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。     

基于模糊逻辑的视频服务器接纳控制

提出一种新的基于模糊逻辑的VBR视频流接纳控制算法。该算法通过对调度周期的在线调整,使得系统所剩的磁盘I/O带宽和缓存空间达到一种等量的动态平衡,从而大大提高了系统资源的综合利用率。仿真结果表明,该算法下的接纳率比最优固定周期算法下的接纳率提高了约25％;同时,也比前人提出的动态调度周期算法的接纳率提高8％,并且算法的可行性也得到明显增强。     

国防科大计算机学院工学博士学位论文摘要

连续媒体数据存储与回取技术的研究作者：刘衡竹（１９９９．６）导师：陈福接教授　　随着存储技术、通讯技术和视频压缩技术的高速发展,使得通过ＢＩＳＤＮ进行视频点播（Ｖｉｄｅｏ－Ｏｎ－Ｄｅｍａｎｄ）服务成为可能。ＶＯＤ服务器以压缩、数字化的形式存储视频数据,并为多个用户并发提供回取和传输服务。为了实现视频数据的优化存储与回取,本文对ＭＰＥＧ流的结构及传输特性进行了讨论,分析了现有磁盘系统的读取过程和延时特性,建立了用于对连续媒体回取过程进行分析的磁盘传输延迟模型。定义了与具体算法无关的用于连续媒体回取…     

视频服务器存储子系统的I/O优化

视频服务器存储子系统的I／O性能决定了视频服务器的总体性能。本文提出的一种新的实时磁盘调度算法（LLF－Window)能有效地服务各种编码格式的视频流，并对传统的SCSI总线不均衡调度机制进行了改造，实验结果表明，新的磁盘调度算法和改造后的SCSI总线调度机制有效地改进了视频服务器存储子系统的I／O性能，保证了视频流的连续播放。     

Cache连续性操作问题研究

Ｃａｃｈｅ调度策略在磁盘操作中占有举足轻重的地位，调度策略设计的好坏直接影响着磁盘Ｉ／Ｏ性能。磁盘上非连续的扇区的存取需要多个Ｉ／Ｏ来完成。当数据读入Ｃａｃｈｅ或Ｃａｃｈｅ腾空时，磁盘旋转等待时间是不可避免的。本文分析了磁盘中常用的Ｃａｃｈｅ调度算法存在的不足，提出了一种新的调度策略，一次Ｉ／Ｏ即可完成非连续扇区的存取操作把旋转延迟缩至最小程度，在某些情况下可达到零延迟。     

一种多路传输可伸缩视频流的分组调度算法

由于无线网络带宽不足,不能满足高质量视频的传输要求,终端用户往往会遭受频繁的播放中断.为了解决上述问题,一种可能的办法是利用终端的多模特性并发地多路传输视频流.多路传输视频流的关键技术之一是分组调度算法,即将视频分组分配到适合的接口进行传输.本文研究了一种多路传输可伸缩编码视频流下基于质量驱动的分组调度算法.为了最大限度地提升接收端的视频质量,该分组调度算法考虑了接入网络的特性以及视频帧的特征.在本文中,视频数据包调度的问题建模为一个受限多重背包问题,而这个问题是已知为NP-hard的.然后,提出了一种分组调度算法,将视频分组调度到合适的接入网进行传输.在NS-2仿真软件中使用真实的视频trace文件去验证该算法利用多模终端传输可伸缩编码视频的性能.仿真结果表明,分组调度算法在PSNR上优于速率控制算法和传统的round-robin算法.     

如何用VB在C/S模式下实现远程数据访问

ＶＩＳＵＡＬＢＡＳＩＣ作为一种流行的开发工具,在开发Ｃ／Ｓ应用程序方面有强大的功能。概括的说在ＶＢ中有四种编程模型可以实现远程数据访问,它们是数据访问对象（ＤＡＯ）和数据控件（ＤＡＴＡ）、远程数据对象（ＲＤＯ）和远程数据控件（ＲＤＣ）、开放数据库互连（ＯＤＢＣ）ＡＰＩ和ＶＢＳＱＬＡＰＩ。本文将结合一个简单的例子,主要讨论如何使用前两种编程模型,对后两种仅做简要介绍。假设服务器的操作系统是ＷＩＮＤＯＷＳＮＴ４．０。服务器名为４０２,并且在服务器上已有一名为ｅｘａｍｐｌｅ的ＳＱＬＳＥＲＶＥＲ６．５数…     

