基于同步会话管理机制的P2PVoD系统研究与设计

在视频点播系统中,由于用户节点的动态性和VCR操作的复杂性,使得资源的定位一直是P2P流媒体点播系统的难题.对典型的视频点播系统的关键技术进行了研究,在此基础上,设计了一种基于同步会话管理定位机制的P2P视频点播系统,加速了节点的资源定位,更有效地支持用户的VCR操作.仿真结果表明,与P2VoD系统相比,该系统减小了节点加入系统的延迟,降低了系统的通信负担.     

P2P VoD系统下的两层关系预取策略

针对如何有效降低P2P VoD系统发生VCR操作时产生的时延问题,提出了一种P2P VoD系统中的两层关系预取策略,根据节点的播放记录找到片段之间可能存在的关系,以此为依据进行预取,并对节点的邻居列表进行优化,使之能更快定位和预取资源。仿真实验结果表明,两层关系策略准确地预取了视频内容,降低了VCR时产生的时延,提高了用户的观看体验。     

P2P视频点播中的VCR方法综述

近几年,P2P视频点播技术得到了广泛的发展,使用P2P流媒体播放器(如PPStream、PPLive)来点播视频已经被广泛接受。但是,由于种种原因,用户在播放视频时进行快进、快退和跳转操作时,总是要等待一个比较长的时间,与用户在本地执行此操作的时间相差较大,因此用户得不到好的点播体验,同时也浪费带宽。为了解决这个问题,研究者们已经提出了许多关于提高VCR质量的方法,其中有被动式技术,也有主动式技术。被动的VCR技术主要是着眼于缩短对资源节点定位时间和从该资源节点下载资源的时间,同时提高节点保存资源节点信息的概率。主动的VCR技术主要是提高预存内容的概率和预存资源节点的信息的概率,同时缩短对资源节点定位的时间。本文将着重介绍这些方法的特征,并比较他们的优缺点,最后对VCR算法研究做出展望。     

关于Hilbert空间量子效应下确界的研究

量子的下确界问题是量子计算和量子信息中的一个重要问题,对于这一问题,首先运用一种简单的方法证明了Kadison的一个结果：设A,B∈Her（B（H））,则A∧B在Her（B（H））存在当且仅当A和B可比较;然后讨论了B（H）⁺和Hilbert空间效应代数ε（H）中的下确界问题。最后,通过一个例子给出：对于两个量子效应A和B,虽然A∧B和A²∧B²在ε（H）中存在,但是A²∧B²≠（A∧B）²。     

de Bruijn序列查寻表标签的k位修正构造法

de Bruijn序列的结构是一个查寻表,其核心是它的表标签。因此构造出查寻表标签对于生成de Bruijn序列十分重要。给出两种k位修正构造法。方法1为k位提升构造法,即对大部分节点将其第k（k=1,2,…,n-1）位提升一个定值c（1≤c≤m）,来作为该节点的标签。方法2为k位收缩构造法,即对大部分节点将其第k（k=1,2,…,n-1）位向定值r（0≤r≤m）收缩,来作为该节点的标签。这些方法构造的查寻表标签数随着m,n增长而成指数式增长。与定值构造法一样,在局部看是有效的,但与查寻表标签本身数目的惊人增长比较起来就很渺小。方法2与定值标签构造法比较其速度提高了关于m,n的指数式倍。     

P2P VOD系统邻居节点查找算法

P2P流媒体点播系统中,由于用户的VCR操作存在不确定性,在查找合作节点时存在一定困难。针对该问题,提出了一种基于预测的邻居节点选择算法。描述了基于虚拟直播频道的点播系统覆盖网构建方式,将系统中的节点通过DHT协议的方式组织起来。提出了一种基于用户行为的学习预测策略模型,根据该模型预测结果提前查找所需邻居节点。仿真实验表明,该算法能改善用户跳转响应延时,促进节点协作。     

