Design of Scalable Continuous Media Servers

Multimedia applications place high demands for quality-of-service (QoS), performance, and reliability on systems. These stringent requirements make design of cost-effective and scalable systems difficult. Therefore efficient adaptive and dynamic resource management techniques in conjunction with data placement techniques can be of great help in improving performance, scalability, and reliability of such systems. This is the focus of our paper.     

A Statistical Admission Control Scheme for Continuous Media Servers Using Caching

In continuous media servers, disk load can be reduced by using buffer cache. In order to utilize the saved disk bandwidth by caching, a continuous media server must employ an admission control scheme to decide whether a new client can be admitted for service without violating the requirements of clients already being serviced. A scheme providing deterministic QoS guarantees in servers using caching has already been proposed. Since, however, deterministic admission control is based on the worst case assumption, it causes the wastage of the system resources. If we can exactly predict the future available disk bandwidth, both high disk utilization and hiccup-free service are achievable. However, as the caching effect is not analytically determined, it is difficult to predict the disk load without substantial computation overhead. In this paper, we propose a statistical admission control scheme for continuous media servers where caching is used to reduce disk load. This scheme improves disk utilization and allows more streams to be serviced while maintaining near-deterministic service. The scheme, called Shortsighted Prediction Admission Control (SPAC), combines exact prediction through on-line simulation and statistical estimation using a probabilistic model of future disk load in order to reduce computation overhead. It thereby exploits the variation in disk load induced by VBR-encoded objects and the decrease in client load by caching. Through trace-driven simulations, it is demonstrated that the scheme provides near-deterministic QoS and keeps disk utilization high.     

An Efficient Data Layout Scheme for Multi-Disks Continuous Media Servers

Recently, zoning technique has been widely applied to disks to increase their capacities. Under the technique, an interesting feature of a disk is that there are a number of various bandwidths on it. Herein, a novel data layout scheme called cluster-pairing on efficiently exploiting this feature for continuous media (CM) servers is proposed. We first applied track-pairing method between a pair of homogeneous disks, and then partitioned each disk into a same number of clusters to facilitate the retrieval of region-based data placement. The proposed method can take the advantages of track-pairing and region-based data placement schemes to fully utilize the various bandwidths from zoned-disks and meanwhile reduce the seek time overhead. According to the simulation results, the disk throughput after applying our approach can be promoted by 35% to 65% than that of the traditional data striping strategies, 10% to 30% than that of region-based data placement method, and about 10% than that of track-pairing scheme. And the wasted storage space is less than 1% which is negligible in terms of the improvement of the disk throughput.     

Design of Multi-User Editing Servers for Continuous Media

Based on a fifteen month investigation of a post production facilities for both the entertainment industry and broadcasters, we identified a number of challenges with the design and implementation of a server in support of multiple editing stations. These include, how to: share the same content among multiple editors, support continuous display of the edited content for each editor, support complex editing operations, compute the set of changes (deltas) proposed by an editor, compare the deltas proposed by multiple editors, etc. It is beyond the focus of this paper to report on each challenge and its related solutions. Instead, we focus on one challenge, namely how to support continuous display of the edited content for each editors, and techniques for physical organization of data to address this challenge.     

A multi-threshold online smoothing technique for variable rate multimedia streams

