基于图多层K路划分的仿真节点映射策略

为了提高网络仿真系统中,多物理服务器情况下,服务器资源的利用率,提出一种基于图多层K路划分的仿真节点映射策略。首先对仿真网络拓扑图进行多层K路划分,将节点映射问题转化为图划分问题,然后依据划分结果将仿真节点映射到物理服务器。经过试验表明,相对于随机映射策略,该策略在保证物理服务器负载均衡的同时,可以有效减少物理服务器资源的消耗。     

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.     

基于热点内容的下载服务Web集群动态负载均衡

文中针对提供下载服务的Web集群，提出了一种新的负载均衡方案，通过对热点内容的动态冗余来提高整个集群的性能，使整个集群达到负载均衡，并由仿真实验和具体的实例验证了文中提出的方案，证明了该方案的实际效果。     

基于轻量级虚拟化的LDDoS仿真方法

低速率分布式拒绝服务(LDDoS)攻击是一种复杂的大规模网络攻击行为,已成为当前网络面临的严重安全威胁之一,建立仿真平台研究LDDoS攻防技术,可以提升仿真的逼真性且保证仿真规模。为此,基于轻量级虚拟化技术,提出一种针对BGP会话的LDDoS仿真方法,通过融合网络拓扑构建、攻击场景配置和采集与分析过程,搭建仿真体系架构,并给出该架构基于轻量级虚拟化技术的实现方法。实验结果表明,相比于GTNeTS和GNS3方法,该方法具有逼真性高、扩展性强和仿真规模大的优势,单物理服务器可构建具备400个路由节点规模的LDDoS仿真场景,可为大规模LDDoS的攻防策略研究提供仿真技术基础。     

Reducing bandwidth requirement for delivering video over wide area networks with proxy server

Due to the high bandwidth requirement and rate variability of compressed video, delivering video across wide area networks (WANs) is a challenging issue. Proxy servers have been used to reduce network congestion and improve client access time on the Internet by caching passing data. We investigate ways to store or stage partial video in proxy servers to reduce the network bandwidth requirement over WAN. A client needs to access a portion of the video from a proxy server over a local area network (LAN) and the rest from a central server across a WAN. Therefore, client buffer requirement and video synchronization are to be considered. We study the tradeoffs between client buffer, storage requirement on the proxy server, and bandwidth requirement over WAN. Given a video delivery rate for the WAN, we propose several frame staging selection algorithms to determine the video frames to be stored in the proxy server. A scheme called chunk algorithm, which partitions a video into different segments (chunks of frames) with alternating chunks stored in the proxy server, is shown to offer the best tradeoff. We also investigate an efficient way to utilize client buffer when the combination of video streams from WAN and LAN is considered.     

Predictive Prefetching on the Web and Its Potential Impact in the Wide Area

The rapid increase of World Wide Web users and the development of services with high bandwidth requirements have caused the substantial increase of response times for users on the Internet. Web latency would be significantly reduced, if browser, proxy or Web server software could make predictions about the pages that a user is most likely to request next, while the user is viewing the current page, and prefetch their content.In this paper we study Predictive Prefetching on a totally new Web system architecture. This is a system that provides two levels of caching before information reaches the clients. This work analyses prefetching on a Wide Area Network with the above mentioned characteristics. We first provide a structured overview of predictive prefetching and show its wide applicability to various computer systems. The WAN that we refer to is the GRNET academic network in Greece. We rely on log files collected at the network's Transparent cache (primary caching point), located at GRNET's edge connection to the Internet. We present the parameters that are most important for prefetching on GRNET's architecture and provide preliminary results of an experimental study, quantifying the benefits of prefetching on the WAN. Our experimental study includes the evaluation of two prediction algorithms: an n most popular document algorithm and a variation of the PPM (Prediction by Partial Matching) prediction algorithm. Our analysis clearly shows that Predictive prefetching can improve Web response times inside the GRNET WAN without substantial increase in network traffic due to prefetching.     

