[Serusers] is that compliant?

Hi all, I have a problem with ringing message coming from our provider. Associate with the message, i find a SDP. Some UACs doesn't like that and doesn't give a ringback (Snom and Grandstream ata 486) SIP/2.0 180 Ringing..Via: SIP/2.0/UDP 192.168.2.101;rport=1039;received=81.247.182.42;branch=z9hG4bKfeb085ba0caf55 99..To: <sip:0495283361@finalcut.be>;tag=507b8a49..From: " Family Taylor" <sip:7321073@finalcut.be>;tag=cf8413e3df61a5a5..Call-ID: ae6f02682bb43efd@192.168.2.101..CSeq: 4667 INVITE..Record-Route: <sip:82.146.123.252>..Content-Type: application/sdp..Content-Length: 217....v=0..o=VoipSwitch 7772 7772 IN IP4 213.246.41.194..s=VoipSIP..i=Audio Session..c=IN IP4 213.246.41.194..t=0 0..m=audio 6772 RTP/AVP 18 101..a=rtpmap:18 G729/8000/1..a=rtpmap:101 telephone-event/8000..a=fmtp:101 0-15.. Is that correct and compliant? Thanks, Olivier