Cost - Quality Tradeo s in the

The data delivery service currently ooered in the Internet is a point-to-point best eeort service. Work is underway in various IETF (Internet Engineering Task Force) working groups to include new services for applications that require a speciic quality of service. Examples of such applications include the so-called real time applications such as audio and videoconferencing, distributed interactive simulation, etc. The cost in terms of network resources for providing these services is higher than that for providing best eeort service. Thus, the existence of new services presents a tradeoo between quality and cost. Furthermore, recent work has shown that many real time applications can adapt their output rates (and hence their network resource requirements) depending on the network conditions (and hence on the available network service). These so-called rate adaptive applications present a further tradeoo between cost and quality of the data sent into the network. In this paper, we describe these tradeoos and analyze their impact on the applications and on the network. We illustrate our points with recent results and measurements obtained with IVS, which is a rate-adaptive audio and videoconference application for the Internet developed at INRIA.