Cisco SIP IP Phone Administrator's Manual page 139

Appendix B SIP Call Flows
Step Action
17. REFER—Cisco SIP IP phone B
to Cisco SIP IP phone A
18. 202 ACCEPTED—Cisco SIP IP
phone A to Cisco SIP IP phone B
19. INVITE—Cisco SIP IP phone A
to Cisco SIP IP phone C
200 OK—Cisco SIP IP phone C
20.
to Cisco SIP IP phone A
21. ACK—Cisco SIP IP phone A to
Cisco SIP IP phone C
22. BYE—Cisco SIP IP phone C to
Cisco SIP IP phone B
23. 200 OK—Cisco SIP IP phone B
to Cisco SIP IP phone C
24. NOTIFY—Cisco SIP IP phone A
to Cisco SIP IP phone B
25. 200 OK—Cisco SIP IP phone B
to Cisco SIP IP phone A
26. BYE—Cisco SIP IP phone B to
Cisco SIP IP phone A
27. 200 OK—Cisco SIP IP phone A
to Cisco SIP IP phone B
A two-way RTP channel is established between Cisco SIP IP phone A and Cisco SIP IP phone C.
Description
Cisco SIP IP phone B sends a REFER message to Cisco SIP IP phone A. The
REFER message contains the following information:
• Refer-To: C
• Replaces: B
• Referred-By: B
The REFER message indicates that the user (recipient) should contact a third
party for use in transferring parties.
Cisco SIP IP phone A sends a SIP 202 ACCEPTED message to Cisco SIP IP
phone B. The 202 ACCEPTED confirms that the REFER message has been
received.
Cisco SIP IP phone A sends a SIP INVITE request to Cisco SIP IP phone C. The
INVITE request contains the following information:
• Referred-By: B
• Replaces: B
Cisco SIP IP phone C sends a SIP 200 OK message to Cisco SIP IP phone A. The
200 OK response notifies Cisco SIP IP phone A that the INVITE request has been
received.
Cisco SIP IP phone A sends a SIP ACK to Cisco SIP IP phone C. The ACK
confirms that Cisco SIP IP phone A has received the 200 OK response from
Cisco SIP IP phone C.
Cisco SIP IP phone C sends a SIP BYE request to Cisco SIP IP phone B.
Cisco SIP IP phone B sends a SIP 200 OK message to Cisco SIP IP phone C. The
200 OK response notifies Cisco SIP IP phone C that the BYE request has been
received.
Cisco SIP IP phone A sends a NOTIFY message to Cisco SIP IP phone B. The
NOTIFY message notifies Cisco SIP IP phone B of the REFER event.
Cisco SIP IP phone B sends a SIP 200 OK message to Cisco SIP IP phone A. The
200 OK response notifies Cisco SIP IP phone A that the NOTIFY request has been
received.
Cisco SIP IP phone B sends a SIP BYE request to Cisco SIP IP phone A.
Cisco SIP IP phone A sends a SIP 200 OK message to Cisco SIP IP phone B. The
200 OK response notifies Cisco SIP IP phone A that the BYE request has been
received.
Call Flow Scenarios for Successful Calls
Cisco SIP IP Phone Administrator Guide
B-29