大型网络文件分发技术探析

以较为流行的网络文件下载软件BitTorrent为例,探讨基于对等网技术的分布式模式下文件分发的工作原理,并采用简单而有效的算法实现了大型文件的高效和可靠下载。     

基于PDNS的BitTorrent算法仿真研究

采用数据包级并行分布式仿真工具对典型BitTorrent算法进行大规模仿真,研究大规模P2P下载算法性能,并介绍其建模方法,模拟并行分布式网络仿真器平台下具有可扩展性框架的BitTorrent算法。实验结果表明,该方案能够有效测试多机仿真分层拓扑中典型用户行为的算法性能,且是有效的。     

基于BitTorrent的P2P安全模型的设计

本文以基于BitTorrent的P2P安全模型设计为研究对象,从基于BitTorrent的P2P安全模型设计原则、设计结构框架这两个方面入手,对其做出了详细说明,在此基础之上侧重从基础安全服务层以及综合安全服务层这两点针对基于BitTorrent系统安全模型的设计作业进行了分析与研究,据此论证了BitTorrent在P2P网络安全建设与安全管理中深远的应用意义与价值。     

基于Krylov子空间投影法的MEMS宏建模方法

基于Krylov子空间投影法结合有限元分析(FEA)建立了一种宏模型提取方法,以便能够在系统级快速地建立器件宏模型.这种方法通过对整个2D或3D器件有限元分析的结果提取宏模型.基于这种方法建立的宏模型具有计算代价低、精度合适的特点,而且能方便地插入到系统级仿真器进行仿真.文中通过一个谐振器结构阐释了这一方法,并且针对所建立的谐振器结构宏模型进行了精确性验证.     

BitTorrent模型的信任机制研究

BitTorrent下载模型得到普遍的应用,但节点缺乏控制,存在虚假资源等安全性问题。针对BitTorrent下载模型的特点,分析了BitTorrent模型的安全问题所在及已有的BitTorrent安全防范机制,结合P2P技术中的信任模型思想,改进BitTorrent安全机制,优化文件的拆分和整合算法,提高下载资源的成功率。仿真实验表明,与传统BitTorrent下载模型相比,改进后的模型能较快发现网络中的虚假资源,具有更高的下载成功率。     

Z80在线仿真器

在IBM PC机上实现的Z80在线仿真器.该仿真器以CP/M80操作系统为运行环境,配有CP/M80支持的Z80宏汇编程序、链接程序及仿真调试程序.     

BitTorrent种子覆盖网络模型

本文分析了BitTorrent文件系统的工作流程,指出了系统在路由方式上的缺点。介绍了覆盖技术,详细分析了弹性网络覆盖技术,说明了其路由选择的灵活性。提出了一种BitTorrent种子覆盖网络模型,将弹性网络覆盖技术引入BitTorrent文件系统,使得BitTorrent文件系统能够依据端用户和应用程序的需求灵活选择路由,有效改善了BitTorrent网络性能。     

BitTorrent系统中瞬间拥挤阶段建模与分析

BitTorrent是目前最流行的P2P内容分发系统之一.使用Kermack-Mckendrick模型对BitTorrent系统中瞬间拥挤(Flash-Crowd)阶段进行建模,研究了系统节点数及服务能力在瞬间拥挤阶段的发展演化过程.与原有模型相比,Kermack-Mckendrick模型能更好的吻合观测数据.最后结合BitTorrent系统的实际特点,给出提高BitTorrent系统处理瞬间拥挤能力的可行方案,如增加初始种子数量,减少文件段的大小,增加激励策略等.     