双头镜像磁盘的实时调度算法及性能评价

本文对双头镜像磁盘系统模型进行实时扩展,并提出了三种实时调度算法：最早截止期优先算法（ＥＤＦ）,可满足的最早截止期优先算法（Ｆ－ＥＤＦ）和忽视超时限请求算法（ＩＧＭ－ＥＤＦ）．这三种算法充分考虑了Ｉ／Ｏ请求的截止期限,使双头镜像磁盘系统能更好地满足实时需求．在进行了性能模拟后,发现实时调度算法比非实时算法能更好地满足实时Ｉ／Ｏ请求的时限要求．三种实时调度算法中,适用于硬实时应用的ＩＧＭ－ＥＤＦ的性能最好,Ｆ－ＥＤＦ算法的性能次之,它适用于软实时环境．     

双头镜橡磁盘的实时调度算法及性能评价

本文对双头镜像磁盘系统模型进行实时扩展,并提出了三种实时调度算法：最早截止期优先算法（ＥＤＦ）,可满足的最早截止期优先算法（Ｆ－ＥＤＦ）和忽视超时限请求算法（ＩＧＭ－ＥＤＦ）。这三种算法充分考虑了Ｉ／Ｏ请求的截止期限,使双头镜像磁盘系统能更好地满足实时需求,在进行了性能模拟后,发现实时调度算法比非实时算法能更好地满足时Ｉ／Ｏ请求的时限要求。三种实时调度算法中,适用于硬实时应用的ＩＧＭ－ＥＤＦ的性能     

5.7GB ORB可携式硬盘

目前大家可以在市面上找到的ＯＲＢ可携式储存媒 体,计有 ２． ２ＧＢ ＥＩＤＥ Ｉｎｔｅｒｎａｌ、 ２． ２ＧＢ ＳＣＳＩ Ｅｘ－ｔｅｒｎａｌ、２．２ＧＢ ＵＳＢ及２．２ＧＢ ＳＣＳＩ Ｉｎｔｅｒｎａｌ,预期明年将推出容量高达１３ＧＢ的ＯＲＢ。一张ＯＲＢ磁盘便能储存２．２ＧＢ的数据,比同类型产品实超前了不少。 虽然ＯＲＢ在１９９７年已经发布,但直到目前为止,可能大家对 ＩＥＥＥ１ ３９４及 ＰＣＭＣＩＡ接回的 ＯＲＢ ２． ２ＧＢ这款储存媒体比较陌生。相比起其它同类型产品,ＯＲＢ的明显优势是它采用制作硬盘的技术,…     

基于在线测量的视频服务器接纳控制

实时多媒体系统中,有限的磁盘I/O带宽和缓存空间使得接纳控制显得更为重要。针对传统算法接纳控制方面的不足,论文提出基于在线测量的VBR视频服务器接纳控制算法。通过在线测量系统所剩资源和周期容限的幅度变化来实时调节调度周期的大小,不但简化了接纳过程,节约了系统资源,提高了算法的可实现性,而且也使得系统的所剩资源达到更优的“等量”平衡。结果表明,系统的综合性能指标明显提高。     

A Design Framework for Multi-Resolution Video Servers

Video can be encoded into multiple-resolution format in nature. A multi-resolution or scalable video stream is a video sequence encoded such that subsets of the full resolution video bit stream can be decoded to recreate lower resolution video streams. Employing scalable video enables a video server to provide multiple resolution services for a variety of clients with different decoding capabilities and network bandwidths connected to the server. The inherent advantages of the multi-resolution video server include: heterogeneous client support, storage efficiency, adaptable service, and interactive operations support.For designing a video server, several issues should be dealt with under a unified framework including data placement/retrieval, buffer management, and admission control schemes for deterministic service guarantee. In this paper, we present a general framework for designing a large-scale multi-resolution video server. First, we propose a general multi-resolution video stream model which can be implemented by various scalable compression techniques. Second, given the proposed stream model, we devise a hybrid data placement scheme to store scalable video data across disks in the server. The scheme exploits both concurrency and parallelism offered by striping data across the disks and achieves the disk load balancing during any resolution video service. Next, the retrieval of multi-resolution video is described. The deterministic access property of the placement scheme permits the retrieval scheduling to be performed on each disk independently and to support interactive operations (e.g. pause, resume, slow playback, fastforward and rewind) simply by reconstructing the input parameters to the scheduler. We also present an efficient admission control algorithm which precisely estimates the actual disk workload for the given resolution services and hence permits the buffer requirement to be much smaller. The proposed schemes are verified through detailed simulation and implementation.     

