Appendix
1087
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 Proxy Server User B User C
F1. INVITE B
F2. INVITE B
F3. 180 Ringing
F8. ACK
F9. INVITE C
F10. INVITE C
F11. 180 Ringing
F12. 180 Ringing
F13. 200 OK
F14. 200 OK
F15. ACK
F16. ACK
F4. 180 Ringing
F5. 302 Move Temporarily
F6. ACK
F7. 302 Move Temporarily
2-way RTP channel established
INVITE—User A to Proxy Server
User A sends the 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:
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.
A unique numeric identifier is
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