Yealink SIP-T48G Administrator's Manual page 595

4. User B accepts the call from User C.
User A
F1. INVITE B
F4. 180 Ringing
F6. 200 OK
F7. ACK
2-way RTP channel established
F10. INVITE A
F11. 180 Ringing
F13. INVITE B ( sendonly )
F316 200 OK
F17. ACK
No RTP Packets being sent
F19. 200 OK
F22. ACK
Step
INVITE—User A to Proxy
F1
Server
Proxy Server
F2. INVITE B
F3. 180 Ringing
F5. 200 OK
F8. ACK
F14. INVITE B ( sendonly )
F15. 200 OK
F18. ACK
2-way RTP channel established
Action
User B
F9. INVITE A
F12. 180 Ringing
F20. 200 OK
F21. ACK
Description
User A sends an INVITE message to a
proxy server. The INVITE request is an
invitation to User B to participate in a
Appendix
User C
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