无线局域网-计算机毕业论文外文翻译
本科毕业论文中英文翻译--Wireless-Communications无线通信【范本模板】
Wireless Communications＊byJoshua S。
Gans，Stephen P。
King and Julian Wright1. IntroductionIn 1895, Guglielmo Marconi opened the way for modern wireless communications by transmitting the three—dot Morse code for the letter ‘S’ over a distance of th ree kilometers using electromagnetic waves。
From this beginning，wireless communications has developed into a key element of modern society. From satellite transmission, radio and television broadcasting to the now ubiquitous mobile telephone，wireless communications has revolutionized the way societies function.This chapter surveys the economics literature on wireless communications。
Wireless communications and the economic goods and services that utilise it have some special characteristics that have motivated specialised studies。
First, wireless communications relies on a scarce resource –namely，radio spectrum –the property rights for which were traditionally vested with the state. In order to foster the development of wireless communications (including telephony and broadcasting）those assets were privatised。
无线局域网(wlan)论文
无线局域网（wlan）论文摘要本文论述了近年来发展迅速的无线局域网技术原理、设备应用，并通过实际工程案例，介绍了相关的知识。
全文共分为四个部分第一部分为无线局域网的概念部分，主要介绍了无线局域网的概念，历史以及无线局域网的技术特点。
第二部分为无线局域网的技术标准，主要介绍了无线局域网的技术的制定机构IEEE和IEEE802.11标准以及IEEE802.11发展简史。
第三部分为无线局域网的设备介绍，介绍了无线局域网应用的AP无线网卡等基础设备。
第四部分为无线局域网的应用范围、连接结构以及经典结构的应用实例。
关键词：IEEE802.11 无线局域网网络技术网络架设AbstractThis article elaborated the recent years to develop the rapid wireless local area network technology principle, the equipment application, and through the actual project case, introduced the related knowledge. the full text altogether divides into four part the first part for the wireless local area network's concept part, mainly introduced the wireless local area network's concept, historical as well as the wireless local area network's technical characteristic. the second part for the wireless local area network's technical standard, mainly introduced wireless local area network's technology formulation organization Institute of Electrical and Electronics Engineers (IEEE) and the IEEE802.11 standard as well as the IEEE802.11 development brief history. the third part introduced for the wireless local area network's equipment that introduced wireless local area network application foundation equipment and so on AP（Access Point）wireless network card. the fourth part for wireless local area network's application scope, connection structure as well as classical structure application example.Key words：IEEE802.11 wireless local area network networking network erects目录引言------------------------------------------------------------------------ 3 1、无线局域网的概念-------------------------------------------------------- 31.1 无线局域网的简介---------------------------------------------------- 31.2 无线局域网的历史----------------------------------------------------- 31.3 无线局域网的技术特点与优点------------------------------------------- 42、无线局域网的技术相关标准------------------------------------------------ 52.1 IEEE 802.11标准概述--------------------------------------------------52.2 无线局域网的连接结构-------------------------------------------------63、无线局域网设备简介------------------------------------------------------ 83.1 无线网卡基本介绍-----------------------------------------------------83.2 无线路由器/AP基本介绍------------------------------------------------104、无线局域网的应用-------------------------------------------------------- 11 4.1 无线局域网的应用领域----------------------------------------------- 11 4.2 无线局域网的类型--------------------------------------------------- 124.3 无线局域网的架设--------------------------------------------------- 135、结论-------------------------------------------------------------------- 156、参考文献---------------------------------------------------------------- 157、致谢引言在这个网络飞速发展的时代，伴随着我国有线网络的广泛应用，传统的局域网、城域网技术渐渐的已经不能满足使用的需要，一种计算机网络与无线通信技术相结合的产物靠着具有快捷高效、组网灵活等特点已经在我国飞速的发展起来,这就是无线局域网（Wireless Local-Area Network，WLAN）技术。
计算机专业英语部分文章翻译
Communication channels are an essential element of every communication system. These channels actually carry the data from one computer to another. There are two categories of communication channels. One category connects sending and receiving devices by providing a physical connection such as a wire or cable. The other category is wireless.通信管道对于每一个通信系统来说是一个至关重要的元素。
这些管道实际上把数据从一台计算机传输到另一台。
有两个类别的通信管道。
一类是有线，另一类是无线。
PHYSICAL CONNECTIONSPhysical connections use a solid medium to connect sending and receiving devices. These connections include telephone lines (twisted pair), coaxial cable,and fiber-optic cable.物理连接使用固体介质连接、发送和接收设备。
这些连接包括电话线路(双绞线)、同轴电缆和光纤电缆。
