Multimedia object modeling and storage allocation strategies

The improvements in disk speeds have not kept up with improvements in processor and memory speeds. Many techniques have been proposed and utilized to maximize the bandwidths of storage devices. These techniques have proven useful for conventional data, but when applied to multimedia data, they tend to be insufficient or inefficient due to the diversified data types, bandwidth requirements, file sizes and structures of complex objects of multimedia data. In this paper, we discuss the design of an efficient multimedia object allocation strategy that strives to achieve the expected retrieval rates and I/O computational requirements of objects; and also effectively balances the loads on the storage devices. We define a multimedia object model, describe the multimedia object and storage device characteristics, the classification of the multimedia objects according to their I/O requirements, and the fragmentation strategies. We use a bipartite graph model for mapping of fragments to storage devices. A cost function based on a disk utilization per allocated space, the amount of free space, and the bandwidth of a storage device is used to determine the optimal allocation for an object's data.     

Efficient storage techniques for digital continuous multimedia

The problem of collocational storage of media strands, which are sequences of continuously recorded audio samples or video frames, on disk to support the integration of storage and transmission of multimedia data with computing is examined. A model that relates disk and device characteristics to the playback rates of media strands and derives storage patterns so as to guarantee continuous retrieval of media strands is presented. To efficiently utilize the disk space, mechanisms for merging storage patterns of multiple media strands by filling the gaps between media blocks of one strand with media blocks of other strands are developed. Both an online algorithm suitable for merging a new media strand into a set of already stored strands and an offline merging algorithm that can be applied a priori to the storage of a set of media strands before any of them have been stored on disk are proposed. As a consequence of merging, storage patterns of media strands may become perturbed slightly. To compensate for this read-ahead and buffering are required so that continuity of retrieval remains satisfied are also presented     

A user-centric network communication broker for multimedia collaborative computing

The development of collaborative multimedia applications today follows a vertical development approach, where each application is built on top of low-level network abstractions such as the socket interface. This stovepipe development process is a major inhibitor that drives up the cost of development and slows down the innovation pace of new generations of communication applications. In this paper, we propose a network communication broker (NCB) that provides a unified higher-level abstraction for the class of multimedia collaborative applications. We demonstrate how NCB encapsulates the complexity of network-level communication control and media delivery, and expedites the development of applications with various communication logics. We investigate the minimum necessary requirements for the NCB abstraction. We identify that the concept of user-level sessions involving multiple parties and multiple media, is critical to designing a reusable NCB to facilitate next-generation multimedia communications. Furthermore, the internal design of NCB decouples the user-level sessions from network-level sessions, so that the NCB framework can accommodate heterogeneous networks, and applications can be easily ported to new network environments. In addition, we demonstrate how the extensible and self-managing design of NCB supports dynamic adaptation in response to changes in network conditions and user requirements.     

Multimedia network file servers: Multichannel delay-sensitive data retrieval

Delay sensitive media such as audio and video are becoming integrated in the standard user interface. In this paper we consider simultaneous multiple access, such as would be performed by a multimedia network file server. To simplify the discussion, we consider only audio retrieval. The extension to storage and other delay sensitive data types is straightforward. This paper builds on the necessity of avoiding starvation of the consumer, and the assumption that certain sets of reads lead to a net increase in the number of samples buffered, to establish a theoretical framework for studying simultaneous multiple access. Our approach allows the possibility of splitting data into sorting sets for the purpose of reducing disk latencies and gives an optimal algorithm for the reduction. It explicitly handles both contiguous and noncontiguous file layouts. Lower bounds on read amounts and buffer requirements are proved. Using the theoretical framework, designers can evaluate the approach that is best suited to their situation.     

