Appendix B SIP Call Flows
Call Flow Scenarios for Failed Calls
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Cisco SIP IP Phone 7960 Administrator Guide
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7
CANCEL (Ring
Timeout)—Gateway 1 to Cisco
SIP IP phone
Because Gateway 1 did not return an appropriate response
within the time allocated in the INVITE request, Gateway
1 sends a SIP CANCEL request to Gateway 2. A CANCEL
request cancels a pending request with the same Call-ID,
To, From, and CSeq header field values.
8
Disconnect—Gateway 1 to PBX
A
Gateway 1 sends a Disconnect message to PBX A.
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.
10
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 confirms that User A has
received the 486 Busy Here response. The call session
attempt is now being terminated.
11
Release Complete—Gateway 1
to PBX A
Gateway 1 sends a Release Complete message to PBX A
and the call session is terminated.
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