Appendix B SIP Call Flows
Call Flow Scenarios for Failed Calls
B-60
Cisco SIP IP Phone 7960 Administrator Guide
78-10497-02
Gateway-to-Cisco SIP IP Phone—Called User Does Not Answer
Figure B-14 illustrates the call flow in which User A initiates a call to User B but
User B does not answer.
Figure B-14 Gateway-to-Cisco SIP IP Phone—Called User Does Not Answer
6
Disconnect (Busy)—Gateway 1
to PBX A
Gateway 1 sends a Disconnect message to PBX A.
7
Release—PBX A to Gateway 1 PBX A sends a Release message to Gateway 1.
8
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 486 Busy Here
response. The call session attempt is now being terminated.
9
Release Complete—Gateway 1
to PBX A
Gateway 1 sends a Release Complete message to PBX A
and the call session attempt is terminated.
Step Action Description
IP
SIP IP Phone
User B
3. Call Proceeding
11. Release Complete
8. Disconnect
6. Alerting
1. Setup
PBX A
User A
GW1 IP Network
4. 100 Trying
10. 200 OK
5. 180 Ringing
7. CANCEL
2. INVITE
9. Release
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