Yealink SIP-T2xP Administrator's Manual page 487

The following figure illustrates successful call forwarding between Yealink SIP IP phones
in which User B has enabled busy call forward. The incoming call is forwarded to User C
when User B is busy. In this call flow scenario, the end users are User A, User B, and User
C. They are all using Yealink SIP IP phones, which are connected via an IP network.
The call flow scenario is as follows:
1. User B enables busy call forward, and the destination number is User C.
2. User A calls User B.
3. User B is busy.
4. User B forwards the incoming call to User C.
5. User C answers the call.
Call is established between User A and User C.
User A
F1. INVITE B
F4. 180 Ringing
F7. 302 Move Temporarily
F8. ACK
F9. INVITE C
F12. 180 Ringing
F14. 200 OK
F15. ACK
Proxy Server
F2. INVITE B
F3. 180 Ringing
F5. 302 Move Temporarily
F6. ACK
F10. INVITE C
F11. 180 Ringing
F13. 200 OK
F16. ACK
2-way RTP channel established
User B
Appendix
User C
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