Erlang, Agner Krarup (1878-1929)

Danish mathematician who applied the theory of probabilities to problems connected with telephone traffic, such as congestion and waiting time. The erlang is now the unit of telephone-traffic flow. Erlang was born near Tarm in Jutland and studied at the University of Copenhagen. From 1908 he was leader of the laboratory of the Copenhagen Telephone Company. Rules determining the amount of traffic to be carried per selector have been established by every telephone authority and company, following Erlang's formulas. Especially important are his formulas for the probability of barred access in busy-signal systems and for the probability of delay and for the mean waiting time in waiting-time systems. Erlang also constructed a measuring bridge to meter alternating current (the so-called Erlang complex compensator), which was a considerable improvement on earlier apparatus of similar function. Of equal significance were his investigations into telephone transformers and telephone cable theory.