Tremendous advances in technology have made possible Giga- and Terabit networks today. Simi- lar advances need to be made in the management and control of these networks if these technologies are to be successfully accepted in the market place. Although years of research have been expended at designing control mechanisms necessary for fair resource allocation as well as guaranteeing Quality of Service, the discovery of the self-similar nature of traffic ows in all packet networks and services, irrespective of topology, technology or protocols leads one to wonder whether these control mech- anisms are applicable in the real world. In an attempt to answer this question we have designed network simulators consisting of realistic client/server interactions over various protocol stacks and network topologies. Using this testbed we present some preliminary results which show that simple ow control mechanisms and bounded resources cannot alter the heavy-tail nature of the offered traffic. We also discuss methods by which application level models can be designed and their impacts on network performance can be studied.