Conventionally, P2P video is regarded as CBR traffic. However, our measurements have shown that the rate reset cannot be neglected in a practical IPTV system because each rate reset often leads to performance degradation. Thus, addressing the problem of inferring playback rate and rate reset in a P2P video system is significant. In this article, an algorithm termed piecewise linear envelope approximation （PLEA） is proposed, in which a follow-up time is introduced to smooth rate fluctuations in a small time scale and to adapt rate jumps in a large time scale automatically. With the PLEA algorithm, discontinuity introduced by blind segmentations adopted by current methods is avoided. Furthermore, unlike existing algorithms in which both segmentation and combinations are performed in multiple runs, only a single computation path is involved in the PLEA algorithm. This makes PLEA algorithm amenable to implementation of low complexity by either software or hardware. Both theoretical analysis and experiment based on measured data show that the PLEA outperforms existing algorithms based on segmentation.
LI Chun-xi CHEN Chang-jia School of Electronics and Information Engineering,Beijing Jiaotong University,Beijing 100044,China
基于可信计算技术的恶意代码防范机制可以弥补传统杀毒方式对未知恶意代码防范能力的不足,但是软件自动在线升级和补丁安装会生成和调用未知的动态代码,对这些动态代码的实时可信判定问题阻碍了可信计算技术的应用普及.动态代码实时可信判定和可信传递方法(Trust Determination and Transitivity Method of Dynamic codes,TDTMD)从代码的调用环境和调用方式出发,对动态代码的来源是否可信进行判定,进而对动态代码是否可信进行判断.TDTMD可以在保证应用软件和系统的运行连续性前提下,提供对各种已知或未知恶意代码攻击的有效防范能力.TDTMD的原型系统及其实验结果表明,它对系统的运行性能影响较小,并且安全有效.
针对互联网现有服务质量(QoS:quality of service)模型的扩展性差、端到端延时高等问题,提出了基于域内全局流标签的QoS保障模型。该模型以WFQ队列调度模型为基础,采用域内全局流标签进行资源预留和路由转发,能够实现灵活的服务质量保证,具有更强的可扩展性。在此基础上,利用网络微积分理论对所提模型进行了端到端延时分析,给出了该模型端到端服务曲线和延时上界的表示式。理论分析和数值实验表明基于域内全局流标签的QoS保障模型具有比现有模型更低的端到端延时上界。
