337360
Distributed queueing in scalable high performance routers
This paper presents and evaluates distributed queueing algorithms for regulating the flow of traffic through large, high performance routers. Distributed queueing has a similar objective to crossbar-scheduling mechanisms used in routers with relatively small port counts, and shares some common high level characteristics. However, the need to minimize communication overhead rules out the iterative methods that are typically used for crossbar scheduling, while the ability to sub-divide the available bandwidth among different ports provides a degree of freedom that is absent in the crossbar scheduling context, where inputs must be matched to outputs. Our algorithms are based on four ideas (1) backlog-proportional-allocation of output bandwidth, (2) urgency-proportional-allocation of input bandwidth, (3) dynamic reallocation of bandwidth and (4) deferred underflow. Our algorithms guarantee congestion-free operation of the switch fabric. Our performance results show that for uniform random traffic, even a very modest speedup is sufficient to reduce the loss of output link bandwidth due to sub-optimal rate allocation to negligible levels, and that even under extreme conditions, a speedup of two is sufficient to eliminate such bandwidth loss.
14708115
Distributed computing systems and checkpointing
This paper examines the performance of synchronous checkpointing in a distributed computing environment with and without load redistribution. Performance models are developed, and optimum checkpoint intervals are determined. The analysis extends earlier work by allowing for multiple nodes, state dependent checkpoint intervals, and a performance metric which is coupled with failure-free performance and the speedup functions associated with implementation of parallel algorithms. Expressions for the optimum checkpoint intervals for synchronous checkpointing with and without load redistribution are derived and the results are then used to determine when load redistribution is advantageous.<<ETX>>
16104056
Performance analysis and design of a logic simulation machine
The high costs associated with logic simulation of large VLSI circuits has led to the need for new computer architectures tailored to the simulation task. Such architectures have the potential for significant speed-ups over software-based logic simulators executing on standard sequential computers. This paper presents a model of one class of multiprocessor simulation architectures and compares the performance of some of these machines using data obtained from simulations of VLSI circuits. In addition, we discuss the implications of our results on machine design and examine the sensitivity of the model to variations in circuit characteristics.
11030217
The open network laboratory
The Open Network Laboratory (ONL) is a remotely accessible network testbed of high performance routers which has been designed with an eye towards ease of use for users from the naïve to the expert. The system is built around a set of high-performance routers that are extendible and easily configurable through the Remote Laboratory Interface (RLI), an intuitive graphical interface. The RLI also makes it easy to configure packet filters in the routers, assign flows or flow aggregates to separate queues with configurable QoS and attach hardware monitoring points to real-time charts. The RLI's real-time charts and user data facility make it easy to directly view the effects of traffic as it moves through a router, allowing the user to gain better insight into system behavior and create compelling demonstrations. Each port of the router is equipped with an embedded processor that supports software plugins which allow users to extend the system's functionality. This paper describes the ONL and how it can be used in networking education. Our web site onl.arl.wustl.edu includes a short video and a tutorial.
14659694
Hybrid term indexing for different IR models
Retrieval effectiveness depends on how terms are extracted and indexed. For Chinese text (and others like Japanese and Korean), there are no space to delimit words. Indexing using hybrid terms (i.e. words and bigrams) were able to achieve the best precision amongst homogenous terms at a lower storage cost than indexing with bigrams. However, this was tested with conjunctive queries. Here, we extended the weighted Boolean models using fuzzy and p-norm measures, as well as the vector space model using the cosine measure, for processing hybrid terms. Our evaluation shows that all IR models using hybrid terms achieve better average precision over those using words. Across different recall values, the weighted Boolean model using fuzzy measures with hybrid terms achieve consistently about 8% higher than those using words. The vector space model using the cosine measures with hybrid terms achieved the best improvement in the average recall and precision.
690242
Improving Quality of Email Categorization with Tournament Methods
The tournament text classification methods are proposed in this article to perform the task of email categorization, in which the essence is to break down the multi-class categorization process into a set of binary classification tasks. We implement the methods of elimination and Round Robin tournament to classify emails within 15 folders. Substantial experiments are conducted to compare the effectiveness and robustness of the tournament methods against the n-way classification method and the voting method. The experimental results show that the tournament methods outperform the n-way method by 11.7% and the voting method by 4.1% regarding precision, and the Round Robin performs slightly better than the Elimination tournament on average.
35278447
An Investigation on Transformation-based Error-driven Learning Algorithm for Chinese Noun Phrase Extraction
Noun phrases are commonly used for generating index terms for information retrieval systems. Therefore, we need an effective noun phrase extraction method. In this paper, we propose an approach to extract maximal noun phrases from Chinese text. Although previous studies have been proposed to extract noun phrases, most of them are only applicable to Western languages. To the best of our knowledge, very few has handled Chinese text. Many existing approaches for Western languages made use of statistical methods. However, due to the complicated structure of maximal Chinese noun phrase, pure statistical approaches are not effective. We attempt to improve the performance of a statistical method by integrating it with the transformation-based error-driven learning (TEL) technique. Our methodology includes two modules. The first module applies a statistical method to extract Chinese noun phrases. The performance of this approach, in terms of precision and recall, is investigated. The second module applies the TEL algorithm to further refine the output of the first module. The TEL algorithm automatically learns a set of transformation rules to fix the errors that are obtained through comparing the output of the first module with the correctly annotated corpus. The learned rules can be applied to sentences in any corpus one by one to correct the errors. The TEL algorithm is shown to be effective in improving the precision.
7779937
Fundamental Properties of the Core Matching Functions for Information Retrieval
Traditional benchmarking methods for information retrieval (IR) are based on experimental performance evaluation. Although the metrics precision and recall can measure the performance of a system, it cannot assess the functionality of the underlying model. Recently, a theory of “aboutness” has been studied and used for reasoning about functional of IR models. Latest research shows the functionality of an IR model is largely determined by its retrieval mechanism, i.e., the matching function; in particular, containment and overlapping (either with or without a threshold value) are core IR matching functions. The objective of this paper is to model the containment and overlapping matching functions within an aboutness-based framework, reason and analyze the inherent functionality of them from an abstract and theoretical viewpoint. Separate aboutness relations for containment, pureoverlapping (i.e. without threshold) and threshold-overlapping are defined, and the sets of properties supported by them are derived and analyzed respectively. These three relations can be used to explain the functionality supported by an IR system and their effects to its performance; and moreover, they provide the design guidelines for new IR systems.
6330846
Component-based software engineering: technologies, development frameworks, and quality assurance schemes
Component-based software development approach is based on the idea to develop software systems by selecting appropriate off-the-shelf components and then to assemble them with a well-defined software architecture. Because the new software development paradigm is very different from the traditional approach, quality assurance (QA) for component-based software development is a new topic in the software engineering community. In this paper, we survey current component-based software technologies, describe their advantages and disadvantages, and discuss the features they inherit. We also address QA issues for component-based software. As a major contribution, we propose a QA model for component-based software which covers component requirement analysis, component development, component certification, component customization, and system architecture design, integration, testing and maintenance.