231.238.215:5060..From: <sip:1234@10.1.90.116;user=phone> tag=1564176202..To: <sip:3056034425@10.1.90.116;user=p hone>;tag=642782702..Call-ID: 2352639743@66.231.238.215..CSeq: 1 ACK. User-Agent: Cisco ATA 186 v2.15 ata18x (030313a).. Content-Length: 0.... # U SER -> Armando ACK sip:3056034425@66.176.127.120:5061;user=phone;transport=udp SIP/2.0. Max-Forwards: 10..Record-Route: <sip:3056034425@ 10.1.90.116;ftag=1564176202;lr=on>..Via: SIP/2.0/UDP 10.1.90.116;branch=0. Via: SIP/2.0/UDP 66.231.238.215:5060..From: <s ip:1234@10.1.90.116;user=phone>;tag=1564176202..To: <sip:3056034425@10.1 90.116;user=phone>;tag=642782702..Call-ID: 23526 39743@66.231.238.215..CSeq: 1 ACK..User-Agent: Cisco ATA 186 v2.15 ata18x (030313a)..Content-Length: 0.... ################## Call 2 caller: Armando , Callee : Bob.... Failed Call Setup .... U Bob -> SER SIP/2.0 200 OK..Via: SIP/2.0/UDP 10.1.90.116;branch=z9hG4bK4544.49cf0507.0 .Via: SIP/2.0/UDP 192.168.0.103:5061;received= 66.176.127.120..Record-Route: <sip:1234@10.1.90.116;ftag=298050148;lr=on>. From: <sip:3056034425@lserver.telecode.com;use r=phone>;tag=298050148..To: <sip:1234@lserver.telecode.com;user=phone> tag=1758946682..Call-ID: 2670895917(a)192.168.0.103. .CSeq: 1 INVITE..Contact: <sip:1234@66.231.238.215:5060;user=phone transport=udp>..Server: Cisco ATA 186 v2.15 ata18x (0 30313a)..Content-Length: 197..Content-Type: application/sdp....v=0..o=1234 1415 1415 IN IP4 66.231.238.215..s=ATA186 Call ..c=IN IP4 66.231.238.215..t=0 0..m=audio 16384 RTP/AVP 0 101..a=rtpmap:0 PCMU/8000/1..a=rtpmap:101 telephone-event/8000. .a=fmtp:101 0-15.. # U SER -> Armando SIP/2.0 200 OK..Via: SIP/2.0/UDP 192.168.0.103:5061;received=66.176.127 120..Record-Route: <sip:1234@10.1.90.116;ftag=298 050148;lr=on>..From: <sip:3056034425@lserver.telecode.com;user=phone> tag=298050148..To: <sip:1234@lserver.telecode.com;u ser=phone>;tag=1758946682..Call-ID: 2670895917@192.168.0.103..CSeq: 1 INVITE..Contact: <sip:1234@66.231.238.215:5060;user =phone;transport=udp>..Server: Cisco ATA 186 v2.15 ata18x (030313a). Content-Length: 235..Content-Type: application/sdp. ...v=0..o=1234 1415 1415 IN IP4 66.231.238.215..s=ATA186 Call..c=IN IP4 66 231.238.115..t=0 0..m=audio 35122 RTP/AVP 0 10 1..a=rtpmap:0 PCMU/8000/1..a=rtpmap:101 telephone-event/8000..a=fmtp:101 0-15..a=direction:active..a=nortpproxy:yes.. # ------ no ACK send back....in this moment Armando UA just open rtp and start sending voice streams ------ Bob User Agent resend this several times , but never get ACK message from Armando UA U Bob -> SER SIP/2.0 200 OK..Via: SIP/2.0/UDP 10.1.90.116;branch=z9hG4bK4544.49cf0507.0 .Via: SIP/2.0/UDP 192.168.0.103:5061;received= 66.176.127.120..Record-Route: <sip:1234@10.1.90.116;ftag=298050148;lr=on>. From: <sip:3056034425@lserver.telecode.com;use r=phone>;tag=298050148..To: <sip:1234@lserver.telecode.com;user=phone> tag=1758946682..Call-ID: 2670895917(a)192.168.0.103. .CSeq: 1 INVITE..Contact: <sip:1234@66.231.238.215:5060;user=phone transport=udp>..Server: Cisco ATA 186 v2.15 ata18x (0 30313a)..Content-Length: 197..Content-Type: application/sdp....v=0..o=1234 1415 1415 IN IP4 66.231.238.215..s=ATA186 Call ..c=IN IP4 66.231.238.215..t=0 0..m=audio 16384 RTP/AVP 0 101..a=rtpmap:0 PCMU/8000/1..a=rtpmap:101 telephone-event/8000. .a=fmtp:101 0-15.. # U SER -> Armando SIP/2.0 200 OK..Via: SIP/2.0/UDP 192.168.0.103:5061;received=66.176.127 120..Record-Route: <sip:1234@10.1.90.116;ftag=298 050148;lr=on>..From: <sip:3056034425@lserver.telecode.com;user=phone> tag=298050148..To: <sip:1234@lserver.telecode.com;u ser=phone>;tag=1758946682..Call-ID: 2670895917@192.168.0.103..CSeq: 1 INVITE..Contact: <sip:1234@66.231.238.215:5060;user =phone;transport=udp>..Server: Cisco ATA 186 v2.15 ata18x (030313a). Content-Length: 235..Content-Type: application/sdp. ...v=0..o=1234 1415 1415 IN IP4 66.231.238.215..s=ATA186 Call..c=IN IP4 66 231.238.115..t=0 0..m=audio 35122 RTP/AVP 0 10 1..a=rtpmap:0 PCMU/8000/1..a=rtpmap:101 telephone-event/8000..a=fmtp:101 0-15..a=direction:active..a=nortpproxy:yes.. # U Bob -> SER SIP/2.0 200 OK..Via: SIP/2.0/UDP 10.1.90.116;branch=z9hG4bK4544.49cf0507.0 .Via: SIP/2.0/UDP 192.168.0.103:5061;received= 138,3 56%