Representation of Quality of Service Preferences by Contract Hierarchies

In an open electronic service market, competing service providers offer services to clients who may choose freely among the service types and service providers. Before the service provision, a client needs to identify a particular server and negotiate a service contract that determines the contractual constraints for the service interactions. Part of the contract will be an agreement on the service quality that is expected by the client and that will be provided by the server. For example, a stock exchange information service may have QoS parameters such as actuality of information, service availability, guaranteed response time, and cost. Obviously, QoS parameters are application specific and their actual values depend on the current state of the whole distributed system, e.g. on the load condition of the server, on the response time of the sub-services that are employed by the information service, on the network thruput, and so on. QoS inherently is an end-to-end issue, i.e. the client’s perception of QoS depends on the QoS of many activities that occur in the context of the service interaction and that together are responsible to guarantee e.g. a certain response time level. In our project MAQS (Management Architecture for Quality of Service) we develop and implement a comprehensive framework for QoS management in distributed object systems. The framework will support all three main phases of QoS management: negotiation, monitoring/adaptation, and accounting/profiling.