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B-52
Cisco Unified IP Phone 7960G and 7940G Administration Guide for Release 8.0 (SIP)
OL-7890-01
Appendix B SIP Call Flows
Call Flow Scenarios for Failed Calls
Cisco SIP IP Phone to Cisco SIP IP Phone in a SIP Network
The following scenarios are Cisco SIP IP phone to Cisco SIP IP phone:
•
Called Number Is Busy, page B-53
•
Called Number Does Not Answer, page B-54
•
Authentication Error, page B-55
5.
4
xx
/5
xx
/6
xx
Failure—Cisco SIP IP phone to
Gateway 1
The phone sends a class 4
xx
, 5
xx
, or class 6
xx
failure response to
the gateway 1. Depending on which class the failure response is,
the call actions differ.
If the phone sends a class 4
xx
failure response (a definite failure
response that is a client error), the request will not be retried
without modification.
If the phone sends a class 5
xx
failure response (an indefinite failure
that is a server error), the request is not terminated, but rather other
possible locations are tried.
If the phone sends a class 6
xx
failure response (a global error), the
search for B terminates because the 6
xx
response indicates that a
server has definite information about 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 phone. The ACK confirms that
PBX A has received the 486 Busy Here response. The call session
attempt terminates.
9.
Release Complete—Gateway 1 to PBX A
Gateway 1 sends a Release Complete message to PBX A, and the
call session attempt terminates.
Step
Action
Description