移动对等网络关键技术

P2P系统在Internet上的成功使研究者关注于分布式更强、参与性更广、更具有对等自治特征的移动网络环境.智能终端的普及和移动应用环境的逐渐成熟使得移动对等网络拥有广阔的发展前景.但当前对移动对等网络的研究还缺乏统一而明确的定义,还存在很多未能很好地解决的问题.首先,概述了移动对等网络的基本概念,给出了其定义、特征以及与移动AdHoc网络的区别,并指出了移动对等网络的相关关键技术;随后,详细综述了移动对等网络体系结构、资源搜索策略、网络结构一致性、数据分发策略、安全与隐私机制等关键技术的研究现状,对各种关键技术的研究成果给出了深入分析,并指出了各自存在的问题和缺陷.最后,讨论了移动对等网络未来的研究方向和发展趋势.     

无线传感器网络中对等数据存储策略研究

在无线传感器网络中,除了基于基站的数据传输和管理模式以外,对等数据传输以及网内数据管理同样具有非常重要的现实意义。本文论述了传感器网络中对等数据传输的应用特点和研究挑战,以及数据存储策略与对等数据传输的关系。如何设计有效的数据存储策略是对等数据传输和网内数据管理、查询的关键技术和重要研究课题。本文分析了无线传感器网络中对等数据存储策略的分类、负载平衡和查询成功率等相关问题。本文采取基于位置的分类方法,根据策略是否依赖节点的位置信息,将节点间的对等数据存储分为基于位置的策略和无位置策略。本文综述了目前的相关研究,比较了各种策略适用的网络环境和数据查询成功率、网络负载平衡等性能指标。     

对等网络环境下的构件查询访问控制框架

阐述对等网络环境下的构件查询访问控制框架及其策略与机制.首先,简要介绍当前应用较多的传统访问控制模型及其机制;接着,分析对等网络环境下构件查询访问控制的特点;最后,针对构件查询访问控制的特点,提出并详细阐述一种基于信任的构件查询访问控制框架.     

数据广播环境下基于数据共享的位置相关skyline查询

数据广播环境下位置相关skyline查询是同时涉及空间位置属性和非空间多维属性的一类新的skyline查询类型,可广泛地应用于地理信息系统、城市规划、智能交通等领域。与传统环境下的位置相关skyline查询相比,数据广播环境下位置skyline查询面临一些新的问题,如广播信道的线性特性、移动设备资源受限性等。针对这些问题,本文提出了基于数据共享的位置相关查询算法,该方法通过共享邻近移动设备缓存的查询结果来改进查询算法的性能。广泛的实验结果显示,在移动设备密度较大的对等网络中,本文提出的算法具有较明显的优势,能显著地提升查询性能。     

一种基于移动P2P改进的Gossip算法

随着移动智能终端设备的普及,移动对等网络的研究不断走向深入.经典的Gossip算法虽然可以用于移动对等网络中的数据分发,但不能很好地适应移动网络的要求,尤其是对扰动的适应性.因此,为了实现拓扑控制信息的有效传播并保持节点资源列表的副本一致性,提出了一种基于特定拓扑结构改进的Gossip算法,其通过动态调节邻居节点数据分发概率来实现同k-派系内所有节点的资源列表更新.模拟实验表明,采用此算法的数据分发效率较经典Gossip算法有明显改善,在保证网络负载较低的同时达到了泛洪数据分发策略的效率.     

嵌入式移动数据库查询优化策略研究

随着通信技术和网络技术的发展,嵌入式移动数据库正成为数据库领域的一个新的研究方向.针对嵌入式移动数据库中频繁断接性、低带宽等特性,介绍了数据广播和客户缓存两种用于嵌入式移动数据库中处理断接操作的方法,提出了基于语义的查询优化策略.研究表明,该策略能够提高移动数据库查询的效率.     

