Erlang B

ErlangB is used to work out how many lines are required if the traffic figure (in Erlangs) during the busiest hour known. The Erlang B distribution is based on the following assumptions:

  • Holding times are constant and exponential
  • Blocked cells are cleared
  • Calls are taken in random order
  • There are an infinite number of sources

To use the Erlang B forecasting method:

  1. Click on  and open the ForecastX_Erlang.xls file. 
    Note: The ForecastX_Erlang.xls file is a data example to demonstrate how the Erlang B method is used. For your company’s purposes, you will have your own data available.
  2. Click on the Erlang B1 sheet.
  3. Click in a cell containing data and open ForecastX by clicking on . ForecastX displays with the Data Capture tab open. 
  4. In the Forecast periods area, type in 4 to forecast for the next four quarters.
  5. Click on the Forecast Method tab.
  6. In the Forecast Technique area, scroll through the list of methods and select Erlang B. The Erlang B Forecasting technique displays.
  7. Select Edit parameters to activate Erlang B’s parameters.
  8. In the Compute Type area, select either N to A, or A to N. N means the number of servers, and A means traffic measured by Erlang B. Select N to A.
  9. In the Lost Possibility area, select one of the options for the percentage of loss that is possible. 
  10. Click Finish.

As you review the results within the standard report, notice how ForecastX has forecasted the number of servers needed for the next 4 quarters, and ForecastX has also given the traffic levels (A).

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