Cisco 7935 System Manual page 47

Chapter 40 Cisco IP Phones
Phone Failover and Fallback
Phone Failover and Fallback
This section describes how phones fail over and fail back if the
Cisco CallManager to which they are registered becomes unreachable. This
section also covers conditions that can affect calls that are associated with a
phone, such as reset or restart.
Cisco CallManager Fails or Becomes Unreachable
The active Cisco CallManager designation applies to the Cisco CallManager from
which the phone receives call-processing services. The active Cisco CallManager
usually serves as the primary Cisco CallManager for that phone (unless the
primary is not available).
If the active Cisco CallManager fails or becomes unreachable, the phone attempts
to register with the next available Cisco CallManager in the Cisco CallManager
Group that is specified for the device pool to which the phone belongs.
The phone device reregisters with the primary Cisco CallManager as soon as it
becomes available after a failure. See the "MaxPhonesFallBackQueueDepth
Service Parameter" section on page 40-45 for information about phone
registration during failover.
Phones do not failover or fallback while a call is in progress.
Note
Phone is Reset
If a call is in progress, the phone does not reset until the call finishes.
Cisco CallManager System Guide
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OL-7135-01