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Failover Based on Telephony Cause Codes
November 2009 230
Failover Based on Telephony Cause Codes
Overview
Identifying call failures within an IP telephony network allows an
application to re-route calls depending on the failure. In many cases,
the failover to other network devices occurs seamlessly when the
network has the following:
H.323 Gatekeepers
SIP Registrar Servers or SIP Redirect Servers
In cases where the network does not have these components, the
failover responsibility falls on the application.
Typically, in the absence of gatekeepers or other call routing devices,
the telephony endpoint, under the control of the application, is in
direct contact with the gateway. In this network configuration, the
application must be able to identify the various types of failures in
order to effectively manage the call routes.
Common Failures
The following are some common failures:
Unreachable IP address
Reachable IP address with no SIP/H.323 response
Gateway SIP/H.323 channels exceeded
Gateway PSTN channels exceeded
Gateway with responding SIP/H.323 and PSTN down (no PSTN
cable connected)
Gateway with responding SIP/H.323 and PSTN down due to an
alarm
Gateway with responding SIP/H.323 and PSTN up but not
waiting for calls
Gateway failure during an active call by disconnecting the
network cable on SR140
Gateway failure during an active call by disconnecting the
network cable on the gateway