Definition of Traffic Intensity: The instantaneous traffic intensity in a pool of resources
is the number of busy resources at a given instant of time.
a = λ·T
λ = number of carried connections per time unit (arrival rate, call rate)
T = mean duration of a connection or holding time
• In a local switch the number of calls in an hour is 1800
• The mean holding time of a call is 3 min
a = 1800 x 3 / 60 = 90 erlang
Typical traffic intensities per a single source are (fraction of time they are being used)
− private subscriber 0.01 – 0.04 erlang
− business subscriber 0.03 – 0.06 erlang
− mobile phone 0.03 erlang
− PBX 0.1 – 0.6 erlang
− coin operated phone 0.07 erlang
A load of 90 erlang is created by a population of some 2250 – 9000 private subscribers.