Telephone lines you see strung on poles consist of twisted-pair cable,which is made up of hundreds of copper wires. A single twisted pair culminates in a wall jack into which you can plug your phone and computer. (See Figure 9-3.) Telephone lines have been the standard transmission medium for years for both voice and data. However, they are now being phased out by more technically advanced and reliable media.Coaxial cable, a high-frequency transmission cable, replaces the multiple wires of telephone lines with a single solid-copper core. (See Figure 9-4.) In terms of the number of telephone connections, a coaxial cable has over 80 times the transmission capacity of twisted pair.Coaxial cable is used to deliver television signals as well as to connect computers in a network..你所看到的电话线，是由上百根铜线缠绕而成的双绞线。
无线局域网论文
无线局域网论文一、引言在当今数字化的时代，网络已经成为人们生活和工作中不可或缺的一部分。
而无线局域网（Wireless Local Area Network，简称 WLAN）作为一种便捷、灵活的网络接入方式，正逐渐普及并改变着我们的通信方式和生活习惯。
无线局域网技术的发展，使得我们能够在不受线缆束缚的情况下，随时随地访问网络资源，极大地提高了工作效率和生活质量。
二、无线局域网的概述（一）无线局域网的定义无线局域网是指利用无线通信技术在局部范围内建立的网络，它通过无线信号进行数据传输，取代了传统的有线网络连接方式。
（二）无线局域网的特点1、灵活性用户可以在覆盖范围内自由移动，不受线缆的限制，实现随时随地的网络接入。
2、安装便捷无需铺设大量的线缆，减少了施工成本和时间。
3、可扩展性强可以根据需求轻松增加或减少接入点，扩大或缩小网络覆盖范围。
三、无线局域网的技术原理（一）无线通信技术常见的无线通信技术包括 WiFi（IEEE 80211 系列标准）、蓝牙、Zigbee 等。
其中，WiFi 是目前无线局域网中应用最广泛的技术。
（二）工作频段无线局域网通常工作在 24GHz 和 5GHz 频段。
24GHz 频段具有较好的穿透能力，但可用信道较少，容易受到干扰；5GHz 频段可用信道较多，传输速率较高，但穿透能力相对较弱。
（三）网络拓扑结构无线局域网的拓扑结构主要有星型、总线型和网状型。
星型结构是最常见的，其中无线接入点（Access Point，简称 AP）作为中心节点，其他无线设备与之连接。
四、无线局域网的安全问题（一）安全威胁1、未经授权的访问攻击者可能通过破解密码等方式非法接入网络，获取敏感信息。
2、数据窃听无线信号在空气中传播，容易被他人截获和监听。
3、网络攻击如拒绝服务攻击（DoS）、中间人攻击等，影响网络的正常运行。
（二）安全措施1、加密技术如 WPA2、WPA3 等加密方式，保护数据传输的安全性。
Cooperative Diversity in Wireless Networks 文献翻译
Cooperative Diversity in Wireless Networks 文献翻译————————————————————————————————作者：————————————————————————————————日期：23 无线网络的协作分集：高效协议和中断行为 摘要：我们研究和分析了低复杂度的协作分集协议用以抵抗无线网络中多径传播引起的衰落，其底层技术是利用协作终端为其他终端转发信号而获得空间分集。
我们略述几种协同通信策略,包括固定中继方法如放大-转发，译码-转发,基于协同终端间的信道估计的选择中继方式，基于目标终端的有限反馈的增量中继方式。
我们在高SNR 条件下以中断事件、相关中断概率指标讨论了其性能特征，以估计协议对传输衰落的鲁棒性。
除固定的解码—转发协议外，所有的协同分集协议就所达到的全分集（也就是在两个终端下的二阶分集）来说是高效的，而且在某些状态下更加接近于最优（小于1。
5dB ）。
因此，当用分布式天线时，我们可以不用物理阵列而提供很好的空间分集效应，但因为采用半双工工作方式要牺牲频谱效率，也可能要增加额外接收硬件的开销。
协作分集对任何无线方式都适用，包括因空间限制而不能使用物理阵列的蜂窝移动通信和无线ad hoc 网络，这些性能分析显示使用这些协议可减少能耗.索引语——分集技术，衰落信道，中断概率,中继信道，用户协同,无线网络Ⅰ 介绍在无线网络中，多径传播引起的信号衰落是一个特别严重的信道损害问题，可以利用分集技术来减小。
II 系统模型在图1中的无线信道模型中，窄带传输会产生频率非选择性衰落和附加噪声。
我们在第四部分重点分析慢衰落，在时延限制相当于信道相干时间里，用中断概率来评价，与空间分集的优势区分.虽然我们的协同协议能自然的扩展到宽频带和高移动情况,其中面临各自的频域和时域的选择性衰落，当系统采用另一种形式的分集时对我们协议的潜在影响将相对减小。
4A 媒体接入当前的无线网络中,例如蜂窝式和无线局域网，我们将有用的带宽分成正交信道，并且分配这些信道终端，使我们的协议适用于现存的网络.这种选择产生的意外效果是，我们能够同时在I —A 处理多径（单个接收）和干扰（多个接收），相当于在信号接收机传输信号的一对中继信号.对于我们所有的协同协议，传输中的必须同时处理他们接收到的信号；但是，网络实现使终端不能实现全双工，也就是,传输和接收同时在相同的频带中实现。
无线局域网毕业论文中英文对照资料外文翻译文献
无线局域网毕业论文中英文对照资料外文翻译文献中英文对照资料外文翻译文献WLANWhy use WLANFor one of the main local area network management, for the laying of cables, or check the cable is disconnected this time-consuming work, it is easy to upset, not easy to break in a short time to find out where. Furthermore, for the business and application environment constantly updating and development of enterprise network must be matched with the original re-layout, need to re-install the network lines, although the cable itself is not expensive, but requested the technical staff to the high cost of wiring, especially the old building, wiring project costs even higher. Therefore, the construction of wireless local area network has become the best solution.What conditions need to use WLANWLAN is not limited to alternative local area network, but to make up for lack of wired local area networks, in order to achieve the purpose of extending the network, the following circumstances may have wireless local area network.●no fixed workplace users●wired local area network set up by the environmental constraints●As a wired local area network backup systemWLAN access technologyCurrently manufacturers in the design of wireless local area network products, there are quite a variety of access design methods can be divided into three categories: narrowband microwave, spread spectrum (Spread Spectrum) technology, andinfrared have their advantages and disadvantages, limitations, and more, followed by detailed discussion of these techniques. (Infrared) technology, each technique has their advantages and disadvantages, limitations, and more, followed by detailed discussion of these techniques.Technical requirementsAs wireless local area network needs to support high-speed, burst data services, need to be addressed in the indoor use of multipath fading, as well as issues such as crosstalk subnets. Specifically, wireless local area network must achieve the following technical requirements:1)Reliability: Wireless LAN system packet loss rate should be lower than 10-5,the error rate should be lower than 10-8.2)Compatibility: For indoor use of wireless local area network, so as far aspossible with the existing wired LAN network operating system and networksoftware compatible.3)Data rate: In order to meet the needs of local area network traffic, wirelessLAN data transfer rate