[SR-Users] an issue on terminating dialog for kamailio 4.2.x

hi, I install kamailio 4.2.x on centos 6.5 via 'yum'. One endpoint called another, where one dialog is created, and caller and callee can talk with each other. But when the caller hangup the phone(i.e. send bye to the callee), the callee can't receive the bye message, and the dialog can't be terminated normally. I have captured the packets via wireshark, and uploaded kamailio.cfg and the captured files as attachment. In the captured file, PRACK and BYE message can be sent to kamailio server successfully, but kamailio server doesn't forward the two messages to the callee. Why PRACK and BYE message can't be sent to the callee? Looking forward to your help! B.R. Andrew