User's Manual

Using reports for ACD planning
136 BCMS Operations
● In the column corresponding to the desired grade of service (for example, 1 percent
blocking probability), choose the nearest higher carried load. The number of trunks
required is then read from the left-most column.
Note:
Note: The entries in the ACD trunk engineering table on page 137 are offered
loads in Erlangs.
Example:
An insurance agency has an ACD that queues calls incoming from the public switched
network. The agency knows that the average caller spends 30 seconds on hold (in queue)
and requires 6 minutes and 20 seconds to service. The busy-hour call arrival rate is 70 per
hour. How many trunks does the agency need to provide a service level of 99 percent (1
percent blocking probability)?
The average call duration is calculated as follows:
average call duration = 30 + 380 = 410 seconds or 0.11389 hours
Therefore, the carried load in Erlangs is:
carried load = 0.11389 x 70 = 7.972
Under the 1 percent column, you will find that 14 trunks can service a carried load of 7.278
Erlangs while 16 trunks can service 8.786 Erlangs. Interpolate as follows:
y
= number o f trunks
y
= y
0
+ (y
1
− y
0
)
x
1
− x
0
x − x
0
_ _______
y
= 14 + ( 16 − 14 )
8. 786 − 7. 278
7. 972 − 7. 278
_____________
y
= 14 + ( 2 × 0. 460 )
y
= 14. 92