or Erlang's loss formula: This formula calculates the probability that a caller will get a busy signal when calling a system where the number of agents equals the number of telephone lines (trunks). The QTPMMS_PrFull function, with Queue Capacity set equal to zero, calculates this quantity.
A formula developed by A.K. Erlang, widely used to determine the number of trunks required to handle a known calling load during a one hour period. The formula assumes that if callers get busy signals, they go away forever, never to retry (lost calls cleared). Since some callers retry, Erlang B can underestimate trunks required. However, Erlang B is generally accurate in situations with few busy signals.