Recommendation B.181)
TRAFFIC INTENSITY UNITY
	The CCITT,
considering
	(a)	that in CCITT texts concerning telephone operations and tariffs and in CCIR texts concerning radiotelephone transmissions (e.g. telephone radio–relay systems and the maritime mobile service radiotelephony), the quantity “traffic intensity” is used together with the unit in which it is expressed. With progress in telecommunications, increasing use will be made of this term and this unit;
	(b)	that the unit of carried traffic intensity is defined in CCITT Recommendation E.600,
recommends
	(1)	that for telecommunications purposes, the unit of carried traffic intensity should be defined as follows:
	Erlang: the unit of carried traffic intensity. The value in erlangs of the intensity of traffic carried by a pool of resources2) over a given period of time is equal to the average number of resources simultaneously busy during this period;
	(2)	that the erlang should be represented by the symbol E.
	Note – The name “erlang” was given to the traffic unit in 1946 by the CCIF, in honour of the Danish mathematician, A. K. Erlang (1878–1929), who was the founder of traffic theory in telephony.