a brief introduction to the calculator.
- You can use this calculator
to work out how many lines you need to provide in a trunk group if you know the number of
minutes of calls which will be offered to that trunk group. The trunk group can be a PSTN
link (CO trunks), a group of leased lines between two private network locations or an
access group to a Virtual Private Network.
- As an example, if you wanted
to know how many lines would need to be provided for a trunk group which was offered 10000
minutes of calls a day:
- Click on the Unknown
radio button in the Lines Required section to indicate that it is the number of
lines you wish to calculate.
- Enter 10000 in the Minutes
per day edit box.
- Press the Calc. button.
- The answer is displayed in the Lines
edit box (40).
- Reverse calculations are
also possible allowing you to calculate the minutes of calls which can be carried by a
trunk group of a particular size. To carry out such a calculation, click on the Unknown
radio button in the Minutes per day section, enter the number of lines in the Lines
required edit box and press the Calc. button. The answer will be shown in
the Minutes per day edit box.
- This calculator uses the
Erlang B traffic model which is discussed in detail in the help system. You have the
opportunity to specify two additional parameters relating to this traffic model and to the
- The busy hour factor is the
percentage of daily minutes which are offered during the busiest hour of the day. 17% (the
default) is a reasonable figure for a business which operates an 8 hour working day, but a
higher figure could be entered if the business in question operates a shorter working day,
or if frequent calls are being made to a different time zone.
- Blocking target is the ratio of
calls which will be blocked because no lines are available. 0.010 (the default) means that
1% of calls would be lost. This is a normal figure for traffic engineering, but other
figures can be entered into this edit box.
- Please note that in order to
make a safe judgement of the number of lines required, traffic figures over a significant
time period are required. One day's traffic figures are not enough.