Handling Updates and Crashes in VoD Systems

Though there have been several recent efforts to develop disk based video servers, these approaches have all ignored the topic of updates and disk server crashes. In this paper, we present a priority based model for building video servers that handle two classes of events: user events that could include enter, play, pause, rewind, fast-forward, exit, as well assystem events such as insert, delete, server-down, server-up that correspond to uploading new movie blocks onto the disk(s), eliminating existing blocks from the disk(s), and/or experiencing a disk server crash. We will present algorithms to handle such events. Our algorithms are provably correct, and computable in polynomial time. Furthermore, we guarantee that under certain reasonable conditions, continuing clients experience jitter free presentations. We further justify the efficiency of our techniques with a prototype implementation and experimental results.     

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.     

A meta-index for querying distributed moving object database servers

Distributed moving object database servers offer a feasible solution to the scalability problems of centralized database systems. In these potentially large-scale systems, querying about the time-varying location of specific moving objects can be particularly expensive in terms of running time. This work proposes a meta-index   based strategy that can significantly speed up the processing of these queries. The meta-index acts as an entry point for spatio-temporal queries and quickly drives the search process to the database servers that contain solutions. It also enables very fast approximated solutions to queries such as top-k$k$ and spatio-temporal range queries.     

低成本可扩展的分布式VoD系统体系结构研究

考虑视频点播(VoD)系统的成本代价要求,给出了一种基于普通PC机的、高性价比的分布式VoD系统方案,论述了系统的体系结构、动态扩展及其负载平衡机制.实验数据表明,系统能有效地解决传统集中式VoD系统的瓶颈问题,具有良好的可扩展性,能够满足大规模VoD应用的要求.     

基于视频推荐技术的无线网络视频服务器设计

无线网络视频服务器中视频推荐技术已成为重要技术之一,视频推荐技术是为了用户在使用无线网络是视频务器时,更快的找到感兴趣的视频;采用当前方法对用户进行视频推荐时,未考虑用户的兴趣偏好是否随着时间有所变化,使视频推荐出现偏差;为此,提出一种基于视频推荐技术的无线网络视频服务器设计方法;该方法首先使用无线网络视频服务器硬件部分的MPEG-4进行视频数据采集,并对MPEG-4采集的视频数据进行整理;在由软件部分把采集到的视频数据储存到缓冲区,进行视频缓冲,并建立视频数据队列进行视频数据输送;以计算无线网络视频的相似度来搜索相近视频,将搜索到的视频与目标用户观看过的视频进行对比,对比相似度越接近1,则说明用户对推荐视频感兴趣的几率大,反之越接近-1用户对推荐视频越不感兴趣;此计算方法能有效的从海量视频数据中快速的搜索出目标用户感兴趣视频;实验结果表明,将视频推荐技术应用到无线网络视频中可以迅速准确的搜索出目标用户感兴趣视频。     

Feature-based design in a distributed and collaborative environment

In this paper, a client/server framework has been developed to enable a dispersed team to accomplish a feature-based design task collaboratively. A manipulation client+modelling server infrastructure has been proposed to facilitate consistent primary information modelling for multiple users and adaptability of the system. Based on feature-to-feature relationships, a distributed feature manipulation mechanism has been proposed to filter the varied information of a working part during a co-design activity to avoid unnecessary re-transferring of the complete large-size CAD files each time when any interactive operation is imposed on the model by a client. In the distributed environment, a design task and the engaged clients are organised and connected through working sessions generated and maintained dynamically with a collaborative server. The environment is open to downstream manufacturing analysis modules to achieve distributed concurrent engineering.     

The evolution of a distributed processing network

Current trends in information systems technology increase the advantages of developing an increasingly complex distributed processing capacity. Distributed processing networks (DPNs) are expected to evolve gradually from centralized systems into more complex configurations. The introduction of major changes in organizational Structure, such as those precipitated by mergers or acquisitions, also require rapid changes to the DPN. This paper describes four distributed processing configurations. It then presents a case: the evolution of the DPN in a large corporate bank and holding company. This case illustrates configuration changes over the life cycle of the DPN of the bank and provides insight into the process of planning for DPN change. A tendency to return toward centralization is noted in this case; this may cause practitioners to rethink their own DPN growth plans.     

