I/O issues in a multimedia system

In future computer system design, I/O systems will have to support continuous media such as video and audio, whose system demands are different from those of data such as text. Multimedia computing requires us to focus on designing I/O systems that can handle real-time demands. Video- and audio-stream playback and teleconferencing are real-time applications with different I/O demands. We primarily consider playback applications which require guaranteed real-time I/O throughput. In a multimedia server, different service phases of a real-time request are disk, small computer systems interface (SCSI) bus, and processor scheduling. Additional service might be needed if the request must be satisfied across a local area network. We restrict ourselves to the support provided at the server, with special emphasis on two service phases: disk scheduling and SCSI bus contention. When requests have to be satisfied within deadlines, traditional real-time systems use scheduling algorithms such as earliest deadline first (EDF) and least slack time first. However, EDF makes the assumption that disks are preemptable, and the seek-time overheads of its strict real-time scheduling result in poor disk utilization. We can provide the constant data rate necessary for real-time requests in various ways that require trade-offs. We analyze how trade-offs that involve buffer space affect the performance of scheduling policies. We also show that deferred deadlines, which increase buffer requirements, improve system performance significantly     

Current issues in high performance computing I/O architectures and systems

The abundance of parallel and distributed computing platforms, such as MPP, SMP, and the Beowulf clusters, to name just a few, has added many more possibilities and challenges to high performance computing (HPC), parallel I/O, mass data storage, scalable architectures, and large-scale simulations, which traditionally belong to the realm of custom-tailored parallel systems. The intent of this special issue is to discuss problems and solutions, to identify new issues, and to help shape future research directions in these areas. From these perspectives, this special issue addresses the problems encountered at the hardware, architectural, and application levels, while providing conceptual as well as empirical treatments to the current issues in high performance computing, and the I/O architectures and systems utilized therein.     

基于SMB的高清机顶盒局域网高速I／O技术研究

在家用局域网中基于Linux的高清机顶盒对局域网内PC上按SMB协议共享的文件读取速度偏低,高清影片等高码率多媒体文件无法流畅播放,这一问题限制了机顶盒的应用。因为现有的支持SMB协议的模块并非针对高速传输而设计,为了解决高码率文件传输速度慢的问题,对读取文件的机顶盒客户端的传输效率及其改进做了研究。针对SMB协议的多媒体应用特点分析了提速原理,阐述了关键技术在于对网络环境的分析并根据分析结果设定有关参数,实现了一种SMB协议客户端在基于Linux的高清机顶盒上的新软件模块。测试表明,在不修改任何硬件的条件下新软件对所有文件的读取速度比现有内置模块快20％左右,可满足某些码率高清影片的流畅播放并能使高清机顶盒的升级成本降低。     

基于SMB的高清机顶盒局域网高速I/O技术研究

在家用局域网中基于Linux的高清机顶盒对局域网内PC上按SMB协议共享的文件读取速度偏低,高清影片等高码率多媒体文件无法流畅播放,这一问题限制了机顶盒的应用。因为现有的支持SMB协议的模块并非针对高速传输而设计,为了解决高码率文件传输速度慢的问题,对读取文件的机顶盒客户端的传输效率及其改进做了研究。针对SMB协议的多媒体应用特点分析了提速原理,阐述了关键技术在于对网络环境的分析并根据分析结果设定有关参数,实现了一种SMB协议客户端在基于Linux的高清机顶盒上的新软件模块。测试表明,在不修改任何硬件的条件下新软件对所有文件的读取速度比现有内置模块快20％左右,可满足某些码率高清影片的流畅播放并能使高清机顶盒的升级成本降低。     

Distributed shared memory: a survey of issues and algorithms

An overview of distributed shared memory (DSM) issues is presented. Memory coherence, design choices, and implementation methods are included. The discussion of design choices covers structure and granularity, coherence semantics, scalability, and heterogeneity. Implementation issues concern data location and access, the coherence protocol, replacement strategy, and thrashing. Algorithms that support process synchronization and memory management are discussed     

