多级存储结构视频点播系统中的接纳控制算法研究

0 引言视频服务器作为视频点播(VOD)系统的核心,需要存储和管理大量经过压缩的视频节目。一方面,为了向用户提供实时、并发的视频流,需要使用高速的磁盘阵列来存放节目,但价格非常昂贵。另一方面,不同的节目受观众的喜爱程度不同,将点播频率极小的节目存放于价格昂贵的磁盘阵列中是不经济的。因此,有必要使用分级存储方案,即将不常被点播的节目存放到磁带库或光盘库等相对廉价的大容量存储设备中去,作为非在线节目,通常这部分存储称为二级库。     

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。     

广域网VoD系统中的视频流组播传输机制设计

本文提出了一种在服务于广域网范围内、带代理服务器群的VoD系统中有效实现视频流组播的传输机制，其主要设计目的是借助代理服务器减轻中心服务器的工作负担以及削减主干网带宽资源消耗，并在各局域网内有效实现视频流组播，提高视频流的传输效率。我们用不同的传输技术响应“热门”视频节目点播和“冷门”视频节目点播，力争用尽量小的资源消耗提供最大范围的优质点播服务。     

IP组播技术在校园网络视频系统中的应用研究

近年来,校园网络视频系统是校园信息化建设中不可缺少的组成部分,具有卫星电视转播、高清视频现场直播、校内资源点播和网络教学等功能。本文结合高校网络特点,构建了以校园网组播部署和组播管理为核心的校园网络视频系统,在提高校园宽带利用率的基础上实现了校园网络视频的广泛应用。     

云环境下基于多虚拟机的在线视频监控系统设计

针对常规视频监控系统在线实时性不强,海量视频数据传输迟滞,任务管理单一等问题,提出了构建在云计算环下基于多虚拟机技术在线视频监控系统;利用云计算平台中的物理资源与服务资源提升在线视频监控系统数据处理能力,虚拟机可同时处理大量的视频监控数据,并将视频数据以云存储的方式存储于云端服务器,降低了设备建设成本,可根据不同用户需求定制相关服务;本系统基于云计算平台设计,应用数十台乃至数百台虚拟机对在线视频监控数据进行处理,设计实现了云平台下在线视频监控系统的结构设计、以太网通信接口设计、服务器硬件配置和虚拟机控制;在软件设计方面通过对各虚拟机资源利用率的计算而动态分配资源,从而可以有效减少网络传输系统状态信息的带宽开销;通过系统功能与性能测试表明,在常规公共网络10 M带宽的情况下,本系统在线视频监控数据的传输延迟时间相比于传统视频监控减少了85％以上,监控视频数据量减少了75％以上.     

混合结构视频网格的构造与性能分析

针对可扩展视频网格结构中,由于加盟服务器数量不足所引起的区域服务器负载波动随在线用户数量变化过大的问题,引入P2P技术构造混合结构的视频网格,实现普通客户端之间视频流数据的直接传输。论述了P2P点播组的构成,资源的管理和调度算法,异常情况的处理过程。实验表明,混合结构的视频网格具有较好的性能,能够降低区域服务器负载的波动范围。     

远程教学中COD的组播实现

本文提出了一种集中式管理、点播服务器分布式放置的远程教学课件点播(Courseware On Demand-COD)系统。在这一体系结构下．采用了新的批处理信道调度策略，对用户实施多播流和补丁流相结合的组播服务。提高了网络带宽利用率，增加了可服务的点播并发流数，同时降低了课件播放延迟时间。     

基于流量控制的视频网格结构设计与性能分析

在二级视频网格和三级视频网格结构的基础上,提出当某区域服务器的网络带宽占用达到所设定的阈值时,将部分具有较高配置的客户端主机作为加盟服务器使用,以降低区域服务器的工作负载,同时原有的结构被扩展为树状的多级结构.详细论述了这种基于数据流量控制的多级视频网格结构的设计和工作模式,以及当加盟服务器突然失效时点播服务的平稳迁移策略.通过视频网格模拟器VGSim对这3种结构的视频网格服务能力进行模拟,结果表明,基于数据流量控制的多级视频网格结构的服务能力被有效增强.     

