This paper describes an architecture that provides support for quality of service (QoS) specification and enforcement in heterogeneous distributed computing systems. The Quartz QoS architecture has been designed to overcome various limitations of previous QoS architectures that have constrained their use in heterogeneous systems. These limitations include dependencies on specific platforms and the fact that their functionality is often limited by design to one particular area of application. Quartz is able to accommodate differences among diverse computing platforms and areas of application by adopting a flexible and extensible platform-independent design, which allows its internal components to be rearranged dynamically in order to adapt the architecture to the surrounding environment. Further significant problems found in other QoS architectures, such as the lack of flexibility and expressiveness in the specification of QoS requirements and limited support for resource adaptation, ar...

Abstract. A case study is presented which concerns the design of an adaptive mechanism for packetized audio for use over the Internet. During the design process, the audio mechanism was modeled with the stochastically timed process algebra EMPA and analyzed via simulation by the EMPA based software tool TwoTowers in order to predict the percentage of packets that are received in time for being played out. The predicted performance figures obtained from the algebraic model illustrated in advance the adequacy of the approach adopted in the design of the audio playout delay control mechanism. Based on these performance figures, it was possible to implement and develop the complete mechanism without incurring in additional costs due to the late discovery of unexpected errors or inefficiency. Performance results obtained from experiments conducted on the field confirmed the predictive simulative results. 1.

SPECIAL-PURPOSE AND APPLICATION-BASED SYSTEMS -- Real-tim e and em bedded system s; J.6 [Computer Applications]: COMPUTERAIDED ENGINEERING -- Com uter-aided design (CAD) General Term3 Algorithm s, Design Additional Key Words and Phrases: synchroni ation, on-chipm em orym inim i ation, high-level em bedded system s synthesis This work was supported by ... Authors' addresses: Gang Qu, Electrical andCom puter Engineering Departm ent and Institute for Advanced Com puter Studies, University of Maryland, College Park, MD 20742;em ail: gangqu@glue.um d.edu; Miodrag Potkonjak, Com puter Science Departm ent, University of California, Los Angeles, CA 90095;em ail:m iodrag@cs.ucla.edu. Perm ission tom ake digital/hard copy of all or part of thism aterial without fee for personal or classroom use provided that the copies are notm ade or distributed for profit orcom m ercial advantage, the ACM copyright/server notice, the title of the publication, and its date appear, and notice is given that co

ions for Continuous Media Support. It is important to notice that currently available distributed computing architectures do not have abstractions to represent a continuous flow of data between two or more elements. The usual approach to interaction between distributed objects through synchronous method calls is not suitable for representing continuous media. The possible approaches -- represent it as a single call or as a sequence of invocations -- cannot be adopted because of implicit temporal requirements that are not handled. A continuous flow of data (e.g. the output of a media device) cannot be represented by a single method invocation because of its unbounded nature. On the other hand, it is neither easy nor natural from the programmer's point of view to associate QoS and temporal requirements to sequences of invocations. The introduction of stream abstractions in the communication model is the usual approach to allow the definition of continuous flows with associated QoS requi...

A mechanism for transmitting packetized audio over wide area, shared networks is presented and its performance is studied via simulative analysis. The proposed mechanism does not need "in advance" allocation of either network bandwidth or computing resources, but maintains satisfiable values of the tradeoff between the audio packet playout delay and the packet loss due to late arrivals. Because of this, the proposed mechanism may be profitably integrated in industrial environments with other hard real time applications for which, instead, resource allocation is desirable. The performance of the proposed mechanism (i.e. the percentage of audio packets that arrive on time for being played out at the destination during an audio communication) is analyzed via simulation by a stochastically timed process algebra based software tool termed TwoTowers. Keywords: packet audio, simulation tools, performance evaluation, process algebras. 1 INTRODUCTION In industrial environments such as power p...