The Erlang traffic model is a method of analyzing telecommunications traffic. E-traffic is the traffic intensity in Erlangs, where one Erlang represents the amount of traffic generated by one channel (or circuit) being occupied for one time unit (typically hour).
When you have a telephone call for half an hour and then idle another half an hour, you produce 0.5 Erlangs of telecom traffic. When you and your friend simultaneously call someone and talk for one hour, your total traffic load will be 2 Erlangs.
Erlang telecommunications traffic measurement unit was named in honor of Danish mathematician A. K. Erlang, who developed telecommunications traffic theory.