The figure below illustrates the principal steps and design
considerations for sizing a call center.
Figure 2. Unified CCX design process – Call center sizing
This figure is a general overview of the design
considerations for call sizing. For a detailed description of the call center
sizing design process, refer to the section on sizing call center resources in the
Cisco Unified Contact Center Enterprise Solution Reference
Network Design Guide, available online at the following URL:
There are similar basic call center sizing considerations and
steps for Unified CCE, and they also can be used in sizing a smaller
contact center for Unified CCX. This call-sizing approach will provide
you with the minimum number of IVR ports to support the total BHCA.
In addition, you should include the following design
considerations, specific to Unified CCX, in your call center sizing
At a minimum, plan on enough capacity to replace your existing
system. The replacement system should perform at least as well as the one it is
After all of the Erlang (C and B) calculations are complete for
the call center sizing, any changes in queue times or agents will affect the
total number of trunks and IVR ports required for an Unified CCX
As you increase the size of the agent pool, very small changes in
the average queue time and percentage of queued calls will affect the required
number of gateway trunks and IVR ports.
Even if you perform all of the calculations for a call center,
there are still some variables that you cannot plan for but that will affect
the ports needed on a Unified CCX system. For example, one or more agents
could call in sick, and that would affect the port count and queue time for
each call. Just two agents calling in sick could increase the port count by
over 12%. This would affect the price of the system and, if not planned for,
would affect the ability of the call center to meet caller requirements.
Properly sizing call center resources is integral to designing an effective
Unified CCX system.
Not all of the Unified CCX system limits are available at the
If all of the call sizing information is available, the next
step is to apply Unified CCX sizing limits to the call center
requirements. For this step, use the Cisco Unified Communications Sizing Tool,
available online at:
The Unified Communications downloadable sizing tools help you with the task of sizing Unified Communications deployments.