Balanced Scheduling toward Loss-Free Packet Queuing and Delay Fairness

In current networks, packet losses can occur if routers do not provide sufficiently large buffers. This paper studies how many buffers should be provided in a router to eliminate packet losses. We assume a network router has m incoming queues, each corresponding to a single traffic stream, and must schedule at any time on-line from which queue to take the next packet to send out. To exclude packet losses with a small amount of buffers, the maximum queue length must be kept low over the entire scheduling period. We call this new on-line problem the balanced scheduling problem (BSP). By competitive analysis, we measure the power of on-line scheduling algorithms to prevent packet losses. We show that a simple greedy algorithm is Θ(log m)-competitive which is asymptotically optimal, while Round-Robin scheduling is not better than m-competitive, as actually is any deterministic on-line algorithm for BSP. We also give a polynomial time algorithm for solving off-line BSP optimally. We also study another on-line balancing problem that tries to balance the delay among the m traffic streams.     

公用电信网间接续质量的研究

“公用电信网间通信质量技术要求——电话呼叫的接通率和拨号后时延”是目前信息产业部已经制定的标准之一,该标准既适用于网间呼叫的接续质量评定,又便于管理部门对运营者网间通信质量进行考核。它包括3部分内容;第一部分规定了全程参考连接下的质量指标及其分配要求;第二部分规定了忙时的接通率和拨号后时延的指标,第三部分主要为网间互联互通通信质量的考核指标,是对电信运营企业在互联互通时,网间通信质量进行考核和管理的最低要求。     

A.I. Kayssi: Delay modeling of CMOS clock drivers

A delay model for CMOS clock drivers loaded by resistive–capacitive interconnect is derived using dimensional analysis. A model for a purely capacitive load is first developed, then the delay model for a capacitor–resistor–capacitor load is derived and verified. The implementation of the delay function for the clock driver uses a combination of lookup table and analytical functions. The accuracy of the models is shown to be within 5% of detailed circuit simulation of a 0.18-micron CMOS process. A simple formula is also given to help in determining whether the resistance of the interconnect has any significant shielding effect on the clock driver.     

Linux包过滤防火墙优化

通过对影响Linux包过滤防火墙性能3个关键因素的分析,采用规则组织、使用State模块以及用户自定义规则链三者相结合对Linux防火墙进行优化,目的在于让数据包做尽可能少的测试,降低包过滤防火墙响应延时.通过实验对比得出经过优化后的防火墙在一定程度上能有效降低包过滤响应延时.     

Making clustering in delay-vector space meaningful

Sequential time series clustering is a technique used to extract important features from time series data. The method can be shown to be the process of clustering in the delay-vector space formalism used in the Dynamical Systems literature. Recently, the startling claim was made that sequential time series clustering is meaningless. This has important consequences for a significant amount of work in the literature, since such a claim invalidates these work’s contribution. In this paper, we show that sequential time series clustering is not meaningless, and that the problem highlighted in these works stem from their use of the Euclidean distance metric as the distance measure in the delay-vector space. As a solution, we consider quite a general class of time series, and propose a regime based on two types of similarity that can exist between delay vectors, giving rise naturally to an alternative distance measure to Euclidean distance in the delay-vector space. We show that, using this alternative distance measure, sequential time series clustering can indeed be meaningful. We repeat a key experiment in the work on which the “meaningless” claim was based, and show that our method leads to a successful clustering outcome. Jason R. Chen received the B.E. degree from Sydney University, Australia, in 1991 and then worked mainly in the banking and finance industry until 1997. From 1997 to 2001, he completed the Ph.D. at Australian National University, Canberra, Australia, in robotics. From 2001 to the present, he has been a Research Engineer in the Research School of Information Science and Engineering, at Australian National University. His research interests broadly include robotics, data mining, and AI.     

一种端到端网络的不相交多路径QoS路由算法

不相交多路径路由算法旨在一个端到端的网络中为应用流选择多个路径，且这些路径在瓶颈链路上是彼此不相交的。本文提出的不相交多路径QoS路由（DMQR）算法在Dijkstra最短路径和最短最宽路径（SWP）算法的基础上，能够动态地计算时延最短、带宽最宽、在瓶颈链路上互不相交的路径，且保证每个路径都是满足一定服务质量的。在视频会议、远程医疗和远程教育等重要的视频通信场合，要求应用层和网络层必须协同工作以保证一些必要的QoS，例如端到端的带宽、时延和包丢失率等。本文针对端到端的网络，重点讨论不相交多路径QoS路由算法在应用层的设计和实现。性能分析和模拟结果显示，所提出的不相交多路径QoS路由算法总是收敛的，且当网络流量增加时，该算法具有较低的包丢失率和较高的吞吐量。     

基于Ticket探测的非精确单播路由算法仿真

TBP(Ticket-based Probing)算法是一种有效的非精确网络状态下单播路由算法.它具有较好的可行性,并且优化了平均路由代价,但仿真时该算法仅针对均匀分布的网络时延变化,因此在应用时有一定的局限性.本文仿真分析了其在均匀分布和正态分布两种时延变化模型下算法的性能,以及不同探测包生成方案对算法性能的影响.仿真结果表明,TBP算法在正态分布下的寻路成功率通常比均匀分布下的要低,而不同探测包生成方案对算法性能各指标的影响各有不同.     

伪邻近点法分析薄膜磁致伸缩测试中异常数据

采用伪邻近点法，对薄膜磁致伸缩系数测试试验中得到的不同性质的测试数据分别进行处理，发现它们具有确定性的特征，从而可得测试中异常状态基本由系统本身引起，这样通过调节及改进测试系统就能减小其影响，得到较为可靠的光点位移数据。     

超细Si粉对Si/Pb3O4延期药热反应活性和摩擦感度的影响

采用机械球磨法,通过对球磨时间、介质流速等参数的控制,最终得到平均粒度d50=1.75μm的超细Si粉,并进行了粒度和SEM分析.结果表明,随着Si/Pb3O4延期药中超细Si粉含量的增加,其反应放热峰提前,放热量增加,但摩擦感度也相应增加.其中,超细Si粉含量为60%的样品不但具有较高的反应放热量,而且摩擦感度很低.因此,选定60%作为普通Si粉与超细Si粉在级配使用时最为合理的比例.     

延期体抗高加速度过载的界面加固性能研究

通过在延期体端面放置纸质垫片的途径来实现界面加固,采用Hopkinson加载试验技术和非线性数值模拟的方法对B/BaCrO4延期体上的应力波传播特性、抗过载界面加固特性进行了研究.研究结果表明:纸垫可以有效地衰减作用到延期体上的应力波,减小延期体的变形量,提高应力/应变分布均匀性,增强延期体的抗过载能力.延期体两个端面加固的效果优于一个端面的加固,应力波输出端加固性能优于应力波输入端加固性能.两端加固的纸垫厚度增加,延期体发生塑性变形的值相对变小.