Cisco Unified Contact Center Enterprise Solution Reference ...

Chapter 3 Design Considerations for High Availability
Unified IP IVR (CRS)
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Understanding Failure Recovery
Cisco Unified CallManager call detail reporting (CDR) shows the call as terminated when the
Cisco Unified CallManager failure occurred, although the call may have continued for several minutes
after the failure because calls in progress stay in progress. IP phones of agents not on calls at the time
of failure will quickly register with the backup Cisco Unified CallManager subscriber. The IP phone of
an agent on a call at the time of failure will not register with the backup Cisco Unified CallManager
subscriber until after the agent completes the current call. If MGCP gateways are used, then the calls in
progress survive, but further call control functions (hold, retrieve, transfer, conference, and so on) are
not possible. H.323 gateways maintain a call survival timer that will maintain an active call for a limited
amount of time (typically, not more than 5 minutes), and then the call will be terminated by the gateway.
When the active Cisco Unified CallManager subscriber fails, the agent desktops show the agents as
being made “not ready,” their IP phones display a message stating that the phone has gone off-line, and
all the IP phone soft keys are grayed out until the phones fail-over to the backup Cisco Unified
CallManager subscriber. To continue receiving calls, the agents must wait for their phones to re-register
with a backup Cisco Unified CallManager subscriber to have their desktop functionality restored by the
CTI server to the state prior to the Cisco Unified CallManager service failure. Upon recovery of the
primary Cisco Unified CallManager subscriber, the agent phones re-register to their original subscriber
to return the cluster to the normal state, with phones and devices properly balanced across multiple active
subscribers.
In summary, the Cisco Unified CallManager call processing service is separate from the CTI Manager
service, which connects to the Cisco Unified CallManager PG via JTAPI. The Cisco Unified
CallManager call processing service is responsible for registering the IP phones, and its failure does not
affect the Cisco Unified CallManager PGs. From a Cisco Unified CCE perspective, the PG does not go
off-line because the Cisco Unified CallManager server running CTI Manager remains operational.
Therefore, the PG does not need to fail-over.
When a CTI Manager service fails, the Unified IP IVR (CRS) JTAPI subsystem shuts down and restarts
by trying to connect to the secondary CTI Manager service on a backup Cisco Unified CallManager
subscriber in the cluster. In addition, all voice calls at this Unified IP IVR (CRS) are dropped. If there is
an available secondary CTI Manager service on a backup subscriber, the Unified IP IVR (CRS) logs into
this CTI Manager service on that subscriber and re-registers all the CTI ports associated with the
Unified IP IVR (CRS) JTAPI user. After all the Cisco Unified CallManager devices are successfully
registered with the Unified IP IVR (CRS) JTAPI user, the server resumes its Voice Response Unit (VRU)
functions and handles new calls. This action does not impact the Unified CVP because it does not depend
upon the Cisco Unified CallManager CTI Manager service for call control.
Unified IP IVR (CRS) Release 3.5 provided for cold standby and Release 4.0 provides hot standby
redundancy, but this configuration is not recommended for use with Unified CCE. These designs make
use of a redundant server that is not used unless there is a failure of the primary Unified IP IVR (CRS)
server. However, during this failover processing, all calls that are in queue or treatment are dropped on
the Unified IP IVR (CRS) as part of the failover. A more resilient design would be to deploy a second
(or more) Unified IP IVR (CRS) server(s) and have them all active, allowing the Unified CCE to
load-balance calls across them automatically. As shown in Figure 3-21, if one of the Unified IP IVR
(CRS) servers should fail, only the calls on that server would fail, but the other active servers would
remain active and be able to accept new calls in the system.
Cisco Unified Contact Center Enterprise 7.x SRND
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