基于关联规则的P2P视频点播缓存替换算法

传统的缓存替换算法缺乏对视频点播系统的针对性,不能有效的重用缓存数据,影响缓存查询命中率.为此,本文针对视频点播系统用户VCR操作的特点,提出了一种基于缓存数据块关联规则的P2P视频点播系统客户端缓存替换算法.此算法根据视频点播用户的VCR操作特征,在每个节点记录用户的播放历史,并利用P2P网络的优势,在节点间互换播放记录.节点从自身收集到的播放记录中提取出视频数据块之间的关联规则,根据关联规则更新数据块的流行度.缓存区被填满后流行度低的数据块就会被流行度较高的数据块替换.实验结果表明,与传统缓存替换算法相比,本算法能够提高缓存查询命中率,减轻服务器的负载.     

树状网络上带度约束的k-tree core问题

考虑到在实际应用中,由于计算机和通信网络中一般每个设备的处理能力是有限的,在k-tree core问题的基础上,提出了同时带有度约束的k-tree core问题,即k-tree core中的每个节点在子树中的度不超过给定常数q,记为q-DTC（k）（Degree constrained Tree Core）。利用动态规划的方法,采用最优化原则先找出文中所定义的局部根核集,然后利用贪婪思想对不满足度限制的节点所在的分支加以删减,对无权树和赋权树得到了复杂度分别为O（kn）和O（max{n log n,kn}）多项式时间算法,其中n是树的节点数。     

支持VCR操作的P2P视频点播服务器容量配置方法

在P2P视频点播系统中,用户交互式操作(VCR操作)行为的异步特征使得用户间的数据共享更加困难,从而对视频源服务器的带宽和处理能力都提出了很高的要求.本文研究如何提高P2P视频点播系统的VCR操作用户体验,提出在P2P视频点播系统中增设一台服务器专用于支持用户的交互性操作,并研究了该服务器的容量配置问题.利用泊松过程描述点播请求到达交互支持服务器的行为,通过排队理论建立了用户点播请求最长允许等待时间与交互支持服务器服务带宽之间的定量关系.数据实验结果表明,只需相对较小的服务器容量,即可满足较大规模的用户点播数据请求.     

P2P流媒体点播的缓存机制研究

基于P2P的流媒体点播系统,由于实时点播和拖动等VCR操作没有得到有效支持,以及用户不能随意发布节点等原因,没有得到广泛应用。本文提出了一种基于混合P2P的流媒体点播模型TTVOD,讨论了模型的缓存机制,提高了数据冗余度和分发性能,最后通过实验验证了模型的有效性。     

一种用于大规模P2P点播系统的拓扑结构

提出了一种基于动态时间坐标的分层DHT拓扑结构,解决了因大规模P2P点播系统要求细粒度追踪而难以应用DHT的问题。在动态时间坐标系中,节点的播放点坐标不再随着节点的播放而移动,从而使得DHT能够用于追踪点播系统节点缓存位置。仿真结果证明了方法的有效性。     

InstantLeap: an architecture for fast neighbor discovery in large-scale P2P VoD streaming

In large-scale peer-to-peer (P2P) video-on-demand (VoD) streaming applications, a fundamental challenge is to quickly locate new supplying peers whenever a VCR command is issued, in order to achieve smooth viewing experiences. For many existing commercial systems which use tracker servers for neighbor discovery, the increasing scale of P2P VoD systems has overloaded the dedicated servers to the point where they cannot accurately identify the suppliers with the desired content and bandwidth. To avoid overloading the servers and achieve instant neighbor discovery over the self-organizing P2P overlay, we design a novel method of organizing peers watching a video. The method features a light-weight indexing architecture to support efficient streaming and fast neighbor discovery at the same time. InstantLeap separates the neighbors at each peer into a streaming neighbor list and a shortcut neighbor list, for streaming and neighbor discovery respectively, which are maintained loosely but effectively based on random neighbor list exchanges. Our analysis shows that InstantLeap achieves an O(1) neighbor discovery efficiency upon any playback “leap” across the media stream in streaming overlays of any size, and low messaging costs for overlay maintenance upon peer join, departure, and VCR operations. We also verify our design with large-scale simulation studies of dynamic P2P VoD systems based on real-world settings.     

