共查询到20条相似文献，搜索用时 281 毫秒
1.
《科技通报》2017,(3)
针对延迟容忍传感网中节点的间歇连通性问题,以及在网络中的节点带有社会自私性和网络消息投递成功率的条件下,对减少传输延迟及通信开销等问题进行了研究。提出了一种基于节点的自私性延迟容忍路由算法(DTSNS)。首先对活动区域网格化,方便利用马尔科夫的性质对节点下一步移动的位置进行预测;再基于节点的自私性对其信誉度进行估算,目的是减少网络的通信开销及提高消息投递成功率;接着在时延约束条件下提出了延迟容忍路由算法;最后经过仿真实验得出,在大规模网络中DTSNS和Spray and Focus、Spray and Wait以及Epidemic等算法相比较,DTSNS数据递交率高、消息时延和资源消耗小的特点。 相似文献
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恶意节点在一段时间内发送相当数量的RREQ消息,正常节点则广播入侵节点的RREQ信息,从而造成正常节点能源、存储资源和网络带宽耗尽,网络遭受破坏。研究了AODV路由协议的缺陷,针对路由请求RREQ消息广播的特性,实现了RREQ泛洪攻击。用NS对攻击过程进行仿真实验,用网络性能的两个重要变量（数据分组递交率和网络延迟）来衡量攻击结果。实验证明,RREQ泛洪攻击十分有效。 相似文献
3.
为了使传统的电信网向下一代网络融合,ITU—T小组提出了与承载无关的呼叫控制协议（BICC协议）,BICC协议是目前一个研究的热点。首先对BICC协议进行简单介绍,然后对其网络和协议模型进行分析,重点是从BICC的消息和服务节点功能的角度介绍BICC的呼叫控制流程。 相似文献
4.
当无线传感器及执行器网络(WSAN)产生服务请求,执行器节点(actor)将相互协调进行任务分配并执行任务。现有的任务分配算法中,基于市场竞拍的分布式简单竞拍聚合协议(SAAP)能够高效的利用节点资源,定向竞拍聚合协议(DSAAP)则在SAAP的基础上对下一跳节点进行筛选,限制不必要的信息转发,进一步减少了节点消耗。针对现在DSAAP在三维环境下应用的研究较少,提出三维环境下DSAAP在WSAN中的一种使用方法。仿真结果表明,在三维环境下相比传统的SAAP,DSAAP在不降低最优actor节点发现率的前提下,降低了信息包数量和竞拍信息转发延迟。 相似文献
5.
Zigbee联盟制定的Zigbee协议是组建无线个域网的一种新技术。其优点之一,就是网络层采用Cluster-Tree AODVir路由算法,支持星形(Star)、树状(Tree)和网格(Mesh)等拓扑,提供强大的组网能力,使得无线节点不仅能自由移动,而且能实现路由查找、数据转发等功能。本文首先讨论了Zigbee无线传感器网络路由方式,接着分析了Zigbee无线传感器网络路由最短最优路径的判定方式,最后研究了Zigbee无线传感器网络路由确认路径和路由算法分析。 相似文献
6.
本文主要讲述了MPLS的概念、MPLS的工作原理、MPLS关键术语、MPLS的优势。MPLS域就是运行MPLS协议的节点范围,包括LSR和LER;LER是MPLS边缘路由器,处于MPLS的网络边缘,MPLS标签交换协议在MPLS域内运行,从而实现设备之间的标签分配。MPLS的工作原理是在MPLS的域以外采用我们传统的IP转发方式,在MPLS的域以内按照标签交换方式转发,而不需要查找IP信息。LSR-标记交换路由器,完成Fec到LSP的建路。最后列出MPLS再现代网络中的优势。 相似文献
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网络编码是一种融合了编码和转发的信息交换技术。使用网络编码技术,中间节点扮演了编码器的角色,来完成编码和转发双重功能。自提出以后,网络编码技术便引起了国内外学术界、工业界的广泛关住。 相似文献
9.
