并行服务器信息流切换的模糊控制

讨论离散时间系统中不同服务率的并行服务器信息流的控制问题.建立了一个模糊控制器来决定排队系统信息流分配的最优策略,使得顾客在通信系统中的平均逗留时间最小.仿真结果表明了该模糊控制器的有效性.     

跳变信息服务系统研究

针对复杂网络空间对抗条件下提升信息服务系统动态主动防御能力的需求,基于动目标防御思想提出了一种跳变信息服务系统架构及构建方法。首先利用多态化的软件栈模板构建出由不同异构虚拟服务器组成的服务器池;然后,通过审计清洗、服务请求调度、服务器动态管控等模块之间的交互控制,实现根据各虚拟服务器的状态信息和负载情况进行服务请求调度和服务器状态切换,在保证服务质量的前提下使得信息服务系统随时间动态、随机地变化。     

切换服务系统的稳定性及交叉口信号配时

当缓冲器内工作量较大时,服务器的“固定顺序清空切换”服务策略使得清空缓冲器内工作量需要较长时间,从而其他缓冲器未能及时得到服务.为此本文提出服务器“带服务时间上限的固定顺序切换”服务策略,服务器在该服务策略下分配给每个缓冲器服务时间上限,以保证各缓冲器公平地得到服务.在满足缓冲器总负荷小于各缓冲器服务时间调整因子的最小值与最大值之比的条件下,证明了所提出服务器服务策略下的切换服务系统是周期稳定的.进一步将交叉口信号配时建模为切换服务系统,并应用所提出的服务器服务策略研究了交叉口信号配时策略.通过对交叉口实际数据的仿真验证了本文方法的有效性.     

并行视频服务器体系结构研究

分析了目前流行的并行视频服务器体系结构：分布式结构、集群式结构、并行通用计算机结构和并行专用视频服务器结构。综合其优点,针对视频应用的特点,提出了可扩展并行视频服务器体系结构,并研制了基于该结构的并行服务系统。     

一种服务容灾系统的设计与实现*

设计并实现了一种服务容灾系统,对本地服务器上的应用数据进行实时异地备份,对基于IP的应用则可实现服务容灾。该系统对本地服务器磁盘卷进行实时监控,并将数据变化在异地灾备中心进行重放,保证了应用数据安全;提供了多种灾难恢复策略,能够快速恢复应用数据;同时对本地服务器进行失效检测,及时发现故障,在较短时间内将服务从本地服务器切换至远程备用服务器,确保服务连续性。     

BGInfo：关注系统信息

您有没有这种体验：在实验环境或生产环境的一大堆服务器中进行远程桌面访问的切换时，常常会被雷同的桌面搞混乱，究竟自己现在在操作哪台服务器呢？如果在桌面上可以显示当前的系统信息，是不是一件很美妙的事情？好，让我们来看一下Sysintemals的一个非常实用的小工具——BGInfo。     

企业网络DNS服务平滑切换实践

DNS作为互联网基础核心服务,牵涉到信息点web应用.当DNS服务器需要大规模切换,会给网络带来重大影响.本文通过搭建在centos5.5平台下bind9.3,响应原有DNS服务器服务,通过IP SLA服务体系保证DNS服务无缝平滑切换.经过生产系统检验实践出一条平滑可靠的DNS服务无缝切换方法.     

基于并行容错网的对等服务器集群的设计与实现

为了提高服务器系统的可靠性、可用性和性能,并改变目前非对称式服务器集群资源利用率低的状况,我们提出了一种新的服务器集群实现方案一基于并行容错网的对等服务器集群。在服务器集群的实现中,我们采用了软件集群的方法,设计实现了服务器集群管理层和并行容错通信层。     

用P2P技术改进网格信息服务

本文根据网格资源信息的特点阐述了由高度分布式的信息提供者和集合目录组成的网格信息服务基本框架。并分析了它的基础LDAP（Lightweight Directory Access Protocol）协议，指出LDAP目录本质是一种分布式的数据库。由于网格信息系统中LDAP目录信息树的动态刷新与复制的频繁发生，我们已提出用环形扩展和线形扩展策略来大幅度提高系统效率；在此基础上，本文进一步提出了文件分块复制法的思想把LDAP数据库文件分成若干块，在多个LDAP服务器端点间并行复制，最后实践证明，它大幅度提高了以LDAP目录分布式数据库为基础与核心的网格信息服务系统的并行效率。     

