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Erlangs and Lines Calculator
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Here is a
brief introduction to the calculator. For more detailed information, press the Help
Button. For a running record of the results calculated, press the Results button.
Both these functions open new browser windows on your desktop.
- This calculator is based on the Erlang B traffic model. Established at the turn
of the last century, it can be used to estimate the number of voice paths required between
two network elements if the traffic volume between those nodes is known. 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.
- The three variables involved in these calculations are Busy Hour Traffic (BHT), Blocking
and Voice paths:
- Busy Hour Traffic (in Erlangs) is the number of hours of call traffic there are
during the busiest hour of operation of a telephone system.
- Blocking is the failure of calls due to an insufficient number of lines being
available. E.g. 0.03 mean 3 calls blocked per 100 calls attempted.
- Voice paths is the number of lines required to carry the traffic.
- If you know two of the figures, you can work out the third as follows:
- Click on the Unknown radio button representing the unknown variable.
- Enter the 2 known figures into their edit boxes.
- Press Calc. and the third figure will be calculated and displayed in the
remaining edit box.
- For example, if from your call logger, you know that the Busy Hour Traffic is 10
Erlangs, and you want to know how many voice paths are required to handle this traffic if
you are prepared to tolerate 2 calls being blocked in every 100 calls attempted then:
- Press the Voice Paths Unknown radio button (this is selected by default).
- Enter 10 in the BHT edit box.
- Enter 0.02 in the Blocking edit box.
- When you press the Calc. button, 17 will be displayed in the Voice paths
edit box indicating that 17 voice paths would be required.
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| The calculator on this page is modelled on the Erlang B Calculator
included with the Westbay Traffic Calculators for Windows. The calculator works up
to 90,000 Erlangs / Lines and has the ability to display and print the results of
any calculations you have made during the previous week. 
Westbay Traffic Calculators main window.
Customers also benefit from an Extended Erlang B Calculator, an Erlang C
Calculator for analysing call centres and a Call Minutes Calculator.
You will also receive a free copy of Erlang for Excel. This 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 95 US
Dollars. If you pay using VISA, MasterCard, American Express or Discovery, you can have
this software working on your PC in five minutes!
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| 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. 
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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