基于IPSec隧道区分服务的研究与实现

随着Internet及网络经济的快速发展，企业在网络的安全性等方面提出了更高的要求，虚拟专用网(VPN)以其安全性好、成本低等优势赢得了越来越多企业的青睐。IP层安全协议(IPSec)能很好地实现VPN。但是基于IPsec的VPN的网络服务质量不能满足用户的需求。针对此问题,文章提出了用区分服务(DiffServ)来实现IPSec隧道的服务质量保障的方案，这样IPSec隧道就可以根据不同的需求提供不同的网络性能。文章深入研究了区分服务和IPSec隧道技术，通过实验进一步证明了该方案的可行性和优势。     

IEEE 80211e中基于自适应信道预留的接纳控制算法*

为了在WLAN标准IEEE 802.11e中高效、高质量地传输各类业务,以及保证业务之间的公平性,提出一种基于自适应信道预留的接纳控制算法。算法中首先采用资源共享的方法提前为业务预留适当的信道资源,使用信道利用率作为接入准则,当网络资源不足时采用自适应地调节已经接入业务流的服务质量来满足新请求的业务流的服务质量需求。结果表明,该算法保证了各业务之间的公平性以及服务质量需求,而且最大程度地接入了更多的业务流,提高了网络的整体性能。     

IPsec和MPLS VPN的集成技术与远程教育网的设计

IPsec在用户端设备使用封装或加密技术,在公共网络上建立安全的隧道连接,将VPN功能都集成在CPE设备之中,管理维护费用高,传输效率较低;而MPLS相比传统VPN而言具有更高性价比,使用该技术构建的专用网络,能够保证很好的传输性能和服务质量.通过分析IPsecVPN和MPLSVPN的技术特点,将二者的优势结合起来,设计了一个适合远程教育的网络方案.该方案既具有IPsec的安全性、伸缩性,又具有MPLS的简洁高效,能较好地支持远程教育的网络课程、试题库、教学管理、在线考试等不同需求.     

利用运动强度自适应传输视频内容

在异构的网络环境下,如何自适应地传输满足多种终端设备和不同用户需求的视频内容具有重要的意义.以达尔文流媒体服务器为实验平台,提出一套基于运动强度的视频自适应传输策略.在服务器端通过检测丢包率来控制发送速率等级,避免网络拥塞,并采取一定策略消除因丢帧而产生的马赛克;在自适应策略中加入了运动强度信息,针对不同的运动强度级别进行不同的处理,使得综合视频质量得到提高.实验结果表明,文中的自适应策略不仅可以避免网络拥塞,而且可以改善视频播放质量.     

信息分发管理仿真系统的设计与实现

针对无线通信网络的服务质量(QoS)和网络拥塞问题,设计基于虚拟覆盖网技术的信息分发管理仿真系统。分析机动环境下无线通信的需求,通过在应用层建立虚拟覆盖网络,实现网络状态感知、QoS路由计算、业务传输优化等关键功能,并在OMNeT++仿真环境下进行系统实现。评测结果表明,该系统能提高无线通信网络的业务传输性能。     

基于自适应神经-模糊推理的计算机网络性能评价研究

根据带宽、时延、丢包率3个网络关键性能指标,建立了网络性能评价的自适应神经-模糊推理系统.通过对网络不同业务服务质量进行分析,实现了在给定输入负载下对网络性能的判定.仿真结果表明,建立的自适应神经-模糊推理系统能描述网络性能指标和输出的映射规律,能较准确的拟和数据,评价结果符合规律.因此,该方法合理有效,能够为网络信息传输提供决策支持.     

基于MPEG-4的视频流传输框架

视频的实时传输存在带宽、传输延迟、包丢失率等方面的要求,而当前的Internet环境下未提供任何QoS(服务质量)服务,所以一个有效的视频传输系统必须自适应于网络状况的动态变化。在充分发掘MPEG-4特性的基础上,该文构造了一个基于MPEG-4的视频流传输框架。通过使用带宽预测、自适应速率调整、SFEC纠错、错误隐藏等机制使视频的传输能够自适应于网络状况的动态变化。同时,提出了一种基于优先级的速率调整算法,克服了传统基于R-D理论的速率调整算法对媒体源支持单一的缺点。试验结果表明,该系统在低比特率、网络状况动态变化的环境中能取得良好的视频传输效果。     

基于SDH城域网混合组网保护方案的研究

传统的SDH传输网络主要用于语音服务,目前以太网的数据带宽需求缺乏可扩展性和灵活性的要求主流网络,特别是在网络故障,带宽服务质量的需求更难于得到满足.基于这些原因,研究一种基于SDH城域网网络保护方案,使得其在网络出现故障时能很好的切换,并且尽量占到相对低的带宽.     