信息流理论及其应用研究

信息流（Information Flow）理论，也称为通道理论（Channel Theory），是一种通用的规则理论，能应用到自然界的生物、物理系统和人工世界的计算系统内在的分布式信息的交流中。信息流理论的基本概念之一是信息射（Infomorphisms），是形成信息通道的重要因素。由于信息流理论能弥补Shannon信息论难以支持语义互操作的不足，因此逐渐受到重视。本文介绍了信息流理论在国际上应用的状况，也介绍了我们在网格信息共享的研究中利用Agent会话机制动态生成信息射的过程。     

使用PVLAN设计有利于信息化教学的校园网

很多校园网因规划设计不合理而导致其对信息化教学的服务程度不高,校园网应不仅仅只提供简单的上网功能,更需要把各种信息化功能的服务器高速无缝地融合到校园网中,为此提出在交换机上使用PVLAN（Private VLAN）技术。根据校园功能区不同划分校园网,使用PVLAN中的Community、Isolated VLAN特点来进一步细化VLAN划分和数据的流控,借助Promiscuous端口模式的特性,灵活接入各种服务器,给师生的教学、学习、办公、实训提供快捷、安全和全方位的信息化服务。     

Optimal node-selection algorithm for parallel download in overlay content-distribution networks

In this paper, we investigate the issue of server selection for parallel download in overlay content-distribution networks. To achieve high performance and resilience to failures, a receiver can make connections with multiple servers simultaneously and receive different portions of the data from the servers in parallel. Prior studies mostly focus on the user-centric performance objectives, such as reducing the round-trip time (RTT) or the completion time of individual download, but tend to ignore the congestion caused by the concurrent connections from different servers or the total network resource usage. The latter performance concerns are important for the service providers who operate content-distribution networks. In this paper, we present a node-selection scheme in a hypercube-like overlay network that generates the optimal server set with respect to the worst-case link stress (WLS) criterion. The algorithm allows scaling to a large system because it is very efficient and does not require network measurement or collection of topology or routing information. It has performance advantages in a number of areas, particularly against the random selection scheme. First, it minimizes the level of congestion at the bottleneck link. This is equivalent to maximizing the achievable throughput. Second, it consumes less network resources in terms of the total number of links used and the total bandwidth usage. Third, it often leads to low average round-trip time to selected servers, hence, allowing nearby nodes to exchange more data, an objective sought by many content-distribution systems.     

A Symmetrical Exponential Open Queue Network with Blocking and Feedback

The exponential open queue network model studied here consists of n symmetrical queues in parallel served by independent first-level servers in tandem with a second-level server. Blocking of the flow of units through a first-level server occurs each time the server completes a service. The server remains blocked until its blocking unit completes its service at the second-level server. An approximate expression of the probability distribution of the number of blocked first-level servers conditioned upon a service completion of a first-level server is obtained. This expression compares well with simulation data. Based on this distribution, an approximate expression of the queue-length probability distribution is derived assuming a processor-sharing type of service. The exact condition for stability of the queue network is also derived. Some potential applications are discussed, and a quantitative evaluation of the model is given through a case study.     

面向服务的线程控制模型研究

为了满足飞速发展的Intemet对服务器性能的要求,由多台服务器构成服务器集群系统来分担负荷已成为实现高可伸缩的、高可用网络服务的有效结构。目前的服务器集群系统大多集中在对服务器（包括虚拟服务器和真实服务器）进行改进或扩展上,而没有考虑对socket协议本身进行扩展,本文提出了一个新的面向服务的线程控制模型,通过对文件系统调用的修改,扩展socket协议,构建了支持集群的服务器集群系统,取得了良好的性能改进。     

Performance prediction of loss and delay Markovian queueing model with nopassing and removable additional servers

