Call Transfer With Consultation - Cisco 7960G Administration Manual

Appendix B SIP Call Flows
Step Action
REFER—Phone B to Phone A
9.
501 Not Implemented—Cisco
10.
SIP IP Phone A to Phone B
BYE—Phone B to Phone A
11.
200 OK—Phone A to Phone B
12.
13. INVITE—Phone A to Phone C
100 Trying—Phone C to
14.
Phone A
180 Ringing—Phone C to
15.
Phone A
200 OK—Phone C to Phone A
16.
ACK—Phone A to Phone C
17.
A two-way RTP channel is established between Phone A and Phone C.

Call Transfer with Consultation

Figure B-9
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.
2.
3.
4.
OL-7890-01
Description
Phone B sends a REFER message to Phone A. The message contains the
following information:
Refer-To: C
•
Referred-By: B
•
The REFER message indicates that Phone A should send an INVITE request to
Phone C.
Phone A sends a 501 Not Implemented message to Phone B. The message
indicates that the REFER message is not supported and that Phone B should
failover to Bye/Also.
Phone B sends a BYE message to Phone A. The message includes the following
information:
Also: C
•
The message indicates that the 501 Not Implemented message was received in
response to a REFER message.
Phone A sends a SIP 200 OK response to Phone B. The response notifies Phone B
that the BYE message was received.
Phone A sends a SIP INVITE request to Phone C. The request is an invitation to
User C to participate in a call session. The request contains the following
information:
Requested-By: B
•
The message indicates that the INVITE was requested by Phone B.
Phone C sends a SIP 100 Trying response to Phone A. The response indicates that
the INVITE request has been received.
Phone C sends a SIP 180 Ringing response to Phone A.
Phone C sends a SIP 200 OK response to Phone A. The response notifies Phone A
that the connection has been made.
Phone A sends a SIP ACK to Phone C. The ACK confirms that Phone A has
received the 200 OK response from Phone C.
illustrates a successful call between Cisco SIP IP phones in which two parties are in a call,
User A calls User B.
User B answers the call.
User B calls User C, and User C consents to take the call.
User B transfers the call to User C.
Cisco Unified IP Phone 7960G and 7940G Administration Guide for Release 8.0 (SIP)
Call Flow Scenarios for Successful Calls
B-23