Analyzing the performance of a cluster-based architecture for immersive visualization systems

Cluster computing has become an essential issue for designing immersive visualization systems. This paradigm employs scalable clusters of commodity computers with much lower costs than would be possible with the high-end, shared memory computers that have been traditionally used for virtual reality purposes. This change in the design of virtual reality systems has caused some development environments oriented toward shared memory computing to require modifications to their internal architectures in order to support cluster computing. This is the case of VR Juggler, which is considered one of the most important virtual reality application development frameworks based on open source code.     

Solving distributed FMS scheduling problems subject to maintenance: Genetic algorithms approach

In general, distributed scheduling problem focuses on simultaneously solving two issues: (i) allocation of jobs to suitable factories and (ii) determination of the corresponding production scheduling in each factory. The objective of this approach is to maximize the system efficiency by finding an optimal planning for a better collaboration among various processes. This makes distributed scheduling problems more complicated than classical production scheduling ones. With the addition of alternative production routing, the problems are even more complicated. Conventionally, machines are usually assumed to be available without interruption during the production scheduling. Maintenance is not considered. However, every machine requires maintenance, and the maintenance policy directly affects the machine's availability. Consequently, it influences the production scheduling. In this connection, maintenance should be considered in distributed scheduling. The objective of this paper is to propose a genetic algorithm with dominant genes (GADG) approach to deal with distributed flexible manufacturing system (FMS) scheduling problems subject to machine maintenance constraint. The optimization performance of the proposed GADG will be compared with other existing approaches, such as simple genetic algorithms to demonstrate its reliability. The significance and benefits of considering maintenance in distributed scheduling will also be demonstrated by simulation runs on a sample problem.     

Large-scale multimedia content delivery over optical networks for interactive TV services

iTVP is a system built for delivery of live TV programming, video-on-demand and audio-on-demand with interactive access over IP networks. It has a nationwide range and is designed to provide service to a high number of concurrent users. Hence, scalability is one of the most important issues. In this paper we described how scalability is achieved in a two-level hierarchical architecture of the delivery system. We present the principles of content caching mechanisms and the management of the resulting distributed content repository. The system is implemented and currently operates in a test installation. Although the range of the test system operations is limited, as far as the number of users and the size of the content repository is concerned, the experience gained with iTVP so far provides an insight into the expected prototype performance. We present a system performance evaluation and describe the experience gained during the iGrid demonstration.     

Highly interactive distributed visualization

We report on our iGrid2005 demonstration, called the “Dead Cat Demo”; an example of a highly interactive augmented reality application consisting of software services distributed over a wide-area, high-speed network. We describe our design decisions, analyse the implications of the design on application performance and show performance measurements.     

深度检测DDoS攻击

为了有效地防御DDoS攻击,需要在检测环节尽可能多地获取攻击信息,而现有的方法大多仅注重检测攻击的存在,很难同时给出攻击协议、攻击强度和攻击方式等信息.提出使用多分类的方式,将攻击分为24个不同的种类,并用快速分类器HSMC-SVM作为分类工具,来完成DDoS攻击的多种信息的获取.实验表明,这种方法可以快速完成训练和测试工作,并以较高的识别率识别出不同种类的攻击,为防御环节提供攻击协议、攻击强度和攻击方式等信息.在实际网络中,能满足准确性和实时性的要求,有较强的可行性.     

Top-down vs bottom-up methodologies in multi-agent system design

Traditionally, two alternative design approaches have been available to engineers: top-down and bottom-up. In the top-down approach, the design process starts with specifying the global system state and assuming that each component has global knowledge of the system, as in a centralized approach. The solution is then decentralized by replacing global knowledge with communication. In the bottom-up approach, on the other hand, the design starts with specifying requirements and capabilities of individual components, and the global behavior is said to emerge out of interactions among constituent components and between components and the environment. In this paper we present a comparative study of both approaches with particular emphasis on applications to multi-agent system engineering and robotics. We outline the generic characteristics of both approaches from the MAS perspective, and identify three elements that we believe should serve as criteria for how and when to apply either of the approaches. We demonstrate our analysis on a specific example of load balancing problem in robotics. We also show that under certain assumptions on the communication and the external environment, both bottom-up and top-down methodologies produce very similar solutions.

An Optimal Model and Algorithm of Distributed Information System

Distributed information system makes itself be placed in changing file storage position according to the users＇ request pattern. In this paper, we rebuild the model for a management system to turn the process of file managing into a 0-1 programming problem, and present a new individual form to improve the operating efficiency. Aiming at the model, we define a neighborhood span to make segmentation for searching space by using the fitness, based on the region contraction algorithm, present a new evolution algorithm which has the capability of self-adaptively generating new individuals, and ultimately solve the management problem of the distributed file system.     

分布式数据库数据复制技术的分析与应用

本文在分布式数据库系统的基础上，针对分布式数据库的数据存储方式进行了概述，细致地讲述了分布式数据库复制技术的几个关键内容，对Oracle、Sybase、SQL Server数据库的复制技术(方案)进行了综合分析比较，并结合实践经验提出了复制技术的方案选择策略，对复制技术的发展进行了展望。     

通用访问控制框架GFAC在MIS中的应用

对管理信息系统(MIS)的访问控制机制进行了研究,提出了将通用访问控制框架GFAC应用于MIS系统的方法,为多种访问控制策略在MIS系统中的集成提供了一种解决方案,克服了传统的单一或混合访问控制策略的缺陷。针对访问控制的效率问题,引入了决策结果缓存机制,提高了系统访问控制决策的效率。     

文件操作访问大容量ODBC数据库的技巧讨论

以访问印花机工艺数据库为实例,简要分析了大容量ODBC数据库存在的问题,并阐述了利用文件操作动态访问Access数据源的两种方法,分析了利用此方法分解大容量数据库为小型数据库的可行性.