基于有线电视网和IP网的视频会议系统设计与实现

设计并实现了一种结合有线电视网和IP网的视频会议系统.该系统以会议服务器为中心单元,协调各会场间的数据流和控制流传递,利用双向IP网,实现会议服务器和各会场间的会议控制等交互操作,以及上传各会场的音视频至会议服务器.它基于多播协议,利用有线电视网稳定可靠的高速下行带宽,将上载的音视频高质量地传送至各会场.     

基于代理的分布式视频流点播传输策略

视频流传输具有带宽高、周期长的特点,使网络带宽成为了制约视频流点播应用发展的主要因素.本文针对现有网络技术条件,充分利用客户端I/O带宽、本地缓存及网络带宽资源,设计了一个适用于大规模点播应用的基于代理的分布式视频点播传输策略.该策略中各本地网络设有一视频流代理服务器用于保存部分视频的部分内容,并按动态批处理的方式来接纳并服务请求用户.视频传输时,服务器与代理端之间采用单播传输机制,在代理与客户端之间采用单播与多播相结合的方式.实验表明该策略可以大大减少对骨干网络带宽的需求,并能为客户端提供理论上的零启动延时服务.     

Modeling and application of moderate prefetching strategy based on video slicing for P2P VoD systems

In peer-to-peer (P2P) video-on-demand (VoD) streaming systems,each peer contributes a fixed amount of hard disk storage (usually 2 GB) to store viewed videos and then uploads them to other requesting p...     

Suitability of DAMA and Contention-Based Satellite Access Schemes for TCP Traffic in Mobile DVB-RCS

The problem of optimizing access and bandwidth sharing among transmission control protocol (TCP) connections in the mobile digital video broadcasting return channel via satellite (DVB-RCS) is tackled in this paper. After sketching the general system architecture, we explicitly deal with the dynamic assignment of bandwidth to TCP connections on the return link, which is accomplished by a network control center (NCC) placed onboard the satellite. Mobile users access the satellite in multifrequency time-division multiple access (MF-TDMA), whereas they receive data from the NCC in time-division multiplexing (TDM). Two different techniques, based on deterministic and random access, are compared in terms of bandwidth usage and average completion time per connection, when the mobile user acts as both server and client. In the server case, to increase the TCP throughput, both packet-level forward error correction (FEC) on data sent by mobile users and a duplicated and delayed acknowledgment technique for TCP acknowledgment traffic from the NCC to the mobile users are applied. An analysis of the packet losses and a simulation campaign of file transfers by employing a realistic channel model has been carried out. The results of the analysis show the convenience of adopting a technique, in addition to the optimal data redundancy in different cases, such as the server or client role of users, their willingness to pay, the file size, and the environment type.     

Optimal video placement scheme for batching VOD services

Advances in broadband technology are generating an increasing demand for video-on-demand (VOD) applications. In this paper, an optimal video placement scheme is proposed for a batching VOD system with multiple servers. Given a specified requirement of the blocking probability, an optimal batching interval is derived and the corresponding file placement is obtained by hybrid genetic algorithm. It is demonstrated that the specified requirement on blocking probability is satisfied, while both batching interval and server capacity usage are minimized simultaneously.     

Adaptive batching scheme for multicast video-on-demand systems

In this paper, an adaptive algorithm is developed for providing true video on demand (VoD) services in a multicast environment. In conventional batching schemes, the batching time of the system is fixed and the performance of such static schemes is highly dependent on the selection of the batching time. If the batching time is wrongly estimated, the performance of the system will be greatly degraded. Our algorithm tries to dynamically find the optimal batching time by the newly updated arrival rate so as to minimize the bandwidth requirement. The results show that the system performance of the adaptive approach is always better than the static scheme in terms of total bandwidth requirement and customer reneging probability, especially in using long batching time for the high arrival rate     

Networking requirements for interactive video on demand

A significant driver for the consumer use of high bandwidth in the near future will be interactive video on demand (IVOD). A range of service types can be deployed, based on a differing sophistication, which must be traded against the network costs (bandwidth) and component costs (switch complexity and memory). The potential aggregate bandwidth required is huge (O(1Pb/s)), and thus it is essential to properly engineer the network to reduce the bandwidth required. This paper describes a variety of IVOD scenarios, and introduces a cost function that captures the combined bandwidth and storage requirements of the network. This cost function is used to compare different network engineering alternatives, particularly program caching and stream sharing. The effects of nonlinear pricing and differing weights of bandwidth and storage are also reflected by the cost function. This cost function can be used by network designers to determine optimal topology, sharing, and caching strategies for desired bandwidth versus memory costs in a particular network deployment. In addition, a simulation model is used to evaluate caching of programs or windows within programs. We show that there are some results that are widely applicable. In particular, the level in the network at which caching should take place is at approximately 80% depth in the distribution tree, above the head end switch in the network hierarchy. We also observe that the bandwidth savings in sharing streams (actually buffered windows of program content) is fairly small for user behavior based on Zipfs law. The overall intent of this work is to evaluate the effects of various server, cache, and sharing strategies on the bandwidth and storage requirements of the network and their proper placement within the network     

