Free Erlang traffic calculators

The world's first online Erlang traffic calculators

Telecom Traffic Online
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Erlang B Calculator
Erlang calculator for Windows
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Erlang B Calculator

Erlang B Calculator
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BHT (Erl.)
A windows version is available for immediate download at just 99 US Dollars.
Click here for more information

Brief instructions

Here is a brief introduction to the calculator.  For more detailed information, press the Help Button. For a running record of the results calculated, press the Results button. Both these functions open new browser windows on your desktop.
  • The Erlang B traffic model is used by telephone system designers to estimate the number of lines required for PSTN connections (CO trunks) or private wire connections.  The three variables involved are Busy Hour Traffic (BHT), Blocking and Lines:
    • Busy Hour Traffic (in Erlangs) is the number of hours of call traffic there are during the busiest hour of operation of a telephone system.
    • Blocking is the failure of calls due to an insufficient number of lines being available.  E.g. 0.03 mean 3 calls blocked per 100 calls attempted.
    • Lines is the number of lines in a trunk group.
  • If you know two of the figures, you can work out the third as follows:
    • Click on the Unknown radio button representing the unknown variable.
    • Enter the 2 known figures into their edit boxes.
    • Press Calc and the third figure will be calculated and displayed in the remaining edit box.
  • For example, if from your call logger, you know that the Busy Hour Traffic is 10 Erlangs, and you want to know how many lines are required in this trunk group if you are prepared to tolerate 2 calls being blocked in every 100 calls attempted then:
    • Press the Lines Unknown radio button (this is selected by default).
    • Enter 10 in the BHT edit box.
    • Enter 0.02 in the Blocking edit box.
    • When you press the Calc button, 17 will be displayed in the Lines edit box indicating that 17 lines would be required in this trunk group.

Windows version of this calculator

The Erlang B Traffic Calculator on this page is modelled on the Erlang B Calculator included with the Westbay Traffic Calculators for Windows. The calculator works up to 90,000 Erlangs / Lines and has the ability to display and print the results of any calculations you have made during the previous week.

Erlang B Calculator on Windows Vista

Customers also benefit from an Extended Erlang B Calculator, an Erlang C Calculator for analysing call centres and a Call Minutes Calculator. These calculators are available for 99 US Dollars. If you pay using VISA, MasterCard, American Express or Discovery, you can have this software working on your PC in five minutes!

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Last modified: 05 June 2017

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