面向对等网信息语义共享的元数据模型框架研究

对等网系统作为一种新型的信息共享模式，往往缺乏对信息语义管理的支持。本文提出了一种基于对等网的信息资源语义共享系统框架，重点对其一体化元数据描述模型进行了设计，结合本体和对等网的相关特征对分布、异构信息资源的语义和相关管理元素进行了封装，并且从元数据知识库的构建、查询处理和信任机制几个方面介绍了元数据摸型的工作机制及关键问题。     

MEMS降阶宏模型仿真平台研究

随着MEMS系统级设计成为研究的热点,MEMS系统级CAD的开发日益重要.论文介绍了一种基于降阶宏模型MEMS系统级仿真平台,通过有限元方法提取MEMS器件几何物理数据.建立MEMS器件有限元模型.利用Krylov子空间算法缩聚自由度建立宏模型,通过系统级仿真平台对此进行系统级仿真. 整个流程通过VC++编译器调用ANSYS、嵌入封装的算法动态链接库、集成SIMULINK系统仿真器完成.并用双端固支梁实例对所有模块加以验证,仿真结果准确,计算效率较高.     

度量和分析BitTorrent

BitTorrent是一个用于内容分发的P2P协议,现在已经发展成为互联网的一项重要的应用.从性能的角度度量BitTorrent的行为,解释BitTorrent协议的关键元素,分析BitTorrent是否是高效的.1)提出一种有效度量BitTorrent式的P2P内容分发协议的仿真实验方法;2)确认BitTorrent协议的Neighbor Selection,Choking/Unchoking和Piece Selection机制存在诸多影响系统性能的缺陷;3)设计ShareStorm协议,作为参照对象,证明BitTorrent的缺陷在协议层可以避免.经仿真实验验证,在下载完成时间这个最主要的性能指标上,ShareStorm比BitTorrent至少减少50%.     

一种基于Netfilter的BitTorrent流量控制方法

BitTorrent是目前互联网上广泛使用的一种基于P2P的文件共享协议。它使用了动态端口,这给BitTorrent流量控制带来了很大的困难。该文在分析BitTorrent协议基础上,给出了一种基于应用层特征匹配的BitTorrent流量控制方法。首先提取出BitTorrent流的应用层特征,利用Linux的Netfilter/Iptables扩展架构实现数据包的应用层特征匹配。并利用TC实现对它的流量控制。     

基于访问控制列表的BitTorrent流量控制策略

BitTorrent是近年来使甬很广泛的一种基于P2P结构的文件共享应用。从客户端，Tracker服务器和元信息文件结构几个方面详细分析了BitTorrent协议。针对目前BitTorrent应用侵占大量带宽的问题，给出了一种基于访问控制列表的解决方案。通过在校园网中的实践证明该方案能有效地限制BitTorrent流量。     

BitTorrent协议Choking／Unchoking机制的度量和分析

BitT0rrent是一个用于内容分发的P2P协议,现在已经发展成为互联网的一项重要的应用.本文从性能的角度,度量BitTorrent的行为,解释BitTorrent协议的关键元素,分析BitTorrent是否是高效的.本文有以下贡献:①提出一种有效度量BitTorrent式的内容分发协议的方法.②确认BitTorrent的Choking/Unchoking机制存在缺陷,不是高效的.③设计ShareStorm协议,证明BitTorrent的缺陷可以避免.经初步验证,在下载完成时间这个最主要的性能指标上,ShareStorm比BitTbrrent至少减少50 %.     

基于BitTorrent的激励机制的研究与改进

BitTorrent系统面临着严重的搭便车问题。研究BitTorrent系统的搭便车问题及其激励机制,对P2P文件共享系统有重要意义。介绍当前BitTorrent系统激励机制的研究现状,分析BitTorrent文件共享系统的搭便车现象及其激励机制,提出了一个种子带宽分配策略。通过模拟实验实现了该策略,并分析了模拟实验的结果。     

