基于最小竞争窗口的IEEE 802.11区分服务机制及其性能分析

针对无线adhoc网络不能提供数据流优先级区分的问题,本文提出了一种基于802.11DCF退避算法的改进机制,该机制通过设置不同的MAC层最小竞争窗口来实现数据流的区分服务,使发送高优先级数据流(如实时数据流)的节点更容易连接信道,从而使高优先级数据流占有更多带宽资源。数学分析表明,该策略能有效的提高高优先级数据流的传输性能。     

基于网络距离度量和分簇的P2P流量控制

针对BitTorrent(BT)系统中对等连接消耗大量骨干网络带宽导致网络拥塞的问题,提出基于网络距离度量和网络分簇的节点分配策略。仿真实验表明,在不影响BT客户端下载性能的情况下,该分配策略能够将更多的数据流量限制在网络簇内部,提高数据流量的局部性,有效地减少BT系统对骨干网络带宽的消耗。     

无线多媒体传感器上的高效的多宿主传输系统

对多媒体传感器网络中的实时视频传输来说,高效而可靠的通信是十分重要的。但是在实际条件下,当传感器向汇聚节点传输数据时,由于带宽的限制及传输链路不稳定等原因,传感器与汇聚节点之间的链接通常会变得不稳定。不稳定数据传输会影响传感器节点的正常数据传输,甚至会导致传感器节点无法与汇聚节点通信。这些问题让使用多媒体传感器网络的用户产生了较差的用户体验。为了解决这些问题,为无线多媒体传感器设计了一个全新的多宿主(multi-homed)多连接系统,并实现了原型系统。该系统的优势主要体现在以下三方面:(1)能够让多媒体传感器同时与多个汇聚节点(服务器)进行通信的系统架构;(2)能够适应多样的Wi-Fi环境和应用场景的多宿主传感器传输协议;(3)后续的实验结果也证明了该系统和协议可以提高多媒体数据传输的可靠性。与传统的单宿主(single-homed)连接模式相比,该系统能够在相同的带宽、内存和CPU资源限制下保持更加稳定的连接。     

新软物语

带宽就要平均分:NetLimiter问:我们几个室友,一起申请了ADSL,结果有一个人特别喜欢用BT下载,占用了所有带宽,我们又不好说他什么,请问有没有可以限制带宽的软件呢?软件版本:1.30答:很简单,使用NetLimiter就能解决你软件大小:542KB的问题,该软件用来专门限制带宽上限,它可软件性质:共享软件(28天使用限制)适用平台:Windows9x/2000/XP以为不同软件设置不同带宽上限,只要将这下载地址:http://www.netlimiter.com/款软件分别安装到宿舍里的每一台电脑上,download/nl_v130.exe并设置好限制带宽即可。安装软件并重启后,软件会自动运行并弹出…     

P2P网络中自适应节点选择策略

以Bittorrent应用为背景,对P2P网络中传统的节点选择策略进行了研究分析,指出了传统节点选择策略中存在的随机选择节点连接与交互以及交互过程中节点带宽利用率偏低的问题.对Tracker以外的节点来源如DHT、PEX节点来源的情况进行分析,以自身上传带宽利用率和网络中各节点的空闲带宽为参考,以减少带宽资源浪费、提高带宽利用率为目的.针对节点选择各阶段特点,设计并实现自适应节点选择机制,实验表明在对原系统的公平性影响很小的情况下,自适应机制能有效的减少网络中带宽资源浪费并将自身上传节点带宽利用率提高8.45％.小规模节点环境下(100节点)平均缩短节点下载完成时间6.7％,大规模下载环境下(500节点)平均缩短下载完成时间36.3％.有效的提高了系统中文件的获得和分发效力.     

P2P视频直播数据调度算法

P2P技术解决了传统流媒体应用中的不能支持大用户的问题.而数据调度算法一直是P2P研究中的热点问题.在给出了P2P视频直播系统中节点能力的定义和计算方法后,结合BT中的Rarest First策略,提出了一种基于节点能力的适用于P2P视频直播系统的数据调度算法.该算法既考虑了流媒体数据具有时间限制的特性,同时也考虑了如何能充分的利用节点的上传带宽,增进了系统的负载平衡.     

基于内容分组与能力匹配的邻居选择算法

邻居选择算法是影响P2P文件共享系统的整体吞吐量和带宽利用率的关键技术之一.目前BT类P2P文件共享系统中的一些常用邻居选择算法一般存在着邻居节点间的内容可交换性差和带宽利用率低等问题.提出一种新的邻居选择算法,将节点按内容分组,由节点上报的上传、下载的字节数计算出带宽能力,让能力匹配的节点成为邻居.计算机仿真实验表明,新算法显著地提高文件共享系统的整体吞吐量,减少用户的平均下载时间,从而有效地改善P2P文件共享系统的整体性能.     

使用移动终端作为SINK节点的无线传感器网络

无线传感器网络由传感器节点,接收发送器(SINK),因特网以及用户管理节点组成.传感器节点通过SINK节点与因特网进行交互.在目前的无线传感器网络中,SINK节点是固定的,而且多采用有线的方式与因特网进行连接,这种方式已经限制了无线传感器网络的发展,这时需要一种具有良好移动性的SINK节点来为网络服务.本文提供了一种将移动终端与SINK节点相结合的实现方法,并且通过这种结合实现了将通信网和无线传感器网络结合起来.     

一种适用于数据网格环境的节点管理策略

针对数据网格的需求,将系统中的节点根据管理域以及网络邻近特性进行组织,同时,根据管理的需求以及节点自身的处理能力,将其组织成为一个分层同构的体系结构.加入系统中的节点粒度可以任意调整,而粗粒度的节点内部对于系统中其他节点是透明的,提高了系统的灵活性,并提高了系统的可扩展性与可管理性.系统中的节点之间根据不同的数据访问规则构成一个多层次、跨管理域的分布式合作缓存,从而降低了主干网带宽的压力.     

利用NBAR来禁止或限制BT流量

Bittorrent是一种点对点的在客户端之间共享各种资源的软件,简称BT。用户无限制地使用该软件,会造成带宽的极大浪费,影响正常的网络使用。因为BT的端口可以很容易的改变,所以通过限制端口来限制BT使用是不大可行的。本文讲述是如何在Cisco路由器上通过NBAR来限制或禁止BT流量。     

利用路由索引技术提高Gnutellar的性能

Gnutella,这是目前应用比较广泛的peer-to-peer网络,但因为它的分布特性,寻找信息是通过广播方式向邻近结点传输的,使得网络带宽被大量浪费.针对这个问题引入路由索引RI(Routing Indices)技术,它允许结点将搜索信息转发到最有可能回复的邻居结点,免去了广播造成的带宽浪费,使得它很可能成为未来P2P的主流协议.     

Downloading trace study for BitTorrent P2P performance measurement and analysis

With the increasing client population and the explosive volume of Internet media content, the peer-to-peer networking technologies and systems provide a rapid and scalable content distribution mechanism in the global networks. The BitTorrent protocol and its derivatives are among the most popular peer-to-peer file sharing applications, which contribute a dominant fraction of today??s Internet traffic. In this paper, we conduct the performance measurement and analysis of BitTorrent systems with an extensive volume of real trace logs. We use several downloading-side metrics, including overall downloading time, maximum of downloading bandwidth, average bandwidth utilization, maximum of downloading connections, and average number of active connections, to derive various interesting results from the downloading-side aspect of network resource usage. Performance examination learns many new observations and characteristics into the virtue of BitTorrent protocols and systems, thereby providing beneficial information for bandwidth allocation and connection control in BitTorrent client applications. Therefore, this study is complementary to many previous research works that mainly focused on system-oriented and uploading-side performance measurements.     

基于网络编码的对等网流媒体传输模型和算法

在对等网(peer-to-peer,简称P2P)流媒体系统中,节点(用户)的输出带宽(上行带宽)容量利用率的提高能够降低服务器的带宽开销.网络编码可以实现组播的最大吞吐率,因而具有提高系统中节点输出带宽容量利用率的潜力.将随机线性网络编码应用到P2P流媒体系统中,建立了基于随机线性网络编码的P2P流媒体传输过程模型,并据此建立传输算法的优化模型,比较研究了贪婪式算法、最少者优先算法和随机算法等.优化结果表明,随机算法可以平等均匀地获取数据包,能够最充分地利用节点的输出带宽容量,降低服务提供商的运营成本.通过对优化模型解的分析对实际系统中的传输算法给出了设计指导原则.     

基于Chord的合作浏览器Cache模型

浏览器cache能够有效降低网络带宽的需求，减少客户的等待时间。然而目前的浏览器cache之间并不能够共享对象，导致数据的重复利用率不高，网站的负载无法得到均衡。P2P（peer-to—peer）技术的基本思想就是希望能够平等处理所有节点，借助节点间的互助实现文件交换、分市计算等功能。在Chord协议及其算法的基础上，提出了一种合作型浏览器cache模型，实现对象的共享，并且通过日志驱动的仿真实验对该模型的节点存储、外部带宽占用和cache命中率以及延迟等指标进行了性能评估。结果和分析显示该模型在这些指标上取得了一定的提高，比如命中率和响应时间，而没有占用更多节点的资源。     

Building resilient low-diameter peer-to-peer topologies

As more applications rely on underlying peer-to-peer topologies, the need for efficient and resilient infrastructure has become more pressing. A number of important classes of topologies have emerged over the last several years, all with various strengths and weaknesses. For example, the popular structured peer-to-peer topologies based on distributed hash tables (DHTs) offer applications assured performance, but are not resilient to attacks and major disruptions that are likely in the overlay. In contrast, unstructured topologies where nodes create random connections among themselves on-the-fly, are resilient to attacks but can not offer performance assurances because they often create overlays with large diameters, making some nodes practically unreachable. We propose Phenix, a peer-to-peer algorithm for building resilient low-diameter peer-to-peer topologies that can resist different types of organized and targeted malicious behavior. Phenix leverages the strengths of these existing approaches without inheriting their weaknesses and is capable of building topologies of nodes that follow a power-law while being fully distributed requiring no central server, thus, eliminating the possibility of a single point of failure in the system. We present the design and evaluation of the algorithm and show through extensive analysis, simulation, and experimental results obtained from an implementation on the PlanetLab testbed that Phenix is robust to network dynamics such as bootstrapping mechanisms, joins/leaves, node failure and large-scale network attacks, while maintaining low overhead when implemented in an experimental network.     

An experimental analysis of Joost peer-to-peer VoD service

Despite strong interest in peer-to-peer (P2P) Video-on-Demand (VoD) services, existing studies mostly focus on peer-to-peer or overlay protocol design based on simulations under various topological constraints. We believe experimental studies on a real-life P2P VoD system will provide valuable information to ISPs, network administrators, and content owners. In this paper we present a comprehensive analytical and experimental study on Joost, one of the first commercial P2P VoD systems used for distributing various forms of video over the Internet. Our extensive experiments prove that Joost is a server-assisted peer-to-peer VoD system. With several envisioned typical scenarios we have further investigated the peer management in terms of time pattern, bandwidth consumption and locality considerations. Our major findings include: (1) the current Joost system is capable of providing high-quality VoD service through the use of an overlay network deployed with a set of centralized content servers; (2) inter-continental links are often used regardless of the number of local users, which may pose a high burden on the network providers; (3) easily reachable, high-capacity nodes are selected as main relaying nodes, similar to super nodes in Skype, to facilitate the traversal of symmetric NATs and firewalls. We also provide insights on the potential ways to construct more efficient P2P VoD systems (e.g. considering topological locality-awareness, using adaptive/layered video).     

Neighbor selection for proportional fairness in P2P networks

This paper analyzes reciprocation strategies in peer-to-peer networks from the point of view of the resulting resource allocation. Our stated aim is to achieve through decentralized interactions a weighted proportionally fair allocation. We analyze the desirable properties of such allocation, as well as an ideal proportional reciprocity algorithm to achieve it, using tools of convex optimization. We then seek suitable approximations to the ideal allocation which impose practical constraints on the problem: numbers of open connections per peer, with transport layer-induced bandwidth sharing, and the need of random exploration of the peer-to-peer swarm. Our solution in terms of a Gibbs sampler dynamics characterized by a suitable energy function is implemented in simulation, comparing favorably with a number of alternatives.     

Receiver-driven bandwidth sharing for TCP and its application to video streaming

Applications using Transmission Control Protocol (TCP), such as web-browsers, ftp, and various peer-to-peer (P2P) programs, dominate most of the Internet traffic today. In many cases, users have bandwidth-limited last mile connections to the Internet which act as network bottlenecks. Users generally run multiple concurrent networking applications that compete for the scarce bandwidth resource. Standard TCP shares bottleneck link capacity according to connection round-trip time (RTT), and consequently may result in a bandwidth partition which does not necessarily coincide with the user's desires. In this work, we present a receiver-based bandwidth sharing system (BWSS) for allocating the capacity of last-hop access links according to user preferences. Our system does not require modifications to the TCP protocol, network infrastructure or sending hosts, making it easy to deploy. By breaking fairness between flows on the access link, the BWSS can limit the throughput fluctuations of high-priority applications. We utilize the BWSS to perform efficient video streaming over TCP to receivers with bandwidth-limited last mile connections. We demonstrate the effectiveness of our proposed system through Internet experiments.     

带宽自适应的P2P网络路由协议

提出一种普适于各种系统环境和网络规模的结构化P2P网络协议SmartBoa.与已有的结构化P2P路由协议(如Pastry,Chord等)相比,SmartBoa结点并不维护同样大小的路由表,而是各结点根据自身的带宽能力决定其路由表的大小(最强的结点可能记录全部结点的指针,最弱的结点可能只记录其中不足1%的一小部分),算法保证路由表大小正比于维护开销,充分利用所有结点的可用带宽,使路由效率达到最优;另一方面,SmartBoa并不因为系统规模的增大而增加对结点带宽的要求,因此与全连通的one-hop overlay相比,SmartBoa可以获得更好的可扩展性;再者,SmartBoa结点根据系统环境的变化动态地调节自身级别,并且可以通过逐渐调高级别的慢启动方式来克服one-hop overlay的启动时间过长的缺陷.总之,SmartBoa是一种可以运行于任何环境,不受限于系统规模的大小、结点能力的强弱、强弱结点的比例、结点出入的频率,并通过动态调节保证路由效率的P2P路由协议,适用于各种广域分布式系统.     

无线传感网络任务分配的能效性控制策略

无线传感网络包含大量密集分布传感节点,各节点测量产生大量数据给传输、存储、管理和分析带来困难,无线传感网络能源不可更换性限制了网络寿命.本文提出基于熵理论和欧式距离的网络能耗评价指标,采用对等(peer-to-peer,简称P2P)计算方法,利用基于蚁群智能的能效性优化任务分配控制策略,针对中心节点工作状态、传输能耗和网络寿命实现动态实时任务控制分配,完成多中心节点并行计算,提高网络工作效率,节约能耗.实验表明基于蚁群智能的能效性任务分配控制策略能实时有效地缩短无线传感网络计算时间,减少网络能耗,提高网络寿命.