基于端到端的单播层析网络时延分布

推断网络内部各链路的特性,已成为管理和评估大型电信网络的重要条件.通过某个特定路径直接监测每个链路是不现实的,所以一般通过发送端到端的探测包,利用网络的终端节点来收集网络链路的特征信息.通过单播探测包方法来推断链路的时延特性.针对网络内部链路时延累积量生成函数(CGF),提出一种基于端到端的单播探测包时延测量的偏差校正...     

一种低复杂度的网络链路时延估计及仿真研究

网络时延是重要的网络性能指标,是网络服务质量测量与分析领域的重要目标之一.在网络拓扑已知且稳定及链路性能时空独立性的假设前提下,给出了网络链路时延估计模型和端时延数据采集方法,提出了一种低复杂度的网络链路时延估计方法.首先应用伪似然估计,然后确定可解的探测单元,通过限制平均采样精度和探测单元链路数的增加来显著降低计算复杂度,解决了计算复杂度过高的链路时延估计求解问题.最后利用基于NS2的仿真研究验证了时延估计方法的有效性和准确性.     

网络链路时延统计量的层析成像方法

传统的连续时延分布估计往往需要假设时延满足某种分布,估计精度受制于假设分布与实际时延分布的相关性。Gianni Antichi等提出了一种链路时延累积量估计的方法,无需假设时延满足某种分布,但需要内部节点的协作。针对上述问题提出一种完全依靠端到端测量的链路时延累积量估计方法,根据端到端的时延构建端到端时延累积量与链路时延累计量的方程,最终利用最优化方法计算出链路时延累积量的最优解。ns-2仿真结果验证了该方法的有效性。     

基于PLE的有确定解的端到端网络链路时延推测方法

网络时延是重要的网络性能指标,端到端网络时延推测能够克服传统的基于路由器或者路由器协作的网络测量技术的弊端。在网络拓扑已知且稳定和链路性能时空独立性的假设前提下,给出了网络链路时延推测模型,提出了一种基于伪似然估计(PLE)的有确定解的端到端网络链路时延推测方法。在应用期望最大化算法的伪似然估计的基础上,控制背靠背发包方式,确定可以求解的探测单元,解决了不满足有确定解拓扑下的求解问题,且有效降低了计算复杂度。最后利用基于模型的计算验证了该方法的准确性和有效性。     

基于时间阈值丢包率估计的网络断层扫描技术

基于现有单播测量技术研究,提出一种改进的单播测量方法——增加时间阈值的测量法,对网络链路丢包率进行测量。该方法通过为探测包的发送方式设定阈值,即设定同一数据包对间的时间阈值与不同数据包对间的时间阈值,并通过对收集到的数据使用伪似然估计方法PMLE计算得到网络链路丢包率。实验结果表明,采用该方法可以获得更多的有效测量数据,测量结果更接近链路性能的真实情况。     

主动端到端离散式时延分布估计方法研究

对于网络质量评估链路性能推测无疑是至关重要的,然而现有的估计方法通常只能推测层次数有限的简单网络,无法应用于大规模网络。提出了一种基于不完整数据极大似然估计算法,估计网络内部链路时延分布,该方法通过不同的发包策略将树状网络拓扑划分成不同的两层三链子树,针对每个子树估计每条＂链＂的时延,随后通过移植算法将路径时延划分到各链路中,逐一对每个子树使用该方法计算从而得到整个网络链路时延情况。利用NS2仿真实验验证了该算法的可行性和准确性。     

一种基于多播推测丢包率的算法

网络层析是近年新兴的一个网络研究领域,它利用端到端的性能测试结果推导网络内部性能特征或拓扑结构,克服了传统网络测量技术的一些缺陷.丢包率层析的主要方法是利用最大似然估计(MLE),但是计算复杂度高且计算时间较长;基于伪似然估计(PMLE)方法可以较快估计各链路丢包率,但是在非叶节点链路的误差较大.为了克服以上缺点,本文基于多播网络的端对端测量,结合MLE和PMLE提出一种推算网络内部各链路的丢包率算法.通过仿真证实该算法估测的结果能真实地反应网络内部丢包趋势,在推测精度较好的情况下,计算量减少,计算复杂度降低.     

一种负载均衡网络中内部链路时延推测算法

了解网络内部链路特征对运维大型IP网络至关重要.前人在假定固定路由条件下采用端到端主动测量的方式从网络边缘推测网络内部链路行为特征.由于网络中存在导致随机路由的负载均衡设备,使以前的主动测量方法无法实施.采用累计生成函数和随机过程方法解决随机路由条件下的网络内部链路时延推测问题.仿真结果表明,算法可以很好地解决随机路由下的内部链路时延推测问题.根据链路时延分布,可以用来判决瓶颈链路,为网络运维提供极具价值的参考.     

单播丢包率的时域特征参数估计

网络链路丢包的时域特征参数（如：平均丢包长度、平均传输长度等）能够表现出链路丢包的突发性。现有的针对多播网络链路丢包时域特征参数的估计方法不能直接应用于单播网络。针对这一问题,提出用探测包群在单播网络中模拟多播端到端的测量过程,然后根据测量得到的数据对链路的连续传输概率（连续传输两个包的概率）和平均丢包长度等进行了估计。采用NS2进行仿真,验证了方法的性能。     

基于包对推测丢包率的简化算法

在进行网络测量时，有时只能获得端到端的数据，然而得到网络内部的信息对网络性能的认识是非常重要的，因此就需要从网络端到端测量得到的数据推测网络内部链路的数据。本算法是基于单播网络的端到端测量的，利用包对进行统计，运用最大似然估计和EM算法进行计算，从而推算网络内部节点的丢包率。我们在文中给出了算法的逻辑分析和仿真结果。     

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.     

Call for Papers The 6^th International Conference on Grid and Cooperative Computing

Recent years have seen rapid advances in various grid-related technologies, middleware, and applications. The GCC conference has become one of the largest scientific events worldwide in grid and cooperative computing. The 6th international conference on grid and cooperative computing (GCC2007) Sponsored by China Computer Federation (CCF),Institute of Computing Technology, Chinese Academy of Sciences (ICT) and Xinjiang University ,and in Cooperation with IEEE Computer Soceity ,is to be held from August 16 to 18, 2007 in Urumchi, Xinjiang, China.     

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)

正~~