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An example Calculation

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How many lines do I need to provide on a trunk group which will be offered 5.5 Erlangs of traffic during its busy hour if I am prepared to accept that 3 calls in 100 will be blocked and that half of those blocked calls will immediately be retried?

 

An example calculation

An example calculation

 

To find the answer to this question, follow the following steps:

 

Select the Extended Erlang B Calculator using the Tab Control at the top of the window.
Click with your mouse on the radio button marked Unknown which is in the Lines section of the calculator. This indicates that it is the lines variable which you wish to calculate.
Enter the figure 50 into the edit box in the Recall factor section of the calculator.
Enter the figure 5.5 into the edit box in the BHT section of the calculator.
Enter the figure 0.03 into the edit box in the Blocking section of the calculator.
Press the Calculate button.

 

After a short time, the figure 11 will be displayed in the Lines edit box indicating that 11 lines will be required to carry 5.5 Erlangs of traffic with a blocking figure of 3% if the assumptions associated with the Extended Erlang B traffic model are met and if 50% of blocked calls are retried.