基于蚁群算法分布式网络可靠性的研究

在分布式网络中,应用软件客户端访问服务器,由于网络节点资源流畅性的变化,影响应用软件客户端对服务器资源的获取和更新的效率.为此,提出了利用蚁群算法的最优化处理,使得客户端能够尽快地得到最可靠的分布式网络服务器资源,提高网络的可靠性.文中采用Powerbuilder模拟程序仿真了在分布式环境中,客户端如何访问服务器组,通过对蚁群算法的分析了解,可以很快使客户端连接到最可靠的网络服务器的地址,这样可以大大节约系统的响应时间,尤其在一些实时性要求很高的系统中.本系统的研究最终也应用到铜陵住房保障系统中.     

Internet环境下分布式曲面拟合系统的处理结构

首先介绍了曲面拟合的概念和方法。并提出了一种在Internet上以分布式处理结构为基础的动态似合工具，这种方法可以使用户在客户端通过网页浏览器使用该工具，而不需要对任何昂贵的软硬件进行维护和投资。此外，由地可用多重处理单元，相对于单个处理单元的环境，减少了每个工作的平均响应时间。     

基于混合索引的浏览器缓存协作系统

构建了一种基于混合索引的浏览器缓存协作系统，它充分利用客户端浏览器缓存的内容，以P2P方式交换Web Cache，克服了集中式代理服务器存在的一些问题。客户端的Internet访问响应时间是系统设计的主要依据。索引技术是系统中影响响应时间的关键技术，为了提高响应时间，对索引技术进行了讨论，并针对该应用的特点进行了改进。系统具有以下优点：易于扩展，网络资源开销小，响应时间短，索引更新及时。     

基于协同商务平台的信息交换技术研究及应用

对分布式企业信息的交互困境进行了描述,并从如何通过企业客户端和网络平台实现企业间业务数据的交互和处理进行了研究,提出了通过将C/S体系结构的客户端系统和BS体系结构的协同商务平台并用的模式解决分布式数据交互和集中式处理的方案。     

基于协同商务平台的信息交换技术研究及应用

对分布式企业信息的交互困境进行了描述，并从如何通过企业客户端和网络平台实现企业间业务数据的交互和处理进行了研究，提出了通过将C／S体系结构的客户端系统和BS体系结构的协同商务平台并用的模式解决分布式数据交互和集中式处理的方案。     

浅析AJAX在Web中的应用

传统的web应用在用户交互性方面存在响应速度慢的缺点,导致用户体验较差。介绍了AJAX的概念和工作原理,通过web实例对AJAX在web中的应用进行分析,证明了AJAX技术具有在客户端与服务器之间进行异步通信的能力,可以有效地减少客户端的响应时间,更友好地改善了用户的实时操作体验。     

Lustre文件系统I/O锁的应用与优化

分布式文件系统需要有一种机制对来自各个客户端的并发访问进行控制,维护文件数据的一致性。锁是实现并发控制最流行的机制。研究了Lustre文件系统的分布式I/O范围锁的模型,并对它的各种应用进行了优化。介绍了Lustre分布式锁的基本概念,对基于锁实现数据客户端写回缓冲以及多写者文件大小的动态获取的算法进行了分析;提出自适应I/O锁策略,基于区间树的范围锁冲突检测优化策略以及客户端锁淘汰策略来增强Lustre锁服务的性能和扩展性。     

开放式车辆远程控制架构研究及应用

为了解决远程控制系统客户端设备类型受限,系统架构不开放及协议不标准问题,实现资源共享,参考NGTP(Next Generation Telematics Pattern),设计了一个车辆远程控制系统架构,并对数据通信协议进行制定;在本系统中,用户通过浏览器登入WebServer,不必开发客户端软件,解决了客户端设备类型受限制问题,提高了系统可维护性;同时为了安全考虑,移动终端不允许直接控制车载终端,设计了后台服务器,用来存储车辆运行状况信息以及转发相应指令;系统中数据通信协议是在NGTP消息协议的基础上进行制定,统一了消息格式,便于管理。运用远程查询和远程控制对系统进行验证,查询的响应时间在3s左右,控制的响应时间在2s之内,均在允许的范围之内,结果证明了系统的可行性。     

分布式入侵检测系统的研究与实现

随着计算机网络的迅猛发展,网络安全问题也日益严重,单一的集中式的入侵检测系统已不能满足网络安全发展的需要,分布式入侵检测系统应运而生.实现了一个分布式的入侵检测系统,将反弹木马的反向连接技术应用到客户端与服务器端的通信上,在客户端采用多线程技术捕包,通过系统进程与端口通信相结合检测特洛伊木马.通过管理端对局域网络各个位置的Agent客户端进行统一部署策略和实时监控,加强了校园网络的安全.     

