The Analysis and Performance of Multi-Rate Service in Distributed Video-on-Demand Systems

In this paper, we develop an end-to-end analysis of a distributed Video-on-Demand (VoD) system that includes an integrated model of the server and the network subsystems with analysis of its impact on client operations. The VoD system provides service to a heterogeneous client base at multiple playback rates. A class-based service model is developed where an incoming video request can specify a playback rate at which the data is consumed on the client. Using an analytical model, admission control conditions at the server and the network are derived for multi-rate service. We also develop client buffer requirements in presence of network delay bounds and delay jitter bounds using the same integrated framework of server and network subsystems. Results from an extensive simulation show that request handling policies based on limited redirection of blocked requests to other resources perform better than load sharing policies. The results also show that downgrading the service for blocked requests to a lower bitrate improves VoD system performance considerably. Combining the downgrade option with restrictions on access to high bitrate request classes is a powerful tool for manipulating an incoming request mix into a workload that the VoD system can handle.     

A VoD Application Implemented in Java

This article describes an implementation of a Video-on-Demand (VoD) system for the VoD interoperability test laboratory of the National Institute of Standards and Technology. It describes how Java can be used to implement the client side of a DAVIC based client-server system, which consists of a video server and a Set-Top Unit (STU) client. The communication between the video server and the STU is based on the Digital Storage Media Command and Control (DSM-CC) protocols. The VoD application is defined as a set of Java classes. These classes implement the graphical interfaces for user navigation and control. While this system is compliant with DAVIC specifications, it also permits an elegant integration of DAVIC services to the Internet environment.     

一个具有高可用性的动态容错VoD系统

提出了一个在VoD系统中具有高可用性的动态容错算法。针对分布式应用的特点,能对控制节点实现服务器切换的容错,数据服务节点负载均衡分配和故障节点提供服务的恢复。同时按照文章一致性保证机制可以实现媒体服务故障恢复对客户端的透明。通过对系统可用性分析和仿真试验表明,该算法可以有救地提高系统的可用性。     

P2P点播系统的客户端磁盘缓存策略

在基于有服务器结构对等网络环境的点播系统中,针对客户端需要缓存部分流媒体数据的问题,提出一种新型预测双缓存模型,给出相应的缓存替换算法。仿真实验表明,该模型在用户数目增多时,客户端缓存的命中率大幅提高,服务器的负载得到改善,显著降低了VCR操作时所引起的等待延迟。     

一种VoD系统视频服务器的设计与实现

论述了一种基于大容量IDE硬盘的分布式VoD系统的视频服务器的存储设计、硬件配置、数据管理模式和实现方法。     

PopCap: popularity oriented proxy caching for peer-assisted Internet video-on-demand streaming services

With the success of Internet video-on-demand (VoD) streaming services, the bandwidth required and the financial cost incurred by the host of the video server becoming extremely large. Peer-to-peer (P2P) networks and proxies are two common ways for reducing the server workload. In this paper, we consider a peer-assisted Internet VoD system with proxies deployed at domain gateways. We formally present the video caching problem with the objectives of reducing the video server workload and avoiding inter-domain traffic, and we obtain its optimal solution. Inspired by theoretical analysis, we develop a practical protocol named PopCap for Internet VoD services. Compared with previous work, PopCap does not require additional infrastructure support, is inexpensive, and able to cope well with the characteristic workloads of Internet VoD services. From simulation-based experiments driven by real-world data sets from YouTube, we find that PopCap can effectively reduce the video server workload, therefore provides a superior performance regarding the video server’s traffic reduction.     

PopCap: popularity oriented proxy caching for peer-assisted Internet video-on-demand streaming services

With the success of Internet video-on-demand (VoD) streaming services, the bandwidth required and the financial cost incurred by the host of the video server becoming extremely large. Peer-to-peer (P2P) networks and proxies are two common ways for reducing the server workload. In this paper, we consider a peer-assisted Internet VoD system with proxies deployed at domain gateways. We formally present the video caching problem with the objectives of reducing the video server workload and avoiding inter-domain traffic, and we obtain its optimal solution. Inspired by theoretical analysis, we develop a practical protocol named PopCap for Internet VoD services. Compared with previous work, PopCap does not require additional infrastructure support, is inexpensive, and able to cope well with the characteristic workloads of Internet VoD services. From simulation-based experiments driven by real-world data sets from YouTube, we find that PopCap can effectively reduce the video server workload, therefore provides a superior performance regarding the video server’s traffic reduction.     

