This paper serves as an introduction to modern local area network (LAN) traffic characterization, reviewing classical results and covering new ones. A scenario is considered in which external aggregated IP data traffic is routed toward an asynchronous transfer mode (ATM) switch network. The objectives of the paper are as follows: to present an easy method of gathering aggregated IP data streams from a router machine; to characterize by a parsimonious model of such IP data traffic; and to use the data traffic model to study the performance of available bit rate (ABR) service over an ATM network seeking for the Cell Loss Rate (CLR) as one important Quality of Service (QoS) parameter.