TRUST BY ASSOCIATION: A META‐REPUTATION SYSTEM FOR PEER‐TO‐PEER NETWORKS

Trust mechanisms are used in peer‐to‐peer (P2P) networks to help well‐behaving peers find other well‐behaving peers with which to trade. Unfortunately, these trust mechanisms often do little to keep badly behaving peers from entering and taking advantage of the network, which makes the resulting network difficult or impossible to use for legitimate purposes such as e‐commerce. We propose trust by association, a way of tying peers together in invitation‐only P2P networks in such a way as to encourage the removal of badly behaving peers. We use invitations to create a structure within the otherwise ad hoc P2P network. Using this structure, we create a meta‐reputation system where we measure a peer’s trustworthiness not only by its own behavior, but also by the behavior of the peers it has invited to join. The connection created between the peers takes advantage of the external social relationship that must exist before a peer can be invited into the network. The result is a P2P network where, rather than just trying to marginalize badly behaving peers, there is incentive to kick them out of the network. We present results from a simple simulation showing that our approach works well in general when combined with and compared to an existing trust mechanism.     

DrawCAD: using deductive object‐relational databases in CAD

Computer‐aided design (CAD) involves the use of computers in the various stages of engineering design. CAD has large volumes of data with complex structures that need to be stored and managed effectively and properly. Database systems provide general purpose programs that can be used to access and manipulate large amounts of data stored in the database. They also provide an independence between the program accessing data and the database. It is therefore important to use database systems to store CAD data in the most efficient and effective manner for easy retrieval and better management. Graphical objects can be created, in CAD, by reusing previously created objects. The data of these objects have references to the other objects they contain. Deductive object‐relational databases not only provide direct support for the effective storage and efficient access to large amounts of data with complex structures on disk, but also perform the inferences and computations to obtain the complete data of graphical objects that reuse other objects. They should be able to play a major role in CAD systems. This is the idea behind the development of the DrawCAD system. DrawCAD is a CAD system built on top of the Relationlog object‐relational deductive database system. It facilitates the creation of graphical objects by reusing previously created objects. The DrawCAD system illustrates how CAD systems can be developed, using database systems to store and manage data and also perform the inferences and computations that are normally performed by the application program. Copyright © 2003 John Wiley & Sons, Ltd.     

The problem of upload competition in peer‐to‐peer systems with incentive mechanisms

As peer‐to‐peer (P2P) file‐sharing systems revolve around cooperation, the design of upload incentives has been one of the most important topics in P2P research for more than a decade. Several deployed systems, such as private BitTorrent communities, successfully manage to foster cooperation by banning peers when their sharing ratio becomes too low. Interestingly, recent measurements have shown that such systems tend to have an oversupply instead of an undersupply of bandwidth designers that have been obsessed with since the dawn of P2P. In such systems, the ‘selfish peer’ problem is finally solved, but a new problem has arisen: because peers have to keep up their sharing ratios, they now have to compete to upload. In this paper, we explore this new problem and show how even highly cooperative peers might in the end not survive the upload competition. On the basis of recent measurements of over half a million peers in private P2P communities, we propose and analyze several algorithms for uploader selection under oversupply. Our algorithms enable sustained sharing ratio enforcement and are easy to implement in both existing and new systems. Overall, we offer an important design consideration for the new generation of P2P systems in which selfishness is no longer an issue. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis and design of peer‐assisted video‐on‐demand services

We propose a deterministic fluid model to understand the trade‐offs in the design of peer‐assisted video‐on‐demand (VoD) services. There are three entities in this model: peers (or end users), seeders (altruistic users that own one or several complete video items), and cache servers that store and forward videos with a limited capacity. Peers join the network, download one or multiple concurrent video streams (possibly different video items), and abort the system when they wish. Peers are assumed to cooperate in a BitTorrent‐based fashion, governed by tit‐for‐tat and fair availability. The issue is to minimize the expected downloading times, choosing the set of video items that should be stored in each cache server. We first prove that the deterministic model is globally stable, and find closed expressions for the expected waiting times. Then, we introduce a combinatorial optimization problem (COP), whose nature is similar to the multiknapsack problem (where the items are videos, and knapsacks are related with the storage of cache servers). The problem turns out to be NP‐complete. Therefore, we heuristically address the problem following a GRASP (greedy randomized adaptive search procedure) methodology. Finally, we simulate the new caching methodology with real‐life traces taken from YouTube logs. The results suggest that the peer‐to‐peer philosophy is both stable and cost‐effective for on‐demand streaming purposes.     

