A quality of service architecture

For applications relying on the transfer of multimedia, and in particular continuous media, it is essential that quality of service (QoS) is guaranteed system-wide, including end-systems, communications systems and networks. Although researchers have addressed many isolated areas of QoS provision, little attention has so far been paid to the definition of an integrated and coherent framework that incorporates QoS interfaces, management and mechanisms across all architectural layers. To address this deficiency, we are developing a Quality of Service Architecture (QoS-A) which offers a framework to specify and implement the required performance properties of multimedia applications over high-performance ATM-based networks. The QoS-A incorporates the notions of flow, service contract and flow management. Flows characterise the production, transmission and eventual consumption of single media streams, service contracts are binding agreements between users and providers and flow management provides for the monitoring and maintenance of the contracted QoS levels. This paper provides an overview of the QoS-A and focuses particularly on the role of the transport service and protocol in the architecture. We describe a multimedia enhanced transport service (METS), flow management and transport layer service contract. We show how QoS levels contracted at the transport service interface can be assured in the context of our local ATM environment.