BitTorrent中一种基于全局贡献的节点选择策略

BitTorrent采用基于速率的Tit-For-Tat（Rate-based TFT）阻塞算法和乐观激活（Optimistic Unchoke,OU）算法为节点选择策略：上传节点采用Rate-based TFT算法选择为自身提供文件块上传速度最快的4个请求节点为下载节点,采用OU算法随机选择其他1个请求节点为下载节点。BitTorrent中Rate-based TFT算法只考虑邻居为上传节点所上传的文件块数即直接贡献,资源利用率不高,不能有效保证上传/下载之间的公平性。提出一种基于全局贡献的节点选择策略（Contribution-based TFT）,从直接贡献和间接贡献（即对其他节点所上传的文件块）两方面来考虑某段时间内节点的全局贡献,贡献越多,获取下载服务的优先权限越高。模拟实验表明,基于全局贡献的节点选择策略提高了上传配额利用率,减少了文件下载时间,并保证了公平性。     

基于自适应组播机制的P2P阻塞算法研究

P2P网络中节点利用阻塞机制作为节点选择算法,以确定节点间相互的服务对象.但是在传统的节点阻塞算法中存在着节点连接时间过高,首块资源获得较慢,系统链路利用率不高等问题.提出一种自适应组播机制,利用动态分组的路由方法,充分考虑各节点间的可用带宽,能够很好的解决在传统阻塞算法中存在的首块资源获取过慢,带宽利用不高等问题.     

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.     

BitTorrent系统中一种自适应阻塞算法

BitTorrent系统主要采用tit-for-tat阻塞算法作为节点选择算法,即节点选择当前向自己提供上传最快的一些节点作为上传服务对象。但是该阻塞算法导致新连接节点间过长的等待和节点在下载完成前夕过少的上传连接问题。提出了一种自适应阻塞的改进算法,当节点上传连接过少时自适应的增加上传连接。模拟实验表明,自适应阻塞算法在对系统公平性影响很小的前提下,有效地缩短节点等待时间、增加上传连接数量以及加快节点获取首块资源的速度,从而提高系统文件分发性能。     

P2P分发网中大容量实时数据传输调度算法

当P2P分发网中一个节点同时从若干个其他节点获取数据时,需要对数据下载任务进行合理调度,并尽量按时完成更多的下载任务.本文提出了一种基于多任务负载均衡的调度算法,该算法在调度下载任务时,将尚未被调度的下载任务也作为调度依据,从而能够有效地解决下载任务之间对带宽资源的恶意竞争,合理地利用各个其他节点提供的下载带宽,最终完成更多的下载任务.实验结果表明该算法能够减少超时下载任务的数目,提高P2P分发网的实时数据分发性能.     

P2P点播系统中资源下载算法的研究

在基于P2P技术的流媒体应用中,数据的实时性至关重要,而它易受网络动荡的影响.采用一个优化的资源下载算法可以有效缓解这一影响.提出了一种基于预连接的动态资源下载算法,算法结合了紧急数据通道策略、数据分片块预下载选择策略和基于预连接的对等节点选择策略等三种策略,实验证明,该算法能有效提高点播系统中数据的及时到达率,均衡网络负载,减少数据重传率,增加系统的稳定性.     

分散P2P网络中资源的自适应共享策略

针对P2P网络中资源共享交换效率问题,提出一种计算网络资源共享可能度的自适应策略,以决定节点对资源的共享抉择。该策略考虑了P2P网络中资源共享存在受限存储空间、下载中断和冗余下载等问题,以资源共享可能度作为资源共享抉择依据,提出资源共享可能度在单个代理的计算方法。实验结果证明自适应策略能够较好地避免资源的冗余下载,提高P2P网络资源共享效率。     

基于Donet的P2P流媒体直播优化调度算法

为了提高P2P流媒体系统的整体性能,改善节点的播放质量,针对现有调度算法启动延迟大和节点带宽利用率不高问题,提出了一种可动态调节各节点中待请求紧急数据的流媒体直播优化调度算法(LOSA).该算法不仅考虑了流媒体直播的时间特性,同时还考虑了如何减少紧急数据请求的等待时间以及对Peer节点上传带宽的充分利用.实验结果表明,LOSA算法缩短了终端用户观看视频的延迟,提高了媒体流的连续性.     

