Virtual network computing

VNC is an ultra thin client system based on a simple display protocol that is platform independent. It achieves mobile computing without requiring the user to carry any hardware. VNC provides access to home computing environments from anywhere in the world, on whatever computing infrastructure happens to be available-including, for example, public Web browsing terminals in airports. In addition, VNC allows a single desktop to be accessed from several places simultaneously, thus supporting application sharing in the style of computer supported cooperative work (CSCW). The technology underlying VNC is a simple remote display protocol. It is the simplicity of this protocol that makes VNC so powerful. Unlike other remote display protocols such as the X Window System and Citrix's ICA, the VNC protocol is totally independent of operating system, windowing system, and applications. The VNC system is freely available for download from the ORL Web site at http://www.orl.co.uk/vnc/. We begin the article by summarizing the evolution of VNC from our work on thin client architectures. We then describe the structure of the VNC protocol, and conclude by discussing the ways we use VNC technology now and how it may evolve further as new clients and servers are developed     

Improving the virtualization of rich applications by combining VNC and streaming protocols at the hypervisor layer

Virtual desktop infrastructure (VDI) solutions seek to provide a satisfactory user experience at the client side when accessing remote desktop applications, even from mobile devices with limited capabilities. This paper presents a new approach, improving on previous work by the authors, in which a combination of Virtual Network Computing (VNC) and streaming protocols allowed efficient remote web access to virtualized applications within a cloud architecture. The new approach simplifies virtual machine templates, from which virtual machine instances are deployed, by centralizing software modules, greatly simplifying their management. Our new contribution consists of an integrated solution with specific WebM video encoding modules in charge of application visual output processing, an Hypertext Transfer Protocol (HTTP) streaming server, and a VNC server. The solution can be installed in the hypervisor of the host machines instead of replicating the servers and modules throughout the guest (virtual) machines that run the virtualized applications. Consequently, their implementations are unique and independent of the operating system of the virtual machines. In short, it is not necessary to provide different implementations for different operating systems, which reduces the complexity of virtual machine templates and greatly simplies platform management. To demonstrate our solution, we have modified the Quick Emulator (QEMU)‐Kernel‐based Virtual Machine (KVM) hypervisor source code accordingly. We also present qualitative and quantitative analyses that demonstrate that the new approach is advantageous in terms of software management and quality of experience, compared with our previous work and other well‐known thin clients, contributing to the enhancement of VDI systems. Copyright © 2015 John Wiley & Sons, Ltd.     

CSCW分布式多任务协作机制的研究

文中对ＣＳＣＷ的多任务协作机制作了深入的研究,系统地描述了多任务协作机制的基本概念和研究内容。给出了一个由群体服务器,应用服务器和应用工具组成的三层结构和多任务协作模型,并重点介绍了基于此模型用Ｊａｖａ语言在ＰＪＶＭ开发平台上实现的一个原型系统－－“网络围棋俱乐部”,该系统可运行在由Ｕｎｉｘ（Ｓｏｌａｒｉｓ２．４）和Ｗｉｎｄｏｗｓ（９５．ＮＴ）组成的异构型网络上。     

Samba服务器共享资源安全系统层次模型研究

Samba是一套使用SMB(Server Message Block)协议的应用程序。通过支持这个协议,Samba允许Unix／Linux服务器与Windows产品之间进行通讯。文中提出了Samba服务器的安全体系层次模型,分析了Samba服务器的各个安全层次,介绍了如何配置参数实现Unix／Linux主机与windows主机之间资源共享的安全性,并针对应用中出现的一些问题讨论了解决的方法。     

P2P多点共享传输软件的设计与实现

采用P2P（Peer-to-Peer）技术多点共享式文件传输,任何一个进行下载的客户,在下载的同时,也能够作为服务器把它已接收到的数据提供给另外一个客户进行下载。这种方式可以有效地均衡上下行线路的数据量,同时每个客户端又可以部分作为服务器端,减轻了服务器的带宽压力。本系统用MicrosoftVisualC＋＋6.0编写,实现了在局域网中若干台机器互为客户端和服务端,共同完成一个下载任务的功能。     

虚拟网络计算中的数据传输保证机制研究

VNC是一个强大的远程桌面共享工具,能够让多个客户端通过互联网查看服务器端的实时桌面状况并可以进行远程操作,但是VNC系统的星形结构使其在实际场景中的可用性大大降低。对VNC系统进行了改进,并在此基础上提出了一种数据传输的保证机制。应用验证表明,其机制在改进后的系统中保证了数据能够实时、可靠地传输。     

