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Reply To: Erlang Vs. BHCA

Richard Arcadi

I’d like to add my viewpoint.

According to ITU, there is a relationship between Erlangs and BHC that can be extracted from the following:

A = M * D * H /(120 * E)

Providing that:

A: Conversational Erlangs
M: Monthly minutes of voice traffic
D: Month to day factor (1/22 to 1/30)
H: Day to Hour factor (1/7 to 1/10)
E: Efficiency factor of the trunk (0.9 avg).
It’s being considered an avg. call duration of 120 sec.

If you play with the formula and have in mind a basic relationship
(for non-blocking trunks) that’s:


Where BHCA: BH Call Attempts
BHC: BH Calls
ASR: Attempting Size Ratio
(bet. 0.65 to 0.8)

you’ll get a relationship between A and BHCA.