[Serusers] SIP registration failed, status=408 (Request Timeout)

hi: I installed ser-0.9.6 on centos 5. I start ser use ser -D -E. ser -D -E Listening on udp: 127.0.0.1 [127.0.0.1]:5060 udp: 121.14.136.107 [121.14.136.107]:5060 tcp: 127.0.0.1 [127.0.0.1]:5060 tcp: 121.14.136.107 [121.14.136.107]:5060 Aliases: tcp: localhost:5060 tcp: localhost.localdomain:5060 udp: localhost:5060 udp: localhost.localdomain:5060 When i registered with sip ua but the "SIP registration failed, status=408 (Request Timeout)" return. The annex is the ser.cfg file and tested result with sipsak.