Service Differentiation of Communication-bound Processes in a Real-Time Operating System

The majority of today’s Internet-based services are generally not concerned about the level of Quality of Service (QoS) presented to their users. For many such services, however, the QoS perceived by users is becoming a critical success factor. The main QoS attributes include those related to the service availability and timeliness. Ensuring them is essential to many services. In our opinion, this has to be achieved not only by providing services with appropriate access bandwidth, or through QoS awareness of the network communication protocols used, but also by means of a differentiation of the usage of system resources by server processes. In this paper, we focus on Internet-based multimedia data delivery services (e.g., services provided by Web, FTP, and video-on-demand servers). These services are run by processes whose activity is typically dominated by network communication; we call them communicationbound processes. We present the design and implementation of an operating system extension for quality-of-service differentiation among classes of communication-bound processes. The system allows to define classes of services with different quality attributes concerning the network data delivery performance. The proposed architecture provides server application developers with an object-based communication library (similar to the standard TCP/IP socket library), that supports different classes of service. Implementation issues and optimization strategies are also discussed. Quantitative measures aimed at evaluating the effectiveness of the proposed architecture are provided.