138 research outputs found

    Online Algorithms for Multi-Level Aggregation

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    In the Multi-Level Aggregation Problem (MLAP), requests arrive at the nodes of an edge-weighted tree T, and have to be served eventually. A service is defined as a subtree X of T that contains its root. This subtree X serves all requests that are pending in the nodes of X, and the cost of this service is equal to the total weight of X. Each request also incurs waiting cost between its arrival and service times. The objective is to minimize the total waiting cost of all requests plus the total cost of all service subtrees. MLAP is a generalization of some well-studied optimization problems; for example, for trees of depth 1, MLAP is equivalent to the TCP Acknowledgment Problem, while for trees of depth 2, it is equivalent to the Joint Replenishment Problem. Aggregation problem for trees of arbitrary depth arise in multicasting, sensor networks, communication in organization hierarchies, and in supply-chain management. The instances of MLAP associated with these applications are naturally online, in the sense that aggregation decisions need to be made without information about future requests. Constant-competitive online algorithms are known for MLAP with one or two levels. However, it has been open whether there exist constant competitive online algorithms for trees of depth more than 2. Addressing this open problem, we give the first constant competitive online algorithm for networks of arbitrary (fixed) number of levels. The competitive ratio is O(D^4 2^D), where D is the depth of T. The algorithm works for arbitrary waiting cost functions, including the variant with deadlines. We also show several additional lower and upper bound results for some special cases of MLAP, including the Single-Phase variant and the case when the tree is a path

    Online algorithms for multi-level aggregation

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    In the multilevel aggregation problem (MLAP), requests arrive at the nodes of an edge-weighted tree T and have to be served eventually. A service is defined as a subtree X of T that contains the root of T. This subtree X serves all requests that are pending in the nodes of X, and the cost of this service is equal to the total weight of X. Each request also incurs waiting cost between its arrival and service times. The objective is to minimize the total waiting cost of all requests plus the total cost of all service subtrees. MLAP is a generalization of some well-studied optimization problems; for example, for trees of depth 1, MLAP is equivalent to the Transmission Control Protocol acknowledgment problem, whereas for trees of depth 2, it is equivalent to the joint replenishment problem. Aggregation problems for trees of arbitrary depth arise in multicasting, sensor networks, communication in organization hierarchies, and supply chain management. The instances of MLAP associated with these applications are naturally online, in the sense that aggregation decisions need to be made without information about future requests. Constant-competitive online algorithms are known for MLAP with one or two levels. However, it has been open whether there exist constant-competitive online algorithms for trees of depth more than 2. Addressing this open problem, we give the first constant-competitive online algorithm for trees of arbitrary (fixed) depth. The competitive ratio is O(D42D), where D is the depth of T. The algorithm works for arbitrary waiting cost functions, including the variant with deadlines

    Performance Evaluation of Communication Software Systems for Distributed Computing

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    In recent years there has been an increasing interest in object-oriented distributed computing since it is better quipped to deal with complex systems while providing extensibility, maintainability, and reusability. At the same time, several new high-speed network technologies have emerged for local and wide area networks. However, the performance of networking software is not improving as fast as the networking hardware and the workstation microprocessors. This paper gives an overview and evaluates the performance of the Common Object Request Broker Architecture (CORBA) standard in a distributed computing environment at NASA Ames Research Center. The environment consists of two testbeds of SGI workstations connected by four networks: Ethernet, FDDI, HiPPI, and ATM. The performance results for three communication software systems are presented, analyzed and compared. These systems are: BSD socket programming interface, IONA's Orbix, an implementation of the CORBA specification, and the PVM message passing library. The results show that high-level communication interfaces, such as CORBA and PVM, can achieve reasonable performance under certain conditions

