Linux下基于Squid的多能代理系统与透明网关解决方案

本文给出一个Linux下基于Squid的多能代理系统与透明网关解决方案，允许内部网络通过NAT透明网关访问外部网络的同日寸，并给出外部网络分享Squid缓存的方法，同日寸给出一套端口密码动态切换和自动封禁的机制。通过在网关开设硬盘空间存放缓存，可以提高40％网络请求的访问速度，效果良好。     

网络缓存技术及应用的研究

网络缓存技术是目前凭来提高互联网的用户响应速度及相关网络性能的关键技术，其中缓存策略及算法对缓存性能的发挥起着重要的作用。本文主要介绍在网络缓存系统中所采用的各种替换算法和更新策略，并说明网络缓存技术的各种应用模式．以目前广泛应用的代理缓存Squid为例，分析网路缓存系统兑现的结构和方法。     

网络缓存的零拷贝优化

数据的冗余拷贝是影响网络缓存软件性能的重要因素.本文详细分析了当前广泛使用的网络缓存程序Squid的数据拷贝流程,利用快速文件传输和数据流拼接两种策略在Linux平台上实现了squid的零拷贝优化.快速文件传输是将文件数据从文件系统内核缓存直接发送到远程主机,数据流拼接则是在网络协议栈内核缓存之间直接交换数据,二者都能够减少数据在内核空间和用户空间流动带来的冗余拷贝.实验证明,经过优化的Squid在主机CPU占用率和请求响应时间等方面的性能均有显著提高.     

统一缓存:基于用户层通信的合作缓存技术

合作缓存机制是集群系统提高整体性能的一种有效方法，其利用高速网络将各个结点的缓存进行合作管理与访问，大幅度提高了缓存的命中率．但传统的合作缓存技术没有考虑到广为应用的高效用户层通信机制的特点．提出一种新的用户层通信与合作缓存技术相融合的缓存机制——集群统一缓存．这一机制充分利用了用户层通信的特点，包括协议精简、零拷贝、虚拟内存映射通信(VMMC)技术等，将缓存与结点通信相融合，减少了集群系统应用程序IO模块的层次与复杂度，提高了系统性能．同时这一机制也顺应了IO子系统日益独立化的发展趋势．该技术已经应用于自行开发的面向对象的Internet服务存储平台——TODS上，具有高效、扩展性好与软件设计简单等特点．     

基于对象存储文件系统的协作式缓存一致性策略

基于对象存储文件系统引入了客户端缓存机制以加快文件访问速度,由此也带来了缓存数据一致性问题。针对多客户端访问共享文件时缓存更新策略存在的延时、网络和服务器负载过大及网络消耗大等问题,基于Lustre对象存储文件系统实现了一种改进的协作式缓存一致性策略。实验结果表明,改进后的缓存更新策略,不仅可以保证缓存数据的一致性,而且减少了客户端与服务器交互次数,降低了访问延迟,提高了系统I/O性能。     

一种基于透明Web Cache的内容过滤实现框架

网络实时内容过滤技术在现实生活中得到了广泛的应用和发展，该文从实时内容过滤存在的种种不足出发，结合现有的网络拓扑结构和网络技术应用，利用多种先进网络技术手段，配合Linux和Squid这一开放源代码的软件系统，提出了一种基于特定网络架构的内容过滤实现框架，该框架采用内容分析和网址过滤相互协同、分时工作的方法，可很好地提高内容过滤的准确性和实时性。     

一种校园网的网络安全策略

随着网络攻击者知识的成熟以及攻击工具与手法的复杂多样，网络安全问题也日益突出起来，单纯的防火墙策略已无法满足网络安全的需要。为了更进一步提高网络安全，必须采用防火墙与入侵检测系统相结合的网络安全技术。另一方面，校园网网络服务平台一般是基于开放源代码软件的，故文中提出了采用Linux系统下IPtables包过滤＋Squid＆Socks代理服务器的防火墙体系和网络入侵检测系统Snort相结合的网络安全策略来增强校园网的安全，并详细地阐述了在校园网环境下如何实现该策略以及相关的关键技术。     

