P2P空间矢量数据索引网络路由机制的研究与实现

随着地理信息系统的普及,越来越多的用户希望在线获取空间服务和空间数据。P2P技术为矢量地理数据的处理提供了充分的计算能力和服务能力,在P2PGIS系统中,索引网络的路由效率是主要问题之一。文中在已有的理论模型基础之上,采用结构化P2P网络协议Chord,扩展和修改JXTA路由协议规范,整合分布式哈希表（DHT）技术,实现了一个高效的、负载均衡的P2P空间矢量数据索引网络。实验结果表明,该索引网络比集中式索引网络具有更高的矢量数据传输效率。     

An Alliance Based Peering Scheme for P2P Live Media Streaming

While recent measurement studies have shown the effectiveness of P2P network in media streaming, there have been questions raised about the quality of service (QoS), reliability of streaming services and sub optimal uplink utilization in particular. P2P streaming systems are inherently less reliable because of churn, internet dynamics, node heterogeneity and randomness in the swarm. We present a new model for P2P media streaming based on clustering of peers, called alliances. We show that alliance formation is a loosely coupled and an effective way to organize the peers. We show that our model maps to a ldquosmall-worldrdquo network, which form efficient overlay structures and are robust to network perturbations such as churn. We present a comparative simulation based study of our model with CoolStreaming/DONet and present a quantitative performance evaluation. Simulation results are promising and show that our model scales well under varying workloads and conditions, delivers near optimal levels of QoS, and for most cases, performs at par or even better than CoolStreaming/DONet.     

基于P2P的数据索引与查询

现有的基于DHT的P2P系统只能通过精确匹配整个数据识别器来查询数据。但用户一般只有部分信息可以确认这些信息,为了在用户需求和基于DHT的P2P系统能力间架起一座桥梁,本文提出了一种新的索引和查询数据的方法。这种方法在数据的XML描述上建立了DHT索引,并方便了Xpath表达式的复杂查询。     

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。     

Workflow Architecture for Interactive Video Management Systems

This paper introduces an interactive video system and its architecture where several systems cooperate to manage the services of interactive video. Each system is specialized according to the data it handles and the functionality it performs. A system can be a database (for billing purposes) or just a video store system (to store the video data) lacking the typical features of a database or an information retrieval system to support indexing and querying of video data. Because quality of service is an important requirement for whole management system, a specific system is introduced in the architecture. Such system monitors the bandwidth of the network, the buffer size and the frame size and rate. The resulting architecture of interactive video system consists of several systems cooperating through an active rules based workflow system to integrate their functionalities while preserving autonomy, extensibility and data integrity where necessary.     

Design and analysis of a peer-assisted VOD provisioning system for managed networks

With the rise of VOD (Video-on-Demand) services provisioning as a successful service on the Internet and managed networks, we are witnessing a drive towards cost-efficiency and economies of scale. Many broadband operators around the world are experimenting with P2P (Peer-to-Peer) systems centered on STBs (Set-Top-Boxes) to increase the competitiveness of their VOD services offering. By leveraging the storage and uplink bandwidth capacities available at a certain number of STBs operated by the broadband operator, the savings in terms of backend streaming capacities will represent sizable and decisive gains in cost. In these systems, video contents are usually fragmented into a number of complementary content fragments, called sub-streams, which are randomly injected in the network of STBs, and the VOD service is essentially provisioned through multisource streaming sessions from neighboring STBs to the requesting STB. One of the main challenges in such peer-assisted streaming systems remains the maximization of the utilization of STB resources utility for a given content popularity pattern. In this paper, we specifically focus on the content injection strategy and how the different content fragments should be dispatched in the network to achieve the highest performance in the VOD services provisioning epoch. We demonstrate that the random injection strategy is not appropriate for maximizing the number of simultaneous VOD streaming sessions in the network. Our objective is to first gain a better understanding of the factors driving P2P-based VOD streaming systems and provide guidelines to better operate such systems and ultimately give service operators the tools to achieve different performance objectives and/or fit specific network configurations. Further, we propose a new content dispatching strategy that maximizes the number of served VOD sessions by balancing the streaming load among the different STBs. Finally, we propose a complementary streaming resources reprovisioning mechanism that acts in real-time to reprovision the resources for serving VOD sessions to new STBs and to release trapped resources for new incoming VOD service requests.     

