A distributed approach to node clustering in decentralized peer-to-peer networks

Connectivity-based node clustering has wide-ranging applications in decentralized peer-to-peer (P2P) networks such as P2P file sharing systems, mobile ad-hoc networks, P2P sensor networks, and so forth. This paper describes a connectivity-based distributed node clustering scheme (CDC). This scheme presents a scalable and efficient solution for discovering connectivity-based clusters in peer networks. In contrast to centralized graph clustering algorithms, the CDC scheme is completely decentralized and it only assumes the knowledge of neighbor nodes instead of requiring a global knowledge of the network (graph) to be available. An important feature of the CDC scheme is its ability to cluster the entire network automatically or to discover clusters around a given set of nodes. To cope with the typical dynamics of P2P networks, we provide mechanisms to allow new nodes to be incorporated into appropriate existing clusters and to gracefully handle the departure of nodes in the clusters. These mechanisms enable the CDC scheme to be extensible and adaptable in the sense that the clustering structure of the network adjusts automatically as nodes join or leave the system. We provide detailed experimental evaluations of the CDC scheme, addressing its effectiveness in discovering good quality clusters and handling the node dynamics. We further study the types of topologies that can benefit best from the connectivity-based distributed clustering algorithms like CDC. Our experiments show that utilizing message-based connectivity structure can considerably reduce the messaging cost and provide better utilization of resources, which in turn improves the quality of service of the applications executing over decentralized peer-to-peer networks.     

面向用户需求的非结构化P2P资源定位泛洪策略

在非结构化P2P网络中,如何对用户所需资源进行快速、准确定位是当前研究的热点问题,也是P2P应用领域面临的核心问题之一.相关的非结构化P2P资源定位算法在查准率、查全率和查询成本上难以同时被优化,这会造成严重的网络带宽负担以及巨大的索引维护开销.为此,提出一种面向用户需求的非结构化P2P资源定位策略(user requirements resource location strategy,简称U2RLS).该策略的创新点是:在原有非结构化P2P网络资源定位泛洪算法的基础上,融入用户需求、用户偏好、用户兴趣度等因素,首先进行用户资源子网划分;采用带有用户需求信息的泛洪和查询索引机制,对用户所需资源进行精确定位.该策略有效避免了因海量信息引起的网络风暴、信息重叠和资源搜索偏覆盖等问题,从而解决了查询节点盲目使用中继节点的现象.实验结果表明:面向用户需求的非结构化P2P资源定位策略U2RLS以其高搜索成功率、有限网络资源消耗和短查询时间响应等优势,能够显著地提高用户资源定位效率.     

Enhancing Search Performance in Unstructured P2P Networks Based on Users' Common Interest

Peer-to-peer (P2P) networks establish loosely coupled application-level overlays on top of the Internet to facilitate efficient sharing of resources. They can be roughly classified as either structured or unstructured networks. Without stringent constraints over the network topology, unstructured P2P networks can be constructed very efficiently and are therefore considered suitable to the Internet environment. However, the random search strategies adopted by these networks usually perform poorly with a large network size. In this paper, we seek to enhance the search performance in unstructured P2P networks through exploiting users' common interest patterns captured within a probability-theoretic framework termed the user interest model (UIM). A search protocol and a routing table updating protocol are further proposed in order to expedite the search process through self organizing the P2P network into a small world. Both theoretical and experimental analyses are conducted and demonstrated the effectiveness and efficiency of our approach.     

基于P2P的语义检索系统设计

P2P是近年来网络研究领域的热点。当前P2P网络的研究多集中在文件共享的应用,其检索机制只支持基于关键词的查询,缺乏对语义检索的支持。本文将语义网技术和P2P的优点结合起来,建立P2P网络的语义检索机制。通过建立基于本体概念的分布式倒排索引,使检索过程不再是关键词的精确匹配,而是通过不同节点本体中的概念之间的语义关系的逻辑推理实现检索请求与文档在语义上的匹配。实验表明,本文提出的结构化P2P网络语义检索方法,比基于关键词精确匹配的检索方法有较高的查全率和查准率。     

基于本体的P2P网络资源检索算法研究

为使基于DHT的结构化P2P网络支持语义检索,提高查全率,提出一种基于DHT和本体的搜索方法SOC (semantic ontology chord).针对结构化P2P网络搜索时只能根据关键词精确匹配的缺点,改进了DHT中的资源标识符,利用本体技术进行模糊搜索,并使兴趣相似节点在逻辑上处于邻近位置,提高了P2P网络中资源检索的查全率.使用Peer-Sim模拟器进行了仿真模拟,仿真实验结果表明,随着网络规模的增加,该搜索方法相比Chord模型具有较高的查全率.     