P2P网络下一种基于DHT的视频点播方案

在基于P2P的视频点播系统中,节点邻居选择策略对服务质量有很大的影响。提出一种基于DHT（Distributed Hash Table）的P2P覆盖网络下视频点播（Video-on—demand）的解决方案。通过网络坐标系统的拓扑发现能力,充分结合DHT网络高速搜索和VoD视频点播的特性、构造一种具有高效邻居选择能力、高用户自由度、高可靠性、扩展性的体系架构。针对架构设计中资源发布份发、资源的搜索、视频点播的实现等关键问题提出了解决方案,分析了系统的特性。     

The interleaved video frame distribution for P2P-based VoD system with VCR functionality

The peer-to-peer (P2P) network structure is widely employed for video streaming applications because of its high stability, flexible extensibility, and ability to distribute data stream loading among different peer nodes. Numerous P2P schemes have been proposed for video on demand (VoD) applications. High video source searching cost and long response latency are always issues in dealing with VCR functionality, such as jump and fast-forward/rewind, because of asynchronous interactive and random join/leave behaviors of end users. To overcome this bottleneck, an interleaved video frame distribution (IVFD) scheme is proposed to support full VCR functionality in a P2P environment without searching for new sources. Instead of acquiring video stream data from a single parent peer in the published schemes, each child peer in the IVFD scheme can simultaneously acquire interleaved video data from multiple parent peers. When a client peer carries out arbitrary VCR operations, such as jump or fast-forward/rewind, its parent peers are still able to provide intermittent video stream data for the client peer; thus, no video source search is necessary. Simulation results reveal excellent load distribution performance and response latency for VCR operations in the proposed IVFD scheme.     

Sharable file searching in unstructured Peer-to-peer systems

The existing sharable file searching methods have at least one of the following disadvantages: (1) they are applicable only to certain topology patterns, (2) suffer single point failure, or (3) incur prohibitive maintenance cost. These drawbacks prevent their effective application in unstructured Peer-to-peer (P2P) systems (where the system topologies are changed time to time due to peers’ frequently entering and leaving the systems), despite the considerable success of sharing file search in conventional peer-to-peer systems. Motivated by this, we develop several fully dynamic algorithms for searching sharing files in unstructured peer to peer systems. Our solutions can handle any topology pattern with small search time and computational overhead. We also present an in-depth analysis that provides valuable insight into the characteristics of alternative effective search strategies and leads to precision guarantees. Extensive experiments validate our theoretical findings and demonstrate the efficiency of our techniques in practice.     

面向跳播优化的P2P视频点播系统

基于P2VoD算法,针对其不足之处进行改变和优化,设计了新的系统。新的系统以树网结合的拓扑结构,实现对等体的加入、跳播、离开等行为的处理,尤其是对点播用户跳播行为的支持进行了特别的优化,减小了系统的延迟抖动。经过仿真,结果表明在相同的网络负载下,对等体初始加入网络时的延迟比P2VoD要小20％,同时系统比P2VoD更加稳定,并且实现了对跳播功能的支持,平均跳播时延约为初始时延的50％。     

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.     

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).     

基于云存储的P2P视频点播系统数据复制策略

交互性支持对P2P视频点播系统具有重要的意义,视频点播服务的大规模普及离不开用户交互性的支持。讨论了如何有效利用对等节点的带宽和存储资源来主动复制数据块,提出了一种基于云存储的数据复制策略CSPR。仿真实验结果表明,相比于现有的数据复制策略,CSPR可以显著提高用户进行随机搜索操作时的响应速度,并降低网络复制开销。