P2P存储网络中的冗余维持

在P2P存储网络中,为保证数据安全可靠,当网络中数据丢失后需生成新的冗余数据.因此,如何快速生成新的冗余数据并保持数据的可靠性就成为评价存储网络性能的关键.网络编码作为一项新兴技术,已被证明可以提高网络吞吐率和鲁棒性.将网络编码思想引入冗余数据维持,可以加快冗余生成速度,从而提高数据可靠性.通过理论分析和仿真给出了快速修复冗余数据的方法、开销和相应的传输策略.仿真结果表明,较传统修复方式所提出的快速修复方法可以节省60%以上的传输时间.     

Visualized cognitive knowledge map integration for P2P networks

This study proposes a visualized cognitive knowledge map integration system, called VisCog, to facilitate knowledge management on P2P networks. By using the SOM (self-organized map)-like model, Egocentric SOM (ESOM), VisCog can merge the other peers' knowledge artifacts (e.g., documents) under a focal peer's knowledge structure and visually present the cognitive knowledge map of the P2P network. The experimental results from evaluating VisCog performance show that VisCog can retain an individual peer's knowledge structure while articulating with those of other peers to build its cognitive knowledge map.     

基于概率预测的P2P分布式存储副本查找

分布式存储系统是Peer-to-Peer技术的一个重要研究领域。如何实现有效的副本存储和副本查找定位是分布式存储系统的关键。DHT（Distributed Hash Tables）能够有效地实现分布式存储。在基于DHT的Peer-to-Peer分布式存储系统中提出了一种基于概率预测的副本查找和定位算法。分析并且详细描述了该算法,实现了算法的仿真模拟,分析了其性能。模拟结果显示,基于概率预测的副本查找算法通过概率的先预测能够实现高效率及高查准率的副本查找。     

A hybrid approach for estimating document frequencies in unstructured P2P networks

Scalable search and retrieval over numerous web document collections distributed across different sites can be achieved by adopting a peer-to-peer (P2P) communication model. Terms and their document frequencies are the main components of text information retrieval and as such need to be computed, aggregated, and distributed throughout the system. This is a challenging problem in the context of unstructured P2P networks, since the local document collections may not reflect the global collection in an accurate way. This might happen due to skews in the distribution of documents to peers. Moreover, central assembly of the total information is not a scalable solution due to the excessive cost of storage and maintenance, and because of issues related to digital rights management. In this paper, we present an efficient hybrid approach for aggregation of document frequencies using a hierarchical overlay network for a carefully selected set of the most important terms, together with gossip-based aggregation for the remaining terms in the collections. Furthermore, we present a cost analysis to compute the communication cost of hybrid aggregation. We conduct experiments on three document collections, in order to evaluate the quality of the proposed hybrid aggregation.     

Chord-PKI: A distributed trust infrastructure based on P2P networks

Many P2P applications require security services such as privacy, anonymity, authentication, and non-repudiation. Such services could be provided through a hierarchical Public Key Infrastructure. However, P2P networks are usually Internet-scale distributed systems comprised of nodes with an undetermined trust level, thus making hierarchical solutions unrealistic. In this paper, we propose Chord-PKI, a distributed PKI architecture which is build upon the Chord overlay network, in order to provide security services for P2P applications. Our solution distributes the functionality of a PKI across the peers by using threshold cryptography and proactive updating. We analyze the security of the proposed infrastructure and through simulations we evaluate its performance for various scenarios of untrusted node distributions.     

认证技术在P2P网络中的应用研究

本文首先简要描述了传统客户服务器模式下的身份认证概念和身份认证机制,综合分析现有认证机制的缺点,提出了一种改进的身份认证机制;然后结合P2P网络的特点,分析了P2P技术三种基本应用实例的安全需求;最后给出了认证机制在P2P网络中的应用。     

Cooperating with free riders in unstructured P2P networks

Free riding is a common phenomenon in peer-to-peer (P2P) file sharing networks. Although several mechanisms have been proposed to handle free riding—mostly to exclude free riders, few of them have been adopted in a practical system. This may be attributed to the fact that the mechanisms are often nontrivial, and that completely eliminating free riders could jeopardize the sheer power of the network arising from the huge volume of its participants. Rather than excluding free riders, we incorporate and utilize them to provide global index service to the files shared in the network, as well as to relay messages in the search process. The simulation results indicate that our mechanism not only can shift the query processing load from non-free riders to free riders, but can also significantly boost the search efficiency of a plain Gnutella. Moreover, the mechanism is quite resilient to high free riding ratio.     

A P2P-based intelligent resource discovery mechanism in Internet-based distributed systems

Internet-based distributed systems enable globally-scattered resources to be collectively pooled and used in a cooperative manner to achieve unprecedented petascale supercomputing capabilities. Numerous resource discovery approaches have been proposed to help achieve this goal. To report or discover a multi-attribute resource, most approaches use multiple messages, with one message for each attribute, leading to high overhead of memory consumption, node communication, and subsequent merging operation. Another approach can report and discover a multi-attribute resource using one query by reducing multi-attribute to a single index, but it is not practically effective in an environment with a large number of different resource attributes. Furthermore, few approaches are able to locate resources geographically close to the requesters, which is critical to system performance. This paper presents a P2P-based intelligent resource discovery (PIRD) mechanism that weaves all attributes into a set of indices using locality sensitive hashing, and then maps the indices to a structured P2P overlay. PIRD can discover resources geographically close to requesters by relying on a hierarchical P2P structure. It significantly reduces overhead and improves search efficiency and effectiveness in resource discovery. It further incorporates the Lempel–Ziv–Welch algorithm to compress attribute information for higher efficiency. Theoretical analysis and simulation results demonstrate the efficiency of PIRD in comparison with other approaches. It dramatically reduces overhead and yields significant improvements on the efficiency of resource discovery.     

改进RML路由算法及其在基于MAS的P2P系统框架中的应用

P2P计算模型很可能会成为下一个Internet技术的新亮点,基于这种模型的分布式计算已经成为当前研究的热点。目前大部分的研究项目旨在解决P2P的安全、可靠性及路由等问题。文章提出了一种改进的RML路由算法,并介绍了该算法在基于Multi-AgentSystem的P2P系统框架中的应用。     

P2P网络中基于多关键字的信息检索研究

P2P网络在信息资源共享方面获得了很大的成功,但是传统的P2P不能兼顾系统的扩展性和基于多关键字信息检索的能力.所提出的P2P模型中,构造了二维索引空间,采用DHT技术实现节点对索引空间的分区管理;依据其内容,文档被映射为索引空间中的多个点,将基于关键字的信息检索转化为在索引空间中寻找特定区域的过程.因此,系统具有很好的扩展性,并对基于多关键字信息检索提供了良好支持.