should be more than 1Mbps.4)The confidentiality of communications: As the data transmitted in the air viawireless media, wireless local area networks at different levels must takeeffective measures to improve communication security and data security.5)Mobility: support for all mobile networks or semi-mobile network.6)Energy Management: When receiving or sending data to the site when themachine is in sleep mode, when activated again when the data transceiver toachieve the savings in power consumption.7)small size and low price: This is the key to the popularity of wireless local areanetwork can be.8)Electromagnetic environment: wireless LAN should consider thehumanbodyand the surrounding electromagnetic environment effects.AndroidGoogle Android is a Linux-based platform for developing open-source phone operating system (registered trademark in China called "Achi;). It includes operating systems, user interface and applications - mobile phone work required by the software, but there is no past, the exclusive right to impede innovation and barriers to mobile industry, called mobile terminal is the first to create a truly open and complete mobile software. Google and Open Handset Alliance to develop the Android, the alliance by including China Mobile, Motorola, Qualcomm and T-Mobile, including more than 30 technology and the composition of a leader in wireless applications. Google with operators, equipment manufacturers, developers and other interested parties to form deep-level partnerships, hoping to establish a standardized, open software platform for mobile phones in the mobile industry to form an open ecosystem .It uses software stack layers (software stack, also known as the software stack) architecture, is divided into three parts: thecore of the underlying Linux-based language developed by the c, only basic functions. Middle layer consists of library. Library and Virtual Machine Virtual Machine, developed by the C +. At the top are a variety of applications, including the call procedures, SMS procedures, application software is developed by the companies themselves to write java.To promote this technology, Google, and dozens of other phone company has established the Open Handset Alliance (Open Handset Alliance).Characteristic●application framework to support component reuse and replacement●Dalvik virtual machine specifically for mobile devices i s optimized●Internal integrated browser, the browser-based open-source WebKit engine●optimization of 2D and 3D graphics library includes graphics library, 3Dgraphics library based on OpenGL ES 1.0 (hardware-accelerated optional)●# SQLite for structured data storage●Multimedia support includes the common audio, video and static image fileformats (such as MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)●GSM phone (depending on hardware)●Bluetooth Bluetooth, EDGE, 3G, and WiFi (hardware dependent)●Camera, GPS, compass, and accelerometer (hardware dependent)●Rich development environment including a device emulator, debugger,memory and performance analysis charts, and the Eclipse integrateddevelopment environment plug-insApplicationsA core Android application package together with the release of the application package, including email client, SMS short messaging program, calendar, maps, browser, contact management procedures. A ll applications are written using JA V A.Android Application Framework Developers have full access to core applications used by the API framework. The application framework designed to simplify the reuse of software components; any application can publish its functional blocks and any other applications can use the function block its release (but must follow the framework of security restrictions). Reuse mechanism allows the application form can be user replaced.All of the following applications by the composition of a range of services and systems, including:●an expanded view (V iews) can be used to build applications, including a list of(lists), grid (grids), text boxes (text boxes), buttons (buttons), and even an embeddable web browser.●Content Manager (Content Providers) allows applications to access data fromanother application program (such as the contact database), or to share their own data.● A resource manager (Resource Manager) to provide access to non-coderesources, such as local strings, graphics, and hierarchical file (layout files).● A notification manager (Notif ication Manager) allows applications to customersin the status bar display notification information.