Zebroid: using IPTV data to support STB-assisted VoD content delivery

IPTV, unlike Internet TV, delivers digital TV and multimedia services over IP-based networks with the required level of quality of service (QoS) and quality of experience (QoE). Linear programming channels in IPTV are delivered through multicast, which is highly scalable with the number of subscribers. Video-on-demand (VoD) content, on the other hand, is typically delivered using unicast, which places a heavy load on the VoD servers and all the network components leading to the end-user set-top boxes (STBs) as the demand increases. With the rapid growth of IPTV subscribers and the shift in video viewing habits, the need to efficiently disseminate large volumes of VoD content has prompted IPTV service providers to consider the use of STBs to assist in video content delivery. This paper describes our current research work on Zebroid, a potential VoD solution for fiber-to-the-node (FTTN) networks, which uses IPTV data on a recurring basis to determine how to select, stripe, and preposition popular content in selected STBs during idle hours. A STB requesting VoD content during the peak hours can then receive necessary stripes from participating STBs in the neighborhood. Recent VoD request access patterns, STB availability data, and capacity data on network components are taken into consideration in determining the parameters used in the striping algorithm of Zebroid. We show both by simulation and emulation on a realistic IPTV testbed that the VoD server load can be reduced by more than 70% during peak hours by allocating only 8 GB of storage on each STB. The savings achieved through Zebroid would also allow IPTV service providers to add more linear programming channels without expensive infrastructure upgrades.     

Dynamic proxy-assisted scalable broadcasting of videos for heterogeneous environments

Periodic broadcasting (PB) is a scalable technique for providing video-on-demand services. It significantly reduces server I/O and backbone network bandwidth requirements at the expense of high storage space and high network bandwidth requirements for clients. Traditional protocols assume homogeneous clients with identical resources. Unfortunately, in practice clients have very different bandwidths, and these are usually insufficient to provide video-on-demand (VoD) service from a PB server. Existing work on heterogeneous clients has focused on devising broadcast schedules to cater to low-bandwidth clients, which inevitably requires an extra backbone network bandwidth between the server and the clients. In our previous work, we proposed to use proxies residing at the edge of backbone network to accommodate low bandwidth clients for PB-based VoD services. The server broadcasts a video using a PB protocol while the proxy receives and stores the data in its local buffer and broadcasts the stored data to the clients in its local network. It significantly reduces the waiting time of low-bandwidth clients without requiring any extra backbone bandwidth by using a proxy buffer and channels. However, although lots of PB protocols have been proposed, the scheme can be applied only to some old PB protocols based on a pyramid protocol. In this paper, we propose a proxy-assisted PB system that can be generally applied to almost all the existing PB protocols, by dynamically managing buffer space and channels in proxy servers. Thus, with our proposed system, PB VoD system can be optimized in terms of the resource usages in backbone networks, proxy servers, and clients, by adopting more suitable PB protocols.     

基于可扩展视频服务器集群的视频点播系统设计

随着计算机技术和高速网络技术的发展,视频点播系统已变成现实,并且具有巨大的潜在需求。利用视频对象简介能够给用户一个友好的互动收视环境。可扩展视频服务器集群可以适应未来的用户需求的快速增长。视频对象分段技术和前缀缓存技术使视频文件按照一定的缓存策略以分段方式分布在协作式的缓存服务器集群中,以利于服务器集群的负载平衡和减少对用户的启动延迟。系统还引入了IP组播技术来减少对网络带宽的开销。该文提出了混合式的协作缓存和IP组播的方式交付视频对象,并描述了它是如何工作的。     

Presentation planning for distributed VoD systems

A distributed video-on-demand (VoD) system is one where a collection of video data is located at dispersed sites across a computer network. In a single site environment, a local video server retrieves video data from its local storage device. However, in distributed VoD systems, when a customer requests a movie from the local server, the server may need to interact with other servers located across the network. In this paper, we present different types of presentation plans that a local server can construct in order to satisfy a customer request. Informally speaking, a presentation plan is a temporally synchronized sequence of steps that the local server must perform in order to present the requested movie to the customer. This involves obtaining commitments from other video servers, obtaining commitments from the network service provider, as well as making commitments of local resources, while keeping within the limitations of available bandwidth, available buffer, and customer data consumption rates. Furthermore, in order to evaluate the quality of a presentation plan, we introduce two measures of optimality for presentation plans: minimizing wait time for a customer and minimizing access bandwidth which, informally speaking, specifies how much network/disk bandwidth is used. We develop algorithms to compute three different optimal presentation plans that work at a block level, or at a segment level, or with a hybrid mix of the two, and compare their performance through simulation experiments. We have also mathematically proven effects of increased buffer or bandwidth and data replications for presentation plans which had previously been verified experimentally in the literature.     