    On the Validity of Flow-level TCP Network Models for Grid and Cloud Simulations

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    International audienceResearchers in the area of distributed computing conduct many of their experiments in simulation. While packet-level simulation is widely used to study network protocols, it can be too costly to simulate network communications for large-scale systems and applications. The alternative is to simulate the network based on less costly flow-level models. Surprisingly, in the literature, validation of these flow-level models is at best a mere verification for a few simple cases. Consequently, although distributed computing simulators are often used, their ability to produce scientifically meaningful results is in doubt. In this work we focus on the validation of state-of-the-art flow-level network models of TCP communication, via comparison to packet-level simulation. While it is straightforward to show cases in which previously proposed models lead to good results, instead we systematically seek cases that lead to invalid results. Careful analysis of these cases reveal fundamental flaws and also suggest improvements. One contribution of this work is that these improvements lead to a new model that, while far from being perfect, improves upon all previously proposed models. A more important contribution, perhaps, is provided by the pitfalls and unexpected behaviors encountered in this work, leading to a number of enlightening lessons. In particular, this work shows that model validation cannot be achieved solely by exhibiting (possibly many) ''good cases.'' Confidence in the quality of a model can only be strengthened through an invalidation approach that attempts to prove the model wrong

    K-Means+ID3 and dependence tree methods for supervised anomaly detection

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    In this dissertation, we present two novel methods for supervised anomaly detection. The first method K-Means+ID3 performs supervised anomaly detection by partitioning the training data instances into k clusters using Euclidean distance similarity. Then, on each cluster representing a density region of normal or anomaly instances, an ID3 decision tree is built. The ID3 decision tree on each cluster refines the decision boundaries by learning the subgroups within a cluster. To obtain a final decision on detection, the k-Means and ID3 decision trees are combined using two rules: (1) the nearest neighbor rule; and (2) the nearest consensus rule. The performance of the K-Means+ID3 is demonstrated over three data sets: (1) network anomaly data, (2) Duffing equation data, and (3) mechanical system data, which contain measurements drawn from three distinct application domains of computer networks, an electronic circuit implementing a forced Duffing equation, and a mechanical mass beam system subjected to fatigue stress, respectively. Results show that the detection accuracy of the K-Means+ID3 method is as high as 96.24 percent on network anomaly data; the total accuracy is as high as 80.01 percent on mechanical system data; and 79.9 percent on Duffing equation data. Further, the performance of K-Means+ID3 is compared with individual k-Means and ID3 methods implemented for anomaly detection. The second method dependence tree based anomaly detection performs supervised anomaly detection using the Bayes classification rule. The class conditional probability densities in the Bayes classification rule are approximated by dependence trees, which represent second-order product approximations of probability densities. We derive the theoretical relationship between dependence tree classification error and Bayes error rate and show that the dependence tree approximation minimizes an upper bound on the Bayes error rate. To improve the classification performance of dependence tree based anomaly detection, we use supervised and unsupervised Maximum Relevance Minimum Redundancy (MRMR) feature selection method to select a set of features that optimally characterize class information. We derive the theoretical relationship between the Bayes error rate and the MRMR feature selection criterion and show that MRMR feature selection criterion minimizes an upper bound on the Bayes error rate. The performance of the dependence tree based anomaly detection method is demonstrated on the benchmark KDD Cup 1999 intrusion detection data set. Results show that the detection accuracies of the dependence tree based anomaly detection method are as high as 99.76 percent in detecting normal traffic, 93.88 percent in detecting denial-of-service attacks, 94.88 percent in detecting probing attacks, 86.40 percent in detecting user-to-root attacks, and 24.44 percent in detecting remote-to-login attacks. Further, the performance of dependence tree based anomaly detection method is compared with the performance of naïve Bayes and ID3 decision tree methods as well as with the performance of two anomaly detection methods reported in recent literature

    3rd Many-core Applications Research Community (MARC) Symposium. (KIT Scientific Reports ; 7598)

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    This manuscript includes recent scientific work regarding the Intel Single Chip Cloud computer and describes approaches for novel approaches for programming and run-time organization

    Markov and Semi-markov Chains, Processes, Systems and Emerging Related Fields

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    This book covers a broad range of research results in the field of Markov and Semi-Markov chains, processes, systems and related emerging fields. The authors of the included research papers are well-known researchers in their field. The book presents the state-of-the-art and ideas for further research for theorists in the fields. Nonetheless, it also provides straightforwardly applicable results for diverse areas of practitioners
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