●An activity class Manager (Activity Manager) to manage the application lifecycle and provides common navigation rollback feature.Ordering the systemOrdering the system information using automated software tools to achieve la carte, side dishes, stir fry vegetables to the transfer of all management processes; completion point, the computer management menu, point the menu and the kitchen, front-end checkout synchronization print; achieved without the menu paper-based operation; backstage manager of inquiry; warehouse inventory management and so on.In addition, ordering the system can also effectively manage customer data, archiving and future reference, put an end to the restaurant "leakage List", "run list" phenomenon; help restaurants using computer data processing capability and powerful ability to process optimization to achieve automated management, streamline workflow restaurant, reduce waste and man-made phenomenon of management oversight, re-optimal allocation of corporate resources, the operating costs to a minimum.Powerful addition to ordering the system to support the general application of stand-alone and LAN in addition to support head office / branch of multi-level framework used for remote network using the POS system to achieve front store sales cashier, sales of small-ticket instantly print sales day-end, reporting sales data and receive information of new featuresdishes.There are three currently ordering the system to achieve mode:First, the touch screen a la carte model: It uses the currently most popular touch-computer ordering process to achieve that members can to order the software screen prompts, simply click on the screen with your fingers can complete the entire ordering process and convenient This model applies to the practice of rich dishes and large restaurants, restaurants, and restaurant, etc..Second,the wireless PDA ordering mode: it uses a wireless WiFi technology, a la carte interface by PDA display, use touch pen to complete the ordering process, virtuallyanywhere, anytime to order real-time response, this model is more suitable for dishes and practices simple restaurant, features a restaurant and special mood of senior restaurants.Third, the wireless ordering Po mode: it uses the ISM band, can be a floor or other obstruction in the case of seamless coverage up to 10 meters away, while the signal remained stable, which is the ratio of the wireless PDA ordering model's greatest strength, this model applies to simple dishes and practices and other requirements with fewer fast food restaurants, pot shops.。
无线通信毕业设计外文翻译
Wireless communicationModern computer technology, industrial revolution, the world economy from the capital into the economy to knowledge economy. Field in the electronic world, from the 20th century into the era of radio to computer technology in the 21st century as the center of the intelligent modern era of electronic systems. The basic core of modern electronic systems are embedded computer systems (referred to as embedded systems), while the microcontroller is the most typical and most extensive and most popular embedded systems.First, radio has created generations of excellence in the worldFifties and sixties in the 20th century, the most representative of the advanced electronic technology is wireless technology, including radio broadcasting, radio, wireless communications (telegraph), Amateur Radio, radio positioning, navigation and other telemetry, remote control, remote technology. Early that these electronic technology led many young people into the wonderful digital world, radio show was a wonderful life, the prospects for science and technology. Electronics began to form a new discipline. Radio electronics, wireless communications began e-world journey. Radio technology not only as a representative of advanced science and technology at that time, but also from popular to professional fields of science, attracting the young people and enable them to find a lot of fun. Ore from the bedside to the superheterodyne radio radio; report issued from the radio amateur radio stations; from the telephone, electric bell to the radio control model. Became popular youth radio technology, science and technology education is the most popular and most extensive content. So far, many of the older generation of engineers, experts, Professor of the year are radio enthusiasts. Fun radio technology, radio technology, comprehensive training, from basic principles of electronics, electronic components to the radio-based remote control, telemetry, remote electronic systems, has trained several generations of technological excellence.Second, from the popularity of the radio era to era of electronic technologyThe early radio technology to promote the development of electronic technology, most notably electronic vacuum tube technology to semiconductor electronictechnology. Semiconductor technology to realize the active device miniaturization and low cost, so more popular with radio technology and innovation, and to greatly broaden the number of non-radio-control areas. The development of semiconductor technology lead to the production of