面向P2P文件共享应用的相似度计算模型

P2P文件共享应用逐渐成为互联网中的主流应用,它们都部署了各自的内容分发网络用于文件的发布与查找。基于内容分发网络,提出了一个节点间相似度计算模型。模型充分挖掘了节点拥有的文件的元信息,在进行相似度计算时将文件名、文件长度、文件类型按照不同的权重进行计算。将模型的求参问题形式化为一个有约束的最优化问题,并以eMule应用为例,对其模型参数进行了确定。相似度计算模型引入了节点的语义信息,可应用于改善内容分发网络的物理拓扑,从而提高其查询性能与路由性能。     

对等网络中基于节点交互和推荐的信誉管理

提出与描述了对等网络中基于节点交互和推荐的信誉管理模型。该模型中的节点在进行文件下载时,可以直接参考推荐节点,而不是去参考其他大量数目的普通节点,节省大量的时间和减少通信代价。该模型认为节点的信誉能力是多方面的, 参考了概率论中的贝叶斯网络,把节点的性能指标按照贝叶斯网络组织起来,在节点交互和文件共享过程中对信誉分数进行更新。构建了信誉管理模型的测试环境,性能分析表明在进行大量的节点和文件上传与下载时,系统可以通过推荐节点使交互数目稳定增加;与普通的对等网络相比,成功的交互数目也稳定增加。     

对等网环境下一种安全有效的信誉体制

提出一种基于公钥体制的安全有效的分布式信誉体制。定义了存储客户端信息的客户证书CCert和存储信誉信息的信誉证书RCert;采用与现有信誉查询方式不同的混和式查询,保证了信誉查询的有效性和安全性;同时生成最近时戳来保障信誉信息的实时性。此外,本体制还具有信誉信息的完整性、不可否认性、防合谋、防报复等特性,从而更好地提高对等网的可用性。     

A D-S evidence theory based fuzzy trust model in file-sharing P2P networks

In this paper we propose an advanced Dempster-Shafer (D-S) Evidence Theory based Fuzzy Trust model (ETFT) for Peer-to-Peer (P2P) networks. The primary goal of ETFT is to be able to address trust information uncertainty and fuzzy trust inference to deal with inconsistent or conflicting recommendation problems in a reputation based P2P environment. The D-S theory is therefore introduced to our trust model. To make the D-S theory fit into P2P systems, we creatively revise the combination rules and achieve greatly improved results. To further improve the accuracy and performance, ETFT filters out noisy referrals before combining the evidences. From the theoretical analyses and experimental results, it is evident that the proposed ETFT has a clear advantage in modeling dynamic trust relationship and aggregating recommendation information. Results also demonstrate that ETFT is more robust and can generate higher successful transaction rate than most existing frameworks.     

P2P文件共享系统中的复制策略

复制技术可以提高P2P文件共享系统的可靠性,改善查询性能和负载均衡。对文献中出现的各种复制策略进行总结综述,列出了各种复制策略背后的思想和拟解决的问题。在详细分析这些复制策略的特点基础上,对复制策略进一步的工作进行了展望并提出了建议。对进一步的研究复制策略有一定的参考价值。     

P2P文件共享应用安全问题分析

介绍以P2P文件共享应用为例,分别从Peer用户安全、Peer的行为及共享文件三个方面讨论其安全问题,为P2P的安全技术研究工作提供比较全面的认识。     

P2P网络激励兼容的声誉评价及服务分配

由自私节点组成的P2P网络常常采用基于声誉的机制激励节点间的合作。当前已经提出了一类基于声誉的方案,但其中大部分方案都忽视了方案的分布式实现中惩罚的激励兼容性问题。在社会学或生态学领域,该问题常被称为二阶搭便车问题:拒绝低声誉节点的服务请求会降低惩罚者自身的声誉,因此对于自私节点而言,这种惩罚并不总是有利的选择。以P2P文件共享为例对该问题进行了分析,提出了一种连续型二阶声誉评价模型及两种服务分配规则,即概率分配规则和比例分配规则,实验表明只有概率分配规则是激励兼容的。     

