B-27
Cisco Unified IP Phone 7960G and 7940G Administration Guide for Release 8.0 (SIP)
OL-7890-01
Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
Call Transfer with Consultation Using Failover
Figure B-10
illustrates a successful call between Cisco SIP IP phones in which two parties are in a call,
one of the participants contacts a third party, and then that participant transfers the call to the third party.
This is called an attended transfer. 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 A calls User B.
2.
User B answers the call.
3.
User B calls User C, and User C consents to take the call.
4.
User B transfers the call to User C.
5.
User B disconnects with User C.
6.
User C and User A connect to each other.
20.
INVITE—Phone A to Phone C
Phone A sends a SIP INVITE request to Phone C. The request contains the
following information:
•
Referred-By: B
•
Replaces: B
21.
200 OK—Phone C to Phone A
Phone C sends a SIP 200 OK response to Phone A. The response notifies Phone A
that the INVITE request has been received.
22.
ACK—Phone A to Phone C
Phone A sends a SIP ACK to Phone C. The ACK confirms that Phone A has
received the 200 OK response from Phone C.
23.
BYE—Phone C to Phone B
Phone C sends a SIP BYE request to Phone B.
24.
200 OK—Phone B to Phone C
Phone B sends a SIP 200 OK response to Phone C. The response notifies Phone C
that the BYE request has been received.
25.
NOTIFY—Phone A to Phone B
Phone A sends a NOTIFY message to Phone B. The message notifies Phone B of
the REFER event.
26.
200 OK—Phone B to Phone A
Phone B sends a SIP 200 OK response to Phone A. The response notifies Phone A
that the NOTIFY request has been received.
27.
BYE—Phone B to Phone A
Phone B sends a SIP BYE request to Phone A.
28.
200 OK—Phone A to Phone B
Phone A sends a SIP 200 OK response to Phone B. The response notifies Phone A
that the BYE request has been received.
A two-way RTP channel is established between Phone A and Phone C.
Step
Action
Description