Security issues in cloud environments: a survey

In the last few years, the appealing features of cloud computing have been fueling the integration of cloud environments in the industry, which has been consequently motivating the research on related technologies by both the industry and the academia. The possibility of paying-as-you-go mixed with an on-demand elastic operation is changing the enterprise computing model, shifting on-premises infrastructures to off-premises data centers, accessed over the Internet and managed by cloud hosting providers. Regardless of its advantages, the transition to this computing paradigm raises security concerns, which are the subject of several studies. Besides of the issues derived from Web technologies and the Internet, clouds introduce new issues that should be cleared out first in order to further allow the number of cloud deployments to increase. This paper surveys the works on cloud security issues, making a comprehensive review of the literature on the subject. It addresses several key topics, namely vulnerabilities, threats, and attacks, proposing a taxonomy for their classification. It also contains a thorough review of the main concepts concerning the security state of cloud environments and discusses several open research topics.     

完成端口实现高性能服务端通信层的关键问题

为实现高性能稳定的网络通信服务,对完成端口(IOCP)应用中信息识别与提取、资源管理、消息乱序处理3个关键问题进行了分析,提出了IOCP参数扩展、内存池、对象池、环形缓冲等改进的解决方法.使用这些方法对IOCP底层进行了封装,并设计和实现了面向企业应用的可扩展网络程序通信模块.压力和性能测试结果表明,该模块能在合理资源消耗基础上支持海量并发连接,具有较高的数据吞吐量,在实际项目应用中也表现出了良好的性能.     

I/O受限的并行加速比模型与可扩展I/O体系结构

为了缓解I/O瓶颈问题,可以从应用程序、可扩展算法、编译器和语言、运行时库、操作系统和体系结构六方面展开研究。其中,I/O体系结构是所有技术途径的关键支撑。当前并行I/O性能分析缺乏科学的理论模型为I/O体系结构设计提供理论依据。本文针对并行计算机系统的可扩展性问题,研究了I/O负载对并行计算机系统可扩展性的影响,建立了I/O受限的并行加速比性能模型,对目前大规模并行计算机系统中三种常用I/O体系结构的可扩展性进行了分析;以此为理论依据,提出了一种面向高性能计算的可扩展并行I/O系统结构。同时,还提出了几种有效降低I/O操作服务时间的策略,从而达到增强系统可扩展性的目的,为后续研究奠定了基础。     

Technology on social issues of videoconferencing on the Internet: a survey

Constant advances in audio/video compression, the development of the multicast protocol as well as fast improvement in computing devices (e.g. higher speed, larger memory) have set forth the opportunity to have resource demanding videoconferencing (VC) sessions on the Internet. Multicast is supported by the multicast backbone (Mbone), which is a special portion of the Internet where this protocol is being deployed. Mbone VC tools are steadily emerging and the user population is growing fast. VC is a fascinating application that has the potential to greatly impact the way we remotely communicate and work. That has many people forecast a significantly widespread adoption. Yet, the adoption of VC is not as fast as one could have predicted. Hence, it is important to examine the factors that affect a widespread adoption of VC. This paper examines the enabling technology and the social issues. It discusses the achievements and identifies the future challenges. It suggests an integration of many emerging multimedia tools into VC in order to enhance its versatility for more effectiveness.     

高效快速融合的双LAN太赫兹无线局域网MAC协议

为了使两个独立运行的太赫兹无线局域网能快速完成协调融合以及提升融合后网络的性能,提出一种高效快速融合的双LAN太赫兹无线局域网MAC协议——EFC-MAC(efficient and fast convergence of MAC protocols)。首先,针对现有网桥节点选举机制不完善以及网络协调融合机制存在不足之处的问题,提出了在第一个网间节点进行申请入网时就开始进行网桥节点的选举,并将选举结果在下一超帧的BP时段进行通告的机制,并根据网络是否已经完成了协调融合而决定是否申请CTA以转发heartbeat消息的机制,使网络能高效快速完成融合;然后,针对网间节点申请公共时隙方式不够灵活的问题,提出根据P-CTAP所剩时隙量来动态申请CTA的机制,提升了网络的性能;最后,针对网桥节点切换机制尚不明确的问题,提出了采用一个CAP时段长度完成网桥节点切换的机制。仿真结果表明,所提协议有效提高了网络吞吐量,提升了时隙利用率以及降低了数据传输时延。     