A cache-based search algorithm in unstructured P2P networks

Peer-to-Peer (P2P) network is an important component to implement next generation Internet, how to quickly and efficiently search the resources in P2P networks has become one of the most critical issues, at the same time, this is one of greatest concern to users. This paper describes the basic Flooding Peer-to-Peer network search method, followed by analysis of several new search methods pros and cons, and then further analysis of these algorithms is proposed based on a cache-based search algorithm: When a node of the remaining load capacity is high, it will become the center node, and form a joint topology area with the nearby nodes together, then the center node and ordinary nodes also need to store the index cache, at the local region the overheating resources will be copied to the local (that is, the contents cache). The simulation shows that the algorithm can effectively improve the hit rates of resources searching, reduce the query delay.     

非结构化P2P网络的增量式查询

基于非结构化P2P网络的应用日益广泛,参与共享资源的节点越来越多,且呈海量增长趋势.如何在海量节点、海量资源的情况下,对同一查询语义进行增量式查询,是一个重要而颇具挑战性的问题.提出了一个通用的近似依相关性大小的非结构化P2P网络增量式查询算法模型,该算法模型使得针对同一查询语义的增量式查询尽力优先访问与语义最为相关的节点,从而在完全分布式的P2P网络中获得类似Google[1]的依据资源相关性排序显示及其"下一页"的功能.     

面向非结构化P2P 网络的双向随机漫步搜索机制

为解决目前Random Walk改进算法中过于依赖历史搜索记录而导致动态网络环境下搜索命中率低、网络开销过高和稀有资源的搜索成功率提高不明显等问题,通过分析随机漫步的基本性质和易转向高度数节点的搜索特性,提出了一种双向随机漫步搜索机制——BRWS(bidirectional random walk search),并证明了其能够提高包括稀有资源在内的搜索成功率,抗扰动性强.分别在静态和动态网络环境中,将Random Walk,APS(adaptive probabilistic search),PQR(path-traceable query routing),P2PBSN(peer-to-peer based on social network)和BRWS基于Random Graph、Scale Free网络、Small World网络3种拓扑进行了对比实验.结果表明,BRWS可以以较少的网络搜索代价,极大地提高搜索成功率;并在动态网络环境中,对稀有资源的搜索成功率也有显著提高.所提出的方法可适用于P2P文件分发网络应用中.     

P2P网络环境中节点信息交换的信任机制研究

P2P网络的匿名性和动态性带来了许多安全问题,传统的信任管理模型并不能很好地适应P2P网络环境,动态信任模型是新的研究热点。本文在对现有P2P环境中的信任机制进行分析的基础上,通过研究消费节点对服务节点的信任,针对节点间的信息交换活动提出了一种改进的信用评估模型,评估服务提供者在信息交换过程中的信用度变化过程;并引入风险机制,分析了P2P网络中节点间进行信息交换的风险。实验证明,该模型能有效地抗信用炒作和抗周期性欺骗。     

P2P网络分布式证书管理方法的研究

在P2P环境下需要证书来构建信任关系和授权访问，选择一种适合P2P环境的SPKI／SDSI证书，并且利用分布式哈希表算法实现了在分布式网络中高效地发布和快速查找到SPKI／SDSI证书。该方法是高效和健壮的。     

Efficient semantic-based content search in P2P network

Most existing peer-to-peer (P2P) systems support only title-based searches and are limited in functionality when compared to today's search engines. We present the design of a distributed P2P information sharing system that supports semantic-based content searches of relevant documents. First, we propose a general and extensible framework for searching similar documents in P2P network. The framework is based on the novel concept of hierarchical summary structure. Second, based on the framework, we develop our efficient document searching system by effectively summarizing and maintaining all documents within the network with different granularity. Finally, an experimental study is conducted on a real P2P prototype, and a large-scale network is further simulated. The results show the effectiveness, efficiency, and scalability of the proposed system.     

