面向HDTV视频存储的专用文件系统

分析了HDTV视频存储的原理,讨论了实际应用中通用文件系统在连续媒体存储方面遇到的问题,归纳出多媒体文件系统应具备的功能和磁盘调度算法,提出了一种满足连续媒体存储策略的专用文件系统,提高了资源利用率和服务质量,并基于系统硬件平台,设计了适用于软件实现的算法逻辑.     

Evaluating video layout strategies for a high-performance storage server

We propose a systems approach to providing video service that integrates the multiresolution data generated by scalable compression algorithms with the high-bandwidth, high-capacity storage provided by disk arrays. We introduce two layout strategies for storing multiresolution video data on magnetic disk arrays, which vary in the degrees of parallelism and concurrency they use to satisfy requests. Our simulation results show that the storage of multiple video resolutions allows a video file server to satisfy considerably more user requests than a server that stores a single resolution of video data.     

请求下降邻域叠加选取分布式P2P 视频点播调度

为实现对等架构的低成本视频流传输和实时播放要求,提出基于请求下降叠加选 取的分布式P2P 视频点播调度算法。首先,基于叠加技术构建P2P 视频点播的技术指标,充分 考虑输入邻域节点、输出邻域节点和媒体服务器负载3 组优化指标,构建叠加架构和分布式算 法流程;其次,利用请求下降策略对发送节点和服务节点选取进行改进,解决可能出现的带宽 低利用率和无效的视频播放问题;最后,通过BitTorrent 视频点播系统对所提算法的有效性进 行了验证。     

基于广域网的多媒体资源存储系统

针对广域网上多媒体资源访问服务质量问题，设计一种面向媒体资源的高性能分布媒体存储系统（DMSS）。系统以按多媒体文件特征设计的高效媒体文件系统（MFS）为基础，通过自适应创建资源副本服务器来保证服务质量，降低网络带宽消耗。给出了系统构架和原型描述，通过性能分析验证了其高效性。     

A Tabu search approach for designing a non-hierarchical video-on-demand network architecture

In this paper, we present a tabu search to design a non-hierarchical and decentralized video-on-demand (VOD) network architecture. To optimize the VOD network resource, we consider optimization of both video server locations and storage allocation subject to the tradeoffs among installation cost for video servers, program storage cost, and transmission (or communication) cost. In applying a tabu search technique to the problem, neighborhood structure and search strategy are elaborated to improve solution quality and to reduce computation time. We report the results of the computational experiments to demonstrate the performance of the proposed tabu search. A comparative study shows that our algorithm is promising.     

基于 Hadoop 的分布式视频处理

中国科学院计算机网络信息中心与青海湖保护区管理局合作,共同建设了青海湖野外网络视频监控。如何高效地处理每天产出的超过 100GB 的视频数据成为了一个难题。现在的视频处理系统采用计算和存储相分离的架构,这需要配置较高的专门服务器进行支撑,本文基于廉价扩展性能较好的 Hadoop 平台对视频处理做出了分布式的实现,并对单个视频文件做出了分布式转码的实现。同时,本文将基于 Hadoop 的分布式视频处理的实现和基于 HTCondor 的分布式视频的批处理实现进行了对比,实验证明,在不损失视频处理效率的条件下,基于 Hadoop 的分布式视频处理的实现拥有分布式文件系统支撑、完善的任务监控等优势。     

Operating system support for a video-on-demand file service

This paper describes the design and implementation of a continuous media file server intended for use in emerging video-on-demand applications. The main focus and contribution of the paper is in scheduling and admission-control algorithms for accessing the server's processor and storage resources. The scheduling algorithms support multiple classes of tasks with diverse performance requirements and allow for the co-existence of guaranteed real-time requests with sporadic, and unsolicited requests. The scheduler maintains performance guarantees for real-time streams in the presence of unpredictably varying non-real-time traffic while ensuring system stability even during overloads. A prototype video file server was implemented on an Intel 486 platform. Performance results show that a large number of streams can be supported, while maintaining efficient utilization of system resources.     

基于DM270的嵌入式网络视频服务器

采用TM S320DM 270双核处理器可设计单芯片网络摄像机,这里为该处理器的ARM核设计网络视频服务器,首先完成了bootloader,移植μc-linux内核,并在内核基础上编写视频捕获驱动、DSP驱动和网络驱动,实现了流媒体协议和视频W eb服务器,为了实验本地存储,还为操作系统增加了文件系统。该服务器可同时支持16用户访问,保证视频流高质量的传输。     

Video placement and configuration of distributed video servers on cable TV networks

A large-scale, distributed video-on-demand (VOD) system allows geographically dispersed residential and business users to access video services, such as movies and other multimedia programs or documents on demand from video servers on a high-speed network. In this paper, we first demonstrate through analysis and simulation the need for a hierarchical architecture for the VOD distribution network.We then assume a hierarchical architecture, which fits the existing tree topology used in today's cable TV (CATV) hybrid fiber/coaxial (HFC) distribution networks. We develop a model for the video program placement, configuration, and performance evaluation of such systems. Our approach takes into account the user behavior, the fact that the user requests are transmitted over a shared channel before reaching the video server containing the requested program, the fact that the input/output (I/O) capacity of the video servers is the costlier resource, and finally the communication cost. In addition, our model employs batching of user requests at the video servers. We study the effect of batching on the performance of the video servers and on the quality of service (QoS) delivered to the user, and we contribute dynamic batching policies which improve server utilization, user QoS, and lower the servers' cost. The evaluation is based on an extensive analytical and simulation study.     