P2P技术在视频网格中的应用研究

研究优化视频效率问题,现有视频网格结构可伸缩性不足的缺点,使系统效率降低.引入P2P技术将客户端主机中缓存的视频流数据发送给同一子网或者相邻子网中的客户端主机,缩短网络中视频流数据的传送路径,节约网络干线的数据流量,降低区域服务器的负载,提高视频网格的可伸缩性.提出了融入P2P技术的PGVOD系统的结构设计方案和节点的运行模式,描述了 LCN的设计及其动态更新过程.最后通过视频网格模拟器VGSim将PGVOD与基于C/S模式的视频网格系统进行对比,结果表明,能够有效减少网络中的视频流流量,提高系统的吞吐量和性能.     

基于校园网带宽利用率最优的视频组播机制

传统的视频点播系统为每个点播用户分配单独的静态通信通道,其系统资源利用率低的缺点使得总体时间段上能并发的点播用户数少。针对网管可控的宽带校园网环境,文章提出了一个采用自适应动态缓存的组播策略,它通过差别服务(Diffserv)比例带宽分配机制保证了一定的视频播送服务质量(QoS),并基于服务端综合调度和客户端回馈的方法动态调整各视频流的播送速度,从而优化了系统整个过程的整体资源利用率,提高了系统的点播性能。     

基于磁盘存取受限的视频流组播策略

在宽带环境下，系统的网络通信能力很强，为了提高视频点播的并发点播数和实时响应性能，需要解决视频服务器端磁盘存取速度的瓶颈效应，文章提出的视频组播策略采用了自适应缓存算法，它在综合考虑网络通信能力和磁盘存取速度的基础上，优化了系统的整体性能，提高了传统视频点播批处理算法的效率。     

Dynamic Buffer Management for Near Video-On-Demand Systems

Advances in networking and storage technology have made it possible to deliver on-demand services over networks such as the emerging video-on-demand (VOD) applications. A variety of studies have been focused on designing a video server suitable for VOD applications. However, the number of concurrent on-demand services supported by the server is often limited by the I/O bandwidth of the storage systems. This paper describes a discrete buffer sharing model which uses batching and buffer sharing techniques in video servers to support a large number of VOD services. Two operations, splitting and merging, enable the model to fully utilize system resources such as buffers and disk bandwidths. Moreover, this paper also introduces the concept of imprecise video viewing which assumes that a limited amount of quality loss is acceptable during video playback. Based upon this assumption, three shrinking strategies are explored to reduce buffer requirements. Finally, the results of experiments show that our methods perform better than traditional buffer management techniques for VOD systems.     

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.     

Delivery of compressed videos from video servers employing cycle-based data-block retrieval discipline

The significant frame size variability exhibited in the compressed videos imposes a great challenge on network delivery. In this paper we propose an efficient flow control scheme, employed in the peer stations (i.e., servers and clients), for delivery of prestored compressed videos in a video-on-demand (VOD) system. This scheme resorts to an off-line analysis on the video frame sizes and server properties for figuring out the necessary buffer space and network bandwidth. The server platform of particular interest obeys a cycle-based data-block retrieval discipline, which is an essential technique to reduce the disk seek time for leveraging the disk throughput for supporting a large number of concurrent video accesses. Such a discipline is taken into account here to guarantee smooth delivery of variable-bit-rate videos. In run-time a server-driven control model is in use, where a server performs the primary flow control task, without relying on any feedback from clients. The scheme has been implemented in our prototype VOD system to support both unicast- and multicast communication paradigms under an RSVP-enabled network.     