A gamma fractal noise source model for variable bit rate video servers

In this paper, we model the statistical behavior of real traces of MPEG-4 encoded variable bit rate video data in a digital video server. As performance measures we calculate bounds for the user disk service rate and buffer size. According to our simulations, the Gamma Fractal Noise model for the increment process, which is self-similar, seems to be very close to the actual data behavior.     

Simulation study of multitasking in distributed server systems with variable workload

The multitasking performance of a distributed server system is considered where the workload is variable. Time varying distributions are proposed for job arrival, job parallelism, and task service demand. A simulation model is used to address performance issues associated with task scheduling. The objective is to identify conditions that produce good overall system performance, while maintaining fairness of individual job execution times. Simulated results show that all task scheduling methods have merit. In all cases, the best policy depends on performance goals. Furthermore, although the paper studies distributed multiprocessor system performance, it also addresses the performance issues of other systems where multitasking and scheduling is used, since no restrictions are imposed on the server/job/task characteristics.     

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.     

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     

Columbia's VoD and Multimedia Research Testbed with Heterogeneous Network Support

This paper reports our progress in developing an advanced video-on-demand (VoD) testbed, which will be used to accommodate various multimedia research and applications such as Electronic News on Demand, Columbia's Video Course Network, and Digital Libraries. The testbed supports delivery of MPEG-2 audio/video stored as transport streams over various types of networks, e.g., ATM, Ethernet, and wireless. Both software and hardware video encoders/decoders are used in the testbed. A real-time video pump and a distributed application control protocol (MPEG-2's DSM-CC) have been incorporated. Hardware decoders and set-tops are being used to test wide-area video interoperability. Our VoD testbed also provides an advanced platform for implementing proof-of-concept prototypes of related research. Our current research focus covers video transmission with heterogeneous quality-of-service (QoS) provision, variable bitrate (VBR) traffic modeling, VBR server scheduling, video over Internet, and video transmission over IP-ATM hybrid networks. An important aim is to enhance interoperability. Accommodation of practical multimedia applications and interoperability testing with external VoD systems has also been undertaken.     

Throughput optimization for video streaming proxy servers based on video staging

A video streaming proxy server needs to handle hundreds of simultaneous connections between media servers and clients. Inside, every video arrived at the server and delivered from it follows a specific arrival and delivery schedule. While arrival schedules compete for incoming network bandwidth, delivery schedules compete for outgoing network bandwidth. As a result, a proxy server has to provide sufficient buffer and disk cache for storage, together with memory space, disk space and disk bandwidth. In order to optimize the throughput, a proxy server has to govern the usage of these resources. In this paper, we first analyze the property of a traditional smoothing algorithm and a video staging algorithm. Then we develop, based on the smoothing algorithm, a video staging algorithm for video streaming proxy servers. This algorithm allows us to devise an arrival schedule based on the delivery schedule. Under this arrival and delivery schedule pair, we can achieve a better resource utilization rate gracefully between different parameter sets. It is also interesting to note that the usage of the resources such as network bandwidth, disk bandwidth and memory space becomes interchangeable. It provides the basis for inter-resource scheduling to further improve the throughput of a video streaming proxy server system.

Assignment of availability objectives to components of heterogenous distributed computer systems

This paper provides a scheme to assign availability objectives to various components of a heterogenous distributed computer system using a minimum cost criteria. The availability is viewed from a user (client) perspective rather than the traditional system perspective. The user availability objectives are classified in terms of operational and inherent availabilities. Such a classification enables the designers to take into account the user expectations in a more realistic way thus minimizing the high cost of providing fault tolerant systems. The user availability objectives are then translated into the system availability objectives by relating the availability needs of each distinct user group to system components utilized by that group.     

