Cisco Unified Contact Center Enterprise Solution Reference ...

Understanding Failure Recovery
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Cisco Unified Contact Center Enterprise 7.x SRND
Chapter 3 Design Considerations for High Availability
to store in the system database. Because the Call Routers are synchronized, the Logger data is also
synchronized. In the event that the two Logger databases are out of synchronization, they can be
resynchronized manually by using the Unified ICMDBA application over the private LAN. The
Logger also provides a replication of its historical data to the customer Historical Database Server
(HDS) Administrative Workstations over the visible network.
In the event that one of the Unified ICM Call Routers should fail, the surviving server will detect the
failure after missing five consecutive TCP keep-alive messages on the private LAN. The Call Routers
generate these TCP keep-alive messages every 100 ms, so it will take up to 500 ms to detect this failure.
Upon detection of the failure, the surviving Call Router will contact the Peripheral Gateways in the
system to verify the type of failure that occurred. The loss of TCP keep-alive messages on the private
network could be caused by either of the following conditions:
Private network outage — It is possible for the private LAN switch or WAN to be down but for both
of the Unified ICM Call Routers to still be fully operational. In this case, the Peripheral Gateways
will still see both of the Unified ICM Call Routers even though they cannot see each other over the
private network. In this case, the Call Routers will both send a Test Other Side message to the PGs
to determine if the Call Router on the other side is still operational and which side should be active.
Based upon the messages from the PGs, the Call Router that previously had the most active PG
connections would remain active in simplex mode, and the Call Router on the other side would go
idle until the private network is restored.
Call Router hardware failure — It is possible for the Call Router on the other side to have a physical
hardware failure and be completely out of service. In this case, only the surviving Call Router would
be communicating with the Peripheral Gateways using the Test Other Side message. The Peripheral
Gateways would report that they can no longer see the Call Router on the other side, and the
surviving Call Router would take over the active processing role in simplex mode.
During the Call Router failover processing, any Route Requests sent to the Call Router from a Carrier
Network Interface Controller (NIC) or Peripheral Gateway will be queued until the surviving Call
Router is in active simplex mode. Any calls in progress in the IVR or at an agent will not be impacted.
If one of the Unified ICM Logger and Database Servers were to fail, there would be no immediate impact
except that the local Call Router would no longer be able to store data from call processing. The
redundant Logger would continue to accept data from its local Call Router. When the Logger server is
restored, the Logger will contact the redundant Logger to determine how long it had been off-line. If the
Logger was off-line for less than 12 hours, it will automatically request all the transactions it missed
from the redundant Logger while it was off-line. The Loggers maintain a recovery key that tracks the
date and time of each entry recorded in the database, and these keys are used to restore data to the failed
Logger over the private network.
If the Logger was off-line for more than 12 hours, the system will not automatically resynchronize the
databases. In this case, resynchronization has to be done manually using the Unified ICMDBA
application. Manual resynchronization allows the system administrator to decide when to perform this
data transfer on the private network, perhaps scheduling it during a maintenance window when there
would be little call processing activity in the system.
The Logger replication process that sends data from the Logger database to the HDS Administrative
Workstations will automatically replicate each new row written to the Logger database when the
synchronization takes place as well.
There is no impact to call processing during a Logger failure; however, the HDS data that is replicated
from that Logger would stop until the Logger can be restored.
Additionally, if the Unified OUTD is used, the Campaign Manager software is loaded on only one of the
Logger platforms (typically Logger A). If that platform is out of service, any outbound calling will stop
until the Logger can be restored to operational status.
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