I have the following problem which I hope the more knowledgeable on here could shed some light on: Between my UA and the SIP server I have set up SRTP/TLS connection on and I can register normally with that enforced. When somebody (over the PSTN network using a regular phone number) tries to ring me, I get the above error. I did a bit of research and found that possible causes could either be wrong codec or the enforcement of SRTP (I have it as "Mandatory" in my UA), but I am still not 100% sure and thought to ask here. The error I am getting from my UA is shown above, though the underlying problem seems to be with the "SIP/2.0 488 Not Acceptable Here" message in packet 4 below. This is the full trace of what is happening (I masked my IDs and the relevant IP subnets): ========== ---------- 15:12:06 Packet 1/6, 976 bytes ---> UDP port 5060 INVITE sip:me at provider.voip audio->212.x.x.x:12706 UDP port 5060 ---------- INVITE sip:me at provider.voip SIP/2.0 Via: SIP/2.0/UDP 85.xx.xx.xx;branch=z9hG4bK12fd.d78b9b71.0 Via: SIP/2.0/UDP 212.x.x.x:5060;received=212.x.x.x;branch=z9hG4bK0679c35a;rport=5060 From: "+49xxxx" <sip:+49xxxx@212.x.x.x>;tag=as1012c966 To: <sip:me at provider.voip> Contact: <sip:%2b49xxxx at 212.x.x.x> Call-ID: 39dacf63231a416e13b2d2804a433687 at 212.x.x.x CSeq: 102 INVITE User-Agent: Provider-VOIP Max-Forwards: 68 Date: Sat, 06 Oct 2012 15:12:06 CET Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO Supported: replaces Content-Type: application/sdp Content-Length: 260 Thor-Scope: lookup-destination Thor-Origin: sip:212.x.x.x:5060 v=0 o=root 1888 1888 IN IP4 212.x.x.x s=session c=IN IP4 212.x.x.x t=0 0 m=audio 12706 RTP/AVP 0 8 3 101 a=rtpmap:0 PCMU/8000 a=rtpmap:8 PCMA/8000 a=rtpmap:3 GSM/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-16 a=ptime:20 a=sendrecv ========== ---------- 15:12:06 Packet 2/6, 1150 bytes <--- UDP port 5060 INVITE sip:me at provider.voip:52222 audio->81.x.x.x:57958 UDP port 5060 ---------- INVITE sip:me at provider.voip:52222;transport=tls;ob SIP/2.0 Record-Route: <sip:81.x.x.x;lr;ftag=as1012c966;did=05.76f75113> Via: SIP/2.0/UDP 81.x.x.x;branch=z9hG4bK12fd.65070351.0 Via: SIP/2.0/UDP 85.xx.xx.xx;branch=z9hG4bK12fd.d78b9b71.0 Via: SIP/2.0/UDP 212.x.x.x:5060;received=212.x.x.x;branch=z9hG4bK0679c35a;rport=5060 From: "+49xxxx" <sip:+49xxxx@212.x.x.x>;tag=as1012c966 To: <sip:me at provider.voip> Contact: <sip:%2b49xxxx at 212.x.x.x> Call-ID: 39dacf63231a416e13b2d2804a433687 at 212.x.x.x CSeq: 102 INVITE User-Agent: Provider-VOIP Max-Forwards: 68 Date: Sat, 06 Oct 2012 15:12:06 CET Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO Supported: replaces Content-Type: application/sdp Content-Length: 260 Thor-Scope: relay-destination Thor-Target: sip:178.x.x.x:52222;transport=tls v=0 o=root 1888 1888 IN IP4 212.x.x.x