When companies design communications networks, they consider how much traffic they expect. The BHCA - busy hour call attempts - represents the average number of times per hour each subscriber tries to make a call. Higher BHCAs strain network processors. Calculate BHCA using subscribers' usage data.

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Multiply a subscriber's monthly minutes of usage by the percentage of traffic that occurs during working days. For instance, if a subscriber talks for 500 minutes in a month, and 80 percent of calls occur during the work week:

500 X 0.80 = 400

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Multiply your answer by the percentage of voice traffic that occurs during the busy hour. For instance, if 10 percent happens during the busy hour:

400 X 0.10 = 40

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Divide your answer by the number of working days per month. If each month contains 20 working days:

40 / 20 = 2

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Divide your answer by 60.

2 / 60 = 0.0333.

This answer shows your phone traffic in Erlangs, a unit that represents hours of usage per subscriber per busy hour.

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Multiply the answer by 3600.

0.0333 X 3600 = 120

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Divide the answer by mean holding time, in seconds. If your mean holding time is 80 seconds:

120 / 80 = 1.5

This answer is your BHCA.