P2P网络中利用推拉模式实现的信誉系统

在现有的信誉模型中,即使节点积极提供良好的服务,节点信誉的累积也需要一个很长的周期,影响了新节点加入网络的积极性.此外,大部分模型在合成全局信誉值时采用多次迭代的方式,大量的迭代运算将导致巨大的计算开销.针对上述问题,通过引入流媒体调度策略中典型的推拉模式,提出一个新的信誉计算模型.在推模式下,对于那些新加入且积极提供优质服务的节点,可以加快其信誉累积速度,在拉模式下,减少了网络消息流量,避免了迭代计算的负面影响.分析及仿真表明,该模型在保证信誉计算准确性的同时,能较大程度改善通信及计算开销.     

P2P文件共享系统中的分组信誉驱动机制

在P2P文件共享系统中,常会出现许多有策略的欺骗行为,而现有的信任模型并不能完全消除交易的风险。综合局部信任机制和全局信任机制,根据节点间相关的共享记录数据提出一种新的信誉计算方法,并进一步提出受信誉驱动的分组组织管理和节点搜索算法。仿真结果证明该信誉驱动机制能搜索到信誉值高的节点作为交易对象,并能有效降低系统面对合谋恶意节点和具有交易策略的恶意节点攻击时的交易风险。     

An Eigentrust dynamic evolutionary model in P2P file-sharing systems

Many reputation systems have been proposed to distinguish malicious peers and to ensure the quality of the service in P2P file sharing systems. Most of those reputation systems implicitly assumed that normal peers are always altruistic and provide their resources unconditionally when requested. However, as independent decision makers in real networks, peers can be completely altruistic (always cooperative, ALLC), purely selfish (always defective, ALLD), or reciprocal (R). In addition, those systems do not provide an effective method to reduce free-riders in P2P networks. To address these two problems, in this paper, we propose an EigenTrust evolutionary game model based on the renowned EigenTrust reputation model. In our model, we use evolutionary game theory to model strategic peers and their transaction behaviors, which is close to the realistic scenario. Many experiments have been designed and performed to study the evolution of strategies and the emergence of cooperation under our proposed EigenTrust evolutionary model. The simulation results showed that rational users are inclined to cooperate (enthusiastically provide resources to other peers) even under some conditions in which malicious peers try to destroy the system.     

A measurement study supporting P2P file-sharing community models

Knowledge of emergent properties of existing peer-to-peer file-sharing communities can be helpful for the design and implementation of innovative peer-to-peer protocols/services that exploit autonomicity, self-configuration, resilience, scalability, and performance. It is well known that the performance of this class of peer-to-peer applications depends on several parameters that represent the topological structure of the overlay network, the users’ behavior, and resource dynamics. Estimation of these parameters is difficult, but it is crucial for analytical models as well as for realistic simulation of peer-to-peer applications.In this paper, we present an active measurement-based study designed to glean insights on the above parameters within the Gnutella network. The measurement software that we developed is able to collect topological information about the overlay network topology in a few minutes; in a second step, it contacts the users discovered during the topological measurement in order to acquire a novel dataset regarding the shared resources.     

HFC网络中P2P文件共享系统的按需广播算法

为了节省在HFC（Hybrid Fiber Cable）网络中进行P2P（Peer to Peer）文件共享的带宽资源,提高带宽利用率,提出了一种数据广播系统与P2P系统混合的网络拓扑结构,利用广播空闲信道对文件资源索引进行广播。在此拓扑结构基础上,提出了一种按需广播PRLS（Preemptive Request-Length-Serial）算法,提高广播调度的效率。仿真实验表明,在用户平均等待时间和冷、热门索引的数据长度平衡两个指标上,PRLS算法有明显优势。     

非结构化对等网络中的信誉管理机制

针对因特网上网络资源共享中存在的恶意节点行为,提出并描述了一种非结构化对等网络中的信誉管理机制.该机制使用非集中式的策略,根据节点与应用的需求计算节点的信誉度,具有独立性,不需要其它节点的参入与辅助.把加入对等网络的节点行为划分为恶意行为与友好行为,既可以统计节点对系统的贡献,也可以根据恶意行为而减少节点的信誉度.描述了信誉管理机制的设计与实现,各种节点行为下的仿真实验结果表明,该信誉管理机制是对等网络中一种真实的,高效的、信誉机制良好的资源共享策略.     