C-DOCSIS技术在双向业务接入系统中的应用

Cable Modem接入技术在我国广电网络中得到广泛的应用,随着广州有线宽带与互动电视用户的逐步增长,传统分前端的CMTS已经难以满足用户对带宽的需求,广州有线在网改中采用C-DOCSIS技术,解决了用户增长与带宽需求的矛盾,同时可达到节约成本的目的。     

直播流媒体传输系统的冗余优化

摘 要: 对HTTP Live Streaming深入研究之后,发现该协议在直播流媒体传输过程中存在视频流索引文件重复传送的问题。详细阐述了服务器与客户端之间的交互过程,并通过对网络监控软件的使用,检测到交互过程中服务器传输给客户端的视频流索引文件存在较大的冗余,造成网络带宽开销增大。提出一种可行的改进方案,在.M3U8文件中添加一个#EXT-X-MEDIA-SEQUENCE-LAST标签,并使服务器和客户端都对该标签进行识别。通过对网络占用率的对比分析,改进后的方案对网络带宽的占用率明显减小,进而验证了该改进方案的可行性。     

VOD系统设计

讨论了低成本的宽带网VOD系统设计方案。由于宽带网VOD系统是一个实时系统，就必须要认真考察诸如网络带宽、I／O带宽、网络结构、视频服务器、存储结构及软件系统等关键技术要素，这样才能设计出一个有效、经济、实用的宽带网VOD系统。文章最后给出了一个宽带网VOD系统的配置实例。     

Multipath routing for video delivery over bandwidth-limited networks

The delivery of quality video service often requires high bandwidth with low delay or cost in network transmission. Current routing protocols such as those used in the Internet are mainly based on the single-path approach (e.g., the shortest-path routing). This approach cannot meet the end-to-end bandwidth requirement when the video is streamed over bandwidth-limited networks. In order to overcome this limitation, we propose multipath routing, where the video takes multiple paths to reach its destination(s), thereby increasing the aggregate throughput. We consider both unicast (point-to-point) and multicast scenarios. For unicast, we present an efficient multipath heuristic (of complexity O(|V|/sup 3/)), which achieves high bandwidth with low delay. Given a set of path lengths, we then present and prove a simple data scheduling algorithm as implemented at the server, which achieves the theoretical minimum end-to-end delay. For a network with unit-capacity links, the algorithm, when combined with disjoint-path routing, offers an exact and efficient solution to meet a bandwidth requirement with minimum delay. For multicast, we study the construction of multiple trees for layered video to satisfy the user bandwidth requirements. We propose two efficient heuristics on how such trees can be constructed so as to minimize the cost of their aggregation subject to a delay constraint.     

基于NGOD的SDV系统会话管理服务器会话处理方案

介绍了一种基于NGOD架构的交换式数字广播电视（SDV）系统架构和其中会话管理服务器的设计实现方案。通过交换式的提供广播电视数据,可以有效的节省广播电视网HFC段带宽,同时提供用户更多可收看节目频道以及更好的用户体验。     

BroadCatch: a periodic broadcast technique for heterogeneous video-on-demand

Many essential multimedia applications rely on video-on-demand technology to deliver a video to different users. A number of periodic broadcast techniques have been proposed for the cost-effective implementation of such systems. Most of these techniques would either try to minimize the server bandwidth, user bandwidth, user storage, user access latency to the video, or a combination of some of the aforementioned parameters. On the other hand, the implementation strategies of these broadcast schemes would necessitate a minimum bandwidth requirement for all users. Multi-resolution techniques address the heterogeneity problem by sacrificing user video quality. In this paper, we consider a different approach that does not possess this disadvantage. Using an incremental channel design at the server side, and a specific broadcast schedule, users can choose among a range of bandwidths to use to download the video at the cost of their access latency and not to the video quality. We prove the correctness of the proposed solution; provide mathematical analysis to demonstrate its heterogeneous behavior, and present performance studies to illustrate its efficiency.     