A multi-tier semantics for Hop

Hop is a multi-tier programming language where the behavior of interacting servers and clients are expressed by a single program. Hop adheres to the standard web programming style where servers elaborate HTML pages containing JavaScript code. This JavaScript code responds locally to user’s interactions but also (following the so-called Ajax style) requests services from remote servers. These services bring back new HTML fragments containing additional JavaScript code replacing or modifying the state of the client. This paper presents a continuation-based denotational semantics for a sequential subset of Hop. Though restricted to a single server and a single client, this semantics takes into account the key feature of Hop namely that the server elaborates client code to be run in the client’s browser. This new client-code dynamically requests services from the server which, again, elaborate new client code to be run in the client’s browser. This semantics details the programming model advocated by Hop and provides a sound basis for future studies such as security of web applications and web continuations.     

计算机远程监控系统关键技术研究

针对计算机远程监控系统中需要解决的若干关键问题,设计一个客户/服务器模式的远父程监控系统.利用套接字和应用程序的伪消息机制,对控制客户端和被控服务器端进行数据交换,从而达到监控与被监控的目的;利用桌面网格技术大大减少了屏幕数据的传输量;根据桌面图形图像的特点,提出了霍夫曼(Huffman)算法和行程(RLE)算法,有效地实现了桌面图形图像的编码和解码.     

Windows2000智能镜像技术

文中介绍了Windows2000的智能镜像技术。智能镜像技术是由一系列强大的桌面修改和设置管理技术组成,它结合了集中计算和分布计算的优点,通过在服务器端和客户段使用智能镜像技术,用户的数据、应用程序、设置在整个网络环境下始终跟随用户。同时,管理员也可以实现Windows2000操作系统的远程安装,Windows2000通过用户数据管理、软件安装和保持、用户设置管理、远程安装服务珲实现智能镜像技术。     

基于Web的跨平台分布式多线程文件服务器设计

分析了以往分布式文件服务器的不足,提出了一种以J2EE技术为核心的基于Web的跨平台分布多线程文件服务器的设计方案,该分布式文件服务器由一个集中控制单元和多个本地文件服务器组成,集中控制单元以数据库的地文件逻辑信息进行集中式管理,文件的物理信息则上位于Web不同节点上的本地文件服务器分布式地管理,本地文件服务器支持多线程文件操作和Windows,Unix,Linux等多种操作系统的文件系统。     

网络编程接口在分布式电网监控系统中的应用

介绍了有关网络编程的基本原理以及Unix,Windows下网络编程接口,并结合示例介绍了基于C／S模式的电网监控系统高级应用软件的开发。     

基于Linux的Nagios服务器监控系统的研究与实现

Nagios系统是一款运行于Linux或Unix上的服务器系统监控开源软件,它强大的功能可以实现对网络上的服务器进行全面监控。本文以Linux操作系统为平台,研究如何利用Nagios提供的众多插件来实现对远端服务器的监控、检测功能。     

A dynamic framework for integrated management of all types of resources in P2P systems

Traditional Peer-to-Peer (P2P) systems were restricted to sharing of files on the Internet. Although some of the more recent P2P distributed systems have tried to support transparent sharing of other types of resources, like computer processing power, but none allow and support sharing of all types of resources available on the Internet. This is mainly because the resource management part of P2P systems are custom designed in support of specific features of only one type of resource, making simultaneous access to all types of resources impractical. Another shortcoming of existing P2P systems is that they follow a client/server model of resource sharing that makes them structurally constrained and dependent on dedicated servers (resource managers). Clients must get permission from a limited number of servers to share or access resources, and resource management mechanisms run on these servers. Because resource management by servers is not dynamically reconfigurable, such P2P systems are not scalable to the ever growing extent of Internet. We present an integrated framework for sharing of all types of resources in P2P systems by using a dynamic structure for managing four basic types of resources, namely process, file, memory, and I/O, in the same way they are routinely managed by operating systems. The proposed framework allows P2P systems to use dynamically reconfigurable resource management mechanisms where each machine in the P2P system can at the same time serve both as a server and as a client. The pattern of requests for shared resources at a given time identifies which machines are currently servers and which ones are currently clients. The client server pattern changes with changes in the pattern of requests for distributed resources. Scalable P2P systems with dynamically reconfigurable structures can thus be built using our proposed resource management mechanisms. This dynamic structure also allows for the interoperability of different P2P systems.     

