Erlang is a measure of the Channel Occupation Rate within Time Period. One Erlang is the Occupation of One Traffic Resource (TCH, SDCCH, PDCH, E1 Device…) for one Hour. It is used to evaluate Subscriber Activity (Money) or to evaluate Resource Usage (Capacity and Dimensioning).
To Plan Resource Capacity the Busy Hour is used (Hour with Highest Usage for the Resource under Dimensioning).
For Dimensioning the target is to find the number of resources needed to handle subscriber demand and at the same time to guaranty certain Service Quality.
This Service Quality is referred to as Grade of Service (GOS); GOS =0.1 is better than GOS =0.2 but requires more Resources (More Money)
To know the Number of Resources Required to Handle Expected Subscriber Demand (x Erlangs) with GoS not less than (GOS >= Y) Erlang B or Erlang C tables can be used.