混合网络中一种基于拥塞概率预测的TCP协议

现有的TCP协议采用丢包事件、拥塞反馈信息或往返时延等信息启动拥塞控制,而这些基于单个数据包信息的方法进行丢包区分的能力较弱,使得有线/无线混合网络中的非拥塞丢包影响了TCP的拥塞控制行为.本文提出了一种新的TCP协议,PceReno(Probability of Congestion or Error),它通过对最近一段数据的拥塞概率预测来决定如何响应当前丢包事件,从而避免盲目的启动拥塞控制.这种先应式拥塞感知和后应式拥塞响应相结合的拥塞控制方法不需要增加额外的开销,完全依赖于原有的拥塞控制.实验结果表明PceReno能够较好地对抗随机错误,有效提高TCP在混合网络中的吞吐量.     

基于OPNET仿真的TCP拥塞控制研究

研究了Reno TCP和New-Reno TCP拥塞控制算法的原理.通过对协议的模拟仿真,研究了在有大量数据丢失情况下两种协议在拥塞控制方面的不同特性.从仿真的结果可以看出,New-Reno TCP在拥塞控制方面表现出了更好的性能.     

基于XCP协议的拥塞控制研究

对一种全新的拥塞控制协议XCP（eXplicit Control Protocol）进行了研究。在分析传统TCP的拥塞控制机制不足的基础上,对XCP协议的拥塞头格式进行了剖析,给出了基于XCP协议实现拥塞控制的基本原理。最后通过对比实验,验证了XCP协议在拥塞控制性能上比传统的TCP协议更优越。     

基于嵌入式TCP／IP协议栈的拥塞控制研究

结合计算机网络和嵌入式系统软件的发展现状,总结了嵌入式TCP／IP协议栈的一般特点和处理过程,进一步详细地讨论了协议栈中的拥塞控制机制,特别是TCP拥塞控制机制和IP拥塞控制机制的分类,以及它们的实现算法,做出了详细的分析和比较、明确地给出了当前嵌入式TCP／IP协议栈中的拥塞控制解决方法。     

基于嵌入式TCP/IP协议栈的拥塞控制研究

结合计算机网络和嵌入式系统软件的发展现状,总结了嵌入式TCP/IP协议栈的一般特点和处理过程,进一步详细地讨论了协议栈中的拥塞控制机制,特别是TCP拥塞控制机制和IP拥塞控制机制的分类,以及它们的实现算法,做出了详细的分析和比较。明确地给出了当前嵌入式TCP/IP协议栈中的拥塞控制解决方法。     

基于延迟抖动分析的TCP友好拥塞控制算法

基于因特网的以UDP为传输协议的实时多媒体数据传输需要在保证实时性和可靠性的基础上,能够与因特网其他服务所使用的TCP协议公平共享有限的带宽。本文采用基于实时传输协议（RTP）和实时传输控制协议（RTCP）的反馈拥塞控制算法,提出一种简单的拥塞控制机制,使UDP数据流能与TCP数据流和平共处;研究了基于速率控制的TCP友好拥塞控制策略-TFRC,分析了其基本机制和关键问题;提出利用延迟抖动作为潜在拥塞信号来改进TFRC的速率控制机制,以适应实时业务低抖动的要求,并通过NS仿真验证了改进的TFRC算法对实时业务的良好性能。     

UDP协议下可靠信息传输的研究与实现

TCP和UDP是传输层的两个重要协议.与TCP相比,UDP协议控制简单,用户数据首部开销小,网络出现拥塞时不会降低发送端的发送速率,所以UDP是一种非常有效的工作方式.但由于UDP是面向无连接的协议,在传输层上无法实现数据的可靠传输,通过在应用层上进行可靠性控制,模拟TCP协议的接收确认和超时重发机制,实现了UDP协议...     

延迟容忍网络中的拥塞避免优化算法仿真

研究延迟容忍网络中的拥塞避免优化算法.在延迟容忍网络中采用托管传输机制,造成网络资源受限性耗尽,形成网络拥塞.传统的TCP拥塞控制算法在控制端存在快速反馈节点的前提下,采用慢开始、快重传的拥塞控制策略,但是容忍网络中不存在固定的控制端,链路上下带宽不对称,很难建立准确的拥塞回执,因此造成控制效果不佳.为了避免上述缺陷,提出了一种基于网络拥塞状态参数优化的延迟容忍网络中的拥塞避免优化算法.根据TCP协议的数据反馈机制,能够估计延迟容忍网络中的带宽.根据传输数据等待时间差值,能够计算待传输数据长度.利用网络拥塞状态参数优化方法,能够实现延迟容忍网络中的拥塞避免优化.实验结果表明,利用本文算法进行延迟容忍网络拥塞避免优化,能够提高数据传输的效率.     

基于UDT协议的印章查询系统

鉴于TCP协议的低效性和UDP协议的不可靠性,提出一种运用了新的可靠UDP协议(UDT)的印章查询系统,大大提高了数据传输的可靠性,同时引入Tinyxml以及Zlib技术来实现印章查询的功能。由于采用新的数据传输协议,并引入相应的拥塞控制和数据可靠性控制机制,使得印章查询系统的效率能够满足用户的需求。     

基于NS2的无线网络拥塞控制仿真研究

传输控制协议(Transmission Control Protocol,TCP)作为一种广泛采用的传输控制协议,其网络拥塞控制最开始时基于有线网络设计的。传统的TCP协议拥塞控制机制导致TCP协议在无线网中性能下降。本文通过对TCP网络拥塞和网络拥塞控制既有算法的分析研究,提出基于判断丢包原因和相应的错误恢复机制的TCP协议优化思路。并采用NS-2网络仿真器进行仿真实验进行验证。     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).