Yealink SIP-T4X Administration Manual page 454

6. User A mixes the RTP channels and establishes a conference between User B and
User C.
User A
F1. INVITE B
F4. 180 Ringing
F6. 200 OK
F7. ACK
Session1 established between User A and User B is active
F9. INVITE(sendonly)
Initiate
three party
conference
F12. 200 OK
F13. ACK
Session 1 established between User A and User B is hold
F15. INVITE C
F18. 180 Ringing
F20. 200 OK
F21. ACK
Proxy Server
F2. INVITE B
F3. 180 Ringing
F5. 200 OK
F8. ACK
F10. INVITE (sendonly)
F11. 200 OK
F14. ACK
F16. INVITE C
F17. 180 Ringing
F19. 200 OK
F22. ACK
Both calls are active, come into three-party conference
Appendix
User B User C
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