Variable bit rate (VBR) compression for media streams allocates more bits to complex scenes and fewer bits to simple scenes. This results in a higher and more uniform visual and aural quality. The disadvantage of the VBR technique is that it results in bursty network traffic and uneven resource utilization when streaming media. In this study we propose an online media transmission smoothing technique that requires no a priori knowledge of the actual bit rate. It utilizes multi-level buffer thresholds at the client side that trigger feedback information sent to the server. This technique can be applied to both live captured streams and stored streams without requiring any server side pre-processing. We have implemented this scheme in our continuous media server and verified its operation across real world LAN and WAN connections. The results show smoother transmission schedules than any other previously proposed online technique. This research has been funded in part by NSF grants EEC-9529152 (IMSC ERC), and IIS-0082826, DARPA and USAF under agreement nr. F30602-99-1-0524, and unrestricted cash/equipment gifts from NCR, IBM, Intel and SUN. Roger Zimmermann is currently a Research Assistant Professor with the Computer Science Department and a Research Area Director with the Integrated Media Systems Center (IMSC) at the University of Southern California. His research activities focus on streaming media architectures, peer-to-peer systems, immersive environments, and multimodal databases. He has made significant contributions in the areas of interactive and high quality video streaming, collaborative large-scale group communications, and mobile location-based services. Dr. Zimmermann has co-authored a book, a patent and more than seventy conference publications, journal articles and book chapters in the areas of multimedia and databases. He was the co-chair of the ACM NRBC 2004 workshop, the Open Source Software Competition of the ACM Multimedia 2004 conference, the short paper program systems track of ACM Multimedia 2005 and will be the proceedings chair of ACM Multimedia 2006. He is on the editorial board of SIGMOD DiSC, the ACM Computers in Entertainment magazine and the International Journal of Multimedia Tools and Applications. He has served on many conference program committees such as ACM Multimedia, SPIE MMCN and IEEE ICME. Cyrus Shahabi is currently an Associate Professor and the Director of the Information Laboratory (InfoLAB) at the Computer Science Department and also a Research Area Director at the NSF's Integrated Media Systems Center (IMSC) at the University of Southern California. He received his M.S. and Ph.D. degrees in Computer Science from the University of Southern California in May 1993 and August 1996, respectively. His B.S. degree is in Computer Engineering from Sharif University of Technology, Iran. He has two books and more than hundred articles, book chapters, and conference papers in the areas of databases and multimedia. Dr. Shahabi's current research interests include Peer-to-Peer Systems, Streaming Architectures, Geospatial Data Integration and Multidimensional Data Analysis. He is currently an associate editor of the IEEE Transactions on Parallel and Distributed Systems (TPDS) and on the editorial board of ACM Computers in Entertainment magazine. He is also the program committee chair of ICDE NetDB 2005 and ACM GIS 2005. He serves on many conference program committees such as IEEE ICDE 2006, ACM CIKM 2005, SSTD 2005 and ACM SIGMOD 2004. Dr. Shahabi is the recipient of the 2002 National Science Foundation CAREER Award and 2003 Presidential Early Career Awards for Scientists and Engineers (PECASE). In 2001, he also received an award from the Okawa Foundations. Kun Fu is currently a Ph.D candidate in computer science from the University of Southern California. He did research at the Data Communication Technology Research Institute and National Data Communication Engineering Center in China prior to coming to the United States and is currently working on large scale data stream recording architectures at the NSF's Integrated Media System Center (IMSC) and Data Management Research Laboratory (DMRL) at the Computer Science Department at USC. He received an MS in engineering science from the University of Toledo. He is a member of the IEEE. His research interests are in the area of scalable streaming architectures, distributed real-time systems, and multimedia computing and networking. Mehrdad Jahangiri was born in Tehran, Iran. He received the B.S. degree in Civil Engineering from University of Tehran at Tehran, in 1999. He is currently working towards the Ph.D. degree in Computer Science at the University of Southern California. He is currently a research assistant working on multidimensional data analysis at Integrated Media Systems Center (IMSC)—Information Laboratory (InfoLAB) at the Computer Science Department of the University of Southern California.     

Design and Configuration Rationales for Digital Video Storage and Delivery Systems

Recent advances in computing technology have brought multimedia information processing to prominence. The ability to digitize, store, retrieve, process, and transport analog information in digital form has changed the dimensions of information handling. Several architectural and network configurations have been proposed for efficient and reliable digital video delivery systems. However, these proposals succeed only in addressing subsets of the whole problem. In this paper, we discuss the characteristics of video services. These include Cable Television, Pay-Per-View, and Video Repository Centers. We also discuss requirements for Video On Demand services. With respect to these video services, we analyze two important video properties: image quality and response time. We discuss and present configurations of a Digital Video Delivery System (DVDS) from three general system components - servers, clients, and connectivities. Pertinent issues in developing each component are also analyzed. We also present an architecture of a DVDS that can support the various functionalities that exist in the various video services. Lastly, we discuss data allocation strategies which impact performance of interactive video on demand (IVOD). We present preliminary results from a study using a limited form of mirroring to support high performance IVOD.     

