Determining a blockage rate

Traffic in Erlangs cannot be translated directly into a number of channels. To determine how many channels you need, you must also know what blockage rate is acceptable to your callers.

Blockage rate indicates what percentage of callers are not connected immediately. For example, a blockage rate of 1% means that if 500 people call during peak hours, five of them will receive busy tones or have to wait in the switch queue.

If you are already operating with a high blockage rate, you might be losing many of the calls you would be getting with a lower blockage rate. So, if you assume a lower blockage rate when you calculate the number of channels you need, you should perhaps assume a higher Erlang number.