Cisco Sip Ip Phone To Cisco Sip Ip Phone In A Sip Network; Called Number Is Busy; Called Number Does Not Answer - Cisco 7960G Administrator's Manual

Call Flow Scenarios for Failed Calls
Step Action
5. 4xx/5xx/6xx Failure—Cisco SIP IP phone to
Gateway 1
Disconnect—Gateway 1 to PBX A
6.
Release—PBX A to Gateway 1
7.
ACK—Gateway 1 to Cisco SIP IP phone
8.
9. Release Complete—Gateway 1 to PBX A

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:
•
•
•
Cisco SIP IP Phone Administrator Guide, Release 6.x and 7.x
B-52
Called Number Is Busy, page B-53
Called Number Does Not Answer, page B-54
Authentication Error, page B-54
Description
The phone sends a class 4xx, 5xx, or class 6xx failure response to
the gateway 1. Depending on which class the failure response is,
the call actions differ.
If the 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 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 phone sends a class 6xx failure response (a global error), the
search for B terminates because the 6xx 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.
Gateway 1 sends a Release message to PBX A.
PBX A sends a Release message to Gateway 1.
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.
Gateway 1 sends a Release Complete message to PBX A, and the
call session attempt terminates.
Appendix B SIP Call Flows