s=session c=IN IP4 81.x.x.x t=0 0 m=audio 57958 RTP/AVP 0 8 3 101 a=rtpmap:0 PCMU/8000 a=rtpmap:8 PCMA/8000 a=rtpmap:3 GSM/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-16 a=ptime:20 a=sendrecv ========== ---------- 15:12:06 Packet 3/6, 481 bytes ---> UDP port 5060 100 Giving a try for INVITE UDP port 5060 ---------- SIP/2.0 100 Giving a try Via: SIP/2.0/UDP 81.x.x.x;branch=z9hG4bK12fd.65070351.0 Via: SIP/2.0/UDP 85.xx.xx.xx;branch=z9hG4bK12fd.d78b9b71.0 Via: SIP/2.0/UDP 212.x.x.x:5060;received=212.x.x.x;branch=z9hG4bK0679c35a;rport=5060 From: "+49xxxx" <sip:+49xxxx@212.x.x.x>;tag=as1012c966 To: <sip:me at provider.voip> Call-ID: 39dacf63231a416e13b2d2804a433687 at 212.x.x.x CSeq: 102 INVITE Server: SIP Thor on OpenSIPS XS 1.8.0 Content-Length: 0 ========== ---------- 15:12:06 Packet 4/6, 722 bytes ---> UDP port 5060 488 Not Acceptable Here for INVITE UDP port 5060 ---------- SIP/2.0 488 Not Acceptable Here Via: SIP/2.0/UDP 81.x.x.x;branch=z9hG4bK12fd.65070351.0 Via: SIP/2.0/UDP 85.xx.xx.xx;branch=z9hG4bK12fd.d78b9b71.0 Via: SIP/2.0/UDP 212.x.x.x:5060;rport=5060;received=212.x.x.x;branch=z9hG4bK0679c35a Record-Route: <sip:85.xx.xx.xx:5061;transport=tls;lr;r2=on;ftag=as1012c966;did=05.c25aa83> Record-Route: <sip:85.xx.xx.xx;lr;r2=on;ftag=as1012c966;did=05.c25aa83> Record-Route: <sip:81.x.x.x;lr;ftag=as1012c966;did=05.76f75113> Call-ID: 39dacf63231a416e13b2d2804a433687 at 212.x.x.x From: "+49xxxx" <sip:+49xxxx@212.x.x.x>;tag=as1012c966 To: <sip:me at provider.voip>;tag=-FBQxyWnTqZHHrOenpJvRCDUnZwCgDYh CSeq: 102 INVITE Content-Length: 0 ========== ---------- 15:12:06 Packet 5/6, 660 bytes <--- UDP port 5060 488 Not Acceptable Here for INVITE UDP port 5060 ---------- SIP/2.0 488 Not Acceptable Here Via: SIP/2.0/UDP 85.xx.xx.xx;branch=z9hG4bK12fd.d78b9b71.0 Via: SIP/2.0/UDP 212.x.x.x:5060;rport=5060;received=212.x.x.x;branch=z9hG4bK0679c35a Record-Route: <sip:85.xx.xx.xx:5061;transport=tls;lr;r2=on;ftag=as1012c966;did=05.c25aa83> Record-Route: <sip:85.xx.xx.xx;lr;r2=on;ftag=as1012c966;did=05.c25aa83> Record-Route: <sip:81.x.x.x;lr;ftag=as1012c966;did=05.76f75113> Call-ID: 39dacf63231a416e13b2d2804a433687 at 212.x.x.x From: "+49xxxx" <sip:+49xxxx@212.x.x.x>;tag=as1012c966 To: <sip:me at provider.voip>;tag=-FBQxyWnTqZHHrOenpJvRCDUnZwCgDYh CSeq: 102 INVITE Content-Length: 0 ========== ---------- 15:12:06 Packet 6/6, 393 bytes ---> UDP port 5060 ACK sip:me at provider.voip UDP port 5060 ---------- ACK sip:me at provider.voip SIP/2.0 Via: SIP/2.0/UDP 85.xx.xx.xx;branch=z9hG4bK12fd.d78b9b71.0 From: "+49xxxx" <sip:+49xxxx@212.x.x.x>;tag=as1012c966 Call-ID: 39dacf63231a416e13b2d2804a433687 at 212.x.x.x To: <sip:me at provider.voip>;tag=-FBQxyWnTqZHHrOenpJvRCDUnZwCgDYh CSeq: 102 ACK Max-Forwards: 69 User-Agent: SIP Thor on OpenSIPS XS 1.8.0 Content-Length: 0 ==========