Distributed optimization of P2P live streaming overlays

Peer-to-peer live media streaming over the Internet is becoming increasingly more popular, though it is still a challenging problem. Nodes should receive the stream with respect to intrinsic timing constraints, while the overlay should adapt to the changes in the network and the nodes should be incentivized to contribute their resources. In this work, we meet these contradictory requirements simultaneously, by introducing a distributed market model to build an efficient overlay for live media streaming. Using our market model, we construct two different overlay topologies, tree-based and mesh-based, which are the two dominant approaches to the media distribution. First, we build an approximately minimal height multiple-tree data dissemination overlay, called Sepidar. Next, we extend our model, in GLive, to make it more robust in dynamic networks by replacing the tree structure with a mesh. We show in simulation that the mesh-based overlay outperforms the multiple-tree overlay. We compare the performance of our two systems with the state-of-the-art NewCoolstreaming, and observe that they provide better playback continuity and lower playback latency than that of NewCoolstreaming under a variety of experimental scenarios. Although our distributed market model can be run against a random sample of nodes, we improve its convergence time by executing it against a sample of nodes taken from the Gradient overlay. The evaluations show that the streaming overlays converge faster when our market model works on top of the Gradient overlay.     

Toward a synergy between P2P and grids

Peer-to-peer (P2P) networks and grids are distributed computing models that enable decentralized collaboration by integrating computers into networks in which each can consume and offer services. P2P is a class of self-organizing systems or applications that takes advantage of distributed resources storage, processing, information, and human presence available at the Internet's edges. A grid is a geographically distributed computation platform comprising a set of heterogeneous machines that users can access through a single interface. Both are hot research topics because they offer promising paradigms for developing efficient distributed systems and applications. Unlike the classic client-server model, in which roles are well separated, P2P and grid networks can assign each node a client or server role according to the operations they are to perform on the network - even if some nodes act more as server than as client in current implementations. In spite of current practices and thoughts, the grid and P2P models share several features and have more in common than we perhaps generally recognize. It is time to consider how to integrate these two models. A synergy between the two research communities, and the two computing models, could start with identifying the similarities and differences between them.     

Assisted Peer-to-Peer Search with Partial Indexing

In the past few years, peer-to-peer (P2P) networks have become a promising paradigm for building a wide variety of distributed systems and applications. The most popular P2P application till today is file sharing, e.g., Gnutella, Kazza, etc. These systems are usually referred to as unstructured, and search in unstructured P2P networks usually involves flooding or random walking. On the other hand, in structured P2P networks (DHTs), search is usually performed by looking up a distributed inverted index. The efficiency of the search mechanism is the key to the scalability of a P2P content sharing system. So far, neither unstructured nor structured P2P networks alone can solve the search problem in a satisfactory way. In this paper, we propose to combine the strengths of both unstructured and structured P2P networks to achieve more efficient search. Specifically, we propose to enhance search in unstructured P2P overlay networks by building a partial index of shared data using a structured P2P network. The index maintains two types of information: the top interests of peers and globally unpopular data, both characterized by data properties. The proposed search protocol, assisted search with partial indexing, makes use of the index to improve search in three ways: first, the index assists peers to find other peers with similar interests and the unstructured search overlay is formed to reflect peer interests. Second, the index also provides search hints for those data difficult to locate by exploring peer interest locality, and these hints can be used for second-chance search. Third, the index helps to locate unpopular data items. Experiments based on a P2P file sharing trace show that the assisted search with a lightweight partial indexing service can significantly improve the success rate in locating data than Gnutella and a hit-rate-based protocol in unstructured P2P systems, while incurring low search latency and overheads.     

User density sensitive P2P streaming in wireless mesh networks

Link rate allocation is very important for supporting high video playback rate in Peer-to-Peer video streaming. Although many studies can be found on resource allocation in P2P streaming in wired networks, very few studies have studied the problem in wireless networks, especially in Wireless multi-hop Mesh Networks (WMNs), which is still challenging. To maximize the users’ satisfaction of P2P streaming in WMNs, this paper focuses on link rate allocation problem and proposes a fully distributed algorithm to efficiently utilize the upload and download bandwidth of wireless mesh nodes. We first build an efficient P2P streaming system based on the experimental results from real deployment of our wireless mesh testbed. Then we design an efficient distributed algorithm based on the solution to a linear optimization model, which optimizes towards a user-density-related objective to decide the best streaming rates among peers. Our scheme is resilient to network dynamics that is characteristic in wireless multi-hop peer-to-peer networks. The simulation experiments demonstrate the significant performance enhancement by using the proposed rate allocation algorithm in WMNs.     

