Scalable QOS control for VBR video servers

This paper accompanies a demonstration of a variable bit-rate (VBR) video server with scalable quality-of-service (QoS) control. Multimedia applications dynamically demand different QoS grades from servers and networks during a session. Since video is a critical component of distributed multimedia applications, video servers have to be responsive to the applications' requirements and to the availability of resources on heterogeneous terminals and networks. For this purpose a video server has to dynamically scale the source's quality in the control space formed by frame resolution, quantization and display rate. Experiences with a proof-of-concept implementation of a server with scalable QoS control show that it is able to jointly match the target quality of applications, the processing limitations of terminals and the capacity limitations of networks.