Special thanks to Jim Carefoot for providing this program to the members of NENA at no cost

Special thanks to Jim Carefoot for providing this program to the members of NENA at no cost. His notes are below and you may download the program including notes. The file is zipped so you'll need an "unzipper" or you can run the program.

The Footbridge Call Calc DOS program is intended as a simple tool in assessing the demand created by incoming telephone calls for service in communication centers. It provides a Quality of Service (QOS) indicator in the form the fraction of calls that will wait longer than 10 seconds for answer, based on the number of available call answerers and the average duration of calls.

It is handy for evaluating data gleaned from various types of vendor logging data collected with the Printer Eliminator™ program.

The Call Calc uses principles rooted in the Erlang "C" formula or E2(N,A). It uses a Poisson distribution for call arrivals and assumes that blocked callers will wait to be served instead of giving up. It produces the same values as the Department of Justice report tables often used for 9-1-1 call answering estimation.

A formula calculation of this kind is a "model" and doesn’t take a lot of real-world influences like mixture of call priority or interruptions into account. The formula simply describes what delays will be encountered when X people queue up for Y seconds of service from Z servers.

The program is written for DOS as a working toolbox item and is not perfect or even bug-free. Use this version at your own risk.

When entering data use the TAB and Shift-TAB keys to move from box to box. It is also possible to use a mouse. When you are ready to calculate the QoS highlight RUN and hit ENTER, or just click on RUN. Entering 2 call takers handling 60-second calls arriving at a rate of 30/hour shows that fewer than 8 percent of callers will wait more than 10 seconds for answer. This is within the commonly quoted 90-percent-within-10-second target. If the calls actually take 60 seconds plus 20 seconds of computer time or record work the program shows that the QOS falls to 14 percent. Staffing for two call receivers plus an overflow call answerer may be indicated.

The program file name is erlangc1.exe. It can be run in DOS or from a DOS window in Windows 3.1 or Win95.

Footbridge
13611 104th PL NE Kirkland, WA 98034-2043 U.S.A.
F F 425 821-2453 e-mail footbridge@worldnet.att.net