IPQAM 在有线电视网络中的发展前景

根据嘉善县政府便民服务和三务公开建设的要求以及高清点播业务在本地的发展，我们采购了数码视讯的IPQAM调制器（型号：10K511），并对嘉善广电网络设备进行了部分调整，把IPQAM调制器安装在中心机房以及下沉至分机房，用于全县的高清点播业务以及三务公开和便民服务的数据广播。     

IN/B-ISDN综合实现视频点播的方案

本文提出了在ＩＮ／Ｂ－ＩＳＤＮ综合的平台上实现视频点播业务的新方案,即用智能网的方法将Ｂ－ＩＳＤＮ宽带网络中的各种ＯＶＤ服务器统一控制和管理起来,既方便用户接入ＶＯＤ业务,又可使ＶＯＤ资源得到充分的利用。     

On optimal broadcasting scheme for popular video service

In order to approach a video-on-demand (VOD) service, we can allocate more bandwidth to broadcast a popular video more frequently to reduce viewers' waiting time. Using a broadcasting scheme to support a popular video periodically, in order to guarantee a given waiting time, the harmonic broadcasting scheme needs the least bandwidth in the existing schemes. In this paper, we show that using any broadcasting scheme, the minimum bandwidth requirement for the same waiting time is the same as the harmonic broadcasting scheme. Therefore, for a popular video, in order to approach a near VOD service, the harmonic broadcasting scheme is an optimal broadcasting scheme that needs the least bandwidth for a given viewers' waiting time     

基于不同业务模型的TCP性能分析

TCP稳定性对网络应用性能有直接的影响。本文根据TCP所承载的不同业务类型，即分别加载FTP业务和具有自相似特性的业务，分别从拥塞窗口的变化特征、TCP连接的同步现象，以及RED参数调节对TCP性能的影响等三个方面分析了TCP性能。实验数据表明，带宽的增加只是影响TCP工作稳定性的一个原因，TCP所承载的业务类型特征的差异对TCP的稳定性有直接的影响。而采用RED和TD这两种不同的缓存管理机制对TCP的工作稳定性的影响基本没有差异。实验还进一步研究了业务特征与TCP同步现象的联系。结果表明，同步现象除了跟TCP连接数与链路的带宽之比有关外，与TCP承载的业务类型也有关系。通过调整RED的两个主要参数和，实验结果表明，它们对TCP性能的影响不显著。     

Fairness and stability of congestion control mechanisms of TCP

In this paper, we focus on fairness and stability of the congestion control mechanisms adopted in several versions of TCP by investigating their time–transient behaviors through an analytic approach. In addition to TCP Tahoe and TCP Reno, we also consider TCP Vegas which has been recently proposed for higher throughput, and enhanced TCP Vegas, which is proposed in this paper for fairness enhancements. We consider the homogeneous case, where two connections have the equivalent propagation delays, and the heterogeneous case, where each connection has different propagation delay. We show that TCP Tahoe and TCP Reno can achieve fairness among connections in the homogeneous case, but cannot in the heterogeneous case. We also show that TCP Vegas can provide almost fair service among connection, but there is some unfairness caused by the essential nature of TCP Vegas. Finally, we explain the effectiveness of our enhanced TCP Vegas in terms of fairness and throughput. This revised version was published online in June 2006 with corrections to the Cover Date.     

TCP在移动环境下的性能及其改善

TCP(传输控制协议)是在有线环境下设计并调整改善的第四层协议。但在移动环境中它的端到端性能有所下降。近年来，有很多新的协议提出用以提高移动环境下TCP的性能。其中大多数协议需要一个中间节点来参与TCP连接，这一点影响了TCP的端到端性能。TCP HACK和Freeze TCP是最近提出的两种真正的端到端协议。本分析了将来TCP的发展方向并比较了现在已有解决方案的优缺点。     

基于DVB-C的数字电视城域VOD系统设计

数字电视VOD业务是我国有线电视发展最具潜力的业务之一。结合当前地方有线电视网络的实际情况,提出一套以现有HFC网为基础,同时支持TVOD和NVOD,基于DVB-C的数字电视城域VOD系统设计方案,以提供高性能、低成本的城域VOD业务。     