integrated circuit, forming the modern electronic technology leap from discrete electronics into the era of era of integrated circuits. Electronic design engineers no longer use the discrete electronic components designed circuit modules, and direct selection of integrated circuit components constitute a single system. They freed the design of the circuit unit dedicated to system design, greatly liberating the productive forces of science and technology, promote the wider spread of electronic systems. Semiconductor integrated circuits in the basic digital logic circuits first breakthrough. A large number of digitallogic circuits, such as gates, counters, timers, shift registers, and analog switches, comparators, etc., for the electronic digital control provides excellent conditions for the traditional mechanical control to electronic control. Power electronic devices and sensor technology to make the original to the radio as the center of electronic technology turned to mechanical engineering in the field of digital control systems, testing in the field of information collection, movement of electrical mechanical servo drive control object. Semiconductor and integrated circuit technology will bring us a universal age of electronic technology, wireless technology as the field of electronic technology a part of. 70 years into the 20th century, large scale integrated circuit appeared to promote the conventional electronic circuit unit-specific electronic systems development. Many electronic systems unit into a dedicated integrated devices such as radios, electronic clocks, calculators, electronic engineers in these areas from the circuit, the system designed to debug into the device selection, peripheral device adapter work. Electronic technology, and electronic products enriched, electronic engineers to reduce the difficulty, but at the same time, radio technology, electronic technology has weakened the charm. The development of semiconductor integrated circuits classical electronic systems are maturing, remain in the large scale integrated circuit other thanthe shrinking of electronic technology, electronic technology is not the old days of radio fun times and comprehensive engineering training.Third, from the classic era of electronic technology to modern electronic technology of the times80 years into the 20th century, the century of economic change is the most important revolution in the computer. The computer revolution in the most important sign is the birth of the computer embedded applications. Modern computer numerical requirements should be born. A long period of time, is to develop the massive computer numerical duty. But the computer shows the logic operation, processing, control, attracting experts in the field of electronic control, they want development to meet the control object requirements of embedded applications, computer systems. If you meet the massive data-processing computer system known as general-purpose computer system, then the system can be the embedded object (such as ships, aircraft, motorcycles, etc.) in a computer system called the embedded computer. Clearly, both the direction of technology development are different. The former requires massive data storage, handling, processing and analysis of high-speed data transmission; while the latter requires reliable operation in the target environment, the external physical parameters on high-speed acquisition, analysis and processing logic and the rapid control of external objects. It will add an early general-purpose computer data acquisition unit, the output driver circuit reluctance to form a heat treatment furnace temperature control system. This general-purpose computer system is not possible for most of the electronic system used, and to make general-purpose computer system meets the requirements of embedded applications, will inevitably affect the development of high-speed numeric processing. In order to solve the contradiction between the development of computer technology, in the 20th century 70s, semiconductor experts another way, in full accordance with the electronic systemembedded computer application requirements, a micro-computer's basic system on a chip, the formation of the early SCM (Single Chip Microcomputer). After the advent of single chip in the computer industry began to appear in the general-purpose computer systems and embedded systems the two branches. Since then, both the embedded system, or general-purpose computer systems have been developed rapidly.Although the early general-purpose computer converted the embedded computer systems, and real embedded system began in the emergence of SCM. Because the microcontroller is designed specifically for embedded applications, the MCU can only achieve embedded applications. MCU embedded applications that best meet