实现分布式数据库环境方法的研究与应用

深入探讨了在分布式数据库环境中如何维护多个副本的一致性,分析与比较了两种方法:分布式事务处理及数据复制,并在MicrosoftSQLServer系统下予以实现。     

分布式数据仓库的一致性维护

数据仓库是一种数据知识库，其中的数据萃取和集成多个异类的、自治的分布数据源，用于决策支持和数据挖掘。本文探讨了分布式数据仓库所要解决的一致性维护的问题。     

普适的宽带路由器IPSec改造方案

网络安全性问题的日益突出迫切要求对现有普通宽带路由器进行支持IPSec的改造。以往的基于加密卡串接网络处理单元的改造方法导致资源利用率低、工程实现难度大及普适性差。文章提出了一种新的改造方案,能够利用宽带路由器的快通道实现加密数据包的高速传输,利用慢通道维护IPSec协议的运行及相关安全信息的下发,以一种母板结构普适地实现了对宽带路由器的高效IPSec改造。     

一种基于DSP的并行信号处理系统的设计

讨论了一种并行信号处理系统，该系统采用高性能的并行DSP芯片作为处理单元，构成了分布式的并行结构，具有很强的可扩充性和灵活性。算法软件和数据传输软件的标准模块用汇编语言完成，以达到高效地实时处理；主程序用高级语言设计，可以方便地调用各标准软件模块，整个程序具备易修改、易维护的特点。     

基于分布式的多级网络拓扑发现研究

文章提出了一种分布式的多级网络拓扑发现方案．将拓扑发现从网络管理角度划分为路由器级和子网级两个层次，分析了两个层次之间的衔接方式；并将路由器级、子网级拓扑发现方法相结合．找出了网络层与链路层之间的拓扑关系，实现单级网络拓扑发现。上级管理中心对本级网络拓扑信息以及所有获取的下级网络拓扑信息进行处理，实现多级网络的拓扑发现，从而以拓扑地域的角度将拓扑发现过程分布化。同时利用XML数据对象作为分布式算法中的数据对象对网络拓扑进行了分布式的计算。     

路由器并行交换体系结构的研究

介绍高速路由器IP报文的处理流程和各处理单元的处理要求,对各处理单元采用的体系结构进行了详细分析和讨论,最后给出高速路由器报文输入,输出的并行处理实现方案。     

一致性协议在分布式安全系统中的应用

随着计算机的发展和大数据的应用进步,分布式系统被广泛部署到生活和工作中的各个方面,在保证数据安全存储的前提之下,系统稳定可靠的运行、对外提供的一致性服务也成了人们重点关注的属性要求。而在种类繁多的软件系统中,安全类软件是对数据一致性要求较高的应用软件系统。一致性协议的出现有效地解决了分布式环境下数据的一致问题,并保证了系统的稳定运行,提高了系统对外服务的效率。文章就一致性协议在分布式安全系统中的应用展开阐述。     

基于星际文件系统的分布式存储系统设计

为了构建更为安全和高效的分布式存储系统，本文结合了分布式存储技术和星际文件系统(IPFS)。加密后的数据被存储在IPFS中，使用Merkle DAG构建数据之间的逻辑结构。单一的IPFS文件存储系统安全性并不高，用户存储的数据信息有可能会受到IPFS本地节点管理者的修改，利用分布式存储的一致性原则使该系统实现了数据可溯源、防篡改等功能，并有效保护了用户的数据安全。同时，结合负载均衡技术使本系统拥有处理大用户访问量的能力，可以更好地分配数据请求和存储，从而提高了系统的读写文件速度，增加了系统的稳定性和可靠性。采用分布式存储技术与IPFS构建的新型分布式存储系统，可以实现数据的安全存储和高效读取。未来，IPFS有望超越HTTP协议，为构建更好的互联网生态提供支持。     

