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Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
B-10
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
ACK—Gateway 1 to Cisco SIP
IP phone
Gateway 1 sends a SIP ACK to the Cisco SIP IP phone. The
ACK confirms that User A has received the 200 OK
response. The call session is now active.
10
Connect ACK—PBX A to
Gateway 1
PBX A acknowledges Gateway 1’s Connect message.
11
INVITE—Cisco SIP IP phone to
Gateway 1
User B puts User A on hold. The Cisco SIP IP phone sends
a SIP INVITE request to Gateway 1.
12
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 Cisco SIP IP
phone that the INVITE was successfully processed.
13
ACK—Cisco SIP IP phone to
Gateway 1
The Cisco SIP IP phone sends a SIP ACK to Gateway 1.
The ACK confirms that the Cisco SIP IP phone has
received the 200 OK response. The call session is now
temporarily inactive. No RTP packets are being sent.
14
INVITE—Cisco SIP IP phone to
Gateway 1
User B takes User A off hold. The Cisco SIP IP phone
sends a SIP INVITE request to Gateway 1.
15
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 Cisco SIP IP
phone that the INVITE was successfully processed.
16
ACK—Cisco SIP IP phone to
Gateway 1
The Cisco SIP IP phone sends a SIP ACK to Gateway 1.
The ACK confirms that the Cisco SIP IP phone has
received the 200 OK response. The call session is now
active.
Step Action Description