A Video Server cost/performance Estimator tool

The Video Server Estimator (VSE) is an analytical tool which allows a user to perform a cost/performance analysis of video servers with hierarchical storage. The underlying model comprises multiple systems, main memory, expanded storage, disks and a tape library. The main objective of the tool is to optimally allocate the video files to different storage media based on the system parameters and the video file request probability distribution. The cost and the size of the video server that can accommodate a customer profile are determined. Furthermore, the impact of design parameters on the cost and performance are examined through a parametric analysis.     

Constant bit rate network transmission of variable bit rate continuous media in Video-On-Demand servers

Multimedia computing is rapidly emerging as the next generation standard for human-computer interaction. One class of multimedia applications that has been gaining much attention is the real-time display of continuous media data such as video and audio, commonly known as Video-On-Demand (VOD) service. Although advances in computer and network technologies have made VOD service feasible, providing guaranteed quality, real-time video delivery still poses many technical challenges. One such challenge involves the transmission of continuous media traffic over high-speed networks.In this paper, we present an algorithm for determining the minimum buffer requirement for avoiding overflow or underflow at the client video display process, allowing the network scheduler at the VOD server to enforce a constant bit rate delivery of variable bit rate encoded continuous media. This strategy results in reduced congestion and cell loss at the network switch, and in simplified admission control parameters. Initial results indicate that buffer requirements for typical video streams range from 3.7 to 14.6 Megabytes, which is acceptable by today's multimedia PC standards. Further, we show that this approach increases the number of streams that can be multiplexed by a factor of 4.6 to 9.9 times when compared to peak and 90%-of-peak bandwidth allocation strategies.ECE Dept., Syracuse University, Syracuse, USACIS Dept., Syracuse University, Syracuse, USA     

多层次周期性广播策略及系统模型——具有良好可扩展性的异步视频传输策略

异步视频服务是基于高速互联网络的典型应用,但是长期以来一直面临着系统可扩展性较差的问题,大量的用户数与有限的带宽资源之间的矛盾成为其主要问题。该文提出了一种具有良好可扩展性的异步视频传输模型,在网络层基于下一代高速互联网络将广泛支持的组播技术,在应用层创造性地使用了多层次的周期性广播策略。从而较为有效地解决了在分布式多视频服务器环境下系统提供异步视频服务的性能、价格以及可扩展性问题。     

三网融合下基于资源池化的视频业务管理策略

对现有KAD协议在高并发、高实时性需求环境中的优缺点进行分析。为减少系统信息的冗余和延迟时间,提出一种在三网融合背景下,基于服务节点资源池划分的改进KAD网络视频业务系统的调度管理策略。采用基于网络连通性的准则将视频业务网的服务节点划分为若干资源池,各池内部网络采用KAD方式进行组织。根据用户请求量的预测,采用池间资源租借的方式解决单个资源池由于业务量增大而导致的服务过载问题。实验结果表明,对于典型的视频业务请求,马尔科夫链预测法能够实现过载漏报率为0的精确预警,从而根据预测结果,并利用KAD网络灵活的扩展性及时地补充服务资源。     

A window-assisted video partitioning strategy for partitioning and caching video streams in distributed multimedia systems

In this paper, we address the issue of efficiently streaming a set of heterogenous videos under the constraint of service latency over a scalable multimedia systems. We propose a novel strategy, referred to as window-assisted video partitioning (WAVP), for rendering cost-effective multimedia services. The objective is to minimize the service cost and maximize the number of requests that can be successfully served under resources constraints (cache capacity and link bandwidth). We formulate the problem of video partitioning as an optimization of both bandwidth resources and cache space, and derive the optimal schedule window for different video portions under consideration of time constraints, the popularities and the sizes of the video portions. In WAVP, video are partitioned into multiple portions and delivered according to by adaptive schedule windows. We prove that WAVP strategy not only optimize the service cost but also be able to serve requests under the time constraints without causing too much delay. We conduct mathematical analysis and derive certain performance bounds that quantify the overall performance of the strategy. It shows that the service cost can be optimized by adjusting the schedule window and resources utilization can be improved as video streams are partitioned into multiple portions. We evaluate the performance under several influencing parameters such as available bandwidth, cache capacity, and partition gradients. Simulation results show that our proposed method can not only significantly reduce the service cost under tight time constraints and with low partition overhead, but also balance the utilization of network resources to achieve high acceptance ratio with low average service cost.     