RMFS：一种支持用户交互的流媒体调度方案

基于组播的流调度算法能够有效降低服务器和网络带宽消耗.但研究表明,在用户进行VCR交互操作情况下,这些算法的性能将急剧恶化.该文提出一种有效支持用户交互的视频点播系统流调度方案:常规组播固定调度RMFS.RMFS采用基于请求类的接纳控制策略,并通过流合并机制来合并单播流.分析了RMFS方案的最佳组播间隔、最佳请求阈值和最小服务器容量需求.仿真结果验证了分析模型的正确性和RMFS方案的可行性.     

应用于P2P网络串流的实时监控系统

点对点(Peer-to-Peer,P2P)传输架构的新技术能利用用户的网络带宽以及运算能力来分担串流服务系统的负担,对于该网络进行实时监控已经成为近年来的一个研究热点.分析了应用于P2P网络串流的实时监控系统,指出跟踪监控的3类主要方法,即网络级别、被动的应用程序级别和主动应用程序级别的监控.给出了主动应用程序级别的监控模式下监控系统的架构与组成,并通过实验分析了其监控性能.     

有线电视网络的互动式点播教学环境

远程教学是构建在电信、计算机、传播科技3者之间的应用,是兼有视觉与听觉的双向学习方式.目前远程教学的发展大致分成实时群播、虚拟网站、课程点播3个系统,虽然已经有完整的系统出现,但均存在受时间限制、网络带宽不足、影片画质差、互动性不佳等缺点.这里提出交互式点播教学环境的概念,是利用有线电视点播视频系统以及有线电视网络控制器,提出一套交互式点播教学系统,以解决目前远程教学发展所遇到的瓶颈.     

A Remote Laboratory in Engineering Measurement

Online engineering practice is offering nowadays new potentials for training of measurement technologies and experimental procedures. In a laboratory mainly devoted to Instrumentation for Measurement by hands-on activity in engineering fields, students and engineering professionals are using, at present, online experiments in a blended-learning approach. A set of experiments has been designed and developed as well as some virtual simulators. The experiments integrated in a Moodle platform are using a web-server system based on LabVIEW 7.1, linked to them by data acquisition interface cards, a video server, and a booking system developed as an extension of the Moodle platform. This paper reports a particular setup specially designed for remotely measuring and determining mechanical material properties and its combination with the design of a highly interactive user interface. The user may remotely conduct the experiment, getting numerical, graphical, and live video output information and receiving e-mailed experimental results.      

Reducing initial latency in media servers

A multimedia server needs to provide high bandwidth and continuous real-time delivery. We present techniques for reducing the initial latency of presentations. This is important in interactive applications such as video games and multimedia document browsing. On-disk partial data replication can significantly reduce initial latency without adversely affecting throughput     

基于虚拟机和软件路由器的组播实验网络研究

通过互联网传输视频会占用大量的网络带宽,而采用组播技术可以减小视频播放对带宽的占用,降低视频服务器的负载。目前只有部分硬件路由器具备组播功能,使用这些路由器搭建组播网络,需要较高的成本。文中提出了一种解决方案,利用虚拟化、软件路由等新兴技术,在虚拟机上组建由多个软件路由器组成的组播网络,搭建组播视频服务器,并通过测试组播网络中视频播放的效果证明方案的可行性。     

Distributed servers approach for large-scale secure multicast

In order to offer backward and forward secrecy for multicast applications (i.e., a new member cannot decrypt the multicast data sent before its joining and a former member cannot decrypt the data sent after its leaving), the data encryption key has to be changed whenever a user joins or leaves the system. Such a change has to be made known to all the current users. The bandwidth used for such re-key messaging can be high when the user pool is large. We propose a distributed servers approach to minimize the overall system bandwidth (and complexity) by splitting the user pool into multiple groups each served by a (logical) server. After presenting an analytic model for the system based on a hierarchical key tree, we show that there is an optimal number of servers to achieve minimum system bandwidth. As the underlying user traffic fluctuates, we propose a simple dynamic scheme with low overhead where a physical server adaptively splits and merges its traffic into multiple groups each served by a logical server so as to minimize its total bandwidth. Our results show that a distributed servers approach is able to substantially reduce the total bandwidth required as compared with the traditional single-server approach, especially for those applications with a large user pool, short holding time, and relatively low bandwidth of a data stream, as in the Internet stock quote applications.