Specifications

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Cisco IP Telephony Network Design Guide
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Chapter 4 Gateway Selection
Cisco CallManager Redundancy
You must enter additional configuration parameters in the Cisco CallManager
MGCP gateway configuration interface.
Cisco CallManager Redundancy
Integral to the Cisco IP telephony solution is the provision for low-cost,
distributed PC-based systems to replace expensive and proprietary legacy PBX
systems. This distributed design lends itself to the robust, fault-tolerant
architecture of clustered Cisco CallManagers. Even in its simplest form (a
two-system cluster), a secondary Cisco CallManager should be able to pick up
control of all gateways initially managed by the primary Cisco CallManager.
Skinny Gateways
When they are booted, the Cisco Access Digital Trunk Gateway DT-24+, the
Cisco Access Digital Trunk Gateway DE-30+, and the Catalyst 6000 digital
gateway are provisioned with Cisco CallManager location information. When
these gateways initialize, a list of Cisco CallManagers, referred to as a
Cisco CallManager redundancy group, is downloaded to the gateways. This list is
prioritized into a primary Cisco CallManager and secondary Cisco CallManager.
In the event that the primary Cisco CallManager becomes unreachable, the
gateway registers with the secondary Cisco CallManager.
IOS H.323 Gateways
Using several enhancements to the dial-peer and voice class commands in
Cisco IOS Release 12.1(2)T, Cisco IOS gateways can now support redundant
Cisco CallManagers. A new command, h225 tcp timeout seconds, has been
added. This command specifies the time it takes for the Cisco IOS gateway to
establish an H.225 control connection for H.323 call setup. If the Cisco IOS
gateway cannot establish an H.225 connection to the primary Cisco CallManager,
it tries a second Cisco CallManager defined in another dial-peer statement. The
Cisco IOS gateway shifts to the dial-peer statement with next highest preference
setting.