分布式交互系统中连续媒体的延迟一致性模型

随着多媒体和网络技术的发展,分布式交互系统被广泛应用.在这种系统中,多个客户端通过局域或广域网交互连接.为使响应时间短,本地节点产生的操作立即在本地执行,并广播到其他远程节点执行.在该系统中,一致性维护是一个关键问题,而文献中研究的一致性问题几乎都是基于不连续媒体的.通过一个实例,指出连续媒体中的一种不一致问题.虽然该问题可以通过绝对一致模型解决,但绝对一致模型应用在广域网中将导致长响应时间.为解决绝对一致模型中响应时间过长的问题,提出了延迟一致性模型(简称为DCM模型).在DCM中,如果节点i产生了作用于对象x上的操作,该操作到达远程节点后强行延迟一段时间并要求在统一规定的时间执行.通过该方法,对象x在其他远程节点上的状态将最终保持一致.DCM很灵活,因为不同的对象可以有不同的强行延迟时间.如果分布式交互系统建立在实时网络上,这种强行延迟时间将成为实时通信中实时消息调度的重要参数.     

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.     

一种流媒体文件的分块放置方法

在研究了文件内部访问倾向性特征的基础上,提出了一种新型的流媒体文件分块放置策略．它能够有效消除流媒体访问倾向性对服务器性能的负面影响,提高流媒体服务器的服务能力．     

Packet Permutation: A Robust Transmission Technique for Continuous Media Streaming Over the Internet

With the growing popularity of the Internet, there is an increasing demand to deliver continuous media (CM) streams over the Internet. However, packets may be damaged or lost during transmission over the current Internet. In particular, periodic network overloads often result in bursty packet losses, degrading the perceptual quality of CM streaming. In this paper, we focus on reducing the impact of this bursty loss behavior. We propose a novel robust end-to-end transmission scheme, referred to as packet permutation (PP), to deliver pre-compressed continuous media streams over the Internet. At the server side, PP permutes, prior to transmission, the normal packet delivery sequence of CM streams in a specific way. The packets are then re-permuted at the receiver side before they are presented to the application. In this way, the probability of losing a large number of packets within each CM frame can be significantly reduced. To validate the effectiveness of PP, a series of trace-driven simulations are conducted. Our results show that for a given quality of service (QoS) requirement of CM streaming, PP greatly reduces the overhead required by traditional error control schemes, such as forward error correction (FEC) and feedback/retransmission-based schemes.     

视频点播服务器的服务质量控制框架

视频点播服务器工作于开放的网络环境中,系统负载难以预测,其运行时资源瓶颈依赖于实时服务类型.基于性能模型和实时负荷估计方法,本文提出视频点播服务器的服务质量控制框架,提供系统负荷监控、准入控制和区分服务等三种服务质量控制.实际系统的验证实验表明,本文的方法可以有效的对系统负荷进行监控,确保系统负荷稳定在服务提供商希望的水平线以下,向不同级别的用户提供不同质量级别的服务.     

一种分布式视频点播系统模型

视频点播（Video-on-Demand）是现代网络上的一个重要多媒体应用，在传统的集中式视频点播系统中，如何用户数目过多，并可能出现服务器I／O及网络带宽的瓶颈，而采用发布式体系结构的VOD系统可以将负载分布到放置在网络不同位置的各个服务器上，能很好地解决系统瓶问题，本文提出了一种分布式视频点播系统模型，包括系统结构、软件结构、功能定义及实现上的考虑。     

连续媒体服务器存储系统中的容错算法

连续媒体服务器(如VOD服务器)要对大量连续媒体数据(如声频、视频)进行管理,按一定速率为用户提供连续的媒体服务。因此,在这样的系统中,作为存储设备的磁盘阵列要具有高可靠性和一定的容错能力。文章提出一种基于奇偶检验的数据重构恢复算法,以保证系统中只有一个盘出现故障时,能使服务器及时重构出故障盘上的数据,并且算法充分利用了媒体流内在特性———回放时数据的连续性,与目前使用的标准故障恢复算法相比,大大减少了磁盘在线故障后数据重构过程的系统开销。最后通过分析、比较证明了算法的有效性。     