MANET中基于缓存的移动数据查询处理算法的研究

针对MANET环境中带宽有限、能量有限、存储有限和链路频繁的断接性等特点,提出了基于缓存的移动数据查询问题,证明该问题是NP完全问题,并给出一个多项式时间的近似算法,即最大节点新覆盖数据算法MD.该算法采用贪心策略,查询新覆盖数据量最大的节点,减少了查询次数,并最大限度地减少了网络中的传输时延.然后在MD算法的基础上,同时考虑了节点新覆盖数据量和链路服务质量问题,提出了一种改进的高效的启发式算法,即基于最大节点DD值的算法MDD,有效地减少了能量消耗,最小化数据传输时延,提高了网络的吞吐量.理论分析及实验结果表明提出的数据查询算法能够充分利用缓存节点的数据信息,较好地完成数据查询工作,有效地减少数据收集时延,提高查询效率.     

一种基于预测的目标跟踪传感器网络数据近似存储查询策略

节能问题是传感器网络设计的一个关键问题,在对目标跟踪传感器网络中的目标位置信息进行存储和查询处理时,也必须通过较低的通信代价来降低消息复杂度,从而达到节能的目的.分析了现存的一些数据存储和数据分发的方法,针对EASE方法查询误差较大的问题,提出了基于预测的近似查询的存储策略(Prediction-based Energy-conserving Approximate StoragE,P-EASE),并就EASE方法查询未考虑选择恰当的存储节点的问题,提出了一种基于地理位置的择优查询(Optimal Query)策略.使用半随机步行移动模型和随机路点移动模型进行了仿真实验,比较了P-EASE与EASE算法的消息量、消息复杂度、平均消息复杂度和查询误差.仿真实验证明,P-EASE比EASE查询更精确、能量更高效.     

移动对等直播流媒体系统的服务质量保证机制研究

随着移动网络及移动智能终端的发展和日益普及,移动对等(P2P)网络流媒体方面的研究已成为当前的热点。然而,P2P流媒体的移动化面临两大问题,一是流媒体的差异化服务,二是终端移动过程中的服务质量保证。针对终端的差异性,本文提出了自适应多码率服务的思想,在一个P2P节目流拓扑中,发布多个子流,用户根据自己的网络状况和能力,缓冲全部或者部分子流,并根据网络环境的变化,动态地改变自身缓冲和播放的流,为邻居节点提供差异化的服务;同时提出了一种跨域移动服务质量保证机制,包括数据预缓存、数据暂存等策略。实验证明上述方法能有效提高移动对等直播流媒体系统的服务质量。     

基于移动Agent的对等网络资源查找技术的研究

对等网络中资源共享的前提是高效的资源查找与准确的资源定位.研究了对等网络资源查找的技术,在分析已有查找策略缺陷的基础上,阐明了在采用super peer结构的对等网上引入移动Agent技术完成资源发现的优点,并给出了经过原型系统验证的实现策略.论文中描述的方法为对等网络资源查找提供了一种新的思路和有效手段.     

E-ARL: An Economic incentive scheme for Adaptive Revenue-Load-based dynamic replication of data in Mobile-P2P networks

In mobile ad hoc peer-to-peer (M-P2P) networks, frequent network partitioning occurs due to peer movement or owing to peers switching ‘off’ their mobile devices. This leads to typically low data availability in M-P2P networks, thereby necessitating data replication. This work proposes E-ARL, which is a novel Economic scheme for Adaptive Revenue-Load-based dynamic replication of data in dedicated M-P2P networks with the aim of improving data availability. Thus, E-ARL considers a mobile cooperative environment, where the MPs are working towards the same goal, and the network performance is facilitated by the economic scheme. E-ARL essentially allocates replicas based on its economic scheme. Each data item has a price in virtual currency. E-ARL requires a query issuing peer to pay the price of its queried data item to the query-serving peer and a commission to relay peers in the successful query path. The main contributions of E-ARL follow. First, it uses an economic scheme for efficiently managing M-P2P resources in a context-aware manner by facilitating effective replica hosting and message relaying by peers. Second, it collaboratively performs bid-based replica allocation to facilitate better quality of service. Third, it incorporates both revenue-balancing and load-balancing to improve peer participation and performance. Fourth, it conserves the energy of low-energy MPs to facilitate network connectivity. Our performance evaluation shows that E-ARL is indeed effective in improving peer participation in M-P2P networks, thereby improving query response times, query success rates, query hop-counts and replica allocation traffic.     

