Notation
Traffic is an arrival process
- calls arrive at some time Ta, measured in sec from 0
- inter-arrival time Ti (time elapsed between call arrivals); thus arrival rate per sec is 1/Ti
and a departure process
- calls have a duration or holding time Tc; thus departure rate is 1/Tc
Traffic is measured by averaging over an integration period, Tp. In Erlangs (utilization): A = Tc / Ti