基于NS-2的网络半实物仿真平台实现

NS-2是一款广泛使用的网络仿真软件,但针对它的半实物仿真方法研究较少。针对这一问题,通过实际实时业务流与虚拟仿真网络的映射,提出并实现一种新的基于NS-2的网络半实物仿真HIL-NS平台。在详细描述HIL-NS平台构成基础上,讨论并解决了其实现的关键技术。在车载通信网络（VANET）实例下对802.11b无线MAC协议性能进行仿真,结果表明HIL-NS平台不但能与NS-2纯仿真的结果趋势保持高度一致性,并且在支持传统数据分析的同时,能有更直观的仿真性能实时输出。     

无线自组网络中TCP流公平性的分析与改进

研究了TCP(transmission control protocol)流在多跳无线自组网络中的公平性问题,发现IEEE802.11DCF协议在此环境下会导致严重的不公平性,即部分节点垄断了网络带宽而其他节点被饿死.首先,通过仿真分析了产生TCP流不公平性的原因,指出其根源在于MAC(media access and control)协议的不公平性,同时,TCP的超时机制加剧了不公平性的产生;然后,利用概率模型定量分析了TCP不公平性与MAC协议参数之间的关系,发现TCP流的公平性与TCP报文长度直接相关,并且增加MAC协议初始竞争窗口的大小能够有效提高公平性.据此,提出了一种根据TCP报文长度动态调节初始回退窗口大小的自适应回退MAC协议改进算法.理论分析和仿真表明,该算法在很大程度上可以有效缓解不公平性问题的产生,并且不会引起网络吞吐量的严重降低.     

基于令牌的无线工业控制网络的信道接入控制

针对无线工业控制网络(WICN)的实时性和可靠性要求,在分析了几种常见的无线局域网的MAC协议(MACA、MA-CAW和IEEE802.11)的不足后,提出了一种基于令牌控制的MAC协议.并且还详细介绍了该协议中的令牌恢复机制、优先级机制和数据帧确认机制,并利用离散事件仿真平台OMNeT 对该协议和CSMA/CA协议进行了仿真对比试验.仿真结果表明,该协议保证了信道接入的公平性,减少了数据传输时延,增强了数据传输的可靠性,适用于无线工业控制网络.     

多速率Ad hoc网络MAC层公平性的分析与改进

在多速率Ad hoc网络中,利用自适应速率调整算法,网络节点可以根据信道质量选择不同的传输速率,从而提高网络的总体通信能力。对多速率Ad hoc网络MAC层公平性进行了仿真和分析,实验结果表明基于IEEE 802.11的多速率Ad hoc网络中存在严重的公平性问题。通过对吞吐率公平和时间公平的讨论,指出在多速率Ad hoc网络中进行MAC层公平性研究,时间公平性标准是较优的选择。另外提出一种针对多速率Ad hoc网络的改进公平回退（EFB）算法,仿真实验的结果表明该算法能够明显提高多速率Ad hoc网络的MAC层公平性。     

基于路由信息的跨层WSNMAC协议

针对MAC协议无法解决节点能耗和网络性能之间矛盾的问题,在AS—MAC协议的基础上,基于跨层的方法提出CLR—MAC协议。该协议利用路由层的路由表信息改变AS—MAC协议的控制帧格式,解决AS—MAC协议中因“强迫唤醒”造成的能量浪费问题,以延长网络寿命。理论分析和仿真实验证明,该协议随网络密度的增加,节能增益呈线性增加。     

无线传感器网络S-MAC协议的分析与算法改进

无线传感器网络（WSN）使用灵活,移动性强,架设便捷,应用范围非常广泛。媒体访问控制（MAC）协议是保证无线传感器网络高效通信的关键网络协议之一。重点分析了WSN中基于竞争的典型MAC协议——S-MAC协议。针对S-MAC协议中采用的退避算法不能良好地解决节点通信公平性等问题,提出了BDQR退避算法。实验结果表明,该算法有效地提高了节点通信公平性,降低了信道的碰撞,延长了网络的生命周期。     