Benefit based cache data placement and update for mobile peer to peer networks

Mobile Peer to Peer (MP2P) networks provide decentralization, self-organization, scalability characters, but suffer from high latency and link break problems. In this paper, we study the cache/replication placement and cache update problems arising in such kind of networks. While researchers have proposed various replication placement algorithms to place data across the network to address the problem, it was proven as NP-hard. As a result, many heuristic algorithms have been brought forward for solving the problem. In this article, we propose an effective and low cost cache placement strategy combined with an update scheme which can be easily implemented in a decentralized way. The contribution of this paper is the adaptive and flexible cache placement and update algorithms designed for real MP2P network usage. The combination of MP2P cache placement and update is the novelty of this article. Extensive experiments are conducted to demonstrate the efficiency of the cache placement and update scheme.     

A pure peer-to-peer approach for kNN query processing in mobile ad hoc networks

Together with advanced positioning and mobile technologies, P2P query processing has attracted a growing interest number of location-aware applications such as answering kNN queries in mobile ad hoc networks. It not only overcomes drawbacks of centralized systems, for example single point of failure and bottleneck issues, but more importantly harnesses power of peers’ collaboration. In this research, we propose a pure mobile P2P query processing scheme which primarily focuses on the search and validation algorithm for kNN queries. The proposed scheme is designed for pure mobile P2P environments with the absence of the base station support. Compared with centralized and hybrid systems, our system can reduce energy consumption more than six times by making use of data sharing from peers in a reasonable mean latency of processing time for networks with high density of moving objects as can be seen in the simulation results.     

An adaptive secure communication framework for mobile peer-to-peer environments using Bayesian games

Peers in Mobile P2P (MP2P) networks exploit both the structured and unstructured styles to enable communication in a peer-to-peer fashion. Such networks involve the participation of two types of peers: benign peers and malicious peers. Complexities are witnessed in the determination of the identity of the peers because of the user mobility and the unrestricted switching (ON/OFF) of the mobile devices. MP2P networks require a scalable, distributed and light-weighted secure communication scheme. Nevertheless, existing communication approaches lack the capability to satisfy the requirements above. In this paper, we propose an Adaptive Trusted Request and Authorization model (ATRA) over MP2P networks, by exploiting the limited historical interaction information among the peers and a Bayesian game to ensure secure communication. The simulation results reveal that regardless of the peer’s ability to obtain the other such peer’s trust and risk data, the request peers always spontaneously connect the trusted resource peers and the resource peers always preferentially authorize the trusted request peers. Performance comparison of ATRA with state-of-the-art secure communication schemes over MP2P networks shows that ATRA can: (a) improve the success rate of node typing identification, (b) reduce time required for secure connections found, (c) provide efficient resource sharing, and (d) maintain the lower average cost.     

An efficient data-centric storage method using time parameter for sensor networks

In wireless sensor networks, various schemes have been proposed to efficiently store and process sensed data. Among them, the data-centric storage (DCS) scheme is one of the most well-known. The DCS scheme distributes data regions and stores the data in the sensor that is responsible for the region. The DCS based scheme was proposed to reduce the communication cost for transmitting data and to efficiently process exact queries and range queries. Recently, a KDDCS scheme was proposed to overcome storage hot-spots by dynamically readjusting the distributed data regions to sensors based on the K-D tree. However, the existing DCS based schemes including KDDCS suffer from query hot-spots that are formed when query regions are not uniformly distributed. As a result, it reduces the lifetime of the sensor network.In this paper, we propose a new DCS based scheme, called Time-Parameterized Data-Centric Storage (TPDCS), that avoids the problems of storage hot-spots and query hot-spots. To decentralize the skewed data and queries, the data regions are assigned by a time dimension as well as data dimensions in our proposed scheme. Therefore, TPDCS extends the lifetime of sensor networks. It is shown through various experiments that our scheme outperforms the existing schemes.     