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.     

SSBIE:P2P覆盖网中基于信息交互的超节点选择

超节点选择是构造基于超节点结构P2P覆盖网的主要问题之一,与通常按节点能力如带宽、CPU处理、存储空间等纯物理性质选择超节点不同,本文充分考虑节点间延时、距离、信息交互频率和时间以及内容相似度等,提出一种基于信息交互的超节点选择方法(SSBIE),按节点Score值选择超节点,以解决P2P网络中搭便车(free-rider)问题.实验结果表明SSBIE较之按节点能力选择的方法使P2P系统性能明显提高,可提高文件查询成功率,减少平均查询跳数,降低查询延时.     

两段式P2P流媒体节点选择算法

现有的点对点(P2P)流媒体系统不能很好地兼顾网络拓扑聚集性和流服务质量,存在延迟过长和覆盖网压力过大的问题.为此,比较典型节点选择算法在流服务质量、网络利用率、网络拓扑聚集性等方面的特征,采用拓扑聚集和带宽优先相结合的方法,提出一种两段式的节点选择算法.在PeerSim软件上的仿真结果表明,该算法相比于其他算法,覆盖...     

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.     

An efficient playout smoothing mechanism for layered streaming in P2P networks

Layered video streaming in peer-to-peer (P2P) networks has drawn great interest, since it can not only accommodate large numbers of users, but also handle peer heterogeneity. However, there’s still a lack of comprehensive studies on chunk scheduling for the smooth playout of layered streams in P2P networks. In these situations, a playout smoothing mechanism can be used to ensure the uniform delivery of the layered stream. This can be achieved by reducing the quality changes that the stream undergoes when adapting to changing network conditions. This paper complements previous efforts in throughput maximization and delay minimization for P2P streaming by considering the consequences of playout smoothing on the scheduling mechanisms for stream layer acquisition. The two main problems to be considered when designing a playout smoothing mechanism for P2P streaming are the fluctuation in available bandwidth between peers and the unreliability of user-contributed resources—particularly peer churn. Since the consideration of these two factors in the selection and scheduling of stream layers is crucial to maintain smooth stream playout, the main objective of our smoothing mechanism becomes the determination of how many layers to request from which peers, and in which order. In this work, we propose a playout smoothing mechanism for layered P2P streaming. The proposed mechanism relies on a novel scheduling algorithm that enables each peer to select appropriate stream layers, along with appropriate peers to provide them. In addition to playout smoothing, the presented mechanism also makes efficient use of network resources and provides high system throughput. An evaluation of the performance of the mechanism demonstrates that the proposed mechanism provides a significant improvement in the received video quality in terms of lowering the number of layer changes and useless chunks while improving bandwidth utilization.     

一种分层P2 P流媒体系统重叠网的构建策略

基于Peer-to-Peer(P2P)技术的流媒体应用具有部署效率高及可扩展性好等突出优势。而采用分层视频编码技术的P2P流媒体系统把原视频流分解为多个视频层数据进行分发,让节点能够选择与自己带宽资源相匹配的视频质量,使其很好地适应节点的异构性。但是各分层视频数据传输的路径存在较大差异,使重叠网构建策略面临更大的挑战。因此定义了基于分层视频编码技术环境下的P2P流媒体重叠网络构建问题,并证明该问题是一个NP难问题。提出了一种构建重叠网的集中启发式算法,同时还提出了一种基于视频组(Streaming Group)的分布式重叠网络构建策略。通过大规模网络仿真实验验证了基于该分布式重叠网构建策略的分层流媒体系统具备低服务器带宽占用、高数据获取率等优点。     

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.     

