ExtErlBBlocking()

To estimate how many lines are required in a trunk group if the offered traffic is known, use:

=ExtErlBLines(x,y,z)

This function takes three parameters:

•	x is the busy hour traffic in Erlangs

•	y is the target blocking figure

•	z is the percentage of calls that are immediately retried

For example, to estimate how the lines are required for 100 Erlangs at 0.025 (2.5%) blocking, assuming that 50% of blocked calls are immediately retried, enter:

=ExtErlBLines(100,0.025,50)

The answer should be 113

As with other Excel functions, you can either enter absolute values as the parameters, or you can add references to other cell on the same workbook or other open workbooks. If reference is made to another cell for the retrial parameter, please note that that cell should be formatted as a number and not as a percentage.