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Reliable Distributed Systems

作者： W.D. Obal W.H. Sanders Department of Electrical and Computer Engineering University of Arizona Tucson Tucson AZ USA Center for Reliable and High-Performance Computing Coordinated Science Laboratory University of Illinois Urbana-Champaign Urbana IL USA

Model-based evaluation of reliable distributed and parallel systems is difficult due to the complexity of these systems and the nature of the dependability measures of interest. The complexity creates problems for analytical model solution techniques, and the fact that reliability and availability measures are based on rare events makes traditional simulation methods inefficient. Importance sampling is a well-known technique for improving the efficiency of rare event simulations. However, finding an importance sampling strategy that works well in general is a difficult problem. The best strategy for importance sampling depends on the characteristics of the system and the dependability measure of interest. This fact motivated the development of an environment for importance sampling that would support the wide variety of model characteristics and interesting measures. The environment is based on stochastic activity networks, and importance sampling strategies are specified using the new concept of the importance sampling governor. The governor supports dynamic importance sampling strategies by allowing the stochastic elements of the model to be redefined based on the evolution of the simulation. The utility of the new environment is demonstrated by evaluating the unreliability of a highly dependable fault-tolerant unit used in the well-known MARS architecture. The model is non-Markovian, with Weibull distributed failure times and uniformly distributed repair times.< >

关键词： Monte Carlo methods Stochastic processes Analytical models Discrete event simulation Availability Sampling methods Stochastic systems computer network reliability computer networks Concurrent computing

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Deblurring of images by cellular neural networks with applications to microscopy

Deblurring of images by cellular neural networks with applic...

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IEEE International Workshop on Cellular Nanoscale Networks and their Applications, (CNNA)

作者： J.P. Miller T. Roska T. Sziranyi K.R. Crounse L.O. Chua L. Nemes Division Neurobiology Department of Molecular & Cell Biology University of California Berkeley CA USA Analogic and Neural Computing Laboratory Computer and Automation Institute Hungarian Academy of Sciences (ATOMKI) Budapest Hungary Electronics Research Laboratory Department of Electrical Engineering and Computer Science University of California Berkeley CA USA

In this paper it is shown how the Cellular Neural Network (CNN) can be used to perform image and volume deblurring, with particular emphases on applications to microscopy. We discuss the basic linear theory of the CNN including issues of stability and template size. It is observed that a CNN with a small template can be used to implement an Infinite Impulse Response filter. It is then shown how general deblurring problems can be addressed with a CNN when the blurring operator is known. The proposed application is to solve the basic 3-D confocal image reconstruction task about the form of the blurring operator, confocal behavior in microscope images can be obtained with only 3-5 acquired image planes. In addition, the stored program capability of the CNN Universal Machine would provide integration of several image processing and detection tasks in the same architecture.< >

关键词： Cellular neural networks Microscopy Application software Biology computing computer networks Laboratories Stability Optical devices Optical distortion Image resolution

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Handwritten sentence recognition: from signal to syntax

Handwritten sentence recognition: from signal to syntax

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International Conference on Pattern Recognition

作者： R. Plamondon S. Clergeau C. Barriere Electrical & Computer Engineering Department Ecole Polytechnique de Montreal Montreal QUE Canada Natural Language Laboratory Computing Science Department Simon Fraser University Canada Centre National d''Etudes Des Telecommunications Lannion France

This paper describes a system dedicated to online handwritten sentence recognition. The prototype is made up of two basic processors. The first controls the data acquisition, pentip trace segmentation, letter identification. The second aims at identifying and correcting the words candidates by integrating syntactic and lexical information. Sentences are parsed to list the grammatical classes of each incorrect candidates then lexical query searches for words in a lexicon according to grammatical classes. A final decision is made using a string comparison algorithm. Tests of the complete system are reported at the end for a typical writer-dependent application.

