Efficient Movie Retrieval Strategies for Movie-on-Demand Multimedia Services on Distributed Networks

In this paper, for a network-based multimedia Video/Movie-on-demand(VoD/MoD) service, we design and analyze efficient retrieval strategies to minimize both the access times of the movies and the block rates. We consider a heterogeneous set of servers and a generic network topology in which clients can request for movies from any site. We design and analyze a multiple servers retrieval strategy (MSRS) to retrieve the movies requested by the clients and present a rigorous analysis on its performance with respect to access times of the requested movies and the block rates. A generalized approach of MSRS is designed in a judicious manner using a two-step approach. In the first step, we partition the available bandwidth among the requested movies and in the second step, we derive optimal portions of the movies to be retrieved from each of the servers for each movie, based on allocated bandwidths in the first step. Thus, with the optimal playback portions of the movies using aggregate retrieval bandwidth from several servers, the access times of the movies are minimized. In the first step, in addition to the access times, we minimize the block rates by balancing the total accesses/requests among the servers. In generating the retrieval schedule, our scheme utilizes the available bandwidth (resource) among the servers and guarantees to use less buffer space than a single server retrieval strategy (SSRS). With this two-step approach, a complete flexibility is provided in tuning the access times of the movies and also shown to be robust to any variations in the user access rates of the movies, in reality. Rigorous simulation experiments are presented to observe the performance of MSRS with respect to some important system dependent parameters. Comparing with SSRS, MSRS shows better performance in the simulation.     

基于能量采集的分布式时分多址协议

纳米节点利用太赫兹通信能获得极高的传输速率,节点间的通信以及协调访问太赫兹信道都需要媒质接入控制(medium access control, MAC)协议．由于太赫兹信道的分子吸收噪声和纳米设备资源受限等特性,经典的MAC协议已不再适用.针对基于时域扩展开关键控(time spread on-off keying, TS-OOK)的太赫兹传感器网络的数据传输存在连续碰撞的问题以及纳米节点能量非常有限的问题,提出一种基于能量采集的分布式时分多址协议(distributed energy harvesting-based time division multiple access, DEH-TDMA).该协议引入压电式纳米能量采集系统,首先将纳米节点剩余能量和缓存区的数据包数量作为状态信息构建Markov决策过程模型,并根据节点的数据包传输量和能耗来设计收益函数,然后求解出最优策略,最终纳米节点根据自身状态和最优策略动态接入信道.仿真结果表明该协议在延长网络生命周期方面存在优势.     

分布式应用中的访问控制规范的研究

针对分布式系统中安全服务规范给安全策略管理带来的不便,文章给出了一个针对分布式系统的访问控制策略设计和管理的访问控制模型,将此模型融入到分布式应用系统程序中,使用视图策略语言来描述访问控制策略,实现对安全访问策略行之有效的管理,并可以进行静态类型检测以保证规范的一致性。文章最后给出了分布式应用程序中执行VPL表示的访问控制策略的基础结构。     

基于Access Grid的共享应用程序开发

为降低基于AG的共享应用程序的开发难度,在AG体系结构以及相关的API基础上实现了一个开发框架。利用此框架,能够在很大程度上提高开发共享应用程序的效率并缩短开发周期。此外,该框架还提供了一个通用访问界面,方便用户集成和调用相应的共享应用程序。     

基于校园网的门禁系统在多媒体教学管理中的应用

针对多媒体教学管理中存在的一些问题,该文介绍了基于校园网的门禁系统的构成,并结合门禁系统的特点,阐述了门禁系统在多媒体教学管理方面的应用及其优点。     

Model-Based Video Classification toward Hierarchical Representation,Indexing and Access

In this paper, we develop a content-based video classification approach to support semantic categorization, high-dimensional indexing and multi-level access. Our contributions are in four points: (a) We first present a hierarchical video database model that captures the structures and semantics of video contents in databases. One advantage of this hierarchical video database model is that it can provide a framework for automatic mapping from high-level concepts to low-level representative features. (b) We second propose a set of useful techniques for exploiting the basic units (e.g., shots or objects) to access the videos in database. (c) We third suggest a learning-based semantic classification technique to exploit the structures and semantics of video contents in database. (d) We further develop a cluster-based indexing structure to both speed-up query-by-example and organize databases for supporting more effective browsing. The applications of this proposed multi-level video database representation and indexing structures for MPEG-7 are also discussed.     

