  Dealing with network congestion is a criterion used to enhance quality of
service (QoS) in distributed multimedia systems. The existing solutions for the
problem of network congestion ignore scalability considerations because they
maintain a separate classification for each video stream. In this paper, we
propose a new method allowing to control QoS provided to clients according to
the network congestion, by discarding some frames when needed. The technique
proposed, called (m,k)-frame, is scalable with little degradation in
application performances. (m,k)-frame method is issued from the notion of
(m,k)-firm realtime constraints which means that among k invocations of a task,
m invocations must meet their deadline. Our simulation studies show the
usefulness of (m,k)-frame method to adapt the QoS to the real conditions in a
multimedia application, according to the current system load. Notably, the
system must adjust the QoS provided to active clients1 when their number
varies, i.e. dynamic arrival of clients.