信息决策中的优先性能需求和体系结构分析

针对美国国防部(Department of Defense,DoD)建立在安全服务基础上的优先和取代技术需求性能特性进行了全面的分析;一方面在语音网络通信中,基于安全服务基础上的优先特性(Precedence-Based Assured Service,PBAS)的实现是通过使用多层优先和取代(Multilevel Precedence and Preemption,MLPP)完成的,目的就是使重要信息在网络中顺利传输;二是在GIG网络技术中,PBAS性能特性必须在所有的网络应用中进行扩展,而且也必须在基于IP基础上的服务质量体系结构中应用;首先,主要对IP基础上的传输网络的PBAS性能特性的技术需求和体系结构的选择进行了分析;其次,对基于技术需求基础上的体系结构、工程设计和操作使用三者之间的选择和折中方案进行了讨论;结果表明,在GIG网络体系结构中,折衷方案的选择对于支持PBAS性能特性具有一定的指导意义。     

QoS需求驱动的服务配置框架

为支持服务质量敏感的基于组件的分布式应用的开发,中间件需要为组件提供并配置各种服务质量服务的非功能性属性.目前的组件架构提供的服务配置方式大多是静态的,且没有考虑不同客户的需求.在对EJB架构进行研究的基础上,提出一种服务质量需求驱动的服务配置框架.研究了根据客户的服务质量需求,在组件实例级别自动生成服务配置决策并实施,实现对不同客户服务差分处理.框架是一个基于服务配置的决策模型,通过多选择背包问题生成服务配置策略.最后通过一个应用实例对框架进行了验证.     

Web服务器负载均衡的研究

目前的WWW负载均衡大多是通过分布式Web服务器的设计来实现的。而分布式Web服务器设计中的传统技术依赖于对中心资源的操纵（如路由器或DNS服务器）。本文是对目前负载均衡技术存在问题解决方案的进一步研究,研究的目的是探索基于应用的负载均衡Web服务器（Application Based Load Balancing Web Server),避免中心资源形成系统瓶颈。     

Performance Evaluation of a Hybrid Run-Time Management Policy for Data Intensive Web Sites

The issues of performance, response efficiency and data consistency are among the most important for data intensive Web sites. In order to deal with these issues we analyze and evaluate a hybrid run-time management policy that may be applied to data intensive Web sites. Our research relies on the performance evaluation of experimental client/server configurations. We propose a hybrid Web site run-time management policy that may apply to different Web site request patterns and data update frequencies. A run-time management policy is viewed as a Web page materialization policy that can adapt to different conditions at run-time. We define a concept that we have named the Compromise Factor (CF), to achieve the relationship between current server conditions and the materialization policy. The issue of Web and database data consistency is the driving force behind our approach. In some cases though, we prove that certain compromises to consistency can be beneficial to Web server performance and at the same time be unnoticeable to users. We first present a general a comparative cost model for the hybrid management policy and three other related and popular Web management policies. We then evaluate the performance of all the approaches. The results of our evaluation show that the concept of the CF may be beneficial to Web servers in terms of performance.     

Web服务器集群请求分配和选择的性能分析

讨论并提出了 Web服务器集群的请求分配和选择控制方案 ,而且提供了这些方案的随机高级 Petri网模型 ,并强调研究这些方案及性能模型和分析方法 .为解决模型状态空间爆炸问题 ,作者提出了一种近似性能分析技术 ,可以显著地简化模型求解的复杂性 .文中的 Web服务器集群模型、请求分配和选择控制方案及近似性能分析技术可以应用于这类复杂系统的性能评价 .     

Web服务器性能评测

Web服务器性能评测是一种理解Web服务器对不同负载反应能力的方法，它对Web服务器的容量规划和性能增强有很大的帮助。讨论了Web服务器性能评测的原理、方法、难点及解决方案，介绍了基于Web负载的特点、ON／OFF源模型及浏览器／服务器体系结构，开发了一个Web服务器性能评测工具－WSBench。WSBench产生渐近自相似的HTTP请求序列，从静态文档、动态文档（没有数据库存取）、动态文档（有数据库存取）及前三者根据Zipf法则的组合4个层次来评测Web服务器的性能。性能测试结果表现为每秒请求数、每秒字节数和往返时间3个指标。最后讨论了Web服务器性能问题及使用WSBench测得的指标来建议Web服务器性能增强可以采用的方法。     