提出一种面向无线Ad Hoc与传感器网络的基于自适应能量阈值的按需节能组播路由协议EMRP.该协议能根据网络能量状态和节点保护比例,自适应地确定能量保护阈值.在按需构造组播路由树的过程中,该阈值抑制网络中能量过低的节点参与组播,从而实现网络能耗均衡.EMRP同时引入目标驱动的策略,以尽量减小组播结构的规模、降低组播代价.EMRP协议执行过程中,不要求节点保存任何全局或局部网络拓扑信息,开销低,实现简单.仿真结果表明,与已有工作相比,EMRP协议能大大降低组播路由的每分组传输能耗,显著延长网络寿命. 相似文献
10.
提出一种适用于无线多跳网络的基于地理位置的多阶邻节点辅助的编码感知路由协议(LFCR).LFCR基于数据流间编码思想,借助地理位置信息,在建立路由时,综合考虑编码机会和传输能够带来的数据包正向前进位移,在创造具有编码机会路径时,避免了路由过度绕远.仿真结果表明,相比于经典编码路由协议COPE,LFCR能够显著提高网络性能. 相似文献
11.
A research group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol-a chemical found in the skins of red grapes in red wine-can improve the sensitivity of mice to the hormone insulin according to a report in the October issue of Cell Metabolism.…… 《中国科学院院刊(英文版)》2008,22(1):14-15
Aresearch group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol--a chemical found in the skins of red grapes and in red wine--can improve the sensitivity of mice to the hormone insulin, according to a report in the October,2007 issue of Cell Metabolism. As insulin resistance is often characterized as the most critical factor contributing to the development of Type 2 diabetes, the findings“provide a potential new therapeutic approach for preventing or treating” both conditions, the researchers said. 相似文献
12.
《中国科学院院刊(英文版)》2008,22(1):2-3
CAS should stick to the principle of rendering service to, and giving impetus for, the development of China＇s science enterprise by making S＆T innovations, said CAS President LU Yongxiang. The CAS president made the remarks in a recent talk to communicate the gist of the winter session of the Party＇s Leading-member Group at CAS, which was held from 7 to 11 January in Beijing. 相似文献
13.
Marjorie Armstrong-Stassen Margaret Landstrom Ramona Lumpkin 《The Information Society》1998,14(2):153-164
This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors. 相似文献
14.
《中国科学院院刊(英文版)》2008,22(1)
With great care, Dr. ZHOU Zhonghe takes out a package wrapped by cotton tissue from a drawer and says: "This is the gem of our collections: the fossil of a bird that lived 125 million years ago!" Then, pointing at a tiny mound, he explains: "Look, this is the claw and that is the head. It was in the egg shell and ready to hatch ... The species fell into a family of waterside inhabitants." 相似文献
15.
A joint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology his co-workers from Norway US Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells suggesting that China's projected climate warming could decrease the pest's numbers. The study was published in Proceedings of the National Academy of Sciences on September .…… 《中国科学院院刊(英文版)》2008,22(1):6-7
Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China＇s projected climate warming could decrease the pest＇s numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007. 相似文献
16.
Caroline Haythornthwaite 《The Information Society》2001,17(3):211-226
A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction. 相似文献
17.
Active biological molecules functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery disease diagnosis therapy new nanodevice construction.…… 《中国科学院院刊(英文版)》2008,22(1):22-22
Active biological molecules and functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery, disease diagnosis and therapy, and new nanodevice construction. 相似文献
18.
Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies. 相似文献
19.
Puay Tang 《The Information Society》1998,14(1):19-31
The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means. 相似文献
20.
Leah A. Lievrouw 《The Information Society》2000,16(2):155-159
This essay focuses on universal service and the Internet as means to support social and political participation. The emphasis on access to telecommunications systems in conventional approaches to universal service is contrasted with access to content. A model of the information environment is described that accounts for the roles of content and conduit, both of which are necessary conditions to achieve true access. A method is outlined for employing information indicators to observe or measure the information environment. 相似文献