environmental requirements, for example, chip-level physical space, large-scale integrated circuits low-cost, good peripheral interface bus and outstanding control of instruction. A computer system microcontroller core, embedded electronic systems, intelligent electronic systems for the foundation. Therefore, the current single chip electronic system in widespread use of electronic systems to enable rapid transition to the classical modern intelligent electronic systems.Forth, single chip to create the modern era of electronic systems.A microcontroller and embedded systems Embedded computer systems from embedded applications, embedded systems for early general-purpose computer adapted to the object system embedded in a variety of electronic systems, such as the ship's autopilot, engine monitoring systems. Embedded system is primarily a computer system, followed by it being embedded into the object system, objects in the object system to achieve required data collection, processing, status display, the output control functions, as embedded in the object system, embedded system computer does not have an independent form and function of the computer. SCM is entirely in accordance with the requirements of embedded system design, so SCM is the most typical embedded systems. SCM is the early application of technical requirements in accordance with the design of embedded computer chip integration, hence the name single chip. Subsequently, the MCU embedded applications to meet the growing demands of its control functions and peripheral interface functions, in particular, highlight the control function, so has international name the single chip microcontroller (MCU, Microcontroller Unit).2 MCU modern electronic systems consisting of electronic systems will become mainstreamMCU is a device-level computer systems, it can be embedded into any object system to achieve intelligent control. Small to micro-machinery, such as watches,hearing aids.Low-cost integrated device-level, low-to a few dollars, ten dollars, enough to spread to many civilian SCM appliances, electronic toys to go. SCM constitutes a modern electronic systems has in-depth to the households, are changing our lives, such as home audio, televisions, washing machines, microwave ovens, telephones, security systems, and air conditioners. SCM innovation the original electronic systems, such as microwave ovens use SCM, it can easily set the clock, the program memory, power control; air conditioner after use of SCM is not only convenient for remote parameter setting, running automatically transform, frequency control can be achieved.At present, many household appliances such as VCD, DVD only single chip to achieve its function may occur before. 3 Embedded Systems led the entire electronics industry Current electronic components industry, in addition to microprocessors, embedded system devices, the most modern electronic systems around the supporting components industries, such as keys used to meet the human-computer interaction, LED / LCD display drivers, LED / LCD display units, voice integrated device, etc., to meet the requirements of data acquisition channel digital sensor, ADC, data acquisition module, signal conditioning modules to meet the servo drive control in the DAC, solid state relays, stepper motor controller, frequency control unit, etc., to meet the communication requirements various bus driver, level converters. Electronic components in the embedded systems world, driven by embedded applications along fully meet requirements of modern electronic systems development. This makes the original classic world of increasingly small electronic systems. Practitioners in the various electronic systems to modern electronic systems as early as possible to stay.Fifth, SCM will create a new generation of electronic elite.If the 50's, radio has created several generations of the world elite, then today's SCM will create a new generation of e-world elite. A single chip with you to the intelligent electronics If we as a dead classic electronic system electronic system, then the intelligent modern electronic systems is a "life" of the electronic system. Application System of hardware, electronic systems, "body", microcontroller applications, the applicationgives it "life." For example, in the design of intelligent machines monitor display, it can boot the system self-test results show, not to enter the work shows a variety of stand-by state, equipment run-time display running processes, work can be displayed after the end of the current results, self results, raw data, reports and other various processing. Unattended, it can run automatically given a variety of functions. Intelligent electronic systems for the endless realm, often without additional hardware resources can achieve all kinds of renovated function. It is also present in many household appliances feature a large number of additional factors. 