基于一致性哈希算法的电力企业分布式数据存储研究

由于电力企业存储数据量比较大,传统方法在电力企业分布式数据存储应用中无法保证电力企业数据的完整性和有效性,存在数据丢失量较大的问题,并且数据存储延迟时间比较长,存储速度比较慢,为此提出基于一致性哈希算法的电力企业分布式数据存储研究。将电力企业数据相应的时间标签当做是分布式数据存储的一个核心属性,根据数据时间标签对数据进行等价线序划分;利用一致性哈希算法计算数据哈希值和节点计算能力,将其作为依据将电力企业数据分组到相应节点上;利用存储模块构建电力企业分布式数据存储组织结构,并设计分布式数据存储逻辑结构,利用电力企业元信息表、参数元信息表以及索引表对电力企业数据进行分布式存储,以此实现了基于一致性哈希算法的电力企业分布式数据存储。经实验证明,设计方法存储数据延迟时间小于传统方法,而且数据丢失量小于传统方法,能够有效确保电力企业数据的完整性。     

电子战系统中分布式数据同步技术

通过分析业界分布式数据同步技术的特点,结合电子战系统对数据同步的具体应用场景,提出一种电子战系统中跨专用网络的分布式数据同步技术方案,用于解决分布式存储技术及分布式计算技术应用于电子战系统时所遭遇的分布式一致性问题,并结合典型场景的应用验证情况给出了相关的试验结果。     

分布式入侵检测系统的体系架构

由于 ＴＣＰ／ＩＰ协议的开放性，目前的网络极易受到攻击。网络入侵行为，特别是分布式入侵行为，给网络的正常运行造成了巨大的危害，阻碍了网络经济的迅速发展。为了能有效地检测和跟踪入侵行为，这里提出了一个基于智能代理的入侵检测系统的体系结构和分布跟踪算法。该系统是一个分布式实时入侵检测系统，它由智能的主机代理、网络代理和路由器／网关代理组咸。每个智能代理都是独立的实体，拥有解决问题的不完全的信息或能力，通过协同工作并使用分布跟踪算法，实时检测网络入侵行为，跟踪网络入侵者，有效地维护网络安全。     

Distributed, scalable routing based on vectors of link states

We have present a new method for distributed routing in computer networks and internets using link-state information. Link vector algorithms (LVA) are introduced for the distributed maintenance of routing information in large networks and internets. According to an LVA, each router maintains a subset of the topology that corresponds to adjacent links and those links used by its neighbor routers in their preferred paths to known destinations. Based on that subset of topology information, the router derives its own preferred paths and communicates the corresponding link-state information to its neighbors. An update message contains a vector of updates; each such update specifies a link and its parameters. The LVA can be used for different types of routing. The correctness of the LVA is verified for arbitrary types of routing when correct and deterministic algorithms are used to select preferred paths at each router and each router is able to differentiate old updates from new. The LVA are shown to have better performance than the ideal link-state algorithm based on flooding and the distributed Bellman-Ford algorithm     

A software support infrastructure for wireless access routers

Routers are expected to play an important role in the Internet protocol-based wireless data network. Although a substantial number of adaptive and intercell coordination techniques have been proposed to improve wireless network performance under dynamic wireless channel conditions and host mobility, a system support framework is still missing. In this paper, we describe DIRAC, a software-based router system that is designed for wireless networks to facilitate the implementation and evaluation of various channel-adaptive and mobility-aware protocols. DIRAC adopts a distributed architecture that is composed of two parts: a router core (RC) shared by the wireless subnets, and a router agent (RA) at each access point/base station. RAs expose wireless link-layer information to the RC and enforce the control commands issued by the RC. This approach allows the router to make adaptive decisions based on link-layer information feedback on both data and control planes. It also permits the router to enforce its policies (e.g., policing) more effectively through underlying link-layer mechanisms. It further enables interaccess-point coordination at the RC. As showcases, we implement under DIRAC the prototypes of three wireless network services: link-layer assisted fast handover, channel-adaptive scheduling, and link-layer enforced policing. Our implementation and experiments show that our distributed wireless router provides a flexible framework, which enables advanced network-layer wireless services that are adaptive to channel conditions and host mobility.     