大规模分布式VoD中可扩展的影片缓存配置策略

提出了在VoD系统中减少综合性资源开销的一种灵活的分布式层次化影片缓存(Cache)配置策略。在采用单播传输情况下分析了标志着系统集成、服务器的流支持、存储及网络连接等的综合性资源开销。性能分析结果表明：用该策略构成的系统比传统的方案具有更小的开销，并且可以用较低的代价获得更多影片的服务。     

一种基于节的视频服务器允许接纳控制算法

提出了一种基于“服务器节”的支持压缩多媒体流的服务器中CPU、磁盘、网络和内存等资源管理的方法和允许接纳控制算法。“服务器节”概念定义了一组客户视频服务特性,如播放、快进、慢进和暂停等,并且确定了视频服务所需资源的分配参。一个“服务器节”包括视频服务器、磁盘设备、网络设备和允许接纳控制。它不但能优化使用单个资源,对于给定系统支持最大数量的客户端,保证其服务质量（QoS),而且其允许接纳控制算法能根据系统所有资源的状况,在不影响原有的视频服务基础上,确定对客户端新提出的视频服务是否接受。     

基于P2P的视频点播系统设计

随着计算机网络和多媒体技术的发展,人们对网络视频点播的需求越来越高,高清、流畅和互动已经成为人们对视频点播的要求,在传统的C/S模式的视频点播系统中,客户终端要观看视频都需要依赖中心化的视频服务器,而且对带宽的要求越来越大,视频服务器就容易成为网络的瓶颈,当网络规模越大时,服务器的负担就会越重,一旦服务器崩溃,整个网络就会瘫痪。另外由于服务器的能力有限,往往不能及时地对每一个客户端的请求作出响应,因此会造成资源利用率低下。P2P网络中没有中心化的服务器,不存在系统瓶颈,每个节点既充当客户端又充当服务器端,因而具有很高的资源利用率。     

Modeling Video on Demand services taking into account statistical dependences in user behavior

The popularity of video services on the Internet, and moreover High Definition (HD) videos, has increased continuously in recent years. This growing demand for high quality video services can cause problems in current communication networks. For this reason, the characterization and modeling of video workloads have become essential factors in evaluating the performance of these services. This paper presents the implementation of a simulation model of a Video on Demand (VoD) service. The model takes into account both the behavior of the users and the server workload. While the former is analyzed through a real VoD service, the latter is analyzed through lab experiments. Nevertheless, the main contribution of our model is that it also considers the dependences among user interactions. The model has been validated using real data and evaluated in different situations. Results show that performance is influenced both by massive access to the contents and by the dependence structure of user interactions.     

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.     

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。     

DPVoD:基于P2P的视频点播体系结构

可扩展性和可靠性是视频点播系统大规模应用的关键,提出了一种P2P点播系统结构DPVoD.系统基于应用层组播,用户以订制的缓存为其他节点提供服务,并形成相对独立的共享并发流组播树,组播树之问根据拥有的视频数据的重合程度而建立不同的组邻居关系,以此为基础,采用多种机制来提高系统性能:组协同工作、父亲点选择策略、状态控制协议和失效恢复等.定义并分析了可能对系统性能有严重影响的结尾雪崩问题并提出解决方案.对系统基本性能进行了理论分析.仿真结果表明,在静态和动态环境中,DPVoD系统的并发流占用数和利用率、可靠性等性能均优于类似系统.     

Secure DACS Scheme

When customers with different membership and position use computers as in the university network systems, it often takes much time and efforts for them to cope with the change of the system management. This is because the requirements for the respective computer usage are different in the network and security policies. In this paper, a new destination addressing control system scheme (DACS Scheme) for the university network services is shown. The DACS Scheme performs the network services efficiently through the communication management of a client. As the characteristic of DACS Scheme, only the setup modification is required by a system administrator, when the configuration change is needed in the network server. Then, the setup modification is unnecessary by a customer, which shows a merit for both a system administrator and a customer. However, there is a problem to be solved. In existing DACS Scheme, it is assumed that DACS Client for controlling the communication must be implemented on all clients. If the client without DACS Client is connected to the network, each network server can be accessed from the client. Therefore, in this paper, secure DACS Scheme with the function to prevent the communication from the client without DACS Client is proposed and examined.