Combining search and trust models in unstructured peer-to-peer networks

Effectiveness of Peer-to-Peer (P2P) systems highly depends on efficiency and scalability of their search algorithms. Moreover, managing trust is a key issue for wide acceptance of P2P computing. Surprisingly, the majority of the available trust systems ignore the underlying search algorithm and assume it is preexisting. We claim that combining search and trust systems yields significant performance gains in terms of network traffic and query success rate. In this paper, we propose a robust and efficient trust based search framework for unstructured P2P networks. Our framework maintains limited size routing indexes combining search and trust data to guide queries to most reputable nodes. By dynamically selecting reputable nodes as score managers, our scheme tracks the reputation of participating peers. In an alternative approach, we aggregate partial reputation values obtained from reverse query paths to introduce a low overhead method for estimating reputation scores of peers. Through P2P network simulation experiments, we find significant performance gains in using our framework.     

封闭式P2P网络中的离线数据存储

随着计算机与网络技术的快速发展,网络分布式存储逐渐成为存储技术研究的重点,但对离线数据存储的研究仍是个空缺.提出一种基于封闭式P2P网络的离线数据存储系统.客户端将离线数据发送至P2P网络,网络中节点利用chord路由算法存储数据;目标用户上线后,提出查询下载请求,从系统中获取与自身相关的离线数据.为了提高离线数据存取效率,每个节点保存一张包含网络中所有节点信息的路由表,离线数据的定位通过本地查找实现;另外,对传统Chord路由算法进行改进,使其更好地适应封闭式P2P网络的离线数据存储.实验表明,在封闭式网络中进行离线数据存取可以获得高的效率.     

基于环结构的传感器网络多分辨率数据存储机制

提出了一套基于环结构的传感器网络多分辨率数据存储机制,结合层次结构的存储查询方案,有效地利用了环结构的特性高效、节能地支持事件信息的不同分辨率的存储和查询操作,并采用优化的环结构参数,在基于环的层次结构数据存储架构中能够最小化网络节点的总体通信能耗.同时,对环结构多分辨率数据存储机制的相关性能从节能性、负载均衡性等多个角度进行了具体理论分析.模拟实验结果表明,基于环的层次结构存储机制能够高效、节能地支持传感器网络事件数据的多分辨率存储和查询操作.     

Top-k query processing for replicated data in mobile peer to peer networks

In mobile ad hoc peer to peer (M-P2P) networks, since nodes are highly resource constrained, it is effective to retrieve data items using a top-k query, in which data items are ordered by the score of a particular attribute and the query-issuing node acquires data items with the k highest scores. However, when network partitioning occurs, the query-issuing node cannot connect to some nodes having data items included in the top-k query result, and thus, the accuracy of the query result decreases. To solve this problem, data replication is a promising approach. However, if each node sends back its own data items (replicas) responding to a query without considering replicas held by others, same data items are sent back to the query-issuing node more than once through long paths, which results in increase of traffic. In this paper, we propose a top-k query processing method considering data replication in M-P2P networks. This method suppresses duplicate transmissions of same data items through long paths. Moreover, an intermediate node stops transmitting a query message on-demand.     

MP2P网络基于动态分组的超级节点选取

提出一种MP2P网络中基于动态分组的超级节点选取机制。根据MP2P网络中节点拥有资源的类型以及节点的物理位置等因素进行动态分组,根据阈值过滤算法和节点综合能力计算选出每组的超级节点群组和备选超级节点集合,根据每组的超级节点负载情况动态更新该组的超级节点群组。理论分析和仿真结果表明,该机制能显著降低MP2P网络中的信息检索延迟,有效提高了网络中资源的定位成功率,具有较好的网络动态扩展性。