应用于通信电源系统的MMC电能路由器研究

本文提出一种基于模块化多电平变换器（MMC）的电能路由器,采用MMC电能路由器构建通信电源微电网系统,对各种通信电源和负载进行管理,以达到不同种类电源设备互联、功率主动灵活控制目的,从而简化通信电源系统,降低电源投资、建设、维护成本,减小损耗,提高电源设备利用率和网络可靠性。本文研究了基于电能路由器的通信电源微电网系统,提出MMC电能路由器的拓扑结构、工作原理、数学模型和控制方法,并通过仿真方法验证了提出方法的正确性,为通信电源系统设计、维护和管理提供新的技术思路。     

AWG-Based Wavelength Router With Nonuniform Number of Transmission Paths

We have developed an arrayed-waveguide-grating (AWG)-based wavelength router with unequal transmission bandwidths for a system with nonuniformly distributed traffic. To realize the router, we designed the aperture width of the input-output waveguides at the border of the slab waveguide. We applied this AWG router to a physical star and logical full-mesh wavelength routing system, and we could create different numbers of paths between the nodes to correspond to the traffic demand     

分布式数据库系统及其一致性方法研究

分布式数据库系统是数据库领域中的一个主要研究方向,数据一致性维护是分布式数据库系统中的一个非常关键的技术问题。在分析分布式数据库系统体系结构的基础上,讨论了两种一致性方法:两阶段提交和复制服务器,并提出一种具有复制服务器的分布式数据库系统的结构框架,它具有有效性和实用性。     

Two 1-Server n-Unit Systems with Preventive Maintenance and Repair

This paper deals with the availability and reliability analysis of two different 1-server n-unit systems with preventive maintenance and repair. Initially, one unit operates and the remaining n - 1 units are kept as cold standbys. In the first system the time to failure and the time to preventive maintenance of a unit are arbitrarily distributed. In the second system, each unit consists of 2 components connected in series. When a unit fails, the failed component is taken up for repair while the other waits for preventive maintenance. Explicit expressions for the Laplace transform of the mean down-time of the system in [0, t] and for the mean time to system failure are obtained. Steady-state availability of the system is also discussed. A few special cases have been studied.     

机场综合运维管理系统设计与实现

为保障导航台内导航设备的稳定运行和安全,设计了一套用于监控导航设备运行情况、环境参数的综合运维管理系统。该系统包括门磁、水侵、烟雾、火警、温度、湿度、空调控制、UPS、低压配电、视频和云台等。对该系统结构进行了详细设计,它由硬件监控传感器、视频采集、动环采集服务器、分布式数据库服务器和客户监控终端组成。该系统的数据库采用分布式系统设计,有效减轻了终端的存储压力。该系统的通信部分包括串口数据通信和视频数据通信。为了与监控单元兼容,设计了串口通信调度模块,并制定了通用串口通信协议。用户人机界面设计了用户管理、设备维护、监控监视、报警、系统设置、地图等功能。     

基于流量分析系统实现对3G基站FE口性能的优化

在移动网络数据业务大发展的背景下,基于现网中阿朗设备基站网管系统无法直观提供基站上下行最大流速、平均流速、坐标流量图和上网用户行为等功能,不便于我们日常对网络进行维护和优化,但通过结合挂接于FE路由器的流量分析系统的流量采集可以弥补此方面的不足。     

Cooperative cache consistency maintenance for pervasive internet access

Cooperative caching is an important technique to support pervasive Internet access. In order to ensure valid data access, the cache consistency must be maintained properly. However, this problem has not been sufficiently studied in mobile computing environments, especially those with ad hoc networks. There are two essential issues in cache consistency maintenance: consistency control initiation and data update propagation. Consistency control initiation not only decides the cache consistency provided to the users, but also impacts the consistency maintenance cost. This issue becomes more challenging in asynchronous and fully distributed ad hoc networks. To this end, we propose the predictive consistency control initiation (PCCI) algorithm, which adaptively initiates consistency control based on its online predictions of forthcoming data updates and cache queries. In order to efficiently propagate data updates through multi‐hop wireless connections, the hierarchical data update propagation (HDUP) algorithm is proposed. Theoretical analysis shows that cooperation among the caching nodes facilitates data update propagation. Extensive simulations are conducted to evaluate performance of both PCCI and HDUP. Evaluation results show that PCCI cost‐effectively initiates consistency control even when faced with dynamic changes in data update rate, cache query rate, node speed, and number of caching nodes. The evaluation results also show that HDUP saves cost for data update propagation by up to 66%. Copyright © 2009 John Wiley & Sons, Ltd.