视频服务器中多网络I/O的调度与接纳控制

在视频服务器中,由于网络I/O带宽比磁盘I/O带宽相对丰富而未得到研究者的重视,但当服务达到一定的规模、网络输出成为瓶颈时,在多网络I/O情况下,网络输出的量化计算则不可避免.着重探讨了视频服务器在多网络I/O并行输出的情况下,如何进行最大输出调度的问题,给出了3个调度算法及相应的接纳计算公式,特别是一个带缓冲的优化调度模型.实验结果显示,调度模型及规划性能是优越而有效的.该项工作对视频服务器的调度设计、资源的有效配置具有指导作用.     

Providing QOS guarantees for disk I/O

In this paper, we address the problem of providing different levels of performance guarantees or quality of service for disk I/O. We classify disk requests into three categories based on the provided level of service. We propose an integrated scheme that provides different levels of performance guarantees in a single system. We propose and evaluate a mechanism for providing deterministic service for variable-bit-rate streams at the disk. We will show that, through proper admission control and bandwidth allocation, requests in different categories can be ensured of performance guarantees without getting impacted by requests in other categories. We evaluate the impact of scheduling policy decisions on the provided service. We also quantify the improvements in stream throughput possible by using statistical guarantees instead of deterministic guarantees in the context of the proposed approach.     

An Admission Control Scheme Based on Online Measurement for VBR Video Streams Over Wireless Home Networks

This paper presents an online measurement-based admission control scheme on the basis that the aggregate VBR video traffic is lognormally distributed. The proposed scheme consists of two components: measurement process and admission decision. The measurement process applies a linear Kalman filter to estimate statistical parameters of aggregate VBR video traffic. The estimated statistical parameters are used to calculate the effective bandwidth for admission decision. Variable bit rate (VBR) video traffic with high data rate is expected to occupy a dominant proportion of bandwidth for future wireless broadband home networks. To guarantee quality-of-service (QoS) of such VBR video streams, while achieving a high level of channel utilization, an efficient admission control scheme is urgently required, especially for emerging wireless multimedia indoor services, such as HDTV, online video game, etc. The proposed scheme is computationally efficient and accurate without much prior traffic information. Simulation results verify its effectiveness and show that it performs well for both a small number of connections and a large number of connections.     

VBR视频在MZR磁盘上的比例安置

文章在分析了变位率（VBR）视频和多区记录（MZR）磁盘特性的基础上,提出了一种比例安置算法：视频数据块按尺寸、分比例安置到相应的记录区上。这种算法和其它算法相比简洁、更有效地利用了磁盘带宽和能支持更多视频流的同时检索。     

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。     

Real-time disk scanning for timely retrieval of continuous media objects

In recent years, demands for multimedia applications have rapidly grown with the advances in computing power and network technology. To fulfill the demands, it is crucial to establish the multimedia information systems supporting continuous media (CM) streams without hiccups. Many useful methods have been proposed in the past so that CM steams with VCR-quality can be supported. Although these earlier approaches can be used for the service of VCR-quality streams, they cannot provide a good system performance for the CM streams with various playback rates and rather short durations of playback. In the paper, we propose a new CM playback method that consists of bulk-scanning and an earliest-deadline-first style scheduling algorithm. Our proposed method provides both good response times and high I/O utilization using the efficient disk scheduling. In addition, our mechanism for admission control makes CM streams never experience hiccups until the ends of playback. Through experimental analyses, we show the performance advantages of the proposed method over the earlier methods.