关键词： Handwriting recognition Prototypes System testing Performance evaluation Natural languages Laboratories Process control Data acquisition Electronic equipment testing Application software

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A SIMPLE DISTRIBUTED LOOP-FREE ROUTING STRATEGY FOR computer-COMMUNICATION NETWORKS

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IEEE TRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS 1993年第12期4卷 1308-1319页

作者： SHIN, KG CHOU, CC Real-Time Computing Laboratory Computer Science and Engineering Division Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

The loops resulting from either component failures or Load changes in a computer communication network degrade the performance and the adaptability of conventional distributed adaptive routing strategies, such as ARPANET's previous routing strategy (APRS). In this paper, we develop a distributed loop-free routing strategy by adding only one additional piece of information-the total number of minimum-delay paths-to the commonly used routing messages and tables. Most conventional approaches to the looping problem suffer high overheads in time and space because each message must either include the first several nodes of its path or trace the entire path to detect a loop. By contrast, the proposed routing strategy requires only easily obtainable information, yet removes loops completely. It is far more efficient in both time and space than its conventional counterparts, especiallyTable Ifor sparse computer networks. The correctness of the proposed strategy is proved, and several illustrative e?xamples are given. The performance of this strategy is shown to be always better than, or at least as good as, that of APRS and any multiorder routing strategies, where the order of a routing strategy is determined by the amount of routing information carried in each routing message.

关键词： ARPANET computer COMMUNICATION NETWORKS DISTRIBUTED ADAPTIVE ROUTING LOOP-FREE OR FAULT-TOLERANT ROUTING NETWORK DELAY TABLES STRATEGY ROUTING MESSAGES

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ANALYTIC MODELS OF ADAPTIVE LOAD SHARING SCHEMES IN DISTRIBUTED real-time SYSTEMS

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IEEE TRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS 1993年第7期4卷 740-761页

作者： SHIN, KG HOU, CJ Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

In a distributed real-time system, nonuniform task arrivals may temporarily overload some nodes while leaving some other nodes idle. As a result, some of the tasks on an overloaded node may miss their deadlines even if the overall system has the capacity to meet the deadlines of all tasks. In a companion paper [1], we proposed, without any modeling analysis, a decentralized, dynamic load sharing (LS) scheme as a solution to this problem. In this paper, we develop analytic queueing models to comparatively evaluate the proposed LS scheme as well as three other schemes: no LS, LS with random selection of a receiver node, and LS with perfect information. The evolution of a node's load state is modeled as a continuous-time semi-Markov process, where cumulative execution time (CET), rather than the commonly-used queue length (QL), is employed to describe the workload of a node. Not only fundamental differences among the different LS schemes are addressed in the analytic models, but also implementation overheads are taken into account Several metrics relevant to real-time performance are derived from these models: in particular, we evaluate the probability of a task missing its deadline, called the probability of dynamic failure. The proposed scheme is compared against other LS schemes using these performance metrics. The validity of analytic models is checked with simulations. Both analytic and simulation results indicate that by using judicious exchange/use of state information and Bayesian decision mechanism, the proposed scheme makes a significant improvement over other existing LS schemes in minimizing the probability of dynamic failure.

关键词： BAYESIAN ANALYSIS CONTINUOUS-time MARKOV CHAINS DEADLINES DISTRIBUTED real-time SYSTEMS LOAD SHARING LOCATION AND TRANSFER POLICIES PERFORMANCE EVALUATION RANDOM PROBING AND SELECTION

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MIXED time-CONSTRAINED AND NON-time-CONSTRAINED COMMUNICATIONS IN LOCAL-AREA NETWORKS

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IEEE TRANSACTIONS ON COMMUNICATIONS 1993年第11期41卷 1668-1676页

作者： SHIN, KG ZHENG, Q Department of Electrical Engineering and Computer Science Real-Time Computing Laboratory University of Michigan Ann Arbor MI USA Mitsubishi Electric Research Laboratories Inc. Cambridge MA USA

It is well known that some time-token medium access protocols for local area networks (LANs) like the IEEE 802.4 token bus and the FDDI token ring can guarantee the medium access delay for time-constrained packets. However, a problem which has been largely overlooked is how these protocols can be made to provide a maximum throughput for nontime-constrained packets while guaranteeing the delay bound of time-constrained packets. We first show how the parameters of the IEEE 802.4 token bus and the FDDI token ring can be set to solve the above problem. Then, we design a new timer mechanism for the timed-token protocols which provides the highest guaranteed throughput of nontime-constrained packets among a set of medium access protocols called the token passing protocol, to which most of the existing non-contention LAN protocols belong. We present numerical examples to compare different protocols, all of which have shown the superiority of the proposed protocol to the others.

关键词： MIXING time Packet token bus Local Area Networks Token ring fiber distributed data interface (FDDI) Media Access Protocol

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Incorporation of optimal timeouts into distributed real-time load sharing 26

Incorporation of optimal timeouts into distributed real-time...

