Through the development for many years , the database system has already developed into a kind of quite ripe data management system . but with the development of computer network , the security of the database system becomes the focal point that database developer and user pay close attention to more and more . various safe means are applied to development and use of the database progressively , including the safety certification mechanism in the system , safe precaution tool and backup of the system outside the system resume the mechanism etc . 经过多年的发展,数据库系统已经发展成为一种相当成熟的数据管理系统,在各行各业各种应用中都少不了数据库的支持,但随着计算机网络的发展以及对各种系统的开放式要求,数据库系统的安全越来越成为数据库开发者和使用者关注的重点,因此各种安全手段逐步应用于数据库的开发和使用,包括系统内的安全认证机制,系统外的安全防范工具以及系统的备份恢复机制等。
The model controls the dynamic security of network information flow on four layers : security entrance layer requires user authentication and encapsulates security information flow ; social intelligence layer makes information flow to have the ability of self - sensing self - protecting and self - adjusting ; business layer carries out business logic in forms of transactions which can be submitted , processed and roll back , in order to provide real - time protecting and online recovering ; tcp / ip security layer ensures security communication for information flow 该模型分4个层次控制网络信息流的动态安全;安全入口层负责用户的身份验证和信息流的安全封装;社会智能层赋予信息流自我感应、自我保护、自我调控的行为能力;事务层实现商业事务的提交、处理、回滚,提供实时保护和在线恢复机制; tcp / ip安全协议层则保障网络信息流的安全传输。
By introducing an " active dscc " field in ds beacon , iapp enhancement protocol improves the management capability of network administrator , and enhances the role of dsc in handover process and query process . the combination of the fault ds beacon detection and dsc detection while handover and query occurring speeds up the invalid dsc detecting procedure . the detail flow , error recovery mechanism , and performance analysis are represented 提出了增强型iapp协议,该协议改进了ds信标帧,增加了“激活的dscc ”域,提高了网络管理员对网络的控制能力,增强了dsc在切换过程、查询过程的作用,通过ds信标帧的检测和利用切换检测dsc的组合方式提高了对失效dsc的检测速度,并给出了具体的通信流程、详细的差错恢复机制和性能分析。
For packet loss result from network congestion , rab adopts the same recovery mechanisms as the original tcp ; for packet loss result from link error , it adopts a recovery mechanism which is called immediate recovery , and the value of congestion window of the source is set to a value that corresponds to the available bandwidth 对于拥塞导致丢包,则采取与传统tcp协议相同的恢复机制(即窗口减半,并进入拥塞避免阶段的线性增加) ,而对于链路错误导致丢包,则采取立即恢复策略,将tcp源端的拥塞窗口设置为与其估计带宽相应的数值。
Because of the unique issues in the networks , including mobility - induced disconnection , network partition , high out - of - order delivery ratios and channel errors , the congestion control and the error recovery in the network is challenging . in this environment , the interaction between tcp and mac layer protocols , the affection of route protocols on the performance of tcp and the particular congestion control and error recovery mechanism are first discussed . then a particular transport layer protocol scheme based on the non - feedback mechanism is presented , with emphasis on the analysis and simulation of the key parameter 文中主要讨论了两种不同网络结构中的无线tcp协议改进方案,其一在最后一跳为无线链路的网络环境中,针对基本tcp拥塞控制机制存在的缺陷,文中在现有解决方案的基础上提出一综合性的方案,其中包括无线链路的高误码率和连接断开问题的解决,并重点对方案中出现的交叉层问题进行分析和仿真;其二,考虑的是分布式网络( adhoc ) ,在文中较为详细的分析了tcp和mac层机制间的相互作用、路由协议中造成tcp性能降低的因素、 adhoc网络中应采取的特殊拥塞控制和差错恢复机制,在此基础上提出了一种采用非反馈机制的解决方案,重点对方案中的关键参数进行分析和仿真,分析和仿真结果表明此机制可在很大程度上提高adhoc网络中tcp的性能。
The paper first analyses the traditional database , their advantages and drawbacks , and gives the concept of mmdb , then discusses the design idea and implementation in detail in such topics as definition of mmdb , design of system front plat , management of main memory of system backend database , memory structure , recovery mechanism , etc . at last , the paper chooses a practicality application system pcs - dbs ( flight control system - database system ) , and uses the example to testify the validity of conclusion 本文首先分析传统数据库的优缺点,提出内存数据库的概念。然后从内存数据库的定义,系统的前台设计、系统后台的内存管理、存储结构、恢复机制等方面详细说明了内存数据库技术的设计思想。最后课题选用应用系统fcs - dbs ( flightcontrolsystem - databasesystem )系统作为实例,并通过这个实例验证了理论研究部分的可行性。
System model of this scheme : in order to solve the problems in the past , a security system model is provided in this scheme according to the characteristic of the e - government of jining , which is made up of five parts : safe service facility of foundation , safe technical support platform , respond and resume the mechanism and application system layer 该方案主要特点如下: 1 、本方案的体系模型:为了解决以往方案中只注重技术保障,不重视安全运作的问题。本文根据济宁市电子政务的特点给出了所采取的安全体系模型,该模型由五部分组成:基础安全服务设施、安全技术支撑平台、安全运作保障体系、响应与恢复机制和应用系统层。
This paper analysis the shortage of traditional concurrency control method in multidatabase and brings froward a new concurrency control algorithm . we also bring forward a new recovery method for multidatabase : synthesis 2pc protocol , which combines many multidatabase recovery methods into one algorithm , and makes the algorithm more useful and more efficient 本文还提出了一种新的多库系统恢复机制:综合2pc协议,它把已有的几种多库系统恢复机制结合在一个算法中使用,使其更适于多库系统的异构性,应用范围更为广泛,效果也更好。
This paper mainly aims at the characteristics of the hardware and software structure of the parallel computer on satellite , and has fulfilled researches of fault tolerant technique in three aspects of control theories and engineering : the first research of the system level fault - tolerant module is based on the system structure of the parallel computer on satellite , a kind of cold backup module and a kind of hot backup module for multiprocessor computer have been put forward . then the research of software fault tolerant technique which is based on the operate system named rtems has been carried , the mission level fault - tolerate arithmetic and the system level fault - tolerate mechanism and strategies based on the check point technique have been put forward , at the same time the self - repair technique of software which has used the technique of system re - inject has been studied . finally the technique of components level fault - tolerant based on fpga has been studied , a kind of two level fault - tolerant project which aims at the fault - tolerant module of the parallel computer on satellite has been put forward , and the augmentative of circuit that project design realization need is little , this project can avoid any breakdown of any part logic circuit of the fpga 本课题主要针对星载并行计算机体系结构及软件结构的特点,从如下三个方面进行了容错控制理论研究和实践工作:首先进行了基于星载多cpu并行计算机体系结构的系统级容错模型研究,提出了一种多cpu冷备份容错模型和一种多cpu热备份容错模型;然后进行了基于rtems操作系统的软件容错技术研究,提出了任务级容错调度算法以及基于检查点技术的系统级容错恢复机制和策略,同时研究了利用系统重注入进行软件在线自修复的容错技术;最后研究了基于fpga的部件级容错技术,提出了对容错模块这一星载并行计算机关键部件的两级容错方案,实现该方案所需增加的电路少,可避免板级芯片以及fpga芯片内部任何逻辑发生单点故障。