The impending introduction of long and short haul links based on ATM h
as led to its application to packet services such as the DARPA Interne
t Protocol (IP). Some earlier work on IP traffic between main IP route
rs (WAN traffic) has led to concerns over the efficiency of using smal
l cells. The authors describe the results of IP traffic traces taken w
ithin a departmental LAN over a 16-day period. This traffic is used to
drive a model of IP-over-ATM to analyze the real efficiency of the te
chnique.