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Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
B-6
Cisco SIP IP Phone 7960 Administrator Guide
78-10497-02
6
Alerting—Gateway 1 to PBX A Gateway 1 sends an Alert message to User A. The Alert
message indicates that Gateway 1 has received a 180
Ringing response from the Cisco SIP IP phone. User A
hears the ringback tone that indicates that User B is being
alerted.
7
200 OK—Cisco SIP IP phone to
Gateway 1
The Cisco SIP IP phone sends a SIP 200 OK response to
Gateway 1. The 200 OK response notifies Gateway 1 that
the connection has been made.
8
Connect—Gateway 1 to PBX A Gateway 1 sends a Connect message to PBX A. The
Connect message notifies PBX A that the connection has
been made.
9
Connect ACK—PBX A to
Gateway 1
PBX A acknowledges Gateway 1’s Connect message.
10
ACK—Gateway 1 to Cisco SIP
IP phone
Gateway 1 sends a SIP ACK to the Cisco SIP IP phone. The
ACK confirms that Gateway 1 has received the 200 OK
response. The call session is now active.
11
BYE—Cisco SIP IP phone to
Gateway 1
User B terminates the call session at his Cisco SIP IP phone
and the phone sends a SIP BYE request to Gateway 1. The
BYE request indicates that User B wants to release the call.
12
Disconnect—Gateway 1 to
PBX A
Gateway 1 sends a Disconnect message to PBX A.
13
Release—PBX A to Gateway 1 PBX A sends a Release message to Gateway 1.
14
200 OK—Gateway 1 to Cisco
SIP IP phone
Gateway 1 sends a SIP 200 OK response to the Cisco SIP
IP phone. The 200 OK response notifies the phone that
Gateway 1 has received the BYE request.
15
Release Complete—Gateway 1
to PBX A
Gateway 1 sends a Release Complete message to PBX A
and the call session is terminated.
Step Action Description