面向智慧矿山管控平台的视频点播技术

针对现有的视频点播技术无法直接在智慧矿山管控平台中直接使用的问题, 基于HTTP的自适应码率流媒体传输协议与FFmpeg开源库设计一种视频点播技术. 该技术包括客户端模块、Web请求处理模块、多媒体处理模块. 该技术中客户端模块通过设定的视频源信息向Web请求处理模块发送视频请求; Web请求处理模块利用请求中的视频源...     

流媒体服务器服务能力基准实验与性能模型

流媒体服务提供商需要了解如何对服务器的服务能力进行测试,如何对系统实时负荷进行估计.本文提出了一组基准实验,测量服务内容为变码率视频时,服务器提供不同质量和方式的视频点播服务的能力,得到与负载相关的服务器性能模型和实时负荷估计方法.实际系统上的验证实验表明,该性能模型可以准确刻画服务器的实时负荷.     

一种媒体点播系统资源对等搜索模型

媒体点播是网络教育中重要的教学方式,但是目前存在标准不同、共享困难等问题。为此引入P2P技术解决资源共享问题。P2P网络是一种自组织、适应性强、负载均衡、可靠性好的网络,目前被广泛运用于文件共享等领域。文中介绍利用P2P技术实现多个媒体点播系统互联,为用户提供可扩展的查询服务和资源共享平台。通过分析得出互联后的媒体点播系统较单个系统具有许多优点。     

大规模视频点播磁盘cache替换算法

在规划视频播（ＫＳＶＯＤ）中ｃａｃｈｅ机制是提高系统效率的有效手段,是支持ＶＯＤ实用化的关键技术之一,由于连续媒体的数据量大,使用周期长等特点,传统的ｃａｃｈｅ替换算法不能直接应用于ＳＶＯＤ。文中根据ＶＯＤ的特点开发了两种基于访问频率的替换算法,ＬＦＲＵ（ｌｅａｓｔ ｆｒｅｑｕｅｎｃｙ ａｎｄ ｒｅｃｅｎｔｌｙ ｕｓｅｄ）和ＰＬＦＵ（ｐｅｒｉｏｄ ｌｅａｓｔ ｆｒｅｑｕｅｎｃｙ ｕｓｅｄ）算法,它     

一种新型VOD系统视频服务器的设计

本文提出了一种带有新颖的视频流分配方案的可伸缩ＶＯＤ系统视频服务器的设计方案,从系统的体系结构方面充分探讨了如何使用单个主机处理越来越多的同时发生的视频点播要求,以及如何利用视频节目的分配文件的存贮特性减少磁盘寻道行为。本文将详细讨论直流视频流泵、磁盘子系统的文件释放策略以及系统的可伸缩性。     

Staggered striping: A flexible technique to display continuous media

During the past decade, information technology has evolved to where it is economically viable to store and retrieve continuous media data types, e.g., audio and video objects. Systems that support this data type are expected to play a major role in many applications including library information systems, entertainment technology, and educational applications. The objects of this new data type should be retrieved at a pre-specified bandwidth. If an object is retrieved at a rate lower than its pre-specified bandwidth then its display will suffer from frequent disruptions and delays termed hiccups.This paper describes staggered striping as a novel technique to support a hiccup-free retrieval of continuous media data types. Its design is based on a multidisk architecture. It is a flexible technique that can support media types whose bandwidth requirements are either lower or higher than the bandwidth of a single disk. Its design allows a system to scale to thousands of disk drives as its incurred overhead is fixed and does not increase as a function of additional disk drives.This research was supported in part by grants from AT&T/NCR/Teradata, Hewlett-Packard, IBM grant SJ92488, NSF grants IRI-9110522, IRI-9203389, and CDA-9216321 and DARPA contract DABT63-91-C-0001. An earlier version of this paper appeared in Proceedings of SIGMOD '94.