一种新型的层次P2P搜索模型

在分析现有P2P模型的基础上，提出了一种新的P2P搜索模型，该模型是分层的混合结构，利用分组和建立搜索空间的机制，来提高搜索的效率，增强系统的可扩展性。同时为低带宽节点引入了搜索代理的机制，提高了带宽的利用率，减少了搜索延迟。而且为了增强网络的自恢复性，利用缓存机制引入了备用连接，使搜索模型具有较好的容错能力。     

A P4P-integrated data-driven P2P system for the live multimedia streaming service

The Proactive network Provider Participation for the P2P (P4P) architecture deploys central servers, which perceives network status and provides peering suggestions to P2P systems in order to achieve better network resource utilization while supporting best possible application performance. However, P4P alone may not be able to make appropriate peering suggestions for live multimedia streaming since it does not include mechanisms to reflect some of the parameters that are important to the QoS of live multimedia streaming such as upload bandwidth and stability of a peer as a stream deliverer. Furthermore, peer synchronization and parent replacement in the middle of a session, which are critical issues to the QoS of live multimedia streaming, are also left as the matters to be dealt with by the P2P systems alone. Most of the existing data-driven P2P systems leverage periodic information exchanges among neighboring peers in order to cope with these problems, which may incur long delay and high control overhead. In this paper, we proposed P4P-integrated data-driven P2P system for live multimedia streaming service. The proposed system includes not only the peering suggestion mechanism appropriate for live multimedia streaming but also the peer synchronization and parent replacement mechanisms, which exploit the centralized P4P framework and do not require periodic control information exchanges. We implemented the system in NS-2 simulator and compared its performance to the P4P and existing data-driven P2P systems. The results from experiments show that the proposed system enhances QoS compared to the existing data-driven P2P systems while maintaining the same level of network efficiency of the original P4P.     

基于节点兴趣和Q-learning的P2P网络搜索机制

将智能手机设备加入基于非结构化P2P网络的资源共享系统中能够满足人们对资源共享的多样化、便利性、高频性、实时性、高效性等要求,但是该系统网络规模的扩张和网络节点互异性的加大,必将导致系统资源搜索效率的降低、冗余信息的剧增以及网络更加不稳定。为了解决这些问题,文中设计了一种改进的基于节点兴趣和Q-learning的资源搜索机制。首先将节点根据兴趣相似度进行兴趣聚类,划分兴趣集,然后根据兴趣集中节点的能力值构建兴趣树,该结构避免了消息环路的产生,极大地降低了冗余信息;在资源搜索中,兴趣树内采用洪泛算法转发消息,兴趣树之间采用基于Q-learning的消息转发机制,不断强化最可能获取目标资源的路径,查询消息优先在这些路径上传播。另外,针对“热点”资源问题,设计了自适应热点资源索引机制,减少了重复路径搜索,进一步减少了冗余消息量;针对节点失效的问题,给出了根节点冗余机制和捎带检测的策略方法,分别解决了根节点失效和普通节点失效导致的兴趣树的不完整性问题,分析表明该方法能够减少消息冗余量。仿真实验结果表明,与GBI-BI算法和Interest CN算法相比,所提搜索算法能够提高命中率,缩短响应时间,减少冗余信息,具有较好的综合性能,最终解决了由于智能手机设备加入P2P网络导致的资源搜索效率下降、网络流量开销大的问题。     

ERSN:一种高效鲁棒的超结点对等网络

超结点对等网络利用对等结点的异构性解决了低带宽结点带宽瓶颈问题,但目前超结点对等网络的构建协议效率低且网络拓扑鲁棒性弱.提出一种高效鲁棒的超结点对等网络ERSN,采用基于漫步算法的结点采样协议,估计网络需求,构建高效的超结点对等网络,并建立叶结点间的应急连接,增强超结点对等网络的鲁棒性.模拟实验证明,与Gnutella0.6超结点对等网络比较,ERSN网络中负责处理定位请求的结点数目最多减少了76%,并在多个超结点和叶结点同时离开网络的情况下,将文件定位命中率最大提高了36.4%.     

基于P4P的CDN系统中内容分发节点选择算法

对内容分发网络(CDN)和对等网络(P2P)分别进行了分析对比,指出了它们各自的优缺点,并根据电信运营商主动参与P2P网络(P4P)技术的特点,给出了一种结合P4P、P2P与CDN技术的混合系统的设计方案,以及混合系统中协助CDN节点分发内容节点(伪CDN节点)的选择算法.该算法利用P4P技术获得运营商提供的网络信息,选择合适的边缘节点,贡献出其容量和带宽,为其他节点服务,以减少了系统边缘代理服务器的数量,增大系统容量,同时减少网络骨干网上的负载.模拟实验分析了考虑底层网络情况后,系统在链路花费、时间花费上的改进,结果表明该算法减少了跨网络运营商(ISP)流量,提高了系统性能.