Erlang

Erlang C

The Erlang C formula expresses the waiting probability in a queuing system.

Erlang C assumes an infinite population of sources, which jointly offer traffic of A erlangs to N servers. However, if all the servers are busy when a request arrives from a source, the request is queued. An unlimited number of requests may be held in the queue in this way simultaneously.

This formula calculates the probability of queuing offered traffic, assuming that blocked calls stay in the system until they can be handled and is used to determine the number of agents needed to staff a call center, for a specified desired probability of queuing.