云应用管理引擎的设计与实现

介绍了云应用管理引擎的设计思想与实现方式,以解决传统上应用程序必须安装在本地才能运行的问题.云应用管理引擎对安装在Windows或Linux应用服务器上的应用程序进行管理,在集群范围或服务器范围内将应用程序发布为远程应用,并将远程应用授权给用户.授权用户可以从各种客户端设备和系统运行交付给自己的远程应用程序,就像运行本地应用程序一样.     

A Universal File Server

A file server is a utility provided in a computer connected via a local communications network to a number of other computer. File servers exist to preserve material for the benefit of client machines or systems. It is desirable for a file server to be able to support multiple file directory and access management systems, so that the designer of a client system retains the freedom to design the system that best suits him. For example, he may wish to use the rile server to support a predefimed directory structure or as a swapping disk. The paper explores the dedgn issues associated with such a file server and proposes some solutions.     

基于多代理的桌面应用分布式迁移工具

该文提出了一种把开放应用接口的单机应用程序从桌面应用环境向分布式应用环境迁移的方法,基于多代理的客户端/服务器结构设计并实现了一个开放式的分布式迁移工具,在Office/AutoCad等应用程序上成功应用。     

Parallel computation with dynamic load distribution for locally distributed Windows NT environments

Today 's requirements for computational power are still not satisfied. One answer for this demand is expensive supercomputers. Another attempt is the collection of computational power in a network. Connected workstations operate for parallel computation. Our approach for collecting unused resources in workstation clusters enables dynamic distribution of computational load over the network. Any computer individually distinguishes the amount of server resources sharing for others in the network. Our architecture is based on the client /server model —clients divide potentially hard problems into sub problems and forward them to different servers in the network. The usage of standardized remote procedure calls (rpc) as the basic mechanism for transmission of data between the workstations allows the extension of the concept for heterogeneous environments. This article gives a discussion of our implementation for Windows NT and presents the latest benchmarks with two special parallel applications.     

Tight Bounds for Selfish and Greedy Load Balancing

We study the load balancing problem in the context of a set of clients each wishing to run a job on a server selected among a subset of permissible servers for the particular client. We consider two different scenarios. In selfish load balancing, each client is selfish in the sense that it chooses, among its permissible servers, to run its job on the server having the smallest latency given the assignments of the jobs of other clients to servers. In online load balancing, clients appear online and, when a client appears, it has to make an irrevocable decision and assign its job to one of its permissible servers. Here, we assume that the clients aim to optimize some global criterion but in an online fashion. A natural local optimization criterion that can be used by each client when making its decision is to assign its job to that server that gives the minimum increase of the global objective. This gives rise to greedy online solutions. The aim of this paper is to determine how much the quality of load balancing is affected by selfishness and greediness.     

A Library for Developing PHIGS Programming Tools in a PEX Environment

The merger of three-dimensional graphics with the X Window System has recently been standardized by adapting PHIGS, the Programmer's Hierarchical Interactive Graphics System, to the X Window System with PEX, the PHIGS Extension to X. The standard programming library for PEX has been defined to be identical to PHIGS PLUS allowing PHIGS programs to port directly to the X environment. X uses a client server model to run applications as client processes which communicate with a server to perform graphical display and input. For improved performance, the PEX extension defines new server resources to reduce network traffic and to take advantage of graphics hardware existing on high-end servers. A side effect of this distributed model of computation is a distribution of PHIGS structures leading to a relaxation of the exclusive access which a PHIGS application usually maintains over its Central Structure Store. We exploit the distributed nature of a PEX/PHIGS client's Central Structure Store to provide access to it for other applications besides the originating PEX/PHIGS client. We refer to these other applications as tools since one of our primary goals is to create development tools for PHIGS programmers. Rather than concentrate on particular debugging tools, we focus upon easing the process of actually developing tools. Our goal is to supply a collection of routines which can be used by PHIGS programmers to create custom tools or other programs which require access to the graphics data of remote PHIGS processes. Our Tool Development Library provides the PHIGS programmer a small number of management routines which orchestrate the connection and mapping to the data of one or more remote PHIGS applications. Manipulation of remote PHIGS structures is accomplished just as easily as local operations and is performed using standard PHIGS calls. The remote application being accessed requires no changes to its source code. Obvious uses for the Tool Development Library are in the construction of PHIGS tools such as structure browsers, editors and debugging aids. Less obvious is the potential for developing collections of cooperating graphics applications which share graphics data.