基于元数据的地下水数据共享

地下水数据共享平台是一个分布式面向网络的系统。采用元数据集中管理、数据体分散存储的策略可以共享分布异构的地下水数据资源。基于RDF/XML框架定制地下水元数据,使得地下水元数据可以与其他元数据标准进行交换,同时可以方便地对其进行扩展。以元数据为核心,以数据汇交—数据查询—数据浏览下载为主线,设计了地下水数据共享平台的功能。在J2EE环境下,实现了地下水数据共享平台,其中空间数据服务采用空间服务元数据和ArcIMS相结合的方式实现。     

Divide, Compress and Conquer: Querying XML via Partitioned Path-Based Compressed Data Blocks

We propose a novel partition path-based (PPB) grouping strategy to store compressed XML data in a stream of blocks. In addition, we employ a minimal indexing scheme called block statistic signature (BSS) on the compressed data, which is a simple but effective technique to support evaluation of selection and aggregate XPath queries of the compressed data. We present a formal analysis and empirical study of these techniques. The BSS indexing is first extended into effective cluster statistic signature (CSS) and multiple-cluster statistic signature (MSS) indexing by establishing more layers of indexes. We analyze how the response time is affected by various parameters involved in our compression strategy such as the data stream block size, the number of cluster layers, and the query selectivity. We also gain further insight about the compression and querying performance by studying the optimal block size in a stream, which leads to the minimum processing cost for queries. The cost model analysis provides a solid foundation for predicting the querying performance. Finally, we demonstrate that our PPB grouping and indexing strategies are not only efficient enough to support path-based selection and aggregate queries of the compressed XML data, but they also require relatively low computation time and storage space when compared with other state-of-the-art compression strategies.     

A dependable multisource streaming system for peer-to-peer -based video on demand services provisioning

In this article, we present the design, implementation, and analysis of a scalable VOD (Video On Demand) distribution architecture for IP networks. The focus of our work is on the underlying multisource streaming architecture upon which the P2P (Peer-to-Peer) -based VOD services provisioning system relies. While multipoint-to-point multisource streaming is the core building block for a distributed VOD services provisioning system, it also introduces new reliability challenges as the streaming failure probability increases with the number of sources in a session. A major contribution of our work is the design of a suite of distinct yet complementary reliability/failover mechanisms that can be leveraged to improve the dependability of multisource streaming, and the viability of P2P-based VOD systems in general. Our work shows that the reliability/failover mechanisms can be arranged, combined, and alternated in advanced adaptation policies in order to deal with different conditions exhibited by the network. Another contribution of our work consists of implementing and assessing the performance of the different reliability mechanisms and adaptation policies in a real prototype system. We evaluate both the accuracy of streaming problems diagnosis, and the efficiency of the reliability mechanisms, in two adaptation strategies: one responsive to loss variation, and the other responsive to delay variation.     