Myriad: scalable VR via peer‐to‐peer connectivity,PC clustering,and transient inconsistency

Distributed scene graphs are important in virtual reality, both in collaborative virtual environments and in cluster rendering. Modern scalable visualization systems have high local throughput, but collaborative virtual environments (VEs) over a wide‐area network (WAN) share data at much lower rates. This complicates the use of one scene graph across the whole application. Myriad is an extension of the Syzygy VR toolkit in which individual scene graphs form a peer‐to‐peer network. Myriad connections filter scene graph updates and create flexible relationships between nodes of the scene graph. Myriad's sharing is fine‐grained: the properties of individual scene graph nodes to share are dynamically specified (in C++ or Python). Myriad permits transient inconsistency, relaxing resource requirements in collaborative VEs. A test application, WorldWideCrowd, demonstrates collaborative prototyping of a 300‐avatar crowd animation viewed on two PC‐cluster displays and edited on low‐powered laptops, desktops, and over a WAN. We have further used our framework to facilitate collaborative educational experiences and as a vehicle for undergraduates to experiment with shared virtual worlds. Copyright © 2006 John Wiley & Sons, Ltd.     

Scalable peer‐to‐peer networking architecture: DIVINE

This paper describes the issues that are involved in designing and implementing a large‐scale cooperative object database server for a collaborative virtual environment. The focus of the paper is about the way to handle the distributing factors and the communication model among nodes within a collaborative virtual environment. Within the system, all objects are decentralized and scattered among three tiers of object databases. By limiting the knowledge and refining the tasks for each server, the network and processor workload can be reduced. The objective of the system is to provide a virtual environment for distributed computing that is k‐fault tolerant and subject to expansion without the interruption of services. Copyright © 2006 John Wiley & Sons, Ltd.     

A comparative study of awareness methods for peer‐to‐peer distributed virtual environments

The increasing popularity of multi‐player online games is leading to the widespread use of large‐scale Distributed Virtual Environments (DVEs) nowadays. In these systems, peer‐to‐peer (P2P) architectures have been proposed as an efficient and scalable solution for supporting massively multi‐player applications. However, the main challenge for P2P architectures consists of providing each avatar with updated information about which other avatars are its neighbors. This problem is known as the awareness problem. In this paper, we propose a comparative study of the performance provided by those awareness methods that are supposed to fully solve the awareness problem. This study is performed using well‐known performance metrics in distributed systems. Moreover, while the evaluations shown in the literature are performed by executing P2P simulations on a single (sequential) computer, this paper evaluates the performance of the considered methods on actually distributed systems. The evaluation results show that only a single method actually provides full awareness to avatars. This method also provides the best performance results. Copyright © 2008 John Wiley & Sons, Ltd.     

Predicting repayment of borrows in peer‐to‐peer social lending with deep dense convolutional network

In peer‐to‐peer lending, it is important to predict the repayment of the borrower to reduce the lender's financial loss. However, it is difficult to design a powerful feature extractor for predicting the repayment as user and transaction data continue to increase. Convolutional neural networks automatically extract useful features from big data, but they use only high‐level features; hence, it is difficult to capture a variety of representations. In this study, we propose a deep dense convolutional network for repayment prediction in social lending, which maintains the borrower's semantic information and obtains a good representation by automatically extracting important low‐ and high‐level features simultaneously. We predict the repayment of the borrower by learning discriminative features depending on the loan status. Experimental results on the Lending Club dataset show that our model is more effective than other methods. A fivefold cross‐validation is performed to run the experiments.     

