Before performing a calculation using the Erlangs and IP Bandwidth Calculator, you should select the VoIP transmission parameters using three drop down boxes (Coding algorithm, Packet duration and RTP header compression). These are described in the previous section.
Then, click on the radio button associated with either Busy hour traffic, Blocking or Bandwidth to indicate which quantity is unknown and to be calculated. Enter the known values into the other two edit boxes, which should be white. When you press the calculate button, the unknown quantity will be displayed in the grey box. Press the Stop button to cancel a long calculation.
You may change the units used to enter and display bandwidth by clicking on the radio buttons to the right of the window. The options are kbps and Mbps.