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Cisco SIP IP Phone 7960 Administrator Guide
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Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
Cisco SIP IP Phone-to-Cisco SIP IP Phone Call Waiting
Figure B-6 illustrates a successful call between Cisco SIP IP phones in which two
parties are in a call, one of the participants receives a call from a third party, 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 C calls User B.
4.
User B accepts the call from User C.
5.
User B switches back to User A.
6.
User B hangs up, ending the call with User A.
7.
User B is notified of the remaining call with User C.
8.
User B answers the notification and continues the call with User C.
14
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.
15
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.
16
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 Cisco SIP IP phone A and Cisco SIP IP phone B.
Step Action Description