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Minutes and Lines Calculator

Minutes and Lines Calculator
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Blocking target
Busy hour factor (%)
Minutes per day
Unknown
Voice paths
Unknown
A windows version of this calculator is
available for immediate download
Click here for more information

Brief instructions

Here 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 voice paths you need to provide through a network if you know the number of minutes of calls which the two voice switches interconnected by that network will generate. Designers of network convergence solutions need to ensure that sufficient bandwidth is available through a network to transport enough voice paths to carry the voice traffic during its busiest hour.
  • As an example, if you wanted to know how many voice paths 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 Voice paths section to indicate that it is the number of voice paths that you wish to calculate.
    • Enter 10000 in the Minutes per day edit box.
    • Press the Calc. button.
    • The answer is displayed in the Voice paths 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 not enough.

Windows version of this calculator

The calculator on this page is modelled on the Call Minutes Calculator included with the Westbay Traffic Calculators for Windows 95/98/NT. 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.

Westbay Traffic Calculators
Westbay Traffic Calculator main window

Customers also benefit from an Erlang B Calculator, an Extended Erlang B Calculator and an Erlang C Calculator for analysing call centres.

You will also receive a free copy of Erlang for ExcelThis is a Add-In for Microsoft Excel version 97 or higher which allows Erlang B functions to be included in your own spreadsheets.

Westbay Traffic Calculators does not support Voice over IP.  For VoIP calculations, please see our VoIP Select Windows calculator.

These calculators are available for 139 US Dollars.  If you pay using VISA, MasterCard, American Express or Discovery, you can have this software working on your PC in five minutes!

Westplan - VoIP design software

Westplan is a revolutionary software package which simplifies the complicated design process involved in creating effective voice networks that are based on either traditional circuit switching or Voice over IP. All calculations are based on an inter-nodal traffic model which you can specify yourself, or allow Westplan to estimate.

Screen snapshot of Westplan
Westplan main window, with a network drawing in view

By allowing you to try different network topologies, Westplan quickly helps you to make informed judgements on the suitability of particular voice networking strategies to your company. You will be in a stronger position to understand your voice network costs and therefore to control your network resources.

Westplan supports these features:

  • Point and click network diagrams
  • Voice over IP bandwidth calculations
  • Layer 2 support for PPP, Frame Relay, Ethernet, ATM and HDLC.
  • Analogue, T1 and E1 transmission facilities
  • User-definable routing rules
  • RTP compression for VoIP
  • Full justification reports for each analysis
  • Clear printed reports
  • Context sensitive help
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Last modified: 10 May 2008

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