- Cisco Unified Communications Manager System Guide, Release 9.0(1)
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Contents
Redundancy
This chapter provides information about redundancy in Cisco Unified Communications Manager which provides several forms of redundancy:
- Call-processing redundancy-Using Cisco Unified Communications Manager groups, you can designate backup Cisco Unified Communications Managers to handle call processing for a disabled Cisco Unified Communications Manager in a form of redundancy known as device failover.
- Media resource redundancy
- CTI redundancy
Cisco Unified Communications Manager redundancy groups
Groups and clusters form logical collections of Cisco Unified Communications Managers and their associated devices. Groups and clusters do not necessarily relate to the physical locations of any of their members.
A cluster comprises a set of Cisco Unified Communications Managers that share a common database. When you install and configure Cisco Unified Communications Manager, you specify which servers belong to the same cluster. For information on database replication in a cluster, see the Database replication in a cluster.
A group comprises a prioritized list of up to three Cisco Unified Communications Managers. You can associate each group with one or more device pools to provide call-processing redundancy. You use Cisco Unified Communications Manager Administration to define the groups, to specify which Cisco Unified Communications Managers belong to each group, and to assign a Cisco Unified Communications Manager group to each device pool.
Cisco Unified Communications Manager groups
A Cisco Unified Communications Manager group comprises a prioritized list of up to three Cisco Unified Communications Managers. Each group must contain a primary Cisco Unified Communications Manager, and it may contain one or two backup Cisco Unified Communications Managers. The order in which you list the Cisco Unified Communications Managers in a group determines the priority order.
Cisco Unified Communications Manager groups provide both redundancy and recovery:
- Failover-Occurs when the primary Cisco Unified Communications Manager in a group fails, and the devices reregister with the backup Cisco Unified Communications Manager in that group.
- Fallback-Occurs when a failed primary Cisco Unified Communications Manager comes back into service, and the devices in that group reregister with the primary Cisco Unified Communications Manager.
Under normal operation, the primary Cisco Unified Communications Manager in a group controls call processing for all the registered devices (such as phones and gateways) that are associated with that group.
If the primary Cisco Unified Communications Manager fails for any reason, the first backup Cisco Unified Communications Manager in the group takes control of the devices that were registered with the primary Cisco Unified Communications Manager. If you specify a second backup Cisco Unified Communications Manager for the group, it takes control of the devices if both the primary and the first backup Cisco Unified Communications Managers fail.
When a failed primary Cisco Unified Communications Manager comes back into service, it takes control of the group again, and the devices in that group automatically reregister with the primary Cisco Unified Communications Manager.
You associate devices with a Cisco Unified Communications Manager group by using device pools. You can assign each device to one device pool and associate each device pool with one Cisco Unified Communications Manager group. You can combine the groups and device pools in various ways to achieve the desired level of redundancy.
For example, the following figure shows a simple system with three Cisco Unified Communications Managers in a single group that is controlling 800 devices.
The figure depicts Cisco Unified Communications Manager group G1 that is assigned with two device pools, DP1 and DP2. Cisco Unified Communications Manager 1, as the primary Cisco Unified Communications Manager in group G1, controls all 800 devices in DP1 and DP2 under normal operation. If Cisco Unified Communications Manager 1 fails, control of all 800 devices transfers to Cisco Unified Communications Manager 2. If Cisco Unified Communications Manager 2 also fails, control of all 800 devices transfers to Cisco Unified Communications Manager 3.
The configuration provides call-processing redundancy, but it does not distribute the call-processing load very well among the three Cisco Unified Communications Managers in the example. For information on load balancing, see the Distributing devices for redundancy and load balancing.
Note
Empty Cisco Unified Communications Manager groups will not function.
Distributing devices for redundancy and load balancing
Cisco Unified Communications Manager groups provide both call-processing redundancy and distributed call processing. How you distribute devices, device pools, and Cisco Unified Communications Managers among the groups determines the level of redundancy and load balancing in your system.
In most cases, you would want to distribute the devices in a way that prevents the other Cisco Unified Communications Managers from becoming overloaded if one Cisco Unified Communications Manager in the group fails. The following figure shows one possible way to configure the Cisco Unified Communications Manager groups and device pools to achieve both distributed call processing and redundancy for a system of three Cisco Unified Communications Managers and 800 devices.
The previous figure depicts the Cisco Unified Communications Manager groups as they are configured and assigned to device pools, so Cisco Unified Communications Manager 1 serves as the primary controller in two groups, G1 and G2. If Cisco Unified Communications Manager 1 fails, the 100 devices in device pool DP1 reregister with Cisco Unified Communications Manager 2, and the 300 devices in DP2 reregister with Cisco Unified Communications Manager 3. Similarly, Cisco Unified Communications Manager 2 serves as the primary controller of groups G3 and G4. If Cisco Unified Communications Manager 2 fails, the 100 devices in DP3 reregister with Cisco Unified Communications Manager 1, and the 300 devices in DP4 reregister with Cisco Unified Communications Manager 3. If Cisco Unified Communications Manager 1 and Cisco Unified Communications Manager 2 both fail, all devices reregister with Cisco Unified Communications Manager 3.
For more information on distributed call processing, see the Balanced call processing.
Media resource redundancy
Media resource lists provide media resource redundancy by specifying a prioritized list of media resource groups. An application can select required media resources from among the available ones according to the priority order that is defined in the media resource list. For more information on media resource redundancy, see the Media resource management.
CTI redundancy
Computer telephony integration (CTI) provides an interface between computer-based applications and telephony functions. CTI uses various redundancy mechanisms to provide recovery from failures in any of the following major components:
CTI uses Cisco Unified Communications Manager redundancy groups to provide recovery from Cisco Unified Communications Manager failures. To handle recovery from failures in Cisco CTIManager itself, CTI allows you to specify primary and backup Cisco CTIManagers for the applications that use CTI. Finally, if an application fails, the Cisco CTIManager can redirect calls that are intended for that application to a forwarding directory number.
