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.     

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。     

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.     

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.     

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。     

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。     

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.     

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...     

多信任域的分布式访问控制模型研究

在目前高度动态、异构化、分布式的现代信息系统中,跨越单个域的限制,在多个信任域之间实现资源共享和进行安全互操作是非常必要的[1].论文研究了多信任域认证授权系统的两种模型:网关模式基本模型和分布式基本模型.并分析了IRBAC(Interoperability Role Based Access Control)2000模型的基本思想及其存在的问题.其不足主要表现在:1)多信任域间角色映射中违背职责分离原则;2)没有考虑某一角色加入或退出时,与之关联角色的处理问题.针对不足,该文提出了MTD-EIRBAC模型.信任度计算和粒逻辑推理的引入,实现了MTD-EIRBAC模型的动态授权,很好地解决了角色变换(如角色的加入或退出)时与之相关联角色的处理和域穿梭时的角色渗透和隐提升问题,使多信任域间能够进行安全、灵活的协作.     

A Framework for Cross-Language Information Access: Application to English and Japanese

Internet search engines allow access to online information from all over the world. However, there is currently a general assumption that users are fluent in the languages of all documentsthat they might search for. This has for historical reasons usually been a choice between English and the locally supported language. Given the rapidly growing size of the Internet, it is likely that future users will need to access information in languages in which they are not fluent or have no knowledge of at all. This papershows how information retrieval and machine translation can becombined in a cross-language information access frameworkto help overcome the language barrier. We presentencouraging preliminary experimental results using English queries toretrieve documents from the standard Japanese language BMIR-J2retrieval test collection. We outline the scope and purpose ofcross-language information access and provide an example applicationto suggest that technology already exists to provide effective andpotentially useful applications.     

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.     

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.     

一种非完全组播网络中的算法可选组播框架

提出了一种新型实用的算法可选组播框架-FMPN（Flexible Multicasting on Partial-multicast Networks），该框架能够在非完全组播网络中实现组播功能，并且可以根据不同的业务和数据类型采用算法可选的组播机制，以达到系统整体最优的组播传输性能．FMPN有三个主要的特点：（1）算法可选组播机制，根据不同的应用需求来灵活地选择组播算法．并且通过IP隧道使得在路由器不支持的情况下也可以使用组播．（2）数据分类，通过对应用类型与数据的分析来调用合适的组播算法．（3）分层传输为可伸缩性码流提供各自独立的组播信道．实验表明，FMPN多媒体传输的系统整体性能高于当前常用的反向路径组播（RPM）、生成树（SpT）等组播算法，特别适合于实时多媒体应用．     

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...     

基于XACML的分布式系统访问控制

分析了传统访问控制中的授权管理策略:强制访问控制,自主访问控制和基于角色的访问控制。然后提出分布式环境下访问控制的特点,并详细介绍了XACML,得出XACML适合于分布式系统的结论。结合XACML研究实现分布式系统的访问控制模型,并通过Sun提供的XACML2.0工具包实现访问控制。     

Storage System for Supporting More Video Streams in Video Server

Video server needs a storage system with large bandwidth in order to provide concurrently more users with the real time retrieval requests for video streams. So, the storage system generally has the structure of disk array, which consists of multiple disks. When the storage system serves multiple video stream requests, it's bottlenecks come from the seeking delay caused by the random movement of disk head and from unbalanced disk access due to disk load unbalance among multiple disks.This paper presents a novel placement and retrieval policy. The new policy retrieves the requested data through sequential movement of disk heads and maintaining disk load balance so that it can diminish the bottlenecks on retrieving and can provide the concurrent real time retrieval services for more users simultaneously. In addition, the novel policy reduces the startup latency for the requests. The correctness of the novel placement and retrieval policy is analyzed with theoretical views. Performance analysis of the novel placement and retrieval policy is provided with simulations.     

DSMAC:一种适于无线多媒体传感器网络的信道接入协议

多媒体传感器网络作为一种多媒体信息获取和处理方式,已在军事、民用及商业领域中显示出广阔的应用前景.信道接入协议能否高效地使用无线信道是保证无线多媒体传感器网络通信的最关键的因素之一.分析支持多媒体业务传输的无线传感器网络信道接入协议的要求,提出适于多媒体传感器网络提供区分服务的信道接入协议--DSMAC(different service medium access control),对实时业务与非实时业务实现了区分服务,在信道接入帧内的随机竞争期实现突发业务及时接入,支持突发多媒体业务实时传输,并提出了多信道簇间传输方式,避免了隐终端冲突.最后,对协议的服务区分、实时性、吞吐量以及能量有效性等性能进行了仿真实验,验证了其优良性能.