Using rotational mirrored declustering for replica placement in a disk-array-based video server

In a video-on-demand (VOD) environment, disk arrays are often used to support the disk bandwidth requirement. This can pose serious problems on available disk bandwidth upon disk failure. In this paper, we explore the approach of replicating frequently accessed movies to provide high data bandwidth and fault tolerance required in a disk-array-based video server. An isochronous continuous video stream imposes different requirements from a random access pattern on databases or files. Explicitly, we propose a new replica placement method, called rotational mirrored declustering (RMD), to support high data availability for disk arrays in a VOD environment. In essence, RMD is similar to the conventional mirrored declustering in that replicas are stored in different disk arrays. However, it is different from the latter in that the replica placements in different disk arrays under RMD are properly rotated. Combining the merits of prior chained and mirrored declustering methods, RMD is particularly suitable for storing multiple movie copies to support VOD applications. To assess the performance of RMD, we conduct a series of experiments by emulating the storage and delivery of movies in a VOD system. Our results show that RMD consistently outperforms the conventional methods in terms of load-balancing and fault-tolerance capability after disk failure, and is deemed a viable approach to supporting replica placement in a disk-array-based video server.     

一种高性能多媒体对象存储系统的研究

通过对多媒体应用中多用户并发访问的特点和性能进行分析,提出一种高性能多媒体对象存储系统MOSS(Multime-dia Object Storage System)的对象数据组织结构.MOSS结构采用两层结构,下层采用RAID5的方式组织数据,这样可以利用RAID5磁盘利用率高的优势.上层放常用的热点数据,通过将不同对象存放在不同磁盘,从而将不同用户的请求尽量分散到不同的磁盘上,可以提高多用户的并发访问性能.通过仿真测试,在4用户情况下,MOSS的性能平均比RAID高90%,随着用户数的增加,传统RAID方式的性能下降明显,而MOSS的性能下降很少,在16用户情况下,MOSS的性能平均比RAID高550%.     

A quality-of-service specification for multimedia presentations

The bandwidth limitations of multimedia systems force trade-offs between presentation-data fidelity and real-time performance. For example, digital video is commonly encoded with lossy compression to reduce bandwidth, and frames may be skipped during playback to maintain synchronization. These trade-offs depend on device performance and physical data representations that are hidden by a database system. If a multimedia database is to support digital video and other continuous media data types, we argue that the database should provide a quality-of-service (QOS) interface to allow application control of presentation timing and information-loss trade-offs. This paper proposes a data model for continuous media that preserves device and physical data independence. We show how to define formal QOS constraints from a specification of ideal presentation outputs. Our definition enables meaningful requests for endto-end service guarantees, while leaving the database system free to optimize resource management. We propose one set of QOS parameters that constitute a complete model for presentation error, and we show how this error model extends the opportunities for resource optimization.     

Generation of fuzzy rules and learning algorithm for servo control in holographic data storage system

Today many media of information storage device are formed as disks. Hence, next generation removable data storage media are shaped as disk types too. The holographic data storage system also uses a disk type photopolymer media. And then, holographic data storage system is most advanced optical memory system. Tracking servo and tilt servo control are very important research in holographic data storage system. In this paper, we propose intelligent servo control by fuzzy rules in holographic data storage system. Hence, we have found pattern of tilt servo control in holographic data storage system through fuzzy system and genetic algorithm. Fuzzy rules were generated by genetic algorithm for controlling tilt servo. Therefore, we control tilt servo using fuzzy rules in holographic data storage system. Consequently, Image input–output patterns of tilt servo control was found by intelligence algorithm in holographic data storage system.     

Fast proxy delivery of multiple streaming sessions in shared running buffers

With the falling price of memory, an increasing number of multimedia servers and proxies are now equipped with a large memory space. Caching media objects in the memory of a proxy helps to reduce the network traffic, the disk I/O bandwidth requirement, and the data delivery latency. The running buffer approach and its alternatives are representative techniques to caching streaming data in the memory. There are two limits in the existing techniques. First, although multiple running buffers for the same media object co-exist in a given processing period, data sharing among multiple buffers is not considered. Second, user access patterns are not insightfully considered in the buffer management. In this paper, we propose two techniques based on shared running buffers in the proxy to address these limits. Considering user access patterns and characteristics of the requested media objects, our techniques adaptively allocate memory buffers to fully utilize the currently buffered data of streaming sessions, with the aim to reduce both the server load and the network traffic. Experimentally comparing with several existing techniques, we show that the proposed techniques achieve significant performance improvement by effectively using the shared running buffers.     

