Cisco Unified Contact Center Enterprise Solution Reference ...

Load Balancing Cisco Unified CallManager
Load Balancing Cisco Unified CallManager
10-10
Cisco Unified Contact Center Enterprise 7.x SRND
Chapter 10 Sizing Cisco Unified CallManager 4.x and 5.x Servers
An additional benefit of using the 1:1 redundancy scheme is that it enables you to balance the devices
over the primary and backup subscriber pairs. Normally (as in the 2:1 redundancy scheme) a backup
server has no devices registered unless its primary is unavailable.
With load balancing, you can move up to half of the device load from the primary to the secondary
subscriber by using the Cisco Unified CallManager redundancy groups and device pool settings. In this
way, you can reduce by 50% the impact of any server becoming unavailable.
To plan for 50/50 load balancing, calculate the capacity of a cluster without load balancing and then
distribute the load across the primary and backup subscribers based on devices and call volume. To allow
for failure of the primary or the backup, the total load on the primary and secondary subscribers should
not exceed that of a single subscriber. For example, MCS-7845 servers have a total server limit of 500
Unified CCE agents. In a 1:1 redundancy pair, you can split the load between the two subscribers,
configuring each subscriber with 250 agents. To provide for system fault tolerance, make sure that all
capacity limits are observed so that Unified CCE agent phones, Unified IP phones, CTI limits, and so
on, for the subscriber pair do not exceed the limits allowed for a subscriber server.
Cisco recommends the equal distribution of all devices and call volumes as much as possible across all
active subscribers. For instance, distributing the Unified CCE agents, CTI ports, gateways, trunks,
voicemail ports, and other users and devices among all subscribers equally, minimizes the impact of any
outage.
For additional information on general call processing topics such as secondary TFTP servers and
gatekeeper considerations, refer to the Cisco Unified Communications Solution Reference Network
Design (SRND) guide, available at
www.cisco.com/go/srnd
Upgrading Cisco Unified CallManager
The 1:1 redundancy scheme allows upgrades with only the failover periods impacting the cluster. The
1:1 redundancy scheme enables you to upgrade the cluster using the following method:
Step 1 Upgrade the publisher server.
Step 2 Upgrade dedicated TFTP and music-on-hold (MoH) servers.
Step 3 Upgrade the backup subscribers one at a time. This step will affect some users if 50/50 load balancing
is implemented.
Step 4 Fail over the primary subscribers to their backups, and stop the Cisco Unified CallManager service on
the primaries. All users are on primaries and are moved to backup subscribers when the Cisco Unified
CallManager service is stopped. CTI Manager is also stopped, causing the Peripheral Gateway (PG) to
switch sides and inducing a brief outage for agents on that particular node.
Step 5 Upgrade the primaries, and then re-enable the Cisco Unified CallManager service.
With this upgrade method, there is no period (except for the failover period) when devices are registered
to subscriber servers that are running different versions of the Cisco Unified CallManager software. This
factor can be important, because the Intra-Cluster Communication Signaling (ICCS) protocol that
communicates between subscribers can detect a different software version and shut down
communications to that subscriber.
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