A QoS support framework for dynamically reconfigurable multimedia applications

The use of multimedia in distributed systems has begun to include such complex and mission-critical domains as digital television production, 'video-on-demand' services, medical and security systems. These applications impose more stringent requirements on the support mechanisms provided by underlying networks and operating systems than most currently deployed continuous media applications. This paper describes the DJINN multimedia programming framework, which is designed to support the construction and dynamic reconfiguration of distributed multimedia applications. We motivate the benefits of a runtime model of the quality of service and other characteristics of multimedia applications, and demonstrate a generic algorithm for scheduling dynamic reconfigurations that maintains QoS guarantees. QoS characteristics are modelled as piecewise-linear or quadratic relations, which are solved using standard constraint programming techniques. During reconfigurations, updates to active components are scheduled so as to maintain temporal constraints on the media streams. We illustrate our approach using experimental results from a real-world application domain.