基于MIDA技术用户的权限认证探讨

分布式多层系统主要由客户端应用程序、应用服务器和数据库服务器三层次构成。本文主要对采用Delphi在MIDAS应用中用户权限的认证进行了具体探讨,提出了其实现方式,进一步探讨了客户端、应用服务器端的数据交互、应用服务器端的无状态维护。     

Archictecture and Performance of Java-Based Distributed Object Models: CORBA vs RMI

This paper presents a comprehensive comparison of thearchitectural differences and similarities of the two most popularJava-based distributed object models: RMI and CORBA. Performanceand timing issues related to the CORBA and RMI architecturesare also considered. The following aspects are studied for clientserver applications, on Sun UltraSparcs under Solaris 2.5.1 andPentium II under Windows NT 4.0: response time for method invocationwithout parameters as well as with variable number of parameters;response time for applet clients, and response time for variablenumber of clients requesting the same service. The goal is toprovide a reference framework that supports the selection ofeither mechanism for the development of web-based distributedreal-time applications: chat programs, interactive games, sharedboards, etc.     

基于透明计算的龙星网络计算机系统测试报告

透明计算模式提出在用户端系统上不安装任何操作系统和应用程序,而在执行时通过网络从服务器上动态调用操作系统和应用程序在端系统上执行,从而使得用户可以在同一终端上选择支持该终端CPU指令结构的任何操作系统及应用程序犤1犦。论文对基于该模式的龙星(LX)网络计算机进行了功能测试和性能测试,包括客户机的启动时间、典型应用启动时间、文件移动时间等功能参数和响应时间、服务器CPU占用率、客户端CPU占用率、网络吞吐量等性能参数,并对测试结果进行了分析。     

适用于实时应用的网络服务自适应系统

随着网络带宽可用性的提高以及网络延迟的减少,如何在端主机上保证网络传输的服务质量(End-hostQoS)已经逐渐成为一个关键的问题。尤其是针对分布式实时应用的环境:媒体流服务器,视频会议以及VoIP((Voiceover Internet Protocol)是一种以IP电话为主,并推出相应的增值业务的技术应用)。End-hostQoS的实现需要操作系统的支持,比如提供网络层的系统调度和流量控制。笔者在这篇文章中提出的QoS自适应系统可以在最优使用系统资源的基础上提供per-flow或者per-service-class的差别服务。并且通过将EDF调度算法同PID控制理论相结合,保证系统的实时响应、适应网络波动,在服务器瞬间过载的情况下,保证网络服务质量的平稳过渡。     

3-Tiers模式的办公自动化系统WUOA的设计与实现

为保证系统提供更好的客户服务、更快的响应,采用3-Tiers模型作为WUOA的软件体系结构;同时,用组件技术设计实现了WUOA中间层的全部软件功能。但3-Tiers结构中,组件在应用服务器与客户机之间的频繁信息传送,必然导致网络瓶颈问题。笔者提出了“虚拟”应用服务器的概念,设计了适用于OA的虚拟应用服务器VOA-APP,根据组件的使用频度、特征,适度地将组件分布在网络节点和客户机上,在组件分布的基础上,VOA-APP完成组件的实时发布与更新,较好地解决了组件集中与分散分布的协调问题。     

Distributed View Divergence Control of Data Freshness in Replicated Database Systems

In this paper, we propose a distributed method to control the view divergence of data freshness for clients in replicated database systems whose facilitating or administrative roles are equal. Our method provides data with statistically defined freshness to clients when updates are initially accepted by any of the replicas, and then, asynchronously propagated among the replicas that are connected in a tree structure. To provide data with freshness specified by clients, our method selects multiple replicas using a distributed algorithm so that they statistically receive all updates issued up to a specified time before the present time. We evaluated by simulation the distributed algorithm to select replicas for the view divergence control in terms of controlled data freshness, time, message, and computation complexity. The simulation showed that our method achieves more than 36.9 percent improvement in data freshness compared with epidemic-style update propagation.     