Efficient resource discovery in self‐organized unstructured peer‐to‐peer networks

In unstructured peer‐to‐peer (P2P) networks, two autonomous peer nodes can be connected if users in those nodes are interested in each other's data. Owing to the similarity between P2P networks and social networks, where peer nodes can be regarded as people and connections can be regarded as relationships, social strategies are useful for improving the performance of resource discovery by self‐organizing autonomous peers on unstructured P2P networks. In this paper, we present an efficient social‐like peer‐to‐peer (ESLP) method for resource discovery by mimicking different human behaviours in social networks. ESLP has been simulated in a dynamic environment with a growing number of peer nodes. From the simulation results and analysis, ESLP achieved better performance than current methods. Copyright © 2008 John Wiley & Sons, Ltd.     

A comprehensive peer‐to‐peer characterization model

A peer‐to‐peer (P2P) characterization model is proposed in this paper. The purposes of this model are (a) to describe through abstraction the behavior and capability of P2P computing independent of any specific application, and (b) to lead to a cost model of P2P computing. Our approach is based on abstracting the service driven nature of P2P computing separate and distinct from its implementation. This supports the first purpose. Next, we consider the integration of the two aspects. This supports the second purpose. A secondary contribution of our work is a cost model. The cost model is applied to indexing, discovery and resource utilization services. In addition, the characterization model and cost model are applied to a JXTA‐based P2P application. Copyright © 2006 John Wiley & Sons, Ltd.     

一种基于设计过程的附加式工程数据库系统的研究与设计

针对传统ＣＡＤ系统在设计信息管理上的薄弱环节,提出了一种基于设计过程的附加式工程数据库系统,将工程数据库通过应用程序和数据接口附加在ＣＡＤ系统上,通过二者的有机结合,实现了设计过程中的数据动态实时交换和在线加载,达到了数据共享、重用以及集成化、结构化管理的目的。附加式工程数据库的应用增强了ＣＡＤ功能,提高了设计效率和质量。     

Zorilla: a peer‐to‐peer middleware for real‐world distributed systems

The inherent complex nature of current distributed computing architectures hinders the widespread adoption of these systems for mainstream use. In general, users have access to a highly heterogeneous set of compute resources, which may include clusters, grids, desktop grids, clouds, and other compute platforms. This heterogeneity is especially problematic when running parallel and distributed applications. Software is needed which easily combines as many resources as possible into one coherent computing platform. In this paper, we introduce Zorilla: peer‐to‐peer (P2P) middleware that creates a single distributed environment from any available set of compute resources. Zorilla imposes minimal requirements on the resource used, is platform independent, and does not rely on central components. In addition to providing functionality on bare resources, Zorilla can exploit locally available middleware. Zorilla explicitly supports distributed and parallel applications, and allows resources from multiple sites to cooperate in a single computation. Zorilla makes extensive use of both virtualization and P2P techniques. We will demonstrate how virtualization and P2P combine into a simple design, while enhancing functionality and ease of use. Together, these techniques bring our goal a step closer: transparent, easy use of resources, even on very heterogeneous distributed systems. Copyright © 2011 John Wiley & Sons, Ltd.     

Distributed Adaptive Event‐Triggered Control for Leader‐Following Consensus of Multi‐Agent Systems

This paper studies the leader‐following consensus problem for Lipschitz nonlinear multi‐agent systems using novel event‐triggered controllers. A distributed adaptive law is introduced for the event‐based control strategy design such that the proposed controllers are independent of system parameters and only use the relative states of neighboring agents, and hence are fully distributed. Due to the introduction of an event‐triggered control scheme, the controller of the agent is only triggered at it's own event times, and thus reduces the amount of communication between controller and actuator and lowers the frequency of controller updates in practice. Based on a quadratic Lyapunov function, the event condition which uses only neighbor information and local computation at trigger instants is established. Infinite triggers within a finite time are also verified to be impossible. The effectiveness of the theoretical results are illustrated through simulation examples.     

