Yealink SIP-T2XP - Page 467

Appendix
451
3. User A places User B on hold.
User A Proxy Server User B
F1. INVITE B
F2. INVITE B
F7. ACK
F8. ACK
F3. 180 Ringing
F6. 200 OK
F5. 200 OK
F4. 180 Ringing
F12. 200 OK
F9. INVITE B (sendonly)
F10. INVITE B (sendonly)
F11. 200 OK
F14. ACK
F13. ACK
No RTP packets being sent
2-way RTP channel established