B-37
Cisco SIP IP Phone Administrator Guide
Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
Cisco SIP IP Phone-to-Cisco SIP IP Phone Network Call Forwarding (Busy)
Figure B-11
illustrates successful call forwarding between Cisco SIP IP phones in which User B has
requested call forwarding from the network in the event the phone is busy. When User A calls User B,
the SIP proxy server tries to place the call to Cisco SIP IP phone B and, if the line is busy, the call is
transferred to Cisco SIP IP phone C. In this call flow scenario, the end users are User A, User B, and
User C. They are all using Cisco SIP IP phones, which are connected via an IP network.
The call flow scenario is as follows:
1.
User B requests that if their phone (Cisco SIP IP phone B) is busy, the network should forward
incoming calls to Cisco SIP IP phone C.
2.
User A calls User B.
3.
User B’s phone is busy.
4.
The network transfers the call to Cisco SIP IP phone C.
Figure B-11 Cisco SIP IP Phone-to-Cisco SIP IP Phone Network Call Forwarding (Busy)
IP
IP
11. 200 OK
5. INVITE B
9. 180 Ringing
10. 200 OK
13. ACK
8. INVITE C
6. 486 Busy Here
7. ACK
1. INVITE B
12. ACK
3. 300 Multiple Choices
2. INVITE B
4. ACK
IP Network
SIP IP
Phone
User A
SIP IP
Phone
User B
SIP IP
Phone
User C
Proxy
Server
Redirect
Server
IP
41472
2-way RTP channel