基于WSNs的军用机场仓库环境监测系统设计

对军用机场后方仓库的环境参数进行实时监测,是保证武器装备正常存储,防止发生意外事故的重要措施。针对军用机场现有仓库环境监测系统的不足,将WiFi无线传感器网络（ WSNs）应用在仓库环境监测系统中,与现有的视频监控局域网融合,解决了传统监测系统组网难、成本高的问题。系统的传感器节点采集环境参数,通过WiFi模块和局域网将数据传送至监测中心的服务器,服务器中的软件采用B/S结构,对数据进行分析、处理、存储和显示。实验结果表明：该监测系统数据采集精度高、效率高,网络通信稳定,能够满足设计要求。     

Mitra: A Scalable Continuous Media Server

Mitra is a scalable storage manager that supports the display of continuous media data types, e.g., audio and video clips. It is a software based system that employs off-the-shelf hardware components. Its present hardware platform is a cluster of multi-disk workstations, connected using an ATM switch. Mitra supports the display of a mix of media types. To reduce the cost of storage, it supports a hierarchical organization of storage devices and stages the frequently accessed objects on the magnetic disks. For the number of displays to scale as a function of additional disks, Mitra employs staggered striping. It implements three strategies to maximize the number of simultaneous displays supported by each disk. First, the EVEREST file system allows different files (corresponding to objects of different media types) to be retrieved at different block size granularities. Second, the FIXB algorithm recognizes the different zones of a disk and guarantees a continuous display while harnessing the average disk transfer rate. Third, Mitra implements the Grouped Sweeping Scheme (GSS) to minimize the impact of disk seeks on the available disk bandwidth.In addition to reporting on implementation details of Mitra, we present performance results that demonstrate the scalability characteristics of the system. We compare the obtained results with theoretical expectations based on the bandwidth of participating disks. Mitra attains between 65% to 100% of the theoretical expectations.     

基于连续式录像机存储的应用层组播系统设计

针对应用层组播系统采用网络硬盘录像机存储模式存在流媒体转发服务器负载较重、传输效率低的问题,提出了基于连续式录像机存储的应用层组播系统设计方案。对于不需要预览的视频通道,利用存储服务器直接从前端编码源获取视频数据,在保证编码源和接收端是单份视频数据的前提下,有效地缓解了流媒体转发服务器的负载,从而保证了矿区视频监控系统的正常运行。现场实际应用验证了该系统的有效性。     

影响多媒体服务器性能的关键因素研究

在构建大规模视频服务系统时 ,基于层次型多服务器群的体系结构在吞吐率、可扩展性、经济性等方面都有其突出的优势 ,尤其适合于在因特网上的应用 .但是 ,要充分发挥和提高视频服务系统的性能 ,还要针对一些主要的瓶颈(如服务器磁盘 I/ O带宽与网络带宽 ) ,解决好一系列的问题 .本文分析了影响多媒体视频服务器性能的一些主要因素 ,如视频服务器的体系结构、服务器与客户端之间的数据传送方式、媒体数据在视频服务器存储子系统中的分布与放置方式、对磁盘访问请求的调度、单服务器中的缓存及多服务器间协同缓存的管理、接入控制策略、流调度策略等 ,这些因素对视频服务器的性能与吞吐率有着极大的影响 .本文还介绍了一些适用于大规模视频服务系统的性能优化技术 ,如广播、批处理等流调度策略 .在构建视频服务器系统时 ,只有综合考虑这些因素 ,才能真正提高服务器乃至整个视频服务系统的吞吐率 ,并较好地满足客户的 Qo S要求     

基于QoS的磁盘调度策略

随着视频点播、视频会议、视频监控、数字图书馆等流媒体应用的普及，流媒体服务器存储资源管理成为制约服务质量的瓶颈之一。根据多媒体服务器的性能要求，提出了一种支持QoS的磁盘调度策略。它由三个主要部分组成：探测模块、负载监测模块和自适应管理模块。探测模块，负责判断当前的资源情况能否满足服务请求；自适应模块，根据负载监删模块检测到的负载变化情况，动态调整服务周期在实时请求和尽力服务请求之间的分配。实验表明此磁盘调度策略能在保证实时请求无抖动执行的同时，明显减少了非实时请求的响应时间。     

Evaluation of the File Redundancy in Distributed Database Systems

This paper treats the file redundancy issue in distributed database systems, asking what is the optimal number of file copies, given the ratio r of the frequency of update requests to the frequency of all file access requests (i.e., queries and updates). Formulations of this type of problem, including optimal file allocation, have been attempted by a number of authors, and some algorithms have been proposed. Although such algorithms can be used to solve particular problems, it seems difficult to draw general conclusions applicable to a wide variety of practical distributed database systems. To probe into this hard to formulate but interesting problem, our paper constructs simplified network models of distributed database systems, and computes the optimal number of file copies, as well as their locations, to minimize the communication cost. For several network types, we plot the optimal number of file copies as a function of the ratio r.