基于有线电视网的数据通信

宽带IP网是以TCP IP协议为基础 ,同时又能提供实时业务 ,保证QoS的网络。介绍了实现高速宽带IP网络实施技术方案的选择 ,详细规划在有线电视网上实现高速数据通信的实施方案 ,以及相应的管理策略 ,并规划了VOD (Videoondemand)点播系统等相关的增值业务。     

基于单向HFC网的数字电视城域视频点播系统

近年来国家广电总局大力推动广播影视数字化发展,各地也加快推进数字电视整体转换工作,视频点播是数字电视增值业务中最重要的增值服务之一,详细介绍在未进行双向改造的网络上进行视频点播的一种利用PSTN作为上行信道的所谓外交互式方案,并提出一套基于单向HFC网的数字电视城域系统设计方案,以提供高性能低成本的点播业务。     

双向HFC网实现可运营高画质VOD增值服务

VOD(Video on Demand)与其他视频服务相比，最能体现数字化多媒体交互性功能，如何在具有丰富带宽的双向HFC网络上开展颇具市场潜力的VOD增值服务是值得关注的问题。结合理论与实践全面论述VOD在双向HFC网络应用中所涉及的双向网络拓扑结构设计、CMTS带宽与用户数匹配、数字视频压缩标准选用、视频服务器使用等关键性问题。     

Relative loss rate differentiation: performance of short‐lived TCP flows

The relative differentiated service model provides assurances for the relative quality ordering between service classes, rather than for the actual service level in each class. In this paper, we describe a relative loss rate differentiation scheme where packet drop probabilities are determined according to an active queue management (AQM) mechanism based on random early detection (RED) in a first‐in first‐out (FIFO) queue, are weighted in inverse proportion to the price that the network operator assigns to each service class. Basically, we describe a scheme where relative loss rate differentiation is incorporated directly into AQM. Most TCP flows today, particularly Web flows, can be characterized as short‐lived flows. Using simulations with short‐lived TCP flows, we show that the scheme is very effective in ensuring relative loss rate differentiation between service classes during times of network congestion. Copyright © 2004 John Wiley & Sons, Ltd.     

电视实时路况视频业务及技术实现

在电视平台上开展实时路况视频业务,需要多种技术的支持。通过视频转码和视频合并技术,采用在电视平台上进行实时路况点播是一种可行的技术方案。测试结果表明,这种方案能够满足在电视平台上提供实时路况视频业务的需求。     

Implementation of the Broad band User AccessNetwork and the Study of the Key Algorithm for Improving the Performance of Asymmetrical Networks

This thesis is based on the design and development of ADSL access networks. We h ave completed the hardware and software functions in two main ADSL equipments: A TU C and ATU R. With the system design, we carry out researches to find out ef fective methods to improved performance in the following aspects: (a) how to all ocate limited bandwith among services with different QoS requirements and (b) what is the effect of asymmetric links on TCP end to end flow control mech anism. We make detailed analyses and propose useful solutions to those problems we find. The main contents of this thesis are as follows: (1) the design and rea l ization of ADSL access system. This part includes the principles of ADSL access technology, ADSL broadband access network architecture, and ATM over ADSL protoc ol models that we use in our system. We give detailed hardware and software desi gn steps in this part, and list system testing results to show the system perfor mance. In our hardware, the CPU is a RISC microprocessor. Combined with a high speed digital signal processor, the whole system can hold high reliability. Our software design platform is a Psos multi task real time operation system. We h ave developed a series of hardware drivers besides other tasks for high level co ntrol and interruption processing. Currently, our system has reached the expecte d performance under test environment. Our next step is the development of DSLAM and in this part we give a feasible design scheme. (2) Packet scheduling policy I n ADSL system. In order to optimize ATU R performance, we need a scheduling pol icy to regulate the order and number of packet output to the uplink. For this pu rpose, we study the scheduling algorithm design methods in a single network node and their performance. After studying the existing algorithms carefully, we fir st conclude certain important design principles and criterions for scheduling po licy evaluation. And then by using service curve function, we make detailed perf ormance analysis of a typical scheduling policy — the earliest deadline first. The advantage of characterizing service by using a function is that the service curve can provide a wide spectrum of service characterization. With this method, we first develop a generalized algorithm for calculating the deadlines used in the service curve based on the earliest deadline first policy, and then design a simplified computing program for an important curve. After that, holding fair b andwidth allocation and packet deadline guarantee as policy evaluation standards , we analyze this scheduling policy performance and propose solutions to those p roblems that we find. Finally, we, in theory, prove these improving algorithms. All these solutions and algorithms we design in this part are now under developm ent in real systems and will enhance system performance. (3) Effects of asymmetr I c links on TCP performance and solutions. TCP is a widely used transmission cont rol protocol. It regulates its forward data sending through reverse ACKs. What a re the new problems to its flow control mechanism on asymmetric links and how to solve them are the two main points of this part. We first study the relationshi p between normalized bandwidth ratio, link buffer capacity and TCP link throughp ut under asymmetric link models. We find that TCP ack transportation on slow bac kward link is a key reason that causes the problems in TCP asymmetric links. Ser ving this as a start point, we present several improving solutions to TCP flow c ontrol algorithm and test them through simulation. Besides, TCP has been widely implemented in many networks. To give compatibility with current TCP end users, we use scheduling solutions to regulate data packet and ack packet transmission ratio onto uplinks. In the theoretical analysis of several typical scheduling po licies, we find a feasible algorithm to control TCP data efficiency on asymmetri c links. Finally, we prove those analyses and propose algorithm through simulati on.     