Measurement,modeling and enhancement of BitTorrent-based VoD system

BitTorrent is one of the most popular Peer-to-Peer (P2P) applications for file sharing over the Internet. Video files take up a large proportion of space among the BitTorrent shared files. Recently, BitTorrent has attracted researchers’ interests, as an alternative method of providing video on demand (VoD) service. In this paper, we concentrate on enabling BitTorrent to support VoD service in existing swarms while maintaining the download efficiency of file-sharing users. We first examine the content properties of the BitTorrent system to explore the demands and challenges of VoD service in BitTorrent swarms. The efficiency of BitTorrent for various piece selection policies is then compared through measurement on PlanetLab. We also use an optimization mathematical model to analyze the hybrid BitTorrent system in which downloading peers and streaming peers coexist. Both measurement results and model analysis indicate the problem of system efficiency decline in the BitTorrent-based VoD systems, in comparison with the original BitTorrent file-sharing system. Our proposed approach, unlike existing strategies that are limited to changing the piece selection policy to allow BitTorrent to support streaming services, modifies both piece and peer selection policies to provide a “streaming while downloading” service in the BitTorrent system with downloading peers. For the peer selection policy, a CAP (Closest-Ahead Peers) method is applied to make better use of the peers’ upload bandwidths. For the piece selection policy, a sliding window-based hybrid method that combines the rarest-first policy with the sequential policy is proposed. To demonstrate the performance of our proposed approach, an evaluation is made using various metrics on PlanetLab. The results show that our proposed method has higher throughput and better streaming continuity than the sequential policy and BiToS.     

一种基于Netfilter的BitTorrent流量测量方法

BitTorrent是目前互联网上广泛使用的一种基于P2P的文件共享协议。它使用了动态端口，这给BitTorrent流量的准确测量带来了很大的困难。本文在分析BitTorrent协议基础上，给出了一种基于应用层特征匹配的BitTorrent流量测量方法。首先提取出BitTorrent流的应用层特征，利用Linux Netfilter／Iptables扩展架构实现数据包的应用层特征匹配。将TCP流分成了BitTorrent流和非BitTorrent流，对BitTorrent流进行统计。实验表明，该方法能实时准确地测量BitTorrent流量。     

Locality-Awareness in BitTorrent-Like P2P Applications

This paper presents the measurement study of locality-aware P2P solutions over real-world Internet autonomous systems (AS) topology. By using the accesses of nodes of PlanetLab testbed, we create a detailed AS-level map including the end-to-end path of all nodes, as well as the relationship of all involved ASes. Based on this map, we evaluate the performance of a set of locality-aware P2P solutions, including an optimal solution guaranteeing the minimum AS hop count, as well as modified BitTorrent system with locality-awareness built into its neighbor selection, peer choking/unchoking, and piece selection processes. Our findings suggest that locality-awareness can help existing P2P solution to significantly decrease load on Internet, and achieve shorter downloading time. By comparing the performance of different kinds of locality-aware and traditional BitTorrent systems, we also point out the necessity to tradeoff between the goals of optimizing AS-related performance and achieving fairness among peers such as intra-AS traffic and peer burden fairness.      

Understanding BitTorrent: A reality check from the ISP’s perspective

During the last decade, Peer-to-Peer (P2P) applications have been one of the dominant components of Internet traffic. Understanding BitTorrent, by far the most popular P2P protocol for data distribution, is extremely valuable to shed some light on the nature of distributed systems. This paper surveys the existing measurement studies and sets out to verify the acquired corpus of knowledge about BitTorrent by analyzing the largest and most comprehensive data-set so far. We collected BitTorrent traffic at four major European ISPs during 2009 and 2010, a vantage point not yet exploited by previous measurement studies. Our analysis puts into perspective and corroborates several well-known findings, such as that: (1) 20% of the most popular torrents represent more than 95% of the BitTorrent activity, (2) only 1–3% of the BitTorrent traffic stays local, i.e., within an ISP, (3) 4–44% of the BitTorrent traffic could be localized using appropriate locality-awareness techniques, and (4) about 20% of downloads get stalled due to scarcity of content pieces.