ProcessAtlas: A scalable and extensible platform for business process analytics

In today's knowledge‐, service‐, and cloud‐based economy, an overwhelming amount of business‐related data are being generated at a fast rate daily from a wide range of sources. These data increasingly show all the typical properties of big data: wide physical distribution, diversity of formats, nonstandard data models, and independently managed and heterogeneous semantics. In this context, there is a need for new scalable and process‐aware services for querying, exploration, and analysis of process data in the enterprise because (1) process data analysis services should be capable of processing and querying large amount of data effectively and efficiently and, therefore, have to be able to scale well with the infrastructure's scale and (2) the querying services need to enable users to express their data analysis and querying needs using process‐aware abstractions rather than other lower‐level abstractions. In this paper, we introduce ProcessAtlas, ie, an extensible large‐scale process data querying and analysis platform for analyzing process data in the enterprise. The ProcessAtlas platform offers an extensible architecture by adopting a service‐based model so that new analytical services can be plugged into the platform. In ProcessAtlas, we present a domain‐specific model for representing process knowledge, ie, process‐level entities, abstractions, and the relationships among them modeled as graphs. We provide services for discovering, extracting, and analyzing process data. We provide efficient mapping and execution of process‐level queries into graph‐level queries by using scalable process query services to deal with the process data size growth and with the infrastructure's scale. We have implemented ProcessAtlas as a MapReduce‐based prototype and report on experiments performed on both synthetic and real‐world datasets.     

Modeling and evaluating IPTV applications in WiMAX networks

Internet Protocol-based Television (IPTV) is a digital television service which delivers television content via an IP network. The rapid growth of wireless network technology in recent years has changed, the way people access the Internet. Adding mobility to IPTV can create a truly compelling ubiquitous service which spans different network domains and varied IP-enabled terminals and devices, such as set-top boxes, PCs and cell phones. However, extending IPTV service to wireless networks requires overcoming bandwidth bottlenecks and high packet loss rates. Following the IEEE 802.16 standard, worldwide interoperability for microwave access (WiMAX) features high data rates and large service coverage, offering a wireless broadband solution for IPTV services. While previous research has focused on creating a broadband IPTV service few studies have practically evaluated IPTV applications in a wireless broadband network environment. In this paper, we model and evaluate a common constant bit rate (CBR)¹ based IPTV application and an IPTV live streaming (PPStreaming)² application while retrieving IPTV content via a WiMAX network. We also use the NS2 simulation tool to evaluate the performance of these two IPTV applications. The evaluation metrics include latency, packet loss, data rate and throughput statistics when the two IPTV applications are run in the WiMAX network. ¹The simplest IPTV solution is to convey video content by CBR. IPTV operators and content delivery networks relay CBR streaming content to control the demand for network capacity. Broadcasters prefer CBR video as it conserves bandwidth resources, but CBR delivery can degrade video quality result in higher overall demand on network capacity. ²PPStreaming (also referred to as P2P streaming Internet TV) is a network for live media streaming. In principle it’s similar to BitTorrent (BT) in that it provides stable and smooth broadcast of TV programs to broadband users. Unlike traditional streaming media, PPStreaming adopts P2P-streaming technology and supports full-scale visits with tens of thousands of simultaneous users. Its client software can be used in the browser or as a standalone executable.     

基于CDN的流媒体点播系统研究

传统的流媒体系统存在响应速度慢、用户点播失败率高、播放不流畅等问题,在一定程度上制约了相关信息的发布。结合CDN技术设计高速的流媒体点播系统,其基本思想是借助CDN技术在原来的媒体点播系统上架构一层新的网络覆盖层,统一管理流媒体资源和用户的访问,进而提高流媒体系统的服务性能,并且完善系统的管理功能。     

基于CDN的流媒体点播系统研究

传统的流媒体系统存在响应速度慢、用户点播失败率高、播放不流畅等问题,在一定程度上制约了相关信息的发布。结合CDN技术设计高速的流媒体点播系统,其基本思想是借助CDN技术在原来的媒体点播系统上架构一层新的网络覆盖层。统一管理流媒体资源和用户的访问,进而提高流媒体系统的服务性能,并且完善系统的管理功能。     

云环境下P2P流媒体传输关键技术

随着流媒体应用需求的日益增加,不断改进和完善现有流媒体系统性能势在必行,将云计算引入流媒体系统成为未来流媒体系统的一大趋势．本文简单分析了云计算、CDN（ContentDeliveryNetwork）St]P2P（PeertoPeer）网络的优缺点和研究现状．主要讨论并分析了云环境下的P2P流媒体传输系统所面临的带宽问题、流媒体数据处理、服务质量问题和系统中的关键技术——虚拟化技术、存储管理技术、调度技术和复制技术．此外,从搭建云计算实验环境角度。本文列举了目前比较流行的5种仿真实验手段．     