Testing software components for integration: a survey of issues and techniques

Component‐based development has emerged as a system engineering approach that promises rapid software development with fewer resources. Yet, improved reuse and reduced cost benefits from software components can only be achieved in practice if the components provide reliable services, thereby rendering component analysis and testing a key activity. This paper discusses various issues that can arise in component testing by the component user at the stage of its integration within the target system. The crucial problem is the lack of information for analysis and testing of externally developed components. Several testing techniques for component integration have recently been proposed. These techniques are surveyed here and classified according to a proposed set of relevant attributes. The paper thus provides a comprehensive overview which can be useful as introductory reading for newcomers in this research field, as well as to stimulate further investigation. Copyright © 2006 John Wiley & Sons, Ltd.     

Assessing the authenticity of subjective information in the blockchain: a survey and open issues

World Wide Web - Blockchain, with its ever-increasing maturity and popularity, is being used in many different applied computing domains. To document the advancements made, researchers have...     

I/O的实施

在设备自动化升级过程中．置换I／O连接通常被看作是一种最基本的设备升级。设备内部I／O系统能够减少制造过程与控制系统之间因置换I／O连接而带来的不便。而且．在某些情况下．I／O系统甚至能够成为控制系统。     

Designing and managing local area networks: A survey of LAN personnel

A survey was conducted of planners of 45 local area networks (LANS) of personal computers used for office work found in a large metropolitan area. Usable responses were obtained from the planners of 27 of the LANS, a response rate of 60%. The planners were asked to rank 79 LAN planning criteria and to identify problems they encountered in managing the LANS.Twenty-one planning criteria were identified by planners as important or very important in the design of LANS. Five planning criteria were identified as unimportant by the planners. The planning criteria considered important varied between general purpose LANS and LANS primarily serving special applications. The planning criteria considered important also varied with LAN size.Few problems were encountered by the planners in this survey and the amount of time the planners felt should be committed to managing the LANS was modest. Installation problems were the most frequently cited.     

水泥生产线上PCS7系统集中和分布式I/O扩展

PCS7近年来在新型干法水泥生产线DCS系统中得到了广泛应用。PCS7与过程信号的连接有两种方式：集中式I／O扩展和分布式I／O扩展,目前这两种方式在新型千法水泥生产线上都有应用,相对而言,分布式I／O扩展在新型干法水泥生产线上具有更大的优势。     

利用缓冲区提高Java应用程序的I／O性能

Java语言的跨平台特性使得其在各个领域得到了广泛应用。与此同时，Java应用程序的性能，特别是I／O性能，也是人们普遍关注的话题。本文采用一个生物信息学应用程序的实例来探讨如何利用I／O缓冲区提高Java应用程序的I／O性能。我们采用三种不同的I／O缓冲区的实现方式来实现该应用程序，对其进行性能分析比较并将其与相应的C＋＋应用程序进行比较。大量实验表明，I／O缓冲区对于Java应用程序的I／O性能起着至关重要的作用。恰当地使用I／O缓冲区，某些场合下能使Java应用程序的I／O性能略高高于相应的C＋＋应用程序的I／O性能。     

微机I/O模块在PLC I/O扩展中的应用

本文在简要介绍PLC常用的I／O扩展技术基础上，重点介绍在I／O控制点较多的PLC控制系统中，如何使用价格相对较低的微机I／O模块来扩展PLC的I／O点，以降低系统的成本，提高经济效益。并以数字电子种LED显示控制为例，详细介绍了PLC控制系统中，采用微机I／O模块来扩展PLC的I／O点时，其硬件连接和梯形图编程方法。