Transport of TCP/IP traffic over assured forwarding IP-differentiated services

The Internet is facing a twofold challenge: to increase network capacity in order to accommodate a steadily increasing number of users; to guarantee the quality of service for existing applications and for new multimedia applications requiring real-time network response. In order to meet these requirements, IETF is currently defining the differentiated service (DiffServ) architecture, which should offer a simple and scalable platform to guarantee differentiated QoS in the Internet. In the DiffServ domain, the assured forwarding service is designed to provide data applications with acceptable performance, overcoming the limits of the Internet's current best-effort service. Since data applications mostly rely on the TCP transport protocol, it is important to examine the interaction between the congestion avoidance and control mechanisms of TCP and assured forwarding. Our main purpose is to shed light on this interaction, and to show that, in the current DiffServ framework, poor performance of TCP traffic flows can result from the existing mismatch between the assured forwarding traffic conditioning procedures and the TCP congestion management. We propose a new adaptive packet marking policy to deal with congestion situations that may occur. We show that, with this policy, the provisioned rate for TCP flows can be achieved.     

基于单向有线电视网络的“交互式”视频点播

在视频点播领域的关键性挑战就是以合理的成本为成千上万的潜在用户提供交互式点播服务。主要对在单向有线电视网络上实现“交互式”视频点播进行分析,并对相关的关键技术进行探讨。     

Timeshared video-on-demand: a workable solution

True video-on-demand (T-VOD) lets you browse, select, view, and scan through programs from a large content repository, at any time, without leaving your home. Imagine choosing and watching what you want, when you want it, and not be constrained by what the TV networks have chosen for you to watch. Actually, the dream of T-VOD has been in the public mind for more than a decade now, but in spite of today's technological advances, such a service is not cost-competitive to the combination of cable TV, digital video disk (DVD), and video cassette rental services. In the past, many researchers have suggested service aggregation to make VOD economical. To achieve aggregation requires us to make a number of assumptions about user behavior and content access patterns. In this article, I argue that these assumptions are impractical for VOD scenarios today. Existing proposals lack a strong business case that appeals to consumers and service providers alike. I present a radically different vision called timeshared VOD that can make commercial T-VOD a practical reality     

一种采用资源预约和多点通信的可伸缩VOD系统

提出了一种具有伸缩性的视频点播（ＳＶＯＤ）系统，该系统可使服务开始时间与服务请求时间相分离，并允许用户设定所需服务的持续时间，如果在用户请求时刻其服务质量不能得到保证，ＳＶＯＤ将会计算出能以用户期望的ＱｏＳ播放影片的最早时间，这一时间会受到是否利用多点通信方式向多用户传送同一部影片的影响。     

基于单向有线电视网络的"交互式"视频点播

在视频点播领域的关键性挑战就是以合理的成本为成千上万的潜在用户提供交互式点播服务。主要对在单向有线电视网络上实现“交互式”视频点播进行分析，并对相关的关键技术进行探讨。