基于静、动态内容分离的Web应用性能优化技术的研究

从目前Web领域的发展状况出发,简要介绍了基于J2EE架构的Web应用的体系结构。讨论了当前主流的将静态和动态内容都部署在应用程序服务器上的部署方式,并在此基础上对Web服务器和应用程序服务器之间划分文件的部署方式进行了研究,提出了通过静、动态分离来提高Web应用效率的新思路。最后IBMHTTPServer+WebSphereApplicationServer为例对这两种方式的执行效率进行了分析和比较。     

Measuring the capacity of a Web server under realistic loads

The World Wide Web and its related applications place substantial performance demands on network servers. The ability to measure the effect of these demands is important for tuning and optimizing the various software components that make up a Web server. To measure these effects, it is necessary to generate realistic HTTP client requests in a test‐bed environment. Unfortunately, the state‐of‐the‐art approach for benchmarking Web servers is unable to generate client request rates that exceed the capacity of the server being tested, even for short periods of time. Moreover, it fails to model important characteristics of the wide area networks on which most servers are deployed (e.g., delay and packet loss). This paper examines pitfalls that one encounters when measuring Web server capacity using a synthetic workload. We propose and evaluate a new method for Web traffic generation that can generate bursty traffic, with peak loads that exceed the capacity of the server. Our method also models the delay and loss characteristics of WANs. We use the proposed method to measure the performance of widely used Web servers. The results show that actual server performance can be significantly lower than indicated by standard benchmarks under conditions of overload and in the presence of wide area network delays and packet losses. This revised version was published online in August 2006 with corrections to the Cover Date.     

基于嵌入式Web服务器的数据监控系统设计

利用ARM开发平台,设计了基于嵌入式Web服务器的数据监控系统方案,实现了一个具体基于串口的数据监控系统.该系统选择Boa服务器作为HTTP服务器,通过串口采集数据实时显示在用户浏览器上,并且可动态修改数据由串口发送到外部设备.     

Web content adaptation to improve server overload behavior

This paper presents a study of Web content adaptation to improve server overload performance, as well as an implementation of a Web content adaptation software prototype. When the request rate on a Web server increases beyond server capacity, the server becomes overloaded and unresponsive. The TCP listen queue of the server's socket overflows exhibiting a drop-tail behavior. As a result, clients experience service outages. Since clients typically issue multiple requests over the duration of a session with the server, and since requests are dropped indiscriminately, all clients connecting to the server at overload are likely to experience connection failures, even though there may be enough capacity on the server to deliver all responses properly for a subset of clients. In this paper, we propose to resolve the overload problem by adapting delivered content to load conditions to alleviate overload. The premise is that successful delivery of a less resource intensive content under overload is more desirable to clients than connection rejection or failures.The paper suggests the feasibility of content adaptation from three different viewpoints; (a) potential for automating content adaptation with minimal involvement of the content provider, (b) ability to achieve sufficient savings in resource requirements by adapting present-day Web content while preserving adequate information, and (c) feasibility to apply content adaptation technology on the Web with no modification to existing Web servers, browsers or the HTTP protocol.     

Keta中的Socket复用技术

随着信息技术的不断发展,提高Web服务器的性能是个亟待解决的问题。内核级Web Server的实现有效地提高了Web服务器的处理能力。然而,目前的内核级Web服务器通常只处理静态请求,而动态请求需要转发到外部传统Web服务器上进行处理。本文针对一种内核级非对称多线程流水线服务器——Keta,研究并改进了动态请求的转发机制,提出了利用Socket复用技术来实现转发的策略,有效地提高了该服务器的效率。     

Architecture of a Web server accelerator

We describe the design, implementation and performance of a high-performance Web server accelerator which runs on an embedded operating system and improves Web server performance by caching data. It can serve Web data at rates an order of magnitude higher than that which would be achieved by a high-performance Web server running on similar hardware under a conventional operating system such as Unix or NT. The superior performance of our system results in part from its highly optimized communications stack. In order to maximize hit rates and maintain updated caches, our accelerator provides an API which allows application programs to explicitly add, delete, and update cached data. The API allows our accelerator to cache dynamic as well as static data. We describe how our accelerator can be scaled to multiple processors to increase performance and availability. The basic design alternatives include a content router or a TCP router (without content routing) in front of a set of Web cache accelerator nodes, with the cache memory distributed across the accelerator nodes. Content-based routing reduces cache node CPU cycles but can make the front-end router a bottleneck. With the TCP router, a request for a cached object may initially be sent to the wrong cache node; this results in larger cache node CPU cycles, but can provide a higher aggregate throughput, because the TCP router becomes a bottleneck at a higher throughput than the content router. We quantify the throughput ranges in which different designs are preferable. We also examine a combination of content-based and TCP routing techniques. In addition, we present statistics from critical deployments of our accelerator for improving performance at highly accessed Sporting and Event Web sites hosted by IBM.