对等网端到端多路径选择建模及算法研究*

在对等网上利用多路径分发视频是一种重要的机制,虽然在一对节点之间找出符合条件的多条路径并不困难,但发送端如何从可用路径集中选出最优路径子集,并为其最优地分配发送速率仍是一个难题。为此,提出一种新的对等网端到端最优多路径选择与速率分配(OMPSRA)算法。首先,应用排队论建立OMPSRA模型,并推导出一种新的OMPSRA公式,公式既给出最优分配的计算方法,也给出路径的最优速率分配与各路径最大可用带宽之间的关系,利用此关系可选出最优路径子集。最后基于公式实现OMPSRA算法。理论分析和仿真实验结果表明提出的算法能对通信量进行全局最优分配,最小化视频传输的端到端时延,有效提高视频传输质量,比同类算法有更好的性能。     

基于往返时延梯度的多路径拥塞控制算法

为更好利用有限的网络带宽资源，提高带宽利用率，提出一种利用往返时延梯度精确感知带宽变化的多路径拥塞控制算法。根据往返时延的大小反馈网络拥塞程度，将拥塞程度量化为时延梯度作为拥塞窗口的控制参数；为保证链路公平，利用往返时延估计链路带宽，经迭代分配带宽，给出公平的资源分配方法。在NS-3上进行仿真，其结果表明，多路径流的吞吐量较单路径流明显提高，保证了链路分配的公平，动态环境下的响应时间较同类算法有所减小。该算法进一步提高了网络带宽的利用率。     

基于多路广播树的SDN多路径路由算法

传统的网络使用基于最短路径的单一路径路由,无法有效地利用网络的全部带宽。软件定义网络(Software Defined Networking,SDN)采用中心化的控制平面能方便地实现对路由的精确控制。针对SDN网络下的多路径路由问题,提出了基于多路广播树的路由存储结构及相应的多路径选择算法。该算法根据各路径的可用带宽和时延进行概率分配,优先选择可用带宽大和时延小的路径。实验结果表明,该算法能快速地进行路由,并有效地减小传输时延和增大吞吐率。     

无线网状网络的多路径路由与调度算法

提出了一种保障服务质量的多路径路由算法,数据分组可通过多条不同的路径进行传输,以提升网络总吞吐量性能.进一步提出了一种多路径调度策略.通过使用调度策略,基于当前可用带宽信息和路径所引入的时延信息,数据分组在传输前可被分成多段并通过不同的路径发送,根据路径时延调整优化调度策略,从而使得数据可通过在不同的路径上进行更高效地传输.仿真实验进一步验证了本文提出的路由机制和调度策略在不同网络负载下的优越性.     

一种端到端网络的不相交多路径QoS路由算法

不相交多路径路由算法旨在一个端到端的网络中为应用流选择多个路径，且这些路径在瓶颈链路上是彼此不相交的。本文提出的不相交多路径QoS路由（DMQR）算法在Dijkstra最短路径和最短最宽路径（SWP）算法的基础上，能够动态地计算时延最短、带宽最宽、在瓶颈链路上互不相交的路径，且保证每个路径都是满足一定服务质量的。在视频会议、远程医疗和远程教育等重要的视频通信场合，要求应用层和网络层必须协同工作以保证一些必要的QoS，例如端到端的带宽、时延和包丢失率等。本文针对端到端的网络，重点讨论不相交多路径QoS路由算法在应用层的设计和实现。性能分析和模拟结果显示，所提出的不相交多路径QoS路由算法总是收敛的，且当网络流量增加时，该算法具有较低的包丢失率和较高的吞吐量。     

基于传输时延预测的多路径并发传输数据分配算法

针对多路径并发传输模型的整体性能在路径性能存在差异时会急剧下降的原因进行分析,给出了获取通信路径传输时延的有效评估方案,并在此基础上提出了一种基于传输时延预测的多路径并发传输数据分配算法.该算法通过获取和预测数据块在各条路径上引入的传输时延,以按序到达为目标对多路径并发传输模型发送回合内和发送回合间的数据分配过程进行优化,能够有效地减少路径传输性能差异对多路径并发传输模型整体性能带来的影响.分析和实验结果表明,该算法相对于默认的轮询数据分配算法能够取得较好的运行性能.     

软件定义网络中基于分段路由的多路径调度算法

针对当前软件定义网络(SDN)在应对大量数据流时造成的流表利用率低、转发响应较慢以及当前网络调度算法容易造成网络局部拥塞和负载不均衡等问题,提出一种基于分段路由的多路径调度算法SRMF。首先,SDN控制器根据网络拓扑连接情况下发初始流表;综合考虑网络链路剩余带宽、丢包率和数据流估测带宽需求进行路径权重计算;最后,根据路径权重选择最优路径并构造分段流表下发到边缘交换机。实验结果表明分段路由转发技术在多种网络拓扑下较一般转发技术在流表项开销方面有明显优势,SRMF算法与Hedera、ECMP相比,在业务流端到端时延、端到端时延抖动、网络吞吐率、丢包率等方面有一定的优势。     

一种可提供绝对服务质量分级的优先调度算法

提出了一种能够提供端到端时延保证和满足丢包率要求的多优先级算法。该算法以分组头中记录的时延、丢包率、保证带宽为权重对分组进行调度,通过对信元的相对优先级及服务质量参数的加权算法,得到一种公平的满足绝对服务质量的算法。还能够使系统避免维护每个流的状态信息以及对单个流进行复杂的队列管理和调度,由此增加了系统的可扩展性。计算机仿真表明该算法具有较高的资源利用率,较低的端到端时延和时延抖动以及较低的分组丢弃率等特点。     

减轻CMT中乱序程度的发送端数据分配方案

为减轻多径并行传输（concurrent multipath transfer,CMT）系统中的接收端数据包乱序对系统传输性能的影响,提出一种新的发送端数据分配方案。方案基于路径带宽、往返传输时延和拥塞窗口预测数据包前向传输时延,并将其作为划分系统中路径传输优先级的度量因子,发送端根据路径传输优先级和发送缓存区状态为各路径分配待发送队列中不会导致接收端乱序的数据包。仿真结果表明,与轮询和一种基于分组到达时间的负载均衡算法（arrival-time matching load-balancing,ATLB）算法相比,所提发送端数据分配方案可有效减少接收端乱序数据包个数。     

一种智能多路径路由及子流分配协同算法

传统单一路径的传输机制难以满足当前以智慧城市为代表的新一代应用对时延、丢包率等网络性能的要求,而现有多路径传输机制在路由算法及子流分配等方面不能根据网络实时状态调整且互相缺乏协同。引入强化学习理论并结合软件定义网络,提出多路径路由及子流分配协同算法。基于Q-learning设计多路径路由算法,并从策略协同角度对其进行改进,实现路由与子流分配的相互协同。在此基础上,通过Q-value的回环消除方法保证路由准确性并提高算法收敛速度。实验结果表明,该算法在网络负载动态变化过程中能实时调整最佳的多路径路由及子流分配协同策略,提高了传输成功率。     

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)

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