基于节点有效通信率的P2P网络拓扑优化

分析了P2P网络中产生大量冗余通信开销的原因,根据不同节点对查询表现出不同的性能,定义了节点有效通信率,让具有更高有效通信率的节点具有更大的连接度。采用了基于流言的闲谈机制来获取整个网络的平均有效通信率和平均节点连接度,提出节点度优化模型及连接策略。实验结果显示文中的拓扑优化方法大幅提高了资源搜索的整体性能。     

PROSE: Proactive, Selective CDN Participation for P2P Streaming

Many production peer-to-peer (P2P) streaming systems use content delivery networks (CDN) to protect the user’s quality of experiences. Thus, how to efficiently utilize the capacity of CDN (e.g., which peers receive services from the CDN nodes) is a problem of practical significance. Existing solutions adopt a passive, on-demand approach, which is inefficient in utilizing CDN resources. In this paper, we propose PROSE, a simple, novel scheme to achieve proactive, selective CDN participation for P2P streaming. PROSE introduces novel concepts such as choke point expansion nodes/super nodes and leads to efficient, light-weighted, and distributed algorithms to identify and serve these nodes using CDN. Our experimental results show that PROSE achieves at least 10%～25% performance improvement and 2～4 times overhead reduction compared with existing general CDN-P2P-hybrid schemes.     

基于校园环境的移动P2P网络体系研究与设计

由于P2P技术的广泛应用以及无线网络和移动设备的普及,人们提出了基于无线网络的移动P2P网络。文中通过分析移动P2P网络的特点和已有的网络模型,结合校园网络环境的特点,设计出基于校园环境的网络体系结构模型,并对模型的资源查找进行详细的描述。模型被划分成三层结构,底层的网络采用改进后的Kelips路由算法通信,该算法的路由复杂度是一个常数,有效减少资源查找时间,保证节点维护状态信息的实时性和正确性;由超级节点组成的中间层,实行分布式管理,采取泛洪搜索算法来通信;顶层是一些域内中心节点,负责连接外网和解决网络的安全问题。仿真实验表明：该模型能够更好地减少资源查找时间,即使大量节点失效,也可以快速检测到节点间关系变化并进行管理。     

CompuP2P: An Architecture for Internet Computing Using Peer-to-Peer Networks

Internet computing is emerging as an important new distributed computing paradigm in which resource intensive computing is integrated over Internet-scale networks. Over these large networks, different users and organizations share their computing resources, and computations take place in a distributed fashion. In such an environment, a framework is needed in which the resource providers are given incentives to share their resources. CompuP2P is a lightweight architecture for enabling Internet computing. It uses peer-to-peer networks for sharing of computing resources. CompuP2P create dynamic markets of network accessible computing resources, such as processing power, memory storage, disk space, etc., in a completely distributed, scalable, and fault-tolerant manner. This paper discusses the system architecture, functionality, and applications of the proposed CompuP2P architecture. We have implemented a Java-based prototype, and our results show that the system is light-weight and can provide almost a perfect speedup for applications that contain several independent compute-intensive tasks     

结构化对等网络中面向信誉机制的资源共享平台

针对目前因特网上提高空闲网络资源利用率的需求,提出并描述了结构化对等网络中一种面向信誉机制的资源共享平台NRSP。NRSP系统可以把因特网上用户提交的各种作业高效地映射到平台中合适的网络资源上运行,充分共享空闲处理器的周期。该系统具有非集中性、可移植性、统计性与公平性的优点,使用分布式哈希表的Pastry网络来组织节点。同时提出一种新型的分布式信誉机制,支持资源的消费者与提供者之间交换信誉信息,完成信誉信息的统计。最后实现了NRSP的原型系统,通过对各种作业场景下的应用进行测试,性能分析表明NRSP采用公平的信誉机制可以更快、更多地共享其他节点的处理器周期。