Evaluating stranger policies in P2P file-sharing systems with reciprocity mechanisms

How to deal with strangers efficiently is a big challenge for designing P2P systems, as ineffective stranger policies will cause the degradation of system performance and fairness. In this work, we focus on an open P2P file-sharing environment with reciprocity incentive mechanisms, and we evaluate the impact of different stranger policies to system performance and fairness using both numerical analyses and agent-based simulations. The results reveal that there exist tradeoffs between system performance and fairness; the optimal performance and fairness of the system cannot be reached simultaneously; free-riders will survive when system performance is optimal. The accuracy of this evaluation is verified through the analysis of stranger policies in BitTorrent and eMule/eDonkey. Therefore, this evaluation can effectively help P2P designers select appropriate stranger policies according to their individual design goals.     

结构化对等网络中基于信誉的乐观路由决策

提出一种结构化P2P网络环境下的路由决策方法.该方法利用Beta评估机制对P2P节点路由行为进行信任度量,并针对P2P节点的短期在线行为,通过引入置信度避免了短期在线节点产生不可靠的信誉值;在基于Chord协议的P2P网络路由决策过程中,提出了乐观路由的思想;采用贪婪决策与信誉决策相结合的方式,实现了合理的多路径路由.该路由方法兼顾了效率和可靠性两方面因素.仿真结果表明,该方法在减少路由跳数和提高路由成功率方面都取得了较好的效果.     

P2P文件共享系统行为特性模型分析

由于P2P文件共享系统具有自组织的特点,其行为特性很大程度上影响了系统可靠性和性能。为了解这种性质,利用统计方法研究了Maze系统用户行为特性分布模型及特点。结论表明,用户上传流量和下载流量、上传带宽和下载带宽可以使用对数正态混合分布来描述,活跃时间和传输时间可以使用对数正态分布来拟合,而请求次数和被请求次数可以使用指数分布和Pareto分布的混合分布来表达。     

Modeling and analysis of passive worm propagation in the P2P file-sharing network

A number of worms, named P2P (peer-to-peer) passive worms, have recently surfaced, which propagate in P2P file-sharing networks and have posed heavy threats to these networks. In contrast to the majority of Internet worms, it is by exploiting users’ legitimate activities instead of vulnerabilities of networks in which P2P passive worms propagate. This feature evidently slows down their propagation, which results in them not attracting an adequate amount of attention in literature. Meanwhile, this feature visibly increases the difficulty of detecting them, which makes it very possible for them to become epidemic. In this paper, we propose an analytical model for P2P passive worm propagation by adopting epidemiological approaches so as to identify their behaviors and predict the tendency of their propagation accurately. Compared with a few existing models, dynamic characteristics of P2P networks are taken into account. Based on this proposed model, the sufficient condition for the global stability of the worm free equilibrium is derived by applying epidemiological theories. Large scale simulation experiments have validated both the proposed model and the condition.     

P2P环境下文件共享的信任建立博弈模型及稳态分析*

P2P环境下文件共享中节点的信任建立是彼此进行安全交互的前提,现有的信任关系的建立依赖于可信的第三方,但在P2P网络中没有中心服务器和可信第三方提供担保,这种节点信任关系的建立相当困难。为此,借助演化博弈理论提出了一种信任建立博弈模型,从而为P2P文件共享中陌生节点提供信任保障。运用复制动态原理对信任建立博弈模型进行了求解分析,并对P2P文件共享系统的稳态进行了分析,给出初步仿真实验结果。     

P2P文件共享网中病毒传播建模

鉴于病毒在P2P文件共享网中的巨大危害性,对P2P文件共享网和P2P病毒的传播特点进行了深入的分析,并在此基础上提出了P2P病毒的传播模型。为了考查模型中各参数对病毒传播的影响,使用了专门的数字分析软件进行了大规模仿真实验。不同参数对病毒传播有着不同影响这一仿真实验结果表明,可以通过控制那些影响大的参数来抑制病毒传播。