2 single chip computer with you to the industrial area The 21st century is the century of humanity into the computer age, many people are not used in the manufacture of computer is the computer. People using the computer, only the people engaged in embedded system applications really into the internal computer system hardware and software systems, can we truly understand the nature of the computer's intelligence and grasp the knowledge of intelligent design. MCU applications starting from the learning technology applications in today's computer software training, hardware and technical personnel of one of the best roads. 3 SCM bring you into the most attractive in the digital world Charming single chip to enable you to experience the true meaning of the computer, you can design intelligent microcontroller hands-on toys, different applications can be designed to achieve different functions. Both software design and hardware making there, both mental and physical, but also hands. Primary level can develop intelligent toys, with macro programming. Intermediate levels can develop some intelligent controller, such as computer mouse, smart cars, all kinds of remote control model. High levels can be developed robots, such as robot soccer, the development of industrial control units, network communications, and high-levellanguage with assembly language or design application. Microcontroller and embedded systems around the formation of the future of the electronics industry, will provide a vast world of electronic fans, an even broader than the current wireless world, richer, more durable, more attractive in the digital world. Plunge into the microcontroller in the world to, will benefit your life.MCU AttacksCurrently, there are four single chip attack technique, namely: (1) software attack The technology is commonly used processor communication interface and use protocol, encryption algorithm or the algorithm of security vulnerabilities to attack. The success of software attack is a typical example of the early ATMEL AT89C MCU attacks. Attacker single chip erase operation of the timing design flaw, erase the encryption used by ourselves locked in place, the next stop on-chip program memory data erase operation, thus bringing into too close a single chip SCM not encrypted, and then use the programmer to read out chip program. (2) electronic detection of attacks The technology is usually a high time resolution to monitor the processor during normal operation of all power and interface simulation features, and by monitoring the electromagnetic radiation characteristics of it to attack. Because SCM is an active electronic device, when it executes a different command, the corresponding changes in the power consumption accordingly. This through the use of special electronic measuring instruments and mathematical statistical analysis and detection of these changes, you can access key information specific microcontroller.(3) fault generation technology Abnormal working conditions of the technology used to make the processor errors, and provide additional access to attack. Produce the most widely used means of attack, including the fault of the impact and the clock voltage shock. Low voltage and high voltage protection circuit attack can be used to prohibit the work of processor execution errors or enforcement action. Clock transition may reset the transient protection circuit will not damage the protected information. Power and clock transients transition effects in certain single-processor instruction decoding and execution. (4) probe This technology is directly exposed to chip connection, and then observe, manipulate, interfere with single chip to achieve the attack purpose. For convenience, these four people will attack techniques are divided into two categories is theintrusion type attack (physical attack), such attack requires destruction of package, then use semiconductor test equipment, microscopes and micro-positioning device, in a special laboratory spend hours or even weeks to complete. All of the micro-probe techniques are invasive type attack. The other three methods are non-invasive type attack, attack the MCU will not be physical damage. In some cases, non-invasive-type attacks are particularly dangerous, but because of non-invasive type attacks can usually be made and the necessary equipment to upgrade, so it is cheap. Most non-invasive type attack requires the attacker have a good knowledge of processors and software knowledge. In contrast, the invasive type of probe do not need too much of the initial attack of knowledge, and usually a set of similar technology available to deal with a wide range of productsMCU general process of invasion-type attackInvasive type of attack