INVITE Client Transaction

INVITE sip:bob@biloxi.com SIP/2.0
Via: SIP/2.0/UDP pc33.atlanta.com;branch=z9hG4bKkjshdyff
To: Bob
From: Alice ;tag=88sja8x
Max-Forwards: 70
Call-ID: 987asjd97y7atg
CSeq: 986759 INVITE

The ACK request for a non-2xx final response to this request would
look like this:

ACK sip:bob@biloxi.com SIP/2.0
Via: SIP/2.0/UDP pc33.atlanta.com;branch=z9hG4bKkjshdyff
To: Bob ;tag=99sa0xk
From: Alice ;tag=88sja8x
Max-Forwards: 70
Call-ID: 987asjd97y7atg
CSeq: 986759 ACK

Client transaction – INVITE 송신
Timer T1이용 (client와 server 사이의 RTT에 의해 설정)

처음 state : Calling state
TU가 INVITE와 함께 새로운 client transaction 생성
Transport layer로 보낸다. (Timer A 설정)
300-699 response => “Completed” state
ACK 생성
2xx => “Terminated” state
Proceeding state
Provisional response을 받았을 때
TU에게 전달
300-699 response => “Completed” state
ACK 생성
2xx => “Terminated” state