基于响应延时预测的流媒体集群服务器负载调度策略

随着流媒体应用的指数级增长,提高流媒体服务器的性能越发重要。本文提出一种流媒体集群服务器的负载调度策略。综合运用多级模糊系统和人工神经网络技术,对用户请求响应延时进行模糊预测,并考虑节点服务器的流媒体节目前缀缓存和补丁预取技术,提出基于响应延时阈值和请求流媒体节目在节点服务器的缓存情况的负载调度算法,并对该算法进行仿真验证。     

基于代理缓存的移动流媒体动态调度算法

提出了一种基于代理缓存的移动流媒体动态调度算法DS2AM2PC（Dynamic Scheduling Algorithm for Mobile Streaming Mediabased on Proxy Caching）,采用代理缓存窗口自适应伸缩和分段缓存补丁块方案,在代理缓存中根据具体情况每次缓存相同或者不同大小的段补丁块,同时隔一段时间,根据移动媒体流行度更新一次缓存窗口大小,动态决定其最大缓存大小,实现了移动流媒体对象在代理服务器中缓存的数据量和其流行度成正比的原则.仿真结果表明,对于客户请求到达速率的变化,DS2AM2PC算法比P3S2A（Proxy-assisted Patch Pre-fetching and Service Scheduling Algorithm）算法和OBP（Optimized Batch Patching）＋prefix ＆ patchcaching算法具有更好的适应性,在最大缓存空间相同的情况下,能显著减少通过补丁通道传输的补丁数据,从而降低了服务器和骨干网络带宽的使用,能快速缓存媒体对象到缓存窗口,同时减少了代理服务器的缓存平均占有量.     

一种基于节点可选度的P2P点播流媒体数据调度算法

当前的P2P(Peer-to-Peer)点播流媒体系统中数据调度算法未能充分利用每个用户节点自身的特性.在分析典型数据调度算法基础上提出一种基于节点可选度的数据调度算法(SSP算法).该算法一方面在调度下载数据块时综合考虑了邻居节点带宽能力及其所拥有的数据信息.另一方面对服务节点的请求处理过程进行了优化.SSP算法有利于提高用户节点播放视频的连续性,降低流媒体服务器的负载压力,从而改善P2P点播流媒体系统的整体服务质量.仿真结果和实际应用表明算法性能良好,适用于用户节点能力差异较大的P2P点播流媒体环境.     

混合P2P流媒体的缓存替换算法研究*

给出一种有服务器的混合P2P流媒体系统模型,针对该模型提出了一种对等节点的缓存替换算法,并通过仿真试验验证了该算法的有效性。     

基于补丁算法的流媒体代理缓存的研究与实现

对流媒体代理缓存和流调度技术进行了分析与研究，结合代理缓存和补丁算法的优点，设计与实现了一种基于补丁算法的流媒体代理缓存的高效方法。分析和实验研究表明，该方法能进一步减少对骨干网络带宽资源和原始服务器的磁盘I/O资源的占用，提高用户访问请求的响应速度。     

P2P技术在缓存集群适应性缓存策略上的应用

缓存服务器集群的适应性缓存策略能够根据用户访问模式,自动调整热点数据在缓存服务器中的分布情况.在分析原有适应性缓存策略之上,提出了一种结合了P2P技术的缓存服务器集群的适应性缓存策略,将热点数据向离用户较近的边缘缓存服务器推进,有效地均衡了整个缓存服务器集群的负载,提高了缓存服务器集群的边缘缓存字节命中率.     

基于代理缓存的流媒体动态调度算法研究

该文研究了在Internet环境下通过代理服务器将流媒体从源服务器传输到多个客户端时的骨干网络及服务器带宽消耗问题．在分析了传统多媒体流动态调度算法不足的基础上,提出了基于代理服务器协助的补丁预取与服务调度算法(P^3S^2A)．由代理服务器通过单播连接从源服务器中获取流媒体数据,然后通过组播方式转发给客户端．同时根据当前客户请求到达的分布状况,代理服务器为后续到达的客户请求进行补丁预取及缓存．理论分析及实验结果表明,与传统的动态调度方法相比,该文提出的算法能够在不消耗更多的缓存空间的情况下,更有效地节省骨干网络的带宽资源,特别是在访问请求强度较高的情况下,效果更为突出。     

针对固定码率(CBR)流媒体的动态替换算法(DRA)

流媒体代理服务器缓存是针对流媒体访问的一项技术,能有效的提高流媒体访问质量。缓存算法是缓存代理服务器的重要技术组成部分,包括缓存保存方式、替换算法及进入策略三个方面。文中将介绍一套针对固定码率(CBR)流媒体的缓存算法,在包含码率分级保存方法的同时,使用了包含流媒体缓存基本特性的动态替换算法(DRA,Dynamic Replication Algorithm)。     

基于缓存区段的P2P流媒体调度算法

由于P2P环境的高度动态性和异构性,以及流媒体服务的高宽带和连续性强的特征,P2P流媒体系统中数据块和发送节点的调度便显得尤为重要。本文针对数据驱动的P2P流媒体系统提出了基于缓存区段的调度算法,即根据时间线将缓存划分为反映不同紧急程度的若干区段,以便节点根据资源副本数和紧急程度作出合理调度。模拟实验表明,在高 动态性的网络情况下,基于缓存区段的调度算法仍然能够很好地保证媒体流的连续性以及节点间的协作。     

基于CDN和P2P技术的混合流媒体内容分发机制研究

采用核心层通过P2P技术对混合流媒体内容分发网络进行优化,即根据区域将边缘代理服务器间以P2P的方式进行协作式内容存储,终端用户以P2P方式进行分发,从而达到更好地利用边缘服务器的缓存空间,增大骨干网的带宽利用率,提升分发能力的目的.     

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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