缓存替换算法研究综述

缓存技术作为提高系统性能的重要手段一直是研究的热点。随着网络存储等新技术的出现，存储的层次越来越复杂，原有的简单缓存管理技术已经不合适日趋复杂的应用。频率和时间综合考虑的缓存替换方法、多级缓存的替换技术成为研究的热点。本文综述了缓存替换算法的研究现状，首先介绍传统简单的缓存替换算法及其存在的局限性，而后对单级缓存算法和多级缓存算法当前最新的研究进行了介绍。最后对研究的趋势进行了简单的展望。     

面向资源广域分布环境的数据复制定位

在资源广域分布的环境中，数据复制和定位是提高数据访问性能的关键技术之一。该文提出了一种分布式、自适应复制定位机制(ALM)，该机制基于复制定位信息分发和网络缓存思想，采用分层的分布式复制目录系统和软状态协议实现。其中，复制目录系统分布存储复制定位信息，软状态协议分发复制定位信息及其改变。因此，ALM具有很好的分布性和自适应性。ALM在复制目录的设计中引入了Web缓存的功能，使得ALM较其它机制具有更广泛的适用性。     

基于WEB在线考试系统实现与优化

在高校教育中,考试工作是学校教育教学工作中重要的角色。随着网络技术的发展及普及,基于Web的在线考试系统已成为趋势。该系统采用B/S结构模式,实现对在线考试和题库进行管理,相对传统的考试模式提高了效率,并利用Squid代理缓存优化系统,使系统响应速度和安全性提高。     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

View-based model-driven architecture for enhancing maintainability of data access services

In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times.     

A pragmatic multi-method investigation of discrepant technological events: Coping,attributions, and ‘accidental’ learning

Discrepant technological events or situations that entail a problem, a misunderstanding or a difficulty with the Information Technology (IT) being employed, are common in the workplace, and can lead to frustration and avoidance behaviors. Little is known, however, about how individuals cope with these events. This paper examines these events by using a multi-method pragmatic approach informed by coping theory. The results of two studies – a critical incident study and an experiment – serve to build and test, respectively, a theoretical model that posits that individuals use a variety of strategies when dealing with these events: they experience negative emotions, make external attributions, and adopt engagement coping strategies directed at solving the event, eventually switching to a disengagement coping strategy when they feel they have no control over the situation. Furthermore, users’ efforts may result in ‘accidental’ learning as they try to overcome the discrepant IT events through engagement coping. The paper ends with a discussion of the results in light of existing literature, future opportunities for research, and implications for practice.     

The Distributed Time-Triggered Simulation Scheme: Core Principles and Supporting Execution Engine

Distributed real-time simulation is a young technology field but its practice is under increasing demands. In recent years the author and his collaborators have been establishing a new approach called the distributed time-triggered simulation (DTS) scheme which is conceptually simple and easy to use but widely applicable. The concept was initiated in the course of developing a new-generation object-oriented real-time programming scheme called the time-triggered message-triggered object (TMO) programming scheme. Some fundamental issues inherent in distributed real-time simulation that were learned during recent experimental studies are discussed along with some approaches for resolving the issues. An execution engine developed to support both the TMOs engaged in control computation and the TMOs engaged in DTS is also discussed along with its possible extensions that will enable significantly larger-scale DTSs.     

Software-Konfigurationsmanagement in großen Softwareprojekten

Zusammenfassung Mit zunehmender Größe der Softwaresysteme verschärfen sich die für die Software-Herstellung typischen Probleme: Beherrschen großer Objektmengen, Erhalten der Systemkonsistenz, Kontrolle der ständigen Änderungseinflüsse und Gewährleisten einer langen Lebensdauer. Die Disziplin Konfigurationsmanagement bildet den methodischen Ansatz, diese Probleme besser zu beherrschen. Software-Konfigurationsmanagement faßt die Herstellung von Softwaresystemen als eine Abfolge von kontrollierten Änderungen an gesicherten Zwischen- und Endergebnissen auf. Dargestellt werden die Objekte und Funktionen des Software-Konfigurationsmanagements sowie die hierfür in großen Software-Projekten benötigten Methoden, Instanzen und Hilfsmittel.     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and     

Editorial:Brain-machine interface(BMI) and cyborg intelligence

正Brain-machine interfaces(BMIs)aim at building a direct communication pathway between the brain and an external device,and represent an area of research where significant progress has been made during the past decade.Based on BMIs,mind information can be read out by neural signals to control     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate     

SCIENCE CHINA Information Sciences SUBJECT INDEX TO VOLUME 57(2014)

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Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate