基于蚁群算法的P2P分发网返源规划

在P2P分发网中,返源策略是影响整个系统吞吐量和带宽利用率的关键技术之一.为了提高节点数据下载阶段的效率及系统总吞吐量,目录服务器需基于先前收集的信息并采用返源策略对系统中各节点之间的连接进行规划.通过描述返源规划问题的模型,提出了一种基于蚁群算法的规划策略来提高互相连接的节点之间数据块的可交换性.仿真结果表明,新算法可以最大化连接节点内容的互补性,继而减少了数据下载时间,提高了系统吞吐量,大大改善了P2P分发网的整体性能.     

一种基于节点可选度的P2P点播流媒体数据调度算法

当前的P2P(Peer-to-Peer)点播流媒体系统中数据调度算法未能充分利用每个用户节点自身的特性.在分析典型数据调度算法基础上提出一种基于节点可选度的数据调度算法(SSP算法).该算法一方面在调度下载数据块时综合考虑了邻居节点带宽能力及其所拥有的数据信息.另一方面对服务节点的请求处理过程进行了优化.SSP算法有利于提高用户节点播放视频的连续性,降低流媒体服务器的负载压力,从而改善P2P点播流媒体系统的整体服务质量.仿真结果和实际应用表明算法性能良好,适用于用户节点能力差异较大的P2P点播流媒体环境.     

一种新颖的P2P文件共享系统的动力学模型

提出一种新颖的P2P文件共享系统的动力性学模型.在模型中定义了描述节点之间相互作用关系的状态量.同时,分析了P2P文件共享系统中最重要的算法,如节点选择算法及带宽分配算法等等,最终给出了模型的具体形式.最后,网络实验和仿真证明了此模型能够反映P2P文件共享系统的本质特征,从而为设计高性能P2P网络,改进现有的P2P算法,以及研究P2P系统的稳定性提供一种新颖的方法.     

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.     

线性网络编码及其在P2P网络中的应用研究

通过对网络编码理论和现有P2P文件共享系统的深入研究,设计了一种基于线性网络编码的P2P文件共享系统.该系统的优点是解决了现有P2P文件共享系统中存在的不能充分利用网络资源、“种子”节点突然退出造成文件下载不完等问题.实验结果表明,该系统克服了现有系统中存在的问题,同时也提高了整个系统的吞吐量并增强了系统的稳定性.     

基于随机性和文件块相似性的结点选择策略

为了提高对等网文件共享系统的服务性能,增强文件共享过程的延续性,通过对比分析目前典型的P2P网络应用BitTorrent和基于临近节点聚类的Bit Torrent文件共享系统中的邻居节点选择策略的优点和不足,提出了一个优化的邻居结点选择策略,服务器tracker为结点优先选择与其具有相近文件块数的结点作为其邻居结点的同时,采用基于随机性的策略来提高文件共享过程的延续性.最后,模拟实验结果表明,该策略提高了共享系统的延续性和服务性能,具有很好的文件共享效率,有效地抑制了"搭便车行为".     

P2P文件共享系统中的一种基于商品市场模型的访问控制机制

随着P2P文件共享系统日益成为流行的文件交换方式,其安全问题势必引起关注,而访问控制是P2P系统安全的关键技术之一.由于P2P系统具有分散性和动态性,传统的访问控制机制不能够直接应用于P2P文件共享系统中.而现有针对P2P文件共享系统的访问控制机制不能很好地解决大量并发文件下载请求或者爆发式的恶意文件下载对节点带来的侵害.针对上述问题,文中提出一种基于商品市场模型的访问控制机制(ACMCM),利用市场调节机制使得文件下载请求均衡地分布在多个文件提供者之间;下载文件的价格随着重复下载次数的增加而呈指数增长,有效遏制了恶意下载行为;通过在并发下载之间合理地分配下载带宽,使得并发文件下载占用的系统时间尽量缩短.ACMCM保留了P2P系统的分散性和动态性.最后给出了ACMCM的分布式协议的主要过程的流程.     

基于随机微分方程的通用P2P文件分发模型*

提出一种基于随机微分方程的流模型来描述对等（P2P）文件分发系统的动态行为。根据实际系统分类节点,分别对各类节点进行量化分析,建立系统的动态模型。所建模型抽象邻居选择策略和节点到达率,能够支持各种邻居选择算法和不同的节点到达率。基于所建模型分析了现有的邻居选择策略和节点到达率。通过与实际系统的跟踪数据进行对比,所提出的模型能够准确描述现有的P2P协作式文件共享系统,是一种通用、实用的模型。该模型有助于评估现有的方案,设计优化的系统。     

基于网络延迟的P2P路由算法的研究

近年来,P2P计算应用已经超过Web应用而成为占用互联网带宽最多的网络应用.针对目前P2P系统中采用的随机选择邻居节点的方法会降低路由效率以及增大网络开销方面的问题,在分析Chord方法特点的基础上,提出一种改进的Chord构建算法DeChord.从逻辑上相邻的点在物理上也相邻这一原则出发,DeChord采用Chord数据定位算法;利用全局网络定位系统计算节点坐标并以此为依据计算节点间的物理距离,节点加入时充分考虑节点之间的逻辑距离与物理距离的一致性,系统节点总是选择距离自己物理距离较近的节点作为邻居节点;DeChord算法使得节点的路由表的信息能得到及时的更新.DeChord中的邻居节点选择方式可以降低消息路由过程中每一跳的网络延时,从而降低整个消息路由的开销.模拟实验表明,利用该算法建立的P2P系统能大幅度降低数据定位的延时.     

基于在线概率的P2P网络系统动力学模型

为了更好地刻画P2P文件共享系统中节点行为的随机性,提出了一种基于在线概率的动力学模型. 首先,引入节点的在线概率来刻画节点行为的随机性,并通过分析系统中节点之间交互演化的过程,建立了基于在线概率的动力学模型. 然后,通过对模型的分析,研究了影响系统演化的多个因素,这主要通过对相关算法的具体形式分析来体现. 之后,对算法进行改进,提出了基于在线概率的节点选择算法、带宽分配算法与节点阻塞算法. 最后,通过仿真实验对模型进行了验证和分析.     

一种分阶段的P2P流媒体数据调度算法

针对当前P2P流媒体中各节点数据调度时独立获取数据而对提高节点间数据协作性考虑不足,导致服务器负载较重的问题,提出一种分阶段的数据调度算法。当多个节点将请求的数据中含有相同数据块时,各节点将分两个阶段合作的获取这些数据。第1阶段按照带宽相对大小各节点以合作的方式先各自获取数据的一个子集,第2阶段节点间再充分共享上一阶段已经获得的子集数据,协作地完成该轮调度的数据传输。仿真实验表明该算法可以提高节点间数据协作性,充分利用节点带宽资源传输媒体数据,提高系统可扩展性。     

SmartPeerCast: a Smart QoS driven P2P live streaming framework

The P2P swarm technologies have been shown to be very efficient for medium scale content distribution systems in the last few years, such as the file sharing and video-on-demand (VOD) applications. However it is still an open topic about how to deploy the P2P paradigm for the real time video broadcasting (RTVB) applications. The P2P RTVB application is different from the cache based P2P system because it has more stringent restrictions for startup time and packet loss ratio. In this paper, an adaptive media broadcasting P2P framework named SmartPeerCast which employs the media transrating service to control the quality of service (QoS), is proposed. SmartPeerCast achieves a network awareness, codec awareness, and high performance RTVB service with four key designs: (1) It groups the newly joined peers into different quality clusters by their uploading capability. This clustering mechanism avoids the bandwidth bottleneck between the heterogeneous peers of the overall P2P overlay by only forwarding the same quality stream over the peers in the same cluster. (2) The streaming quality is adjusted adaptively between the sending and the receiving peers by a Smart QoS algorithm to compensate for the network jitters to reduce the receiving peer’s playback jitter. (3) The receiving peer monitors the data forwarding QoS of the sending peer to select the best suitable parent node dynamically. The SmartPeerCast uses this Smart QoS framework to implement an incentive mechanism to award the peers with high uploading contributions by migrating them to a higher quality cluster. (4) A transrating engine is used at the leaf nodes of the high quality cluster to forward the stream with suitable bits rate to the nodes of the low quality cluster; this transrating service not only can fully utilize the uploading bandwidth of the peers in the higher quality cluster but also avoids the bandwidth bottleneck of stream forwarding between the heterogeneous peers. Our experiment results and the real deployment show that SmartPeerCast can eliminate the bandwidth bottleneck and content bottleneck between the heterogeneous peers with a smaller startup time and packet loss and it is a high performance and medium scale P2P RTVB framework.     

基于改进粒子群算法的P2P流媒体数据调度策略

根据P2P流媒体数据调度特点,改进了粒子群优化算法,并提出适用于离散粒子群算法（MDPSOA）的数字串编码方式。调度策略引入资源紧急度以及资源稀缺度来选择调度数据片,然后用改进离散粒子群算法来进行节点寻优,找出最优调度节点集。最后通过实验仿真算法收敛性、数据调度时间、网络利用带宽和节点负载平衡,从而验证调度策略的可行性和有效性。     

Incorporating contribution-awareness into mesh-based Peer-to-Peer streaming systems

While Peer-to-Peer streaming has become increasingly popular over the Internet during recent years, the proper allocation of available resources among peers in a resource constraint environment, remains a challenging problem. In a resource constraint environment, the allocated resources and thus delivered quality to individual peers should be proportional to their contribution to the system, i.e., resource allocation should be contribution aware. This in turn results in fairness among peers and encourages active contribution from participating peers which is essential for scalability of P2P systems. However, contribution-aware resource allocation is challenging due to the distributed and dynamic nature of resources in P2P systems. In this paper, we present a tax-based contribution-aware scheme for live mesh-based P2P streaming approaches. In our proposed scheme, individual peers use a tax function to determine their number of parent peers (i.e., their share of resources) based on the number of their child peers (i.e., peers’ contributed resources) and the aggregate available resources in the system. We examine the behavior of a commonly used tax function, and describe how the contribution aware scheme can leverage the tax function. Through extensive simulations we demonstrate the ability of our proposed scheme to properly allocate available resources among participating peers over a wide range of scenarios. We show that the amount of resources (i.e., bandwidth) is divided across peers proportional to their contribution and in our default simulation setting the median delivered quality to high bandwidth peers with high contribution is improved by 100%. We believe that our results shed an insightful light on the dynamics of resource utilization and allocation in the context of live mesh-based P2P streaming.     

WuKong: a practical video streaming service based on native BitTorrent and scalable video coding

Many researches on peer-to-peer video streaming have focused on dealing with highly dynamic, high-churn P2P environment. Most of P2P streaming protocols were modified from a P2P file sharing protocol. Inspired by the high performance on peer-to-peer file sharing of BitTorrent, we propose an overlaying streaming mechanism on the native BitTorrent protocol and realize a practical P2P video streaming service, called WuKong. WuKong not only takes advantages of BitTorrent but also combines the video scalability of layered video coding. In this paper, we depict an overlaid streaming mechanism in WuKong and an adaptive layer-downloading process to balance between the video quality and bandwidth utilization on heterogeneous peers. WuKong is carried out by using an open-sourced library of the BitTorrent protocol, coding schemes of the Windows Media Video (WMV), and the Scalable Video Coding (SVC). We measured and compared the service quality of end-users served by WuKong on heterogeneous peers. In addition, we evaluated the effectiveness of WuKong with peers that are randomly joining and leaving the P2P network. The results show that WuKong not only provides high quality P2P video streaming services but also supports different scaling abilities over heterogeneous devices.     

P2P文件共享系统中基于访问控制的信任模型

在P2P文件共享系统中,节点之间共享彼此的文件.但是由于对等网络的匿名性和开放性,在文件共享系统中存在很多信任方面的问题,如恶意节点和自私节点的大量存在.为了孤立恶意节点和鼓励节点共享自己的文件,提出了基于访问控制的信任模型.首先,定义了一种信任机制,它引入了直接信任,推荐信任,时间衰减等因子.其次,对每个共享文件都加入了两个阈值--可信性总评价阈值和贡献量阈值来控制访问.对于每个请求者,只有当它有了对文件的访问资格后才能访问该文件.最后,通过大量的实验证明了本模型的可行性和高效性,特别是对恶意节点具有很好的孤立作用.     

Dynamic Bandwidth Auctions in Multioverlay P2P Streaming with Network Coding

In peer-to-peer (P2P) live streaming applications such as IPTV, it is natural to accommodate multiple coexisting streaming overlays, corresponding to channels of programming. In the case of multiple overlays, it is a challenging task to design an appropriate bandwidth allocation protocol, such that these overlays efficiently share the available upload bandwidth on peers, media content is efficiently distributed to achieve the required streaming rate, as well as the streaming costs are minimized. In this paper, we seek to design simple, effective, and decentralized strategies to resolve conflicts among coexisting streaming overlays in their bandwidth competition and combine such strategies with network-coding-based media distribution to achieve efficient multioverlay streaming. Since such strategies of conflict are game theoretic in nature, we characterize them as a decentralized collection of dynamic auction games, in which downstream peers bid for upload bandwidth at the upstream peers for the delivery of coded media blocks. With extensive theoretical analysis and performance evaluation, we show that these local games converge to an optimal topology for each overlay in realistic asynchronous environments. Together with network-coding-based media dissemination, these streaming overlays adapt to peer dynamics, fairly share peer upload bandwidth to achieve satisfactory streaming rates, and can be prioritized.     

Gnutella网络文件共享属性的测量与分析

以Gnutella网络为测量对象,分析了Gnutella网络的基本特点和关键协议,利用Limewire的源代码设计了一个Gnutella网络内容爬虫,测量了Gnutella网络中用户的共享文件类型、共享文件数目、共享空间、文件副本、用户日均在线时长和节点应用层带宽,并对以上测量结果进行统计分析。统计分析表明文件共享数目与共享空间存在显著的相关关系,应用层带宽与日均在线时长则存在弱相关关系。此外,对Gnutella网络中的用户按照共享文件数目、共享空间、应用层带宽、日均在线时长这4个方面进行了聚类分析,分析结果表明,Gnutella网络中的平庸用户占所统计用户数的97%。     

Robust control in cloud assisted peer to peer live streaming systems

Existing live video streaming systems can be classified as server (cloud) based or as peer-to-peer (P2P). The client–server approach promises stability and (Quality of Service) QoS by incurring expensive bandwidth provision cost on the server. On the other hand, P2P architecture is scalable with low bandwidth and maintenance cost. Here we propose a cloud assisted P2P live streaming architecture which is scalable and stable. In order to achieve this we have developed: (i) a scalable gossip protocol that monitors dynamically the total available bandwidth resources of the participating peers, (ii) a control strategy that dynamically allocates the bandwidth that is required.The first step towards this direction is to create a theoretical model that captures the dynamic relationship between the total bandwidth surplus/deficit and peers’ bandwidth utilization in order to be able to apply a control theoretical approach. Moreover, we quantify the impact of monitoring inaccuracies and peers’ dynamic bandwidth changes and we calculate analytically, as a function of them, the minimum amount of bandwidth overprovision that ensures the undisturbed distribution of the stream. System is evaluated through a detailed simulator of a complete P2P live streaming system and testified the uninterrupted and complete stream delivery even in very adverse bandwidth changes.