Yealink T46G Administrator's Manual page 393

The call flow scenario is as follows:
User A calls User B.
1.
User B answers the call.
2.
User B hangs up.
3.
User A
F1. INVITE B
F4. 100 Trying
F6. 180 Ringing
F8. 200 OK
F9. ACK
F12. BYE
F13. 200 OK
Step
F1 INVITE—User A to Proxy Server
Proxy Server
2-way RTP channel established
Action
User A sends a SIP INVITE message to a
proxy server. The INVITE request is an
invitation to User B to participate in a call
session.
In the INVITE request:


F2. INVITE B
F3. 100 Trying
F5. 180 Ringing
F7. 200 OK
F10. ACK
F11. BYE
F14. 200 OK
Description
The IP address of User B is inserted in
the Request-URI field.
User A is identified as the call session
initiator in the From field.
Appendix
User B
379