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26th Hawaii International Conference on System sciences, HICSS 1993

作者： Hou, C.-J. Shin, K.G. Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109-2122 United States

ISBN: (纸本)0818632305

This paper addresses the problem of designing and incorporating a timeout mechanism into load sharing (LS) with state-region change broadcasts in the presence of node failures in a distributed real-time system. Failure of a node is diagnosed by the other nodes through communication timeouts, and the timeout period used to diagnose whether a node is faulty or not depends on the dynamic changes in system load, the task attributes at the node, and the state the node was initially in. We formulate the problem of determining the 'best' timeout period Tiout for node i as a hypothesis testing problem, and maximize the probability of detecting node failures subject to a prespecified probability of falsely diagnosing a healthy node as faulty. The parameters needed for the calculation of Tiout are estimated on-line by node i using the Bayesian technique and are piggybacked in its region-change broadcasts. The broadcast information is then used to determine Tiout. If node n has not heard from node t for T Tiout since its receipt of node i's broadcast, it will consider node i failed. On the other hand, each node n also determines its own timeout period Tnout, and broadcasts its state not only at the time of state-region changes but also when it has remained within a broadcast-threshold interval throughout Tnout. Our simulation results show that the LS algorithm which combines the on-line parameter estimation, the timeout mechanism, and a few extra, timely broadcasts can significantly reduce the probability of missing task deadlines. © 1993 IEEE.

关键词： Probability

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Evaluation of load sharing in HARTS while considering message routing and broadcasting 93

Evaluation of load sharing in HARTS while considering messag...

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1993 ACM SIGMETRICS Conference on Measurement and Modeling of computer Systems, SIGMETRICS 1993

作者： Shin, Kang G. Hou, Chao-Ju Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109-2122 United States

In this paper, we apply the load sharing (LS) mechanism proposed in [1, 2] to HARTS, an experimental distributed realtime system [3] currently being built at the real-time computing laboratory of the University of Mic... 详细信息

ISBN: (纸本)0897915801

关键词： Distributed computer systems

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Determination of an optimal retry time in multiple-module computing systems 2

Determination of an optimal retry time in multiple-module co...

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2nd International Symposium on Uncertainty Modeling and Analysis, ISUMA 1993

作者： Hou, C.-J.J. Shin, K.G. Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109-2122 United States

ISBN: (纸本)0818638508

The optimal amount of time used for retrying an instruction on detection of an error in a computing system is usually determined under the assumption that the system is composed of a single module, within which all fault activities are confined until some module-replacement action is taken. The authors consider fault activities in multiple-module systems. They first relax the single-module assumption and model the fault activities in a multiple-module system as a Markov process. The randomization approach is applied to decompose the Markov process into a discrete-time Markov chain subordinated to a Poisson process. Using this decomposition, several interesting measures can be derived such as the conditional probability of successful retry given a retry period and the fact that a non-permanent fault has occurred, and the mean time until which all modules in the system enter a fault-free state. All the measures derived are used to determine, along with the parameters characterizing fault activities and costs of recovery techniques, whether or not retry should be used as a first-step recovery means on detection of an error;and the best retry period subject to a specific probability of successful retry. © 1993 IEEE.

关键词： Markov processes

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Adaptive Deadlock-Free Routing in Multicomputers Using only One Extra Virtual Channel

Adaptive Deadlock-Free Routing in Multicomputers Using only ...

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1993 International Conference on Parallel Processing, ICPP 1993

作者： Su, Chien-Chun Shin, Kang G. Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109-2122 United States

ISBN: (纸本)0849389836

We present three protocols defin ing the relationship between messages and the chan nel resources requested: request-then-hold, requestthen wait, and request-then-relinquish. Based on the three protocols, we develop an adaptive deadlockfree routing algorithm called the SP routing. The SP routing uses shortest paths and is fully-adaptive, so messages can be routed via any of the shortest paths from the source to the destination. Since it is a minimal or shortest routing, the SP routing guar antees the freedom of livelocks. The SP routing is not limited to a specific network topology. The main requirement for an applicable network topology is that there exists a deterministic, minimal, deadlock-free routing algorithm. Most ex isting network topologies are equipped with such an algorithm. In this paper, we present an adaptive deadlock-free routing agorithm for n-dimensional meshes by using the SP routing. The hardware re quired by the SP routing uses only one extra virtual channel as compared to the deterministic routing. © 1993 IEEE.

关键词： Network topology

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