The data delivery service currently offered in the Internet is a point
-to-point best effort service. Work is underway in various IETF (Inter
net Engineering Task Force) working groups to include new services for
applications that require a specific 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 i
s higher than that for providing best effort service. Thus, the existe
nce of new services presents a tradeoff between quality and cost. Furt
hermore, recent work has shown that many real-time applications can ad
apt their output rates (and hence their network resource requirements)
depending on network conditions (and hence on the available network s
ervice). Such tate adaptive applications present a further tradeoff be
tween cost and quality of the data sent into the network.In this paper
, we describe these tradeoffs and analyze their impact on the applicat
ions 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.