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Appendix B
SIP Call Flows
Step
Action
17.
ACK—Cisco SIP IP phone B to
Cisco SIP IP phone A
A two-way RTP channel is reestablished between Cisco SIP IP phone A and Cisco SIP IP phone B.
18.
BYE—Cisco SIP IP phone B to
Cisco SIP IP phone A
19.
200 OK—Cisco SIP IP phone A
to Cisco SIP IP phone B
The RTP channel between Cisco SIP IP phone A and Cisco SIP IP phone B is torn down.
INVITE—Cisco SIP IP phone B
20.
to Cisco SIP IP phone C
200 OK—Cisco SIP IP phone C
21.
to Cisco SIP IP phone B
ACK—Cisco SIP IP phone B to
22.
Cisco SIP IP phone C
A two-way RTP channel is reestablished between Cisco SIP IP phone B and Cisco SIP IP phone C.
Cisco SIP IP Phone-to-Cisco SIP IP Phone Call Transfer Without Consultation
Figure B-6
and then one of the participants transfers the call to a third party without first contacting the third party.
This is called a blind or unattended 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.
Description
Cisco SIP IP phone B sends a SIP ACK to Cisco SIP IP phone A. The ACK
confirms that Cisco SIP IP phone B has received the 200 OK response from
Cisco SIP IP phone A.
The call continues and then User B hangs up. Cisco SIP IP phone B sends a SIP
BYE request to Cisco SIP IP phone A. The BYE request indicates that User B
wants to release the call.
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 B that the BYE request has been
received. The call session between User A and User B is now terminated.
Cisco SIP IP phone B sends a mid-call INVITE to Cisco SIP IP phone C with the
same call ID as the previous INVITE (sent to Cisco SIP IP phone C) and new
SDP session parameters (IP address), which are used to reestablish the call.
Call_ID=2
SDP: c=IN IP4 181.23.250.2
Cisco SIP IP phone C sends a SIP 200 OK response to Cisco SIP IP phone B.
Cisco SIP IP phone B sends a SIP ACK to Cisco SIP IP phone C. The ACK
confirms that Cisco SIP IP phone B has received the 200 OK response from
Cisco SIP IP phone A.
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 transfers the call to User C.
Call Flow Scenarios for Successful Calls
Cisco SIP IP Phone Administrator Guide
B-17
- Quick Links:
- Using the Command-Line Interface
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