基于对等组的P2P安全通信机制

当前对P2P网络系统安全的研究大多着眼于构造信任和名誉模型,而对通信过程的安全问题研究较少。提出了一种基于对等组实现的P2P安全通信机制——P2PSCM。P2PSCM首先为通信节点构建安全对等组。组内节点相互通信时,先通过交换公私密钥和对称密钥建立节点间安全通信渠道;然后采用对称密钥加密传输数据;最后对接收数据进行身份确认与完整性验证,确保相互间安全通信。     

A telematics service discovery platform using the distributed peer‐to‐peer networking system

In this paper, a distributed telematics peer‐to‐peer networking system is proposed to provide an efficient and feasible service discovery mechanism for mobile users. When mobile users travel on the road, they may request for some services from service providers to meet their demands. Mobile users in vehicles are assumed to go through a lot of regions, in which each region is associated with a region server. Related information of all service providers in a region is stored in its region server, and each region server is in charge of the service discovery requests from all vehicles located in its region. This paper focuses on the issues of developing a distributed peer‐to‐peer telematics service discovery networking system over the vehicular network environment for mobile users. To provide the communication mechanism for telematics service discovery among region server, mobile users, and service providers, the Telematics Service Markup Language is proposed. According to clients' demands, three types of query scenarios are proposed, which are (1) reference point based query, (2) continual query, and (3) route‐based query. Finally, we present usage examples and system implementation of distributed telematics peer‐to‐peer. Copyright © 2012 John Wiley & Sons, Ltd.     

Event‐triggered MPC design for distributed systems toward global performance

This paper studies the coordination control problem of stabilizing large‐scale dynamically coupled systems via a novel event‐triggered distributed model predictive control (DMPC) approach. In order to achieve global performance, certain constraints relevant to the triggering instant are imposed on the DMPC optimization problem, and triggering mechanisms are designed by taking into account coupling influences. Specifically, the triggering conditions derived from the feasibility and stability analysis are based on the local subsystem state and the information received from its neighbors. Based on these triggering mechanisms, the event‐triggered DMPC algorithm is built, and a dual‐mode strategy is adopted. As a result, the controllers solve the optimization problem and coordinate with each other asynchronously, which reduces the amount of communication and lowers the frequency of controller updates while achieving global performance. The recursive feasibility of the proposed event‐triggered DMPC algorithm is proved, and sufficient parameter conditions about the prediction horizon and the triggering threshold are established. It shows that the system state can be gradually driven into the terminal set under the proposed strategy. Finally, an academic example and a realistic simulation problem to the water level of a 4‐tank system are provided to verify the effectiveness of the proposed algorithm.     

基于改进Kademlia协议的分布式爬虫

随着互联网信息的爆炸式增长,搜索引擎和大数据等学科迫切需要一种高效、稳定、可扩展性强的爬虫架构来完成数据的采集和分析.本文借助于对等网络的思路,使用分布式哈希表作为节点间的数据交互的载体,同时针对网络爬虫自身的特点,对分布式哈希表的一种实现——Kademlia协议进行改进以满足分布式爬虫的需求.在此基础上设计并完善了具有可扩展性和容错性的分布式爬虫集群.在实际试验中,进行了单机多线程实验和分布式集群的实验,从系统性能角度和系统负载角度进行分析,实验结果表明了这种分布式集群方法的有效性.     

火灾报警器布线系统的设计与实现

为了方便消防工程的设计人员和管理人员,利用同一个系统界面进行工作,因此采用面向对象方法开发该系统.该系统既具备一般绘图软件的功能,能为设计人员提供一个设计报警器布线的平台;又具备数据库管理功能,可以让管理人员浏览楼层的布线,录入及查询报警器的相关信息,还能对火灾情况进行实时监控并自动生成报警日志等.     

Independent updates and incremental agreement in replicated databases

Update propagation and transaction atomicity are major obstacles to the development of replicated databases. Many practical applications, such as automated teller machine networks, flight reservation, and part inventory control, do not require these properties. In this paper we present an approach for incrementally updating a distributed, replicated database without requiring multi-site atomic commit protocols. We prove that the mechanism is correct, as it asymptotically performs all the updates on all the copies. Our approach has two important characteristics: it is progressive, and non-blocking.Progressive means that the transaction's coordinator always commits, possibly together with a group of other sites. The update is later propagated asynchronously to the remaining sites.Non-blocking means that each site can take unilateral decisions at each step of the algorithm. Sites which cannot commit updates are brought to the same final state by means of areconciliation mechanism. This mechanism uses the history logs, which are stored locally at each site, to bring sites to agreement. It requires a small auxiliary data structure, called reception vector, to keep track of the time unto which the other sites are guaranteed to be up-to-date. Several optimizations to the basic mechanism are also discussed. Recommended by: Ahmed Elmagarmid