MidCloud: an agent‐based middleware for effective utilization of replicated Cloud services

The Cloud relies heavily on resource replication to support the demands of the clients efficiently. Replicated Cloud services are distributed across large geographic areas and are accessible via the Internet. This paper describes MidCloud; an agent‐based middleware that provides Cloud clients with dynamic load balancing and fault tolerance mechanisms for effective utilization of replicated Cloud services and resources. MidCloud can be used to connect clients with multiple replicated Cloud services and provide fast and reliable service delivery from multiple replicas. Several approaches for load balancing and fault tolerance in distributed systems were introduced; however, they require prior knowledge of the environment's operating conditions and/or constant monitoring of these conditions at run time that allows the applications to adjust the load and redistribute the tasks when operational conditions change and when failures occur. These techniques work well when there is no high communication delay. Yet, this is not true in the Cloud, where data storage and computation servers are scattered all over the world and communication delays are usually very high. MidCloud deploys approaches to reduce the negative impact of high and dynamic delays on the Cloud servers and the Internet. The experimental results show the positive effects of using MidCloud to provide efficient load balancing and fault tolerance. Copyright © 2013 John Wiley & Sons, Ltd.     

An adaptive quality of service aware middleware for replicated services

A dependable middleware should be able to adaptively share the distributed resources it manages in order to meet diverse application requirements, even when the quality of service (QoS) is degraded due to uncertain variations in load and unanticipated failures. We have addressed this issue in the context of a dependable middleware that adaptively manages replicated servers to deliver a timely and consistent response to time-sensitive client applications. These applications have specific temporal and consistency requirements, and can tolerate a certain degree of relaxed consistency in exchange for better response time. We propose a flexible QoS model that allows clients to specify their timeliness and consistency constraints. We also propose an adaptive framework that dynamically selects replicas to service a client's request based on the prediction made by probabilistic models. These models use the feedback from online performance monitoring of the replicas to provide probabilistic guarantees for meeting a client's QoS specification. The experimental results we have obtained demonstrate the role of feedback and the efficacy of simple analytical models for adaptively sharing the available replicas among the users under different workload scenarios.     

Distributed advance reservation of real-time connections

The ability to reserve real-time connections in advance is essential in all distributed multiparty applications (i.e., applications involving multiple human beings) using a network that controls admissions to provide good quality of service. This paper discusses the requirements of the clients of an advance reservation service, and a distributed design for such a service. The design is described within the context of the Tenet Real-Time Protocol Suite 2, a suite being developed for multiparty communication, which will offer advance reservation capabilities to its clients, based on the principles and the mechanisms proposed in the paper. Simulation results providing useful data about the performance and some of the properties of these mechanisms are also presented. We conclude that the one described here is a viable approach to constructing an advance reservation service within the context of the Tenet Suites as well as that of other solutions to the multiparty real-time communication problem.     

基于XML的通用目录服务检索引擎设计与实现*

目录服务在现代分布式系统中处于非常重要的地位,但是在Web Service环境下,应用程序自身的运行和调用都是通过XML形式进行描述与展现的,而传统的目录服务专有协议不支持这种形式的请求。通过适配器、转换器和DSML网关,设计了一种基于XML的通用目录服务检索引擎架构。可以使目录服务支持多种客户端,提高了目录的透明性、通用性和可达范围,适应了分布式技术由传统技术转向Web Service等转变的需要。     

Secure spread: an integrated architecture for secure group communication

Group communication systems are high-availability distributed systems providing reliable and ordered message delivery, as well as a membership service, to group-oriented applications. Many such systems are built using a distributed client-server architecture where a relatively small set of servers provide service to numerous clients. In this work, we show how group communication systems can be enhanced with security services without sacrificing robustness and performance. More specifically, we propose several integrated security architectures for distributed client-server group communication systems. In an integrated architecture, security services are implemented in servers, in contrast to a layered architecture, where the same services are implemented in clients. We discuss performance and accompanying trust issues of each proposed architecture and present experimental results that demonstrate the superior scalability of an integrated architecture.