When proving the correctness of algorithms in distributed systems, one generally considers safety conditions and liveness conditions. The Input Output I O automaton model and its timed version have been used successfully, but have focused on safety conditions and on a restricted form of liveness called fairness. In this paper we develop a new I O automaton model, and a new timed I O automaton model, that permit the veri cation of general liveness properties on the basis of existing veri cation techniques. Our models include a notion of environment-freedom which generalizes the idea of receptiveness of other existing formalisms, and enables the use of compositional veri cation techniques. The presentation includes an embedding of the untimed model into the timed model which preserves all the interesting attributes of the untimed model. Thus, our models constitute a coordinated f r amework for the description of concurrent and distributed systems satisfying general liveness properties.
This paper considers the problems of admission control and virtual circuit routing in high performance computing and communication systems. Admission control and virtual circuit routing problems arise in numerous applications, including video-servers, real-time database servers, and the provision of permanent virtual channels in large-scale communications networks. The paper describes both upper and lower bounds on the competitive ratio of algorithms for admission control and virtual circuit routing in trees, arrays, and hypercubes (the networks most commonly used in conjunction with high performance computing and communication). Our results include optimal algorithms for admission control and virtual circuit routing in trees, as well as the first competitive algorithms for these problems on non-tree networks. A key result of our research is the development of on-line algorithms that substantially outperform the greedy-based approaches that are used in practice.
When proving the correctness of algorithms in distributed systems, one generally considers safety conditions and liveness conditions. The Input Output I O automaton model and its timed version have been used successfully, but have focused on safety conditions and on a restricted form of liveness called fairness. In this paper we develop a new I O automaton model, and a new timed I O automaton model, that permit the veri cation of general liveness properties on the basis of existing veri cation techniques. Our models include a notion of environment-freedom which generalizes the idea of receptiveness of other existing formalisms, and enables the use of compositional veri cation techniques. The presentation includes an embedding of the untimed model into the timed model which preserves all the interesting attributes of the untimed model. Thus, our models constitute a coordinated f r amework for the description of concurrent and distributed systems satisfying general liveness properties.
Recent work in queueing theory has provided a means by which queue lengths can be estimated based solely on information about service completions. The work yields algorithms that permit the estimation of invisible or disperse queues which would be difficult to measure directly. These algorithms may be applied to resources in communications networks at which difficult-to-measure queues exist. The following paper presents an algorithm for queue estimation and measures its accuracy on transmission data taken from an ethernet environment. Results show the algorithm to be fairly accurate despite its simplifying assumption that the arrival process of the data packets is Poisson; for about 2/3 of the queues analyzed, the ratio of the root mean square difference between the real queue and the estimated queue to the average real queue is less than 1/2.
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