is a brief introduction to the calculator. For more detailed information, press the Help
button which opens a new browser window on your desktop.
- 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 traffic pattern:
- 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
The calculator on this page is modelled on the Call
Minutes Calculator included with the Westbay Traffic Calculators for Windows. The
calculator works up to 30,000,000 million minutes per day and has the ability to
display and print the results of any calculations you have made during the previous week.
Customers also benefit from an Erlang B Calculator, Extended Erlang B
Calculator and an Erlang C Calculator for analysing call centres. These calculators are
available for 98 US Dollars. If you pay using VISA,
MasterCard, American Express or Discovery, you can have this software working on
your PC in five minutes!