A formula developed by AK Erlang, which can be used to determine the number of lines needed to handle a set amount of calls during one hour. The formula assumes that callers who have a busy tone hear, then do not attempt to call again. Because some callers do attempt to call again, there is a risk that the application of Erlang B the chance that the number of lines is set too low. In general the Erlang However, B formula is suitable, especially when it is rare that all lines are busy. In practice Erlang B mainly used in automated systems.
See Erlang, Erlang C, Line load