Analysis of Randomized Protocols for Conflict-Free Distributed Access

We study the following distributed access problem which arises naturally in many settings: given a set of n data items shared among n nodes in a distributed network, all nodes want to access all (or a subset of) the items residing on different nodes in a conflict-free manner. In addition, items may move from one node to the other during access. Our goal is to design distributed protocols so that all nodes access all the desired items as quickly as possible, while at the same time not overloading the storage space of any one node. Using centralized coordination among the nodes it is easy to design an optimal scheme in which all nodes can access all the items in n−1 steps storing only one item at any time. We show that a simple randomized distributed protocol performs almost as well as the optimal (centralized) scheme but with no coordination overhead. Our protocol takes O(n) time with high probability to access all n items which is asymptotically as good as the optimal centralized scheme. The protocol guarantees that the maximum load (the maximum number of items stored in any node) at any time is at most O(log n/log log n) with high probability which is only slightly larger compared to the Ω(1) load of the optimal scheme. Our analysis involves a stochastic analysis of a “balls into bins” problem in a dynamic setting where balls (data items) move into bins (nodes) on request and we study the time and load requirements to move all the balls to the requested bins. A short version of this paper appeared in the Proceedings of the 24th Annual ACM Symposium on Principles of Distributed Computing (PODC), 2005.     

时间管理在软件项目中的应用

针对当今软件项目中普遍出现的工期拖延、进度失控问题,介绍了时间管理的基本概念,接着从活动定义、活动排序、活动工期估算、进度安排、进度控制几个方面介绍了时间管理的过程。     

移动计算环境中数据广播访问时间优化算法

移动计算是近年来新兴的一个研究热点，具有极大的市场潜力和需求，数据广播是提高移动计算系统可伸缩性的一项重要技术，本文对无线移动计算环境中数据广播的平均访问时间优化进行了研究和实验，首先分析了平均访问时间的理论最小值，然后提出了向理论最小值逼近的NASA 算法，实验表明NASA算法具有良好的性能，优于MDS等其他调度方法。     

A Resource Reservation Scheme for Synchronized Distributed Multimedia Sessions

Guarantees of services in a networked environment are provided by the proper allocation and scheduling of network and system resources. A lot of research in packet scheduling, QoS routing, traffic multiplexing, etc. has been aimed at providing deterministic or statistical service guarantees, while utilizing resources efficiently. In this paper, we propose a resource reservation scheme for a class of multimedia presentations. We characterize this class of multimedia presentations as synchronized distributed multimedia sessions, which we believe are important components of many multimedia applications. In addition to multimedia presentations, the reservation scheme applies to applications with synchronized resource requirements. Based on resource inquiry and interval analysis, the scheme is also able to find feasible resource allocation schedules for resource reservation requests. Built upon a layer of resource abstraction, the scheme suits well with today's heterogeneous network environment.     

分布式多媒体系统中音频和视频实时传输

本文在分析了分布式多媒体实时传输系统的基础上 ,并说明了 RTP/ RTCP协议和 IP Multicast在单频和视频传输及控制中的应用。     

基于同步时间Petri网的细粒度多媒体同步模型研究

多媒体同步是分布式多媒体信息系统的关键问题。在分析和比较几种已有的典型的多媒体同步模型的基础上．本文提出了一种新的模型：同步时间Petri网(简记为STPN)。STPN不仅能完整、准确地对媒体流内和媒体流间的时间层次行为进行形式化描述,而且解决了时间流Petri网中存在的死托肯问题。特别地,通过引入抑止弧,STPN有效地克服了随机延迟、阻塞、丢包等因素的不良影响。尤其当丢失率较高时．STPN更能体现其优越性和鲁棒性。     

带有时间约束支持冲突检测的访问控制模型

为确保存储在系统中的访问策略都是无冲突的,提高策略冲突检测的效率,使系统能够正确有效的运行,将本体的概念应用到访问控制中,提出了一种基于本体的支持策略冲突检测的访问控制模型,并对该模型中的核心模块—策略冲突检测模块进行了详细说明。在此基础上,为使系统中的授权具有时效性,更加符合实际应用,将时间特征引入模型,根据时间约束的特征,将资源分为4类,细化了资源的类别,增强了系统授权的能力。最后,针对这4类资源的访问控制,给出了模型的时间约束算法。     

