Cisco Cisco Unified IP Interactive Voice Response (IVR) 8.0(1) Release Note

 illustrates the principal steps and design considerations for sizing a call center.

 is a general overview of the design considerations for call sizing. For a detailed description 

of the call center sizing design process, refer 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 Cisco Unified CCE, and they also 
can be used in sizing a smaller contact center for Cisco Unified CCX. This call sizing approach will 
provide you with the minimum number of IVR ports to support the total BHCA.

97636

Si

z

in

g

BHCA Seen at

Queue Ports

Average Queue

Time (AQT)

Busy Hour Traffic

(BHT) In Erlangs

% Blockage

(Grade Of

Service)

Avg. queue duration
from ErlangC
calculator

BHT=(BHCA * AQT

seconds)/3600 (for all\
duration types)

BHT = (BHCA * AQT

seconds/3600 (for all
duration types)

% Blockage

(Grade Of

Service)

BHCA seen at

IVR ports

Erlang Load on

IVR port.

Call Center

INPUT

Call Center

OUTPUT

BHT=(BHCA * IVR Port Time)/3600

% calls blocked when no ports
available( lowest % possible)

Busy Hour Traffic=(BHCA * AHTsec)/3600

(Erlangs)

% Blockage = 0.01 (1%  for PSTN Trunks)

    =   0.001 (0.1% for IVR Ports)

# IVR

 Ports for

P&C

BHCA (T): Total Busy

Hour Call Attempts

Use Erlang C Calculator

Use Erlang B Calculator

Use Erlang B Calculator

# Agents

# IVR

Ports for

Q’ing

Queued

Calls

(%)

Avg. Q-Time

Total #

IVR

PORTS

Average Hold

time for IVR Port

Includes Prompt Playout/
Menu Navigation(if any)

Size Unified

CCX Agents

Size IVR Ports 

for Queueing

Size IVR

Ports

AHT for call

treatment

BHCA for call

treatment

BHCA (T)

AHT (secs)

Service Level

Goal (% in secs)

Unified Contact Center