Network Call Forwarding (Busy - Cisco 7960G Administrator's Manual

Appendix B SIP Call Flows
Step Action
3. 302 Moved Temporarily—SIP
redirect server to SIP proxy
server
4. ACK—SIP proxy server to
redirect server
INVITE—SIP proxy server to
5.
Phone C
6. 180 Ringing—Phone C to SIP
proxy server
7. 200 OK—Phone C to SIP proxy
server
200 OK—SIP proxy server to
8.
Phone A
ACK—Phone A to SIP proxy
9.
server
ACK—SIP proxy server to
10.
Phone C

Network Call Forwarding (Busy)

Figure B-12
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 Phone B, and, if the line is busy, the call is transferred to
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.
2.
3.
4.
Description
The SIP redirect server sends a SIP 302 Moved temporarily message to the SIP
proxy server. The message indicates that User B is not available at Phone B and
includes instructions to locate User B at Phone C.
The SIP proxy server sends the SIP ACK to the SIP redirect server.
The SIP proxy server sends a SIP INVITE request to Phone C. The request is an
invitation to User C to participate in a call session.
Phone C sends a SIP 180 Ringing response to the SIP proxy server.
Phone C sends a SIP 200 OK response to the SIP proxy server.
The SIP proxy server forwards the SIP 200 OK response to Phone A.
Phone A sends a SIP ACK to the SIP proxy server. The ACK confirms that the SIP
proxy server has received the 200 OK response from Phone C.
The SIP proxy server forwards the SIP ACK to the Phone C. The ACK confirms
that Phone A has received the 200 OK response from Phone C.
illustrates successful call forwarding between Cisco SIP IP phones in which User B has
User B requests that if Phone B is busy, the network should forward incoming calls to Phone C.
User A calls User B.
User B is busy.
The network transfers the call to Phone C.
Call Flow Scenarios for Successful Calls
Cisco SIP IP Phone Administrator Guide, Release 6.x and 7.x
B-33