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题名:
社区宽带综合业务网络系统中的同步问题研究
作者: 江何
答辩日期: 2007-06-05
授予单位: 中国科学院软件研究所
授予地点: 软件研究所
学位: 博士
关键词: 用户驻地网 ; 时钟同步 ; 频率校准
其他题名: Clock Synchronization Research in Community Broadband Network System with Integrated Services
摘要: 在可预见的将来,视频播放类业务在用户驻地网上仍将占据主导地位。这类业务对音视频的同步非常敏感,为了保证播放质量,引入流整形技术,在网络出入口处理数据的时间戳信息,因此系统的同步至关重要。本文以此为背景,深入研究了社区宽带综合业务网络系统中的同步问题,本文的主要贡献在于以下几点: (1)提出、设计和实现基于TSC读取和时钟比对的频率校准同步算法 对于操作系统和其它的应用程序来说,平滑准确的时钟频率才是系统稳定可靠的保证。目前在计算机网络中应用广泛的NTP同步协议,主要是通过调整软件时钟频率来达到同步。因此其时钟频率并不稳定。 本文提出了一种基于TSC读取和时钟对比的频率校准同步算法。这个算法分为两部分:首先利用CPU本身的高精度部件时间戳计数器TSC,通过对其的读取提供一个日常可用的频率平稳的时钟;其次在设定的时段,利用NTP的同步消息得到一系列客户机/服务器的时间对,基于改进的预设值估计同步方法,便可以得到本地时钟与标准时钟之间的频率偏差和相位偏差,从而校准本地时钟。 试验结果表明:采用该算法可以达到NTP在局域网内的同步精度,但是免除了被同步本地时钟频率的振荡。 (2)提出、设计和实现适合社区宽带综合业务网络系统的时钟同步协议RCP 在社区宽带综合业务网络系统中,各个节点之间也需要同步,然而前述对单个时钟有效的同步算法是可能造成同一个网络内的节点互相之间反而不同步,因为它们都不能保证自己一定严格与标准钟同步。因此,本文提出了适合社区宽带综合业务网络系统服务器群的时钟同步协议RCP。该协议基本思想是本地的各个服务器互相交换校准结果,按照少数服从多数的选举规则来决定自己是否需要重新启动校准过程。 (3)提出、设计和实现在社区宽带综合业务网络系统中使用RCP后的同步性能的评估方法 对RCP的性能评估包括两个部分:首先是同步的精度与误差分析;然后是RCP应用在网内的节点之间的同步效果。本文基于对阿伦方差(Allan Variance)的分析提出了一种统计意义上的精度评估方法,度量了前面着重考虑的频率稳定度。
英文摘要: According the fact, Video play service will still dominate the CPN in future. Since this kind of service is sensitive to the lost of synchronization of audio and video, in order to keep the play quality, the stream shaping technique was introduced. And it is very important to keep synchronization to the system. The main contributions are the following: (1) Propose, design and realize the frequency calibrating synchronization algorithm based on TSC reading and clock comparing. The NTP widely used in computer network calibrates the local time by speeding or slow down the clock rate, the frequency rate of local clock is not stable. But for operating system and other applications, a smooth and accurate clock is the promise of stable and reliable. We propose a frequency calibrating synchronization algorithm based on TSC reading and clock comparing. The algorithm utilize the TSC time stamp counter with very high accuracy in modern computer, by reading its value, we can provide a daily usable and smooth clock; and at the adjust time, the algorithm use an improved pre-set value and estimating synchronization method, after dealing by probability processing and curve simulating method, we can get the offset and skew and use them to calibrate local clock. Experiment result shows that it can reach the precision of NTP deployed in LAN, but avoid the vibration of clock frequency. (2) Propose, design and realize the Reliable Clock Protocol for Integrated services broad band network for community. The algorithm effective to one clock can reversely cause the asynchronization of different clocks, because they can not be sure that they are all synchronized with standard clock. In order to resolve it, here we propose a RCP protocol suitable for broad band network. With the rule of minority conform to majority, RCP will keep the synchronization of the whole system. (3) Propose, design and realize the synchronization quality estimating and evaluating method for broad band network. The evaluation of RCP quality includes two parts: at first, it is the accuracy of synchronization and error analysis; then the synchronization result of applying RCP to network. This article proposes an accuracy evaluating method in the sense of probability by Allan variance. estimating the frequency stability emphasized before. The result shows the effectiveness of applying this method.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.iscas.ac.cn/handle/311060/6010
Appears in Collections:中科院软件所

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Recommended Citation:
江何. 社区宽带综合业务网络系统中的同步问题研究[D]. 软件研究所. 中国科学院软件研究所. 2007-06-05.
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