Accessing and Customizing Services in Distributed Systems

In a distributed system, entities access services provided to them by other entities at remote sites. While it may be unimportant to the service users which entities act as service providers, they often have other requirements on the services they use. On the other hand, service providers only have certain possibilities. Both the requirements and possibilities can be described by means of quality-of-service parameters (QOSPs), which have to be determined for each service session. In this paper we design a session establishment service (SES) which takes QOSP values into account. The SES can be used for any kind of QOSPs since it uses badness specifications as a uniform means to identify the usefulness of a certain QOSP value to a service user, to determine the relative importance of single QOSPs, and to calculate the overall quality of a service. Three kinds of QOSPs are distinguished: Static parameters do not change as long as the service is available, dynamic parameters depend on the current state of a service provider, and retrospective parameters result from evaluations of the service which are obtained from previous service users. While some QOSP values are available others can only be accomplished if the service provider schedules its resources appropriately. The reservation of resources can be integrated within the SES. This is especially important for real-time services.

ICSI Technical Report TR-89-059

Technical Report