Web缓存技术的应用与研究

缓存技术是一种在本地存储经常访问的信息的方法。通过将普通的Web请求重定向到本地Cache服务器，减少WAN链路和Web服务器上的传输量，为ISP、企业网络及终端用户提供了较好的网络出口解决方案。     

一种基于半实物仿真的新型网络模拟模型研究

网络模拟是现代进行网络协议设计验证和测试普遍采用的方法,而半实物网络仿真是一种能够更直观精确地进行网络软硬件的验证与测试的新型技术。文章将介绍半实物网络仿真概念,阐述该仿真技术的原理,并基于半实物网络仿真的思想,与传统的网络模拟模型进行比较,提出了一种新型的网络模拟模型,探讨其实现技术。     

虚拟化与数字仿真融合的网络仿真任务划分

为提升网络仿真性能,面向虚拟化与数字仿真融合的网络仿真体系架构,研究相应的网络仿真任务划分方法。综合考虑虚拟化与数字仿真各自优势,将网络拓扑分为虚拟化拓扑区域与数字仿真拓扑区域,结合给定物理资源,以负载均衡与远程通信量最小化为目标,对两种区域进行融合划分。实验表明,通过该方法进行网络仿真任务划分相对于随机算法与均衡负载平衡算法,远程通信量分别平均降低33.7%,25.1%,负载均衡度分别平均提升56.3%,38.0%。该方法可有效降低远程通信量与提升负载均衡度。     

基于.NET的分布式网络管理软件框架

随着Intranet的发展,其本身的结构变得越来越复杂。传统的网络管理方式已经不适应当前的管理需求。文中提出了一个基于Microsoft.NET的分布式网络管理软件框架,在广域网环境下通过Web service通信。同时拥有客户端功能强和可以在广域网环境下轻松跨越防火墙的优点。     

Web服务器的过载模拟和性能测量

本文对典型Web服务器的过载机理进行了分析,并采用事件驱动和异步I/O技术设计和实现了一种高效Web服务器负载生成器aLoad,而且使用它对Apache Web服务器进行了过载模拟、性能测量和分析。通过对比实验表明,aLoad可产生大大高于传统性能评测工具的并发负载。     

Case of ARM emulation optimization for offloading mechanisms in Mobile Cloud Computing

The Mobile Cloud Computing (MCC) paradigm depends on efficient offloading of computation from the resource constrained mobile device to the resource rich cloud server. The computational offloading is assisted by system virtualization, application virtualization, and process state migration. However, system and application virtualization techniques force unnecessary overhead on applications that require offloading to the cloud and applications that do not. Moreover, smartphones and cloud data centers are based on heterogeneous processor architectures, such as, ARM and x86. As a result, process migrated from a smartphone needs translation or emulation on the cloud server. Therefore, instruction emulation is a necessary criterion for a comprehensive MCC framework. In this paper, we evaluate the overhead of the system and application virtualization techniques and emulation frameworks that enable MCC offloading mechanisms. We find that the overhead of system and application virtualization can be as high as 4.51% and 55.18% respectively for the SciMark benchmark. Moreover, ARM to Intel device emulation overhead can be as high as 55.53%. We provide a proof of concept of emulation speedup by utilizing efficient Single Instruction, Multiple Data (SIMD) translations. We conclude that the overhead of virtualization and emulation techniques need to be reduced for efficient MCC offloading frameworks.     

电信网脆弱性仿真实验平台模式的研究

搭建仿真实验平台是网络安全研究中重要的组成部分。针对电信网,对电信网脆弱性的仿真实验平台进行了研究,提出了仿真实验平台的功能要求,对仿真实验平台搭建模式进行了探讨,给出了一个仿真平台的搭建方法。     

Design a progressive video caching policy for video proxy servers

Proxy servers have been used to cache web objects to alleviate the load of the web servers and to reduce network congestion on the Internet. In this paper, a central video server is connected to a proxy server via wide area networks (WANs) and the proxy server can reach many clients via local area networks (LANs). We assume a video can be either entirely or partially cached in the proxy to reduce WAN bandwidth consumption. Since the storage space and the sustained disk I/O bandwidth are limited resources in the proxy, how to efficiently utilize these resources to maximize the WAN bandwidth reduction is an important issue. We design a progressive video caching policy in which each video can be cached at several levels corresponding to cached data sizes and required WAN bandwidths. For a video, the proxy server determines to cache a smaller amount of data at a lower level or to gradually accumulate more data to reach a higher level. The proposed progressive caching policy allows the proxy to adjust caching amount for each video based on its resource condition and the user access pattern. We investigate the scenarios in which the access pattern is priorly known or unknown and the effectiveness of the caching policy is evaluated.     

