[SR-Users] CANCEL message within transaction not being relayed

Hi, We tested the following on Kamailio 3.x and 4.x and observed the same behavior. INVITE and CANCEL are sent to Kamailo from the same source within the same transaction. (branch value in the first via header are the same in both INVITE and CANCEL message. Also FROM and TO header are same as well). However, Kamailio does not relay CANCEL message. UAC keep sending CANCEL till timeout. Apparently, t_check_trans() returns false. Can anyone help me on this issue on why Kamailio does not relay CANCEL message? Thanks, AS INVITE received by Kamailio INVITE sip:1111111@10.10.10.10:5060;user=phone SIP/2.0 Via: SIP/2.0/UDP 20.20.20.20:5060;branch=z9hG4bKkjhg4n100gagvkoup741.1 Max-Forwards: 69 From: <sip:2222222@20.20.20.20>;tag=SDl9eu701-1c1026774897 To: <sip:1111111@10.10.10.10;user=phone> Call-ID: SDl9eu701-36d75c874d3f463f6c83c5c94cc98b77-8q7ug02 CSeq: 1 INVITE Contact: <sip:2222222@20.20.20.20:5060;transport=udp> Supported: em,timer,replaces,path,resource-priority,sdp-anat Allow: REGISTER,OPTIONS,INVITE,ACK,CANCEL,BYE,NOTIFY,PRACK,REFER,INFO,SUBSCRIBE,UPDATE User-Agent: CS-CustomerName/v.6.60A.274 Content-Type: application/sdp Content-Length: 237 P-Asserted-Identity: tel:2222222 P-Asserted-Identity: sip:2222222@192.168.0.1 after 70 msec CANCEL received by Kamailio in the same transaction CANCEL sip:1111111@10.10.10.10:5060;user=phone SIP/2.0 Via: SIP/2.0/UDP 20.20.20.20:5060;branch=z9hG4bKkjhg4n100gagvkoup741.1 CSeq: 1 CANCEL Max-Forwards: 69 From: <sip:2222222@20.20.20.20>;tag=SDl9eu701-1c1026774897 To: <sip:1111111@10.10.10.10.;user=phone> Call-ID: SDl9eu701-36d75c874d3f463f6c83c5c94cc98b77-8q7ug02 Content-Length: 0 Reason: Q.850 ;cause=16