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How many lines does a trunk group need? It is offered 50000 minutes of traffic per day and I accept that 3% of calls will be blocked. I estimate that 19% of daily calls are made during the busiest hour?

An example calculation

To find the answer to this question, carry out the following steps:

 • Select the Call Minutes Calculator using the tab control at the top of the window.
 • Click with you mouse on the radio button next to the Number of lines entry in the top section of the calculator. This indicated that it is the lines quantity which you wish to calculate.
 • Enter 50000 into the Total traffic per day edit box.
 • Enter 0.030 into the Blocking target edit box.
 • Enter 19 into the Busy hour factor edit box.
 • Press the Calculate button.

After a short time, the figure 168 will be displayed in the Number of lines edit box indicating that 168 lines will be required if a blocking figure of 3% is to be maintained and if the assumptions associated with the Erlang B traffic model are met.

With a busy hour factor of 19%, the traffic entered equates to 158.333 Erlangs (5699.988 C.C.S.) of busy hour traffic.