UNIX进程服务器

进程服务器是ＵＮＩＸ模拟系统中的一个重要服务器，本文介绍了怎样用Ｍａｃｈ提供的功能模拟ＵＮＩＸ的进程、与进程相关的操作和对信号的处理。     

A performance study of the Squid proxy on HTTP/1.0

This paper presents a performance study of the state‐of‐the‐art caching proxy called Squid. We instrumented Squid to measure per request network and disk activities and conducted a series of experiments on large Web caches. We have discovered many interesting and consistent patterns across a wide variety of environments. Our data and analysis are essential for understanding, modeling, benchmarking, and tuning performance of a proxy server. This revised version was published online in August 2006 with corrections to the Cover Date.     

基于交互式流量回放的用户行为仿真技术

流量回放可为网络靶场提供逼真的流量数据并支持网络新技术验证与安全评测。面向复杂虚拟网络的交互式用户行为仿真需求,设计一种交互式流量链路的用户行为仿真架构。采用基于云平台的分布式流量仿真策略,以实现面向复杂虚拟网络用户的行为仿真多样化和可扩展加载。对交互式流量回放过程中延时修复与补偿策略进行研究,提升交互式用户行为仿真的时序逼真性。仿真实验结果表明,该仿真架构能够在保证流量时序准确性的前提下,实现交互式的大规模用户行为仿真,与传统的ITRM、Tcpreplay等方法相比,在仿真行为的多样性、规模性、逼真性上具有一定优势,可为安全评测提供有效支撑。     

基于半实物网络仿真的包截获关键技术研究

半实物网络仿真是一种能够更直观精确地进行网络软硬件的验证与测试的新型技术。本文将介绍半实物网络仿真概念,并探讨该仿真技术的原理,重点研究在半实物网络仿真中涉及的网络包截获的核心实现技术,提出其基于Windows平台的实现框架。     

Netkit: network emulation for education

In the era of virtualization, virtual networking plays an important role. Besides production use, virtual networking can be effectively adopted in many other contexts where accurate emulation of functionalities is important, like testing before deployment, evaluation of what‐if scenarios, research, and, increasingly, didactics. In this paper, we describe our 10‐year experience in designing, implementing, using, and maintaining Netkit, an environment for simple, inexpensive, and lightweight network emulation targeted at didactics. We analyze the peculiar requirements in this context and discuss how the architecture chosen for Netkit is tailored to fulfill them. We show that Netkit is particularly well suited for a quick preparation of complex network scenarios comprising a wide range of networking technologies. These scenarios can be specified using configuration languages that are similar to those used on real devices and, once set up, can be easily distributed via email or published on the Web. Netkit comes with a rich set of ready‐to‐use pre‐configured networks, accompanied by lecture slides that enable users to immediately experiment with specific case studies. To complete the picture, we report our experience in supporting and fostering the growth of the community of users revolving around Netkit: more than 15 educational institutions worldwide take advantage of Netkit, allowing teachers and students to practice with realistic networks without the need of expensive laboratories. We also detail how we profitably use Netkit within advanced academic‐level networking courses and related examinations at the Roma Tre University. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis of task assignment policies in scalable distributedweb-server systems

A distributed multiserver Web site can provide the scalability necessary to keep up with growing client demand at popular sites. Load balancing of these distributed Web-server systems, consisting of multiple, homogeneous Web servers for document retrieval and a Domain Name Server (DNS) for address resolution, opens interesting new problems. In this paper, we investigate the effects of using a more active DNS which, as an atypical centralized scheduler, applies some scheduling strategy in routing the requests to the most suitable Web server. Unlike traditional parallel/distributed systems in which a centralized scheduler has full control of the system, the DNS controls only a very small fraction of the requests reaching the multiserver Web site. This peculiarity, especially in the presence of highly skewed load, makes it very difficult to achieve acceptable load balancing and avoid overloading some Web servers. This paper adapts traditional scheduling algorithms to the DNS, proposes new policies, and examines their impact under different scenarios. Extensive simulation results show the advantage of strategies that make scheduling decisions on the basis of the domain that originates the client requests and limited server state information (e.g., whether a server is overloaded or not). An initially unexpected result is that using detailed server information, especially based on history, does not seem useful in predicting the future load and can often lead to degraded performance