Over the past few years, the fast growth of internet made it a new target for some operators which decided to use it as a new infrastructure to offer their services such as voice and video to the customers via internet. In order to fulfill this, they developed multimedia applications which changed the nature of traffic over the internet. As a result, it seemed that there is a need to a new mechanism to guarantee the quality of service. Therefore, to make these applications widely used, QOSr equirements must be met. In this article we are going to talk about the QOS challenges specifically for video conferencing as a multimedia application, and we try to explain how to reach the appropriate quality for this applications in a congested network.