Cisco SIP IP Phone User Manual

B-9
Cisco SIP IP Phone Administrator Guide
Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
Cisco SIP IP Phone-to-Cisco SIP IP Phone Call Hold with Consultation
Figure B-4 illustrates a successful call between Cisco SIP IP phones in which one of the participants
places the other on hold, calls a third party (consultation), and then returns to the original call. 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 places User A on hold.
4. User B calls User C.
5. User B disconnects from User C.
6. User B takes User A off hold.
7. The original call continues.
6. 200 OK—Cisco SIP IP phone A
to Cisco SIP IP phone B
Cisco SIP IP phone A sends a SIP 200 OK response to Cisco SIP IP phone B.
7. ACK—Cisco SIP IP phone B to
Cisco SIP IP phone A
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 RTP channel between Cisco SIP IP phone A and Cisco SIP IP phone B is torn down.
8. INVITE—Cisco SIP IP phone B
to Cisco SIP IP phone A
Cisco SIP IP phone B sends a mid-call INVITE to Cisco SIP IP phone A with the
same call ID as the previous INVITE and new SDP session parameters (IP
address), which are used to reestablish the call.
Call_ID=1
SDP: c=IN IP4 181.23.250.2
To reestablish the call between phone A and phone B, the IP address of phone B
is inserted into the c= SDP field.
9. 200 OK—Cisco SIP IP phone A
to Cisco SIP IP phone B
Cisco SIP IP phone A sends a SIP 200 OK response to Cisco SIP IP phone B.
10. ACK—Cisco SIP IP phone B to
Cisco SIP IP phone A
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.
A two-way RTP channel is reestablished between IP phone A and IP phone B.
Step Action Description

Cisco SIP IP Phone Specifications

General

Brand	Cisco
Model	SIP IP Phone
Category	IP Phone
Language	English