Data Management for Multiuser Access to Digital Video Libraries

To support heterogeneous application types a video digital library will contain a large number of video objects with various lengths and display requirements. Multiuser access to the same video objects is required in order to increase the availability of video information and to make full use of the limited computing and storage resources. The access frequency and delay sensitivity of video objects require special methods to guarantee smooth playback of video objects and to minimize average waiting time. We propose an integrated approach to buffer and disk management for dynamic loading and simultaneous delivery of multiple video objects to multiple users. The allocation of buffer and disk resources in this study is based on quality of service variables such as average waiting time, display continuity, and viewer enrollment.     

Storage System and Multimedia: Classification and Extensions

With the increasing processing speeds, there is a shift away from the paradigm of centralized, sequential storage systems towards distributed and network based storage systems. Further, with the new imaging and real time multimedia applications, it is becoming more than ever important to design powerful, efficient and scaleable I/O systems. In this paper, the requirements of storage subsystems in multimedia environment were presented. The storage system components relating to those requirements were analyzed. Current solutions were surveyed and classified. Then we proposed approaches to improve storage subsystem performance for multimedia. The first approach applies constrained layout currently used for single disk model to multi-disk system. The second calls for using a stripping unit that meets both media and storage system optimization criteria. The third uses a pool of buffers instead of single buffer per stream.     

一种新型网络视频点播的存储层次

针对多媒体应用中快速存储资源上对匮乏和磁盘速度受限问题,实现了使用网络空闲内存资源作为快速设备缓冲媒体的机制,扩展了多媒体环境中的存储层次,并给出了一种简单快速的cache替换算法,初步结果表明,该机制可以加速多媒体环境中存储数据的访问速度。     

Resilient overlay network for real-time interactive multimedia sessions in corporate networks

Real-time interactive multimedia communications are becoming increasingly useful for education, business, e-commerce and e-government, providing an enriched user experience in teleconferencing, e-meetings, distance training and product demonstrations. Large corporations are usually located at several sites, so real-time multipoint sessions within corporations are especially difficult. IP multicast is available or feasible within each site of an organization. Thus, corporate networks can be considered as various multicast-capable networks interconnected through a wide area network without multicast connectivity. This paper proposes a resilient self-managed overlay network to support real-time multipoint interactive sessions within corporate networks. The proposed overlay takes advantage of the configuration of corporate networks to self-organize and provide an efficient media delivery service, making use of multicast communications wherever available. Various self-healing techniques are implemented allowing for the continuity of ongoing sessions in spite of network disruptions and entity failures. Extensive simulations and tests have been carried out to assess the performance and resilience of the overlay facing several types of disruptions.     

Let''s talk about it: dialogues with multimedia databases: Database support for human activity

We describe two scenarios of user tasks in which access to multimedia data plays a significant role. Because current multimedia databases cannot support these tasks, we introduce three new requirements on multimedia databases: multimedia objects should be active objects, querying is an interaction process, and query processing uses multiple representations. We discuss three techniques to handle multimedia objects as active objects. Also, we introduce a promising database architecture to meet the new user requirements. Agents within the database handle objects' representations, and a search engine on top of a conventional database handles relevance feedback and multiple representations.     