Airborne laser scanning data storage and indexing: state-of-the-art review

While the rapid growth in the availability and quality of airborne laser scanning data offers unprecedented information, it challenges the existing data management and dissemination solutions. Data management has become a bottleneck to effective laser scanning data exploration. This paper documents the state-of-the-art techniques for aerial laser scanning (ALS) data storage and indexing during the post-processing stage. A brief history of laser scanning technology is presented with the intention to offer an overview about the evolution of the technology from the data point of view inclusive of full waveform data management. The key strategies for data handling, including data modelling and indexing, are extensively discussed.     

Data storage practices and query processing in XML databases: A survey

With the rapid emergence of XML as a data exchange standard over the Web, storing and querying XML data have become critical issues. The two main approaches to storing XML data are (1) to employ traditional storage such as relational database, object-oriented database and so on, and (2) to create an XML-specific native storage. The storage representation affects the efficiency of query processing. In this paper, firstly, we review the two approaches for storing XML data. Secondly, we review various query optimization techniques such as indexing, labeling and join algorithms to enhance query processing in both approaches. Next, we suggest an indexing classification scheme and discuss some of the current trends in indexing methods, which indicate a clear shift towards hybrid indexing.     

基于网络编码的对等网流媒体传输模型和算法

在对等网(peer-to-peer,简称P2P)流媒体系统中,节点(用户)的输出带宽(上行带宽)容量利用率的提高能够降低服务器的带宽开销.网络编码可以实现组播的最大吞吐率,因而具有提高系统中节点输出带宽容量利用率的潜力.将随机线性网络编码应用到P2P流媒体系统中,建立了基于随机线性网络编码的P2P流媒体传输过程模型,并据此建立传输算法的优化模型,比较研究了贪婪式算法、最少者优先算法和随机算法等.优化结果表明,随机算法可以平等均匀地获取数据包,能够最充分地利用节点的输出带宽容量,降低服务提供商的运营成本.通过对优化模型解的分析对实际系统中的传输算法给出了设计指导原则.     

面向嵌入式机顶盒终端的P2P网络电视直播系统的设计与实现

针对当前IPTV直播应用中,集中服务模式对服务器性能和网络设施要求较高、可扩展性较差的问题,提出了一种基于P2P(点对点)技术的直播系统Clear Live。与现有的P2P视频系统只针对PC终端的情况不同,该系统主要面向IPTV应用,面向嵌入式机顶盒终端,并兼容PC终端。Clear Live针对机顶盒终端的特点和IPTV应用的环境做了适当的和针对性的设计。实际系统测试结果表明,Clear Live系统能在较低的硬件配置下为大量用户提供高质量的直播服务。     

一种基于城市交通网络的移动对象全时态索引

高效地管理移动对象以支持查询是一个重要课题.为了支持在城市交通网络上的移动对象过去、现在和将来位置查询,提出了一种新的索引技术.首先提出基于模拟预测的位置表示模型来改进对移动对象将来运动轨迹的预测精度;其次根据城市交通网的特征,设计了一种全新的动态结构自适应单元(AU),将其开发为一个基于R树的索引结构(current-Au);最后在AU的基础上进行扩展(past-AU)使其支持移动对象历史轨迹查询并且避免了大量的死空间.实验证明,AU索引优于传统的TPR树和TB树索引.     

基于QoS的P2P网络服务及流媒体传输

现有的P2P网络服务缺乏服务质量保证,很难应用于商业领域。将服务质量属性引入P2P网络服务,提出了P2P网络中服务组合模型,提出了基于P2P的数字音视频流媒体传输的问题及解决办法。