Design of an interactive video-on-demand system

We design an interactive video-on-demand (VOD) system using both the client-server paradigm and broadcast delivery paradigm. Between the VOD warehouse and customers, we adopt a client-server paradigm to provide an interactive service. Within the VOD warehouse, we adopt a broadcast delivery paradigm to support many concurrent customers. In particular, we exploit the enormous bandwidth of optical fibers for broadcast delivery, so that the system can provide many video programs and maintain a small access delay. In addition, we design and adopt an interleaved broadcast delivery scheme, so that every video stream only requires a small buffer size for temporary storage. A simple proxy is allocated to each ongoing customer, and it retrieves video from optical channels and delivers video to the customer through an information network. The proposed VOD system is suitable for large scale applications with many customers, and has several desirable features: 1) it can be scaled up to serve more concurrent customers and provide more video programs, 2) it provides interactive operations, 3) it only requires point-to-point communication between the VOD warehouse and the customer and involves no network control, 4) it has a small access delay, and 5) it requires a small buffer size for each video stream.     

Efficient support for interactive service in multi-resolution VOD systems

Advances in high-speed networks and multimedia technologies have made it feasible to provide video-on-demand (VOD) services to users. However, it is still a challenging task to design a cost-effective VOD system that can support a large number of clients (who may have different quality of service (QoS) requirements) and, at the same time, provide different types of VCR functionalities. Although it has been recognized that VCR operations are important functionalities in providing VOD service, techniques proposed in the past for providing VCR operations may require additional system resources, such as extra disk I/O, additional buffer space, as well as network bandwidth. In this paper, we consider the design of a VOD storage server that has the following features: (1) provision of different levels of display resolutions to users who have different QoS requirements, (2) provision of different types of VCR functionalities, such as fast forward and rewind, without imposing additional demand on the system buffer space, I/O bandwidth, and network bandwidth, and (3) guarantees of the load-balancing property across all disks during normal and VCR display periods. The above-mentioned features are especially important because they simplify the design of the buffer space, I/O, and network resource allocation policies of the VOD storage system. The load-balancing property also ensures that no single disk will be the bottleneck of the system. In this paper, we propose data block placement, admission control, and I/O-scheduling algorithms, as well as determine the corresponding buffer space requirements of the proposed VOD storage system. We show that the proposed VOD system can provide VCR and multi-resolution services to the viewing clients and at the same time maintain the load-balancing property. Received June 9, 1998 / Accepted April 26, 1999     

基于流媒体技术的校园网电视直播系统

随着网络带宽的提高,和网络流媒体技术的发展,网上看电视越来越普及。文章结合成功应用案例,介绍了建立在校园网上基于流媒体技术的直播系统基本原理和解决方案。使用该系统,可实现在网络直播的同时,将需要的节目录制下来。结合学院的VOD视频点播系统,使录制的内容随时供校园网用户点播。     

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.     

Use of analytical performance models for system sizing and resourceallocation in interactive video-on-demand systems employing data sharingtechniques

In designing cost-effective video-on-demand (VOD) servers, efficient resource management and proper system sizing are of great importance. In addition to large storage and I/O bandwidth requirements, support of interactive VCR functionality imposes additional resource requirements on the VOD system in terms of storage space, as well as disk and network bandwidth. Previous works have used data sharing techniques (such as batching, buffering, and adaptive piggybacking) to reduce the I/O demand on the storage server. However, such data sharing techniques complicate the provision of VCR functions and diminish the amount of benefit that can be obtained from data sharing techniques. The main contribution of this paper is a simple, yet powerful, analytical modeling approach which allows for analysis, system sizing, resource allocation, and parameter setting for a fairly general class of data sharing techniques which are used in conjunction with the providing of VCR-type functionality. Using this mathematical model, we can determine the proper amount of resources to be allocated for normal playback as well as for service of VCR functionality requests while satisfying predefined system performance requirements. To illustrate the usefulness of our model, we focus on a specific data sharing scheme which combines the use of batching, buffering, and adaptive piggybacking, as well as allows for the use of VCR functions. We show how to utilize this mathematical model for system sizing and resource allocation purposes     

基于流媒体的视频点播(VOD)技术研究与应用

随着宽频技术和数字化视频技术的发展,视频点播系统VOD得到大规模的应用及推广。视频点播的应用,改变了用户与有线电视的关系,扩大用户获取信息来源。该文就点播技术、点播系统的关键技术及应用范围及发展方向进行了探索。