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Reply To: Erlang Vs. BHCA


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.

Joseph Brew – 22 Dec 2000

there is a mathmatical relationship between erlang and BHCA this is given above. both erlang are parameters for in trafffic measuremnts. can you provide additional information on wha you are using the erlang and BHCA values for? this may help me explain the issues better

Jean-Hugues ROBERT – 15 Dec 2000

A BHT (Busy Hour Traffic) of XXX
Erlang with YYYY BHCA means that
the average call length is
(XXX / YYY) * 3600 seconds.
BHCA = (BHT * 3600) / Call-Length.
Call-Length = (BHT * 3600) / BHCA.
BHT = (BHCA * Call-Length) / 3600.
Call Length is also called
“Hold time”.