A CORBA Based QOS Support for Distributed Multimedia Applications

Advance object oriented computing platform such as the Common Object Request Broker Architecture (CORBA) provides a conducive and standardized framework for the development of distributed applications. Most of the off-the-shelf CORBA are implemented over legacy network transports and distributed processing platforms such as TCP/IP and RPC. They are not suitable for real-time applications due to their high processing overheads, and lack of features and mechanisms in supporting quality of service both at the network level and at the end-host level. To overcome this limitation we have designed and implemented a CORBA-based Real Time Stream Service (RTSS) that allows real-time streams to be managed through the CORBA channel but by-passing the heavy CORBA protocol stacks. RTSS aims to achieve an integrated QOS framework that incorporates both host scheduling and end-to-end network-level QOS to better support the processing of distributed multimedia applications over ATM networks. For host scheduling, a novel scheme of frequency-based scheduling mechanism has been proposed to cope with dynamic CPU load condition. The scheme has been implemented for a stand-alone host and will be extended to the networked environment. At the network-level QOS, RTSS provides object-oriented application programming interfaces (APIs) which guarantee end-to-end QOS when operating directly over ATM adaptation layers. The benefits of RTSS for the development of real-time multimedia distributed applications are demonstrated through a number of experiments.     

广域存储虚拟化系统的文件访问

广域存储虚拟化所要解决的一个问题是如何实现对分布的文件进行方便高效的访问。本文在分析了几种常见的文件系统后，针对广域存储虚拟化系统的特征，设计了客户端的文件访问模式，并实现了一套应用于该系统的文件访问接口，使用户能够像使用本地系统一样使用广域存储虚拟化系统的存储资源。     

基于时间访问轨迹的文件的智能推荐

随着计算机用户个人信息量的日益扩大,如何帮助用户在系统中快速找到所需资源已成为当前智能交互行为模型的重要课题.过往的研究大多集中于个人信息管理,力求以更加便于用户理解的个性化方式重新组织计算机资源结构.然而,由于上述系统往往需要用户大量的额外操作,并且重构用户的知识系统需要较为漫长的时间而不被用户采用.考虑到用户访问文件的主题性和目的性(用户往往会出于同一目的在同一时间段内同时访问多个同主题相关的文件),提出基于用户时间访问轨迹的智能文件推荐,并设计实现基于时间访问轨迹的智能文件推荐桌面工具(intelligent file recommendation desktop toolkit,简称IFRDT),将根据用户访问文件的轨迹,针对用户当前正在访问的文件向用户推荐最有可能被访问到的同主题的其他文件,以减少用户查找所需资源花费的时间开销.实验结果表明,使用IFRDT向用户推荐文件比仅仅向用户呈现访问历史更能为用户节省查找文件的时间;被试用户可以在IFRDT中找到一半以上的所需文件,这就是为用户节约了一半以上的查找开销.     

Reevaluating Data Stall Time with the Consideration of Data Access Concurrency

Data access delay has become the prominent performance bottleneck of high-end computing systems. The key to reducing data access delay in system design is to diminish data stall time. Memory locality a...     

Dynamic Video Playout Smoothing Method for Multimedia Applications

Multimedia applications including video data require the smoothing of video playout to prevent potential discontinuity. In this paper, we propose a dynamic video playout smoothing method, called the Video Smoother, which dynamically adopts various playout rates in an attempt to compensate for high delay variance of networks. Specifically, if the number of frames in the buffer exceeds a given threshold (TH), the Smoother employs a maximum playout rate. Otherwise, the Smoother uses proportionally reduced rates in an effort to eliminate playout pauses resulting from the emptiness of the playout buffer. To determine THs under various loads, we present an analytic model assuming the Interrupted Poisson Process (IPP) arrival. Based on the analytic results, we establish a paradigm of determining THs and playout rates for achieving different playout qualities under various loads of networks. Finally, to demonstrate the viability of the Video Smoother, we have implemented a prototyping system including a multimedia teleconferencing application and the Video Smoother performing as part of the transport layer. The prototyping results show that the Video Smoother achieves smooth playout incurring only unnoticeable delays.     

基于移动应用的智能配网调度视频及图像感知系统设计

为解决目前配网调度中无法直观掌握网络运行以及操作流程等问题,提出了基于移动应用的配网调度视频作业以及调度图像感知方法.首先分析了调度业务对实时可视化的需求,然后分析了移动应用技术和图像感知技术的原理和智能配网调度的形式和业务.设计了基于移动应用的配网调度视频作业平台的系统构架和功能构架,详细说明了移动应用模块的内容和组...     

Integrated Video and Text for Content-based Access to Video Databases

This paper introduces a new approach to realize video databases. The approach consists of a VideoText data model based on free text annotations associated with logical video segments and a corresponding query language. Traditional database techniques are inadequate for exploiting queries on unstructured data such as video, supporting temporal queries, and ranking query results according to their relevance to the query. In this paper, we propose to use information retrieval techniques to provide such features and to extend the query language to accommodate interval queries that are particularly suited to video data. Algorithms are provided to show how user queries are evaluated. Finally, a generic and modular video database architecture which is based on VideoText data model is described.