关键词： Data communication systems  

摘要： The popularity and usefulness of the Internet seem to grow exponentially every day. As a result of this rapid growth, mobile users expect to access the Internet's information resources and to communicate with other Internet users. However, providing efficient and reliable stream transmissions in mobile computing environments presents a significant obstacle to the development of mobile computing systems over the Internet. This paper presents three approaches-known as fast retransmissions, data interceptions, and packet interceptions-that can be used to improve the performance and reliability of transmission protocols in mobile computing environments. The paper also discusses how packet interception has become the most effective approach of the three and describes its implementation.

关键词： 业界要闻   电脑用户   康柏电脑公司   英特尔公司   电脑爱好者   电子消费品   图形加速   数字影像技术   世纪广场   移动计算   笔记本电脑   笔记本计算机   普及活动   计算领域  

摘要： ●正在举办全国性全系列新产品发布、技术展示以及电脑普及活动的方正电脑,挟方正电脑覆盖移动计算、办公商用计算、多媒体网络计算直至高级工程与图形计算领域的全系列新品亮相京交会,以方正电脑新品为平台,向电脑爱好者、普及电脑用户展示包括MMX多能奔腾处理器技术、In-ternert可视电话、数字影像技术、3维图形加速技术在内的电脑科技最新发展。 ●一直被世界电脑界注目的多用户NT操作系统Win-Frame和Windows终端——Winterm近日正式落户北京万通新世纪广场。

关键词： Substituents   Chemical structure   Chemical calculations   Pyridines  

摘要： For three series of mono-, di-, and trisubstituted pyridines, respectively, available incremental methods and calculation programs for estimating the corresponding ¹³C NMR chemical shifts were employed and compared with the results obtained. The following methods and programs were used for testing them for their accuracy: simple pyridine increments, a simplified increment calculation on the base of benzene increments (program AROSIM^1,2), the calculation method of Fürst and Pretsch^3-6 (Carbon-13 module for ChemWindows), SPECAL from Specinfo⁷ (a database founded calculation program), CSPEC2,^8,9 gNMR,¹⁰ CNMR,¹¹ and HyperNMR,¹² respectively.

关键词： 蓄电池组   移动通信   PC   笔记本   上市量   日元   本位币   野村综合研究所   移动计算   厂家   锂离子   能量密度   能量浓度  

关键词： 移动计算   商务人员   通讯   新闻   现代商务   资讯  

摘要： 现代社会商业竞争日趋激烈,要求商务人员具有极快的反应能力和极强的创造性,他们需要先进的通讯和资讯工具,利用有限的时间创造最多的效益。于是,随着信息科学的发展,移动通讯、移动电话已经被广泛应用,而今一种新的资讯容量更大的移动办公设备……移动计算机(又称便携式计算机),正被越来越多的商务人员所使用。它可以在出差、访客、会议、旅游时记录、处理文档,可以通过电迁线收发传

关键词： Computer network protocols   Mobile computing   Wireless communication systems  

摘要： Technological advances of VLSI and wireless communication in the 90's have been reshaping the existing form of network computing in the Internet into what is known as "Wireless Mobile Computing?. Host mobility and wireless access are two newly introduced design considerations which pose challenging problems at all layers of the networking protocol stack in the Internet. This thesis investigates their impacts on the designs of the link and transport layer protocols, particularly focusing on the Transmission Control Protocol (TCP)；At the transport layer, flow and congestion control are the most important problems. Although MobileIP at the network layer provides continuous network connectivity to mobile hosts, it cannot shield the effects due to host movement and wireless medium characteristics (noisy, long and varying latencies) from the TCP protocol at the transport layer. Mismatches between wired and wireless access thus cause severe performance degradation to TCP whose congestion control mechanisms are optimized for wired networks with stationary hosts；This thesis makes observations on the effects of noisy channels and temporary disconnections on the control mechanisms in a particular version of TCP, 4.3 BSD TCP-Reno. Three phenomena, namely false congestion control trigger, multiple corruptions in a single window, and corruptions of retransmissions, are found to be the main causes of TCP through-put degradation in noisy medium. Based on these observations, an analytical methodology is developed to evaluate the throughput performance of TCP over noisy channels and to study the influences of the parameter such as fast retransmit threshold；Making use of a proposed negative acknowledgment implemented in the TCP option, this thesis proposes a scheme called NACK which has simple modifications to the congestion control mechanisms of TCP to improve its end-to-end performance with respect to the noisy channels. Two other designs based on an existing proposal, Last-Hop-ACKn

摘要： There is a growing trend in developing applications for mobile computing systems in which mobile host computers retain their network connections while in transit. This paper proposes an algorithm that enforces a useful property, namely, causal ordering, that delivers messages among mobile hosts. This property ensures that causally related messages directed to the same destination will be delivered in an order consistent with their causality, which is important in applications that involve human interaction such as mobile e-mail and mobile teleconferencing. Such applications are envisioned by the proponents of Personal Communications Services (PCS). Without this property, users may receive and read original messages and the corresponding replies out of order. Our algorithm, when compared with previous proposals, provides an alternative with a low handoff cost, medium message overhead, and low probability of unnecessary inhibition in delivering messages.

关键词： 销量   笔记本电脑   Compaq   笔记本计算机   移动计算   方正  

摘要： 据有关权威机构统计,Compaq笔记本电脑在国内市场的份额已由排名第六位升至第四位。据权威人士分析,Compaq笔记本电脑在国内销量的飞速增长,主要得益于北大方正的加入,关键在于二者能够优势互补:一方面,Compaq公司作为世界级的计算机生产企业,且有优秀的产品;另一

关键词： 硬盘   硬磁盘   磁盘   移动计算  

摘要： 在移动计算应用领域,IBM 提供了 Travelster 系列高效和大容量的2.5英寸硬盘驱动器.它不仅具有同3.5英寸硬盘驱动器同样的功能,而且体积纤巧,只有100克至180克。

关键词： 电池   笔记本电脑   笔记本计算机   移动计算   序幕   情节  

摘要： Lithium Technology 公司9月底宣布,该公司已获得550万美元的私人投资,用于开发下一代高聚合锂电池。这家位于宾夕法尼亚州 PlymouthMeeting 的公司是目前业界唯一能生产这种电池的厂家。该公司许诺将生产一种全系列的电池产品用于极薄的移动计算设备中,包括笔记本电脑、个人数字