Hi, Just encountered this in master branch: 1. pjsua is sending the INVITE with Via header still using the local IP address, and not the received/rport address (after successful REGISTER) 2. UAC -> kamailio -> UAC - make a call - send CANCEL - INVITE and CANCEL use different IP addresses in Via header - SIP proxy rejects CANCEL as not being part of a known transaction // IP address fixed up after NAT REGISTER: SIP/2.0/TLS 10.0.0.4:56394;rport;branch=z9hG4bKPjAjmLUcOq.RTRbAbmpU108Yw2PWW5lj.P;alias // this is the local IP address, pre-NAT! INVITE: SIP/2.0/TLS 192.168.0.2:34541;rport;branch=z9hG4bKPjQkOe7VO1tujCMj77tCQUFfZcvtQd8Ydu;alias // Correct! Uses the same Via line as REGISTER CANCEL: SIP/2.0/TLS 10.0.0.4:56394;rport;branch=z9hG4bKPjQkOe7VO1tujCMj77tCQUFfZcvtQd8Ydu;alias This occurs about 30% of the time. Anthony