Cisco SIP IP Phone Administrator's Manual page 150

Call Flow Scenarios for Successful Calls
Figure B-12 Cisco SIP IP Phone-to-Cisco SIP IP Phone Network Call Forwarding (No Answer)
IP
SIP IP
Phone
User A
1. INVITE B
7. 180 Ringing
13. 200 OK
14. ACK
2-way RTP channel
Cisco SIP IP Phone Administrator Guide
B-40
IP Network
Proxy
Server
2. INVITE B
3. 300 Multiple Choices
4. ACK
5. INVITE B
6. 180 Ringing
8. CANCEL
9. 200 OK
10. INVITE C
11. 180 Ringing
12. 200 OK
15. ACK
Appendix B
IP
SIP IP
Redirect
Phone
Server
User B
SIP Call Flows
IP
SIP IP
Phone
User C