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Cisco SIP IP Phone 7960 Administrator Guide
78-10497-02
Appendix B SIP Call Flows
Call Flow Scenarios for Failed Calls
5
4xx/5xx/6xx Failure—Cisco SIP
IP phone to Gateway 1
The Cisco SIP IP phone sends a class 4xx, 5xx, or class 6xx
failure response to Gateway 1. Depending on which class
the failure response is, the call actions differ.
If the Cisco SIP IP phone sends a class 4xx failure response
(a definite failure response that is a client error), the request
will not be retried without modification.
If the Cisco SIP IP phone sends a class 5xx failure response
(an indefinite failure that is a server error), the request is
not terminated but rather other possible locations are tried.
If the Cisco SIP IP phone sends a class 6xx failure response
(a global error), the search for User B is terminated because
the 6xx response indicates that a server has definite
information about User B, but not for the particular
instance indicated in the Request-URI field. Therefore, all
further searches for this user will fail.
6
Disconnect—Gateway 1 to PBX
A
Gateway 1 sends a Release 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