基于半实物仿真的Semi-TCP协议的实现与测试

针对Semi-TCP协议在软件仿真下可信度较差和硬件仿真下难以实现且网络规模较小的问题,提出基于Exata仿真内核和TiPot开发板的半实物仿真方法.方法 中搭建的Semi-TCP半实物仿真平台包括两部分,一部分是基于Exata搭建的虚拟场景,在其中构建多跳无线网络,并在Exata无线网络协议模型库中加入semi-TCP协议;另一部分是基于TiPot开发板搭建的真实场景,将外部实物节点与虚拟场景中的虚拟节点进行映射,并通过网关将两部分连接为一个整体.然后在真实-虚拟-真实的网络配置模式下,实现并测试Semi-TCP在半实物仿真下的通信效率.仿真结果表明,半实物仿真的方法比软件仿真更真实可靠,比硬件仿真更容易实现且网络规模更大,Semi-TCP通信效率优于TCP和其它无线TCP.     

无线传感器网络TDMA MAC协议的对比和改进研究

无线传感器网络MAC协议对网络的生命期有着重要影响,为找到适合一定环境所使用的MAC协议,必须对不同的MAC协议进行必要的分析。从数据帧着手,分析了不同的基于TDMA的调度式MAC协议的差异。针对原有TDMA MAC协议数据传输量不高、实现难度大等问题,提出相应的改进方法,并对三个基于LEACH的TDMA MAC协议进行了仿真实现,仿真结果与数据分析的结果一致。     

第三代短波网多址接入协议的研究与改进

为了解决短波资源有限问题,对短波网络MAC协议进行了研究.针对在短波可利用信道有限时,第三代短波网络MAC协议不能有效解决冲突的问题,提出了一种根据网络节点的重要程度设置不同接入概率的协议改进方法.分析了第三代短波网络多址接入协议,通过仿真研究了该"时隙CSMA"协议产生冲突的原因,然后针对该问题提出了一种有效解决冲突的改进方法.最后,建立了冲突产生的教学模型,在理论上证明了所提出方法的正确性,仿真分析表明了改进方法在解决冲突问题时具有良好的效果.     

Ad Hoc网络MAC协议的性能度量

信道接入层(MAC)协议是Ad Hoc网络协议的重要组成部分,其行为对网络性能起决定性作用.详细地分析如何用时延、吞吐量、公平性这三个指标评价MAC协议的性能,以802.11为例具体介绍MAC协议的性能度量方法的应用,仿真结果表明该性能度量方法是可行的.     

凹凸科技进军网络安全领域

2006年2月28日,网络安全及电源管理芯片供应商凹凸科技(O2Micro)向中国用户隆重推介凹凸科技在网络安全领域的独特理念和全新方案.此举标志着凹凸科技已正式进军网络安全领域.特别在ASIC防火墙和SSL VPN技术和产品的竞争中,凹凸科技已经担负了不可或缺的重要角色.而其在模拟与数字集成电路方面拥有的强大设计和制造能力,无疑将为其最终成为全球网络安全领域的主要供应商增加关键筹码.凹凸科技在评述中国安全市场发展趋势的同时,还将携两款最具代表性的成熟产品--ASIC防火墙SifoWorks和SSL VPN产品Succendo一起亮相.     

2006 Sun科技日在中国举行——"Java之父"James Gosling再来中国

继成功举办2005年Sun JAVA中国开发者大会之后,Sun一年一度全球规模的开发者大会——2006Sun科技日又分别于今年9月23～24日和27～28日相继在中国上海和北京两大都市举行“。Java之父”James Gosling再次来到中国,与中国的开发者讨论软件开发者所关心的问题,讲述Sun的软件发展策略、介绍Solaris10操作系统的独特的特性和新的Java开发工具、展望Java技术发展前景,特别是阐明Sun实施Java技术开源的策略。Sun科技日是Sun公司最重要的全球开发者的大会,它针对Java技术、Solaris10OS、NetBeans、OpenSolaris、开源技术、开发工具和Web…     

陕西省第一届国防科工系统内网安全研讨会召开

2006年3月15日,“陕西省第一届国防科工系统内网信息安全建设专题研讨会”在西安市隆重召开。此次会议的议题是,在当前的信息安全形势下,陕西省国防科工系统内网面临的信息安全问题,以及如何采取有效的解决方案进一步提高国家机要部门内部网络的安全保护等级,以适应形势发展的需要。此次会议由陕西省国防科工委主办,陕西省国防科工委信息中心和北京榕基网安科技有限公司、北京理工先河科技发展有限公司、陕西金叶西工大共同承办,国家保密局和陕西省国防科工委的有关领导出席会议并发表了重要讲话。在为期两天的会议中,共有100多名国防科工系…     

