I shorten the trace to (hopefully) the relevant things. Asterisk is on 192.168.10.75, port 25060. Proxy is OpenSIPS on the same machine with port 5060 the phone which is ringing is on 192.168.10.200. Asterisk => Proxy U 192.168.10.75:25060 -> 192.168.10.75:5060 INVITE sip:kwe@192.168.10.75 SIP/2.0. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. Max-Forwards: 70. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: . Contact: . Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 INVITE. ... sdp cut of ... Proxy => Asterisk U 192.168.10.75:5060 -> 192.168.10.75:25060 SIP/2.0 100 Giving a try. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: . Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 INVITE. Proxy => Phone U 192.168.10.75:5060 -> 192.168.10.200:5060 INVITE sip:kwe@192.168.10.200:5060;transport=udp SIP/2.0. Via: SIP/2.0/UDP 192.168.10.75;branch=z9hG4bK425b.8a4be074.0. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. Max-Forwards: 69. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: . Contact: . Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 INVITE. ... sdp cut of ... Phone => Proxy U 192.168.10.200:5060 -> 192.168.10.75:5060 SIP/2.0 180 Ringing. Via: SIP/2.0/UDP 192.168.10.75;branch=z9hG4bK425b.8a4be074.0. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: ;tag=866953864. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 INVITE. Contact: "Karsten Wemheuer" ;+sip.instance="". Proxy => Asterisk U 192.168.10.75:5060 -> 192.168.10.75:25060 SIP/2.0 180 Ringing. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: ;tag=866953864. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 INVITE. Contact: "Karsten Wemheuer" ;+sip.instance="". When canceling the call, asterisk sends CANCEL to Proxy Asterisk => Proxy (Thanks to the solution in ASTERISK-19358) U 192.168.10.75:25060 -> 192.168.10.75:5060 CANCEL sip:kwe@192.168.10.75 SIP/2.0. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. Max-Forwards: 70. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: . Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 CANCEL. Proxy => Asterisk U 192.168.10.75:5060 -> 192.168.10.75:25060 SIP/2.0 200 canceling. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: ;tag=fc7bec6af74f3dd97fe73542f53baeeb-212f. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 CANCEL. Proxy => Phone U 192.168.10.75:5060 -> 192.168.10.200:5060 CANCEL sip:kwe@192.168.10.200:5060;transport=udp SIP/2.0. Via: SIP/2.0/UDP 192.168.10.75;branch=z9hG4bK425b.8a4be074.0. From: "Fred Feuerstein" ;tag=as16fd4c8c. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. To: . CSeq: 102 CANCEL. Phone => Proxy U 192.168.10.200:5060 -> 192.168.10.75:5060 SIP/2.0 200 OK. Via: SIP/2.0/UDP 192.168.10.75;branch=z9hG4bK425b.8a4be074.0. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: ;tag=866953864. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 CANCEL. Phone => Proxy U 192.168.10.200:5060 -> 192.168.10.75:5060 SIP/2.0 487 Request Terminated. Via: SIP/2.0/UDP 192.168.10.75;branch=z9hG4bK425b.8a4be074.0. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: ;tag=866953864. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 INVITE. Proxy => Phone U 192.168.10.75:5060 -> 192.168.10.200:5060 ACK sip:kwe@192.168.10.200:5060;transport=udp SIP/2.0. Via: SIP/2.0/UDP 192.168.10.75;branch=z9hG4bK425b.8a4be074.0. From: "Fred Feuerstein" ;tag=as16fd4c8c. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. To: ;tag=866953864. CSeq: 102 ACK. Proxy => Asterisk U 192.168.10.75:5060 -> 192.168.10.75:25060 SIP/2.0 487 Request Terminated. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: ;tag=866953864. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 INVITE. Asterisk => Phone (This differs to Asterisk 1.8.8.2, where ACK is sent to Proxy) U 192.168.10.75:25060 -> 192.168.10.200:5060 ACK sip:kwe@192.168.10.200:5060;transport=udp SIP/2.0. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. Max-Forwards: 70. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: ;tag=866953864. Contact: . Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 ACK. Proxy repeats 487 message, cause no ACK received U 192.168.10.75:5060 -> 192.168.10.75:25060 SIP/2.0 487 Request Terminated. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: ;tag=866953864. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 INVITE. Proxy repeats 487 message U 192.168.10.75:5060 -> 192.168.10.75:25060 SIP/2.0 487 Request Terminated. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: ;tag=866953864. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 INVITE. Proxy repeats 487 message U 192.168.10.75:5060 -> 192.168.10.75:25060 SIP/2.0 487 Request Terminated. Via: SIP/2.0/UDP 192.168.10.75:25060;branch=z9hG4bK0f3574a4. From: "Fred Feuerstein" ;tag=as16fd4c8c. To: ;tag=866953864. Call-ID: 7681f2214742d4c912e1dab171616baf@192.168.10.75. CSeq: 102 INVITE. ...