In this investigation, the loss and delay Markovian queueing system with nopassing is proposed. The customers may balk or renege with certain probability, on finding all servers busy on their arrival. To cope up with the balking and reneging behaviour of the customers, there is provision of removable additional servers apart from permanent servers so as to provide the better grade of service at optimal cost operating conditions. The customers are classified into two classes depending upon whether they can wait or lost when all servers are busy. The customers can also be categorized into two classes from service point of view. Type A customers have zero service time whereas type B customers have exponential service time. The explicit expressions for the average number of customers in the system, the expected waiting time for both types of customers, etc., are derived by using steady-state queue size distribution. Some earlier results are deduced by setting appropriate system parameters. The system behaviour is examined with the help of numerical illustrations by varying different parameters.Scope and purposeThe performance prediction of various systems in communication switching network, remote border security check post, jobs processing in computers, etc., are influenced by the customers behaviour, in particular, when nopassing constraints are prevalent. The incorporation of loss and delay phenomena is likely to bring about understanding whether the customers would like to wait in the queue or would be lost in case when all servers are busy. The provision of additional removable servers will be helpful in upgrading the service and to reduce the discouragement behaviour of the customers in such congestion situations.     

Stability properties of constrained queueing systems and schedulingpolicies for maximum throughput in multihop radio networks

The stability of a queueing network with interdependent servers is considered. The dependency among the servers is described by the definition of their subsets that can be activated simultaneously. Multihop radio networks provide a motivation for the consideration of this system. The problem of scheduling the server activation under the constraints imposed by the dependency among servers is studied. The performance criterion of a scheduling policy is its throughput that is characterized by its stability region, that is, the set of vectors of arrival and service rates for which the system is stable. A policy is obtained which is optimal in the sense that its stability region is a superset of the stability region of every other scheduling policy, and this stability region is characterized. The behavior of the network is studied for arrival rates that lie outside the stability region. Implications of the results in certain types of concurrent database and parallel processing systems are discussed     

Performance analysis of a pull-based parallel video server

In conventional video-on-demand systems, video data are stored in a video server for delivery to multiple receivers over a communications network. The video server's hardware limits the maximum storage capacity as well as the maximum number of video sessions that can concurrently be delivered. Clearly, these limits will eventually be exceeded by the growing need for better video quality and larger user population. This paper studies a parallel video server architecture that exploits server parallelism to achieve incremental scalability. First, unlike data partition and replication, the architecture employs data striping at the server level to achieve fine-grain load balancing across multiple servers. Second, a client-pull service model is employed to eliminate the need for interserver synchronization. Third, an admission-scheduling algorithm is proposed to further control the instantaneous load at each server so that linear scalability can be achieved. This paper analyzes the performance of the architecture by deriving bounds for server service delay, client buffer requirement, prefetch delay, and scheduling delay. These performance metrics and design tradeoffs are further evaluated using numerical examples. Our results show that the proposed parallel video server architecture can be linearly scaled up to more concurrent users simply by adding more servers and redistributing the video data among the servers     

基于防火墙的内网信息发布探讨

本文主要是探讨对Windows XP系统中自身内置的防火墙ICF1服务功能进行设置,把架设在内网计算机中的Web服务器、FTP服务器、Telnet服务器、邮件服务器等网络服务信息发布到互联网中,让更多的人通过互联网随时随地分享架设在内网中的资源,实现资源共享。     

拟态通用运行环境的框架设计

为实现信息系统安全防御的目的,针对动态异构冗余(DHR)架构设计拟态通用运行环境(MCOE)框架。以拟态化改造后功能等价的异构冗余信息系统应用程序,以及异构化的信息系统运行环境设施为对象,为N异构执行体构建面向服务请求的资源调度、分发、执行、表决、安全威胁清洗恢复以及管理的自动化运行支撑环境,提供拟态产品的分发、表决统一集成接口规范。在该框架中,服务请求主键驱动的N个异构执行体和MCOE分发、内部表决、外部表决、协同执行、管理5个服务器交互运行。仿真结果表明,该设计可有效抵御软硬件后门和漏洞引发的网络攻击。