IT in teacher training in France

Abstract To understand what is going on in France at the moment in the domain of computers and related communication technologies in teacher training, there are two major developments that have to be kept in mind. Firstly, the ways of becoming a teacher in France underwent major changes in 1991. It is therefore too early to come to general conclusions about the effects of this reform in the field of new information technologies. Secondly, French IT in schools policy has shifted from a large-scale centralized equipment operation, which provided microcomputers in each school from 1985 to 1987, to a more regional management of equipment funding, with less national piloting in the field. This paper describes what happened during the previous period and what is taking place now. With matters still evolving the paper represents a snapshot rather than an exhaustive survey; such a survey remains to be done.     

Informatics in teacher education in Japan

Abstract This paper charts the developments in information technology (IT) policies in education in Japan over the past decade with particular emphasis on the impacts on teacher education. Beginning with the work of the National Council on Educational Reform in 1985, the Japanese education system initiated a thorough analysis of the role of information technology in all aspects of education from kindergarten through to high school, vocational education and pre- and in-service teacher education. The various approaches culminated in guidelines and statutory requirements relating to both schools' curricula and teacher training, published in the period 1990–1992. More recently other ministries have contributed to developments including the Ministry for International Trade and Industry which has categorized the different types of information engineers and among these is the new Educational Engineer. The paper reports the processes leading to these developments.     

IT in teacher education in Denmark

Abstract As with many European countries Denmark is experiencing change in teacher education and most notably in the wake of an act of government in 1992 which was designed to set out common aims for teacher education. Prior to that the content and structure of teacher education had been highly specified including, for example, the requirement that student teachers should take a course of 42 hours IT-related lessons. This paper provides a brief history of the background to the changes in teacher education and focuses on the implications that the more flexible aims for teacher education have for the future integration of IT in teacher education.     

Teacher education in IT in Germany

Abstract In 1988 the eleven West-German Kultusminister , with responsibility for the school systems in their respective Bundeslaender , reached agreement with the Federal Ministry of Education and Science on the broad concept of 'Information and Communications Technology', ITG. After four years of discussion it was agreed that ITG should be introduced into the secondary level of the general schools. In spite of strong disagreements about the ways and speed of implementation, and after several years of experiments, important parts of the concept have become a reality in practically all of the old Bundeslaender. While acknowledging the complexity of the German educational system the paper attempts to outline the development of the concept of Information and Communications Technology and its consequences in teacher education. The development in the eastern part of Germany, the former GDR, has been completely different to that in the western part and this is also commented upon in the paper.     

在网络层实现安全传输通道技术的研究

安全传输通道是对传输的原始信息进行加密和协议封装处理,从而实现安全传输的技术,本文在TCP/IP的网络层上提出了实现安全传输通道的技术和解决方案。并对网络层的安全传输通道技术提出了实现机制。     

IT in teacher education in Scotland

Abstract This paper outlines the consensual approach to the formulation of curriculum policy in general, and in relation to information technology (IT) in particular, in Scotland. It outlines the approaches to IT that have emerged as a result. These are founded on the premises that all children should develop knowledge and understanding about IT and skills in using IT; that IT should influence both content and delivery of the curriculum; and that IT (computing studies in Scotland) should be an elective for secondary school pupils. Against this background, the paper describes the evolution of policy and practice relating to IT in teacher education. It appraises the strategies which institutes are using for developing the professional skills necessary to deliver IT in the Scottish curriculum. It notes significant progress but highlights the need to develop strategies which integrate IT more deeply with other professional studies so that student teachers develop deeper, more reflective approaches to IT.     

Recent developments in ergonomics in China

Ergonomic thought and practice were introduced in ancient China in relation to modern developments in Chinese ergonomics. Despite the ten-year interruption of the 'cultural revolution’ in the late 1960s and 1970s, ergonomics has made great progress in China in the last decade. In this paper some general developments in recent ergonomics’ teaching and in professional organizations are described. Four major areas of ergonomics research are illustrated: (1) Visual displays and signal design; (2) Human-computer interface with Chinese computers; (3) Cognitive strategies and decision support; (4) Mental workload and occupational stress. The main characteristics of Chinese ergonomics are discussed and new directions are highlighted, based on recent developments and progress.