Design of fault-tolerant large-scale VOD servers: With emphasis onhigh-performance and low-cost

Recent technological advances in digital signal processing, data compression techniques, and high-speed communication networks have made Video-on-Demand (VOD) servers feasible. A challenging task in such systems is servicing multiple clients simultaneously while satisfying real-time requirements of continuous delivery of objects at specified rates. To accomplish these tasks and realize economies of scale associated with servicing a large user population, a VOD server requires a large disk subsystem. Although a single disk is fairly reliable, a large disk farm can have an unacceptably high probability of disk failure. Furthermore, due to real-time constraints, the reliability requirements of VOD systems are even more stringent than those of traditional information systems. Traditional RAID solutions are inadequate due to poor resource usage. Thus, in this paper, we present alternative schemes which provide a high degree of reliability at low disk storage, bandwidth, and memory costs for on-demand multimedia servers. Moreover, we discuss some of the main issues and trade-offs associated with providing fault tolerance in multidisk VOD systems. We would like to impress upon the reader that one of the main points of this paper is the exposition of trade-offs and issues associated with designing fault-tolerant VOD servers. It is not the case that one fault tolerance scheme is absolutely better than another, but rather that one must understand the trade-offs as well as one's system constraints and then choose a fault tolerance scheme accordingly     

Adapting multimedia Internet content for universal access

Content delivery over the Internet needs to address both the multimedia nature of the content and the capabilities of the diverse client platforms the content is being delivered to. We present a system that adapts multimedia Web documents to optimally match the capabilities of the client device requesting it. This system has two key components. 1) A representation scheme called the InfoPyramid that provides a multimodal, multiresolution representation hierarchy for multimedia. 2) A customizer that selects the best content representation to meet the client capabilities while delivering the most value. We model the selection process as a resource allocation problem in a generalized rate distortion framework. In this framework, we address the issue of both multiple media types in a Web document and multiple resource types at the client. We extend this framework to allow prioritization on the content items in a Web document. We illustrate our content adaptation technique with a web server that adapts multimedia news stories to clients as diverse as workstations, PDA's and cellular phones     

SuiteSound: a system for distributed collaborative multimedia

SuiteSound, a programming environment with integrated support for multimedia, is discussed. SuiteSound is built in the Suite object-based system on a conventional UNIX operating system. SuiteSound objects incorporate multimedia by creating flows and filters. Flows are streams of multimedia data moving through a sequence of objects. They bridge the gap between objects representing the state of an entity at a discrete point in time and space and continuous media such as live audio or video. Filters are intermediate objects between the source and destination of a flow. They take flow as input, perform one of several operations such as multiplex-in, multiplex-out, gain control, or silence deletion on it, and send the resulting flow to its destination. In effect, they provide a virtual device interface for the application programmer that is uniform and independent of any physical device. The design and implementation of SuiteSound on the Sun SparcStation are described. Experiments performed to determine the network and CPU load of the sound tool are reviewed     

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.     

Highly available and heterogeneous continuous media storage systems

A number of recent technological trends have made data intensive applications such as continuous media (audio and video) servers a reality. These servers store and retrieve large volumes of data using magnetic disks. Servers consisting of multiple nodes and large arrays of heterogeneous disk drives have become a fact of life for several reasons. First, magnetic disks might fail. Failed disks are almost always replaced with newer disk models because the current technological trend for these devices is one of annual increase in both performance and storage capacity. Second, storage requirements are ever increasing, forcing servers to be scaled up progressively. In this study, we present a framework to enable parity-based data protection for heterogeneous storage systems and to compute their mean lifetime. We describe the tradeoffs associated with three alternative techniques: independent subservers, dependent subservers, and disk merging. The disk merging approach provides a solution for systems that require highly available secondary storage in environments that also necessitate maximum flexibility.     

Real time servo control of the holographic data storage system with an additional servo beam

Holographic data storage is a next generation data storage device, which has high storage density, high data transfer rate and short access time. The device is very sensitive to disturbances due to its enormous storage density. In the disk type holographic data storage device deviation occurs successionally on the position of the data as the disk rotates. Therefore the spot where the probe beam is illuminated should directly be corrected in order to exactly retrieve the desired data. In this paper we suggest a method using an additional beam containing a servo pattern in order to detect the deviation of the media. We also propose a real time servo control method to compensate the affect of the unpredicted disturbance.