Designing an effective P2P system for a VoD system to exploit the multicast communication

A distributed video-on-demand system (DVoD) with multiple server-nodes is a cost-effective and fault-tolerant solution for a high scalable enterprise video-on-demand (VoD) system. However, such a server-oriented design is highly vulnerable to workload variations given that the service capacity is limited. Peer-to-Peer (P2P) has been introduced as an architectural solution with self-growing capacity. However, the characteristics of a pure P2P system such as the peer transient nature and high network overhead make this kind of architecture unsuitable for a fully interactive VoD system. In this paper, we propose a new efficient integrated VoD architecture, called DPⁿ2P^m$D{P}^{n}2P^m$, that combines DVoD with a P2P system and multicast communications. The DVoD’s server-nodes provide a minimum required quality of service (QoS) and the P2P system is able to offer the mechanism to increase the system service capacity according to client demands. Multicast communication, wherever it is possible, is effectively exploited by our P2P system. In our design, each client is able to send video information to a set of m$m$ clients using only one multicast channel. Furthermore, the collaboration mechanism is able to coordinate a set of clients to create one collaboration group to replace the server, providing an extensive, efficient and low network-overhead collaboration mechanism from n$n$-peers to m$m$-peers. Regardless of the video the client is watching, our P2P scheme allows every active client to collaborate with the server. The P2P scheme is complemented with recovery mechanisms that are able to replace the failed client before affecting the QoS, offering continuous playback. The proposed approach has been broadly evaluated, firstly using a mathematical model to derive the theoretical performance and secondly using a simulation environment to analyze the system’s dynamic behavior, the VCR interaction impact and the client failures. Comparing DPⁿ2P^m$D{P}^{n}2P^m$ with other DVoD architectures and the most relevant P2P delivery policies, we show that our design is an improvement on previous solutions, providing a higher scalability.     

A new approach to performance modelling of Client/Server distributed data base architectures

The recent technological advances in the field of computer and communication lead to distributed data base (DDB) architectures based on the Client/Server paradigm. Available DDB performance prediction methodologies are not sufficiently adequate being too expensive both in the model definition and in the model analysis because of the structural complexity and the large system dimension.

This paper concentrates on a new approach to performance modeling of DDB systems called “independent modelling approach”. This approach separates the DDB software model from the DDB machinery model, and models from solution techniques. This way the aspects related to data contention can be analysed as a pure software characteristic and separated from resource contention, considered as a machinery characteristic. Furthermore, it is possible to analytically model some system aspects (e.g., the software only, or part of it, without involving the machinery model), and apply combined analytical/simulation methods for the remaining system aspects. This results in higher flexibility at lower computational cost in the performance analysis of complex DDB architectures.

A case study is developed and experimental results are discussed to show the effectiveness of the approach.     

基于Web的VOD服务器的设计与实现

VOD(Video On Demand)即视频点播,是随着计算机技术和网络通信技术的发展,综合了计算机、通信技术、电视技术而迅速新兴的一门综合性技术。介绍了流媒体技术的基本概念,基本主流技术,VOD系统的基本结构及工作原理以及实现的过程,设计出一种基于Web的VOD服务器,实现视频点播。     

The Vidboard: A video capture and processing peripheral for a distributed multimedia system

This paper describes a network-based video capture and processing peripheral, called the Vidboard, for a distributed multimedia system centered around a 1-Gbit/s asynchronous transfer mode (ATM) network. The Vidboard is capable of generating full-motion video streams having a range of presentation (picture size, color space, etc.) and network (traffic, transport, etc.) characteristics. The board is also capable of decoupling video from the real-time constraints of the television world, which allows easier integration of video into the software environment of computer systems. A suite of ATM-based protocols has been developed for transmitting video from the Vidboard to a workstation, and a series of experiments are presented in which video is transmitted to a workstation for display.     

CEA: A Cyclic Expansion Algorithm for data migration in parallel video servers

Parallel video servers can achieve highly storage-saving and granularly load-balancing, but they suffer from a system expansion problem. As the number of users continuously increases, the system inevitably needs to expand the number of video servers. However, the expansion of a parallel video server system is not as simple as that of a replicated video server system. Hence, this work develops an efficient expansion algorithm, called the Cyclic Expansion Algorithm (CEA), for parallel video servers. The proposed CEA algorithm has several good features. First, the data layout of each video content exhibits periodicity. Consequently, the meta-data size of each video and the complexity of the CEA algorithm are reduced. Second, the number of required data movements during a system expansion is optimized. Third, the total number of required XOR recomputations for updating parity blocks during an expansion is also minimized. Additionally, the new CEA can be applied to a variety of distributed storage systems, such as the cloud-based storage systems using striping and parity check techniques.