is thrown off its first chip package. There are two ways to achieve this goal: the first one is completely dissolved out chip package, exposed metal connections. The second is only removed to the top of the plastic package silicon core. The first method is the need to bind to the test fixture on the chip, using bind Taiwan to operate. The second method requires the attacker in addition to a certain degree of knowledge and necessary skills, but also the wisdom and patience, but operate relatively easy. Above the plastic chips can be opened with a knife, epoxy around the chip can be eroded by concentrated nitric acid. Hot concentrated nitric acid will dissolve out without affecting the chip, chip packaging and connection. This process usually very dry conditions, because the presence of water may erode the aluminum wire connections have been exposed. Then, in ultrasonic cleaning of the pool first chip with acetone to remove residual nitric acid, then washed with water to remove salt and dried. No ultrasound pool, are generally skip this step. This case, the chip surface, a bit dirty, but do not affect the operation of UV effects on the chip. The final step is to find the location of the protection fuse and fuse protection under exposure to UV light. General use at least a 100 times magnification microscope, from the programming voltage input pin of the connection tracking in, to find protection fuse. If there is no microscope, theuse of different parts of the chip is exposed to ultraviolet light and observe the results under the simple search mode. Operation applied opaque paper cover to protect the program memory chips are not erased by ultraviolet light. Will protect the fuse exposed under UV light 5 to 10 minutes to destroy the protection bit of the protective effect, use a simple programmer can directly read the contents of program memory. The use of the protective layer to protect the MCU EEPROM cell, using ultraviolet light reset protection circuit is not feasible. For this type of MCU, the general use of micro-probe technology to read the memory contents. In the chip package is opened, the chip placed under the microscope can easily find from the memory circuit connected to other parts of the data bus. For some reason, the chip lock-bit programming mode is not locked in the memory of the visit. Advantage of this flaw on the data lines to probe the above data can be read all you want. In programming mode, restart the process of reading and connect probe to the other data can be read online program and data memory, all of the information. There is also a possible means of attack is the use of microscopy and laser cutting machines and other equipment to find the fuse protection to this part of the circuit tracing and linking all the signal lines. Because of the design defects, so long as cut off from other circuit protection fuse to a one signal line, you can ban the entire protection. For some reason, this thread is very far from the other line, so the use of laser cutting machine can cut the wire without affecting the adjacent line. In this way, using a simple programmer can directly read the contents of program memory. Although the most common single chip microcontroller has fuse blown inside the code protection features, but because of general low-end MCU is not positioning the production of safe products, so they often do not provide targeted preventive measures and the low level of security. MCU applications with a broad, large sales volume, commission processing and transfer of technology between firms frequently spilled a lot oftechnical data, making use of loopholes in the design of such chips and test interface manufacturer, and by modifying the invasive type fuse protection bits, etc. means of attack or invasion-type attack to read MCU's internal procedureshave become easier.About common single chipSTC microcontroller STC's mainly based on the 8051 microcontroller core is a new generation of enhanced MCU, the instruction code is fully compatible with the traditional 8051, 8 to 12 times faster, with ADC, 4 Road, PWM, dual serial ports, a global unique ID, encryption of good, strong anti-interference. PIC Microcontroller: MICROCHIP's products is its prominent feature is a small, low power consumption, reduced instruction set, interference, reliability, strong analog interface, the code of confidentiality is good, most of the chip has its compatibleFLASH program memory chips. EMC SCM: Elan's products in Taiwan, with much of the PIC 8-bit microcontroller compatible, and compatible products, resources, compared to the PIC's more, cheap, there are many series of options, but less interference. ATMEL microcontroller (MCU 51): ATMEl company's 8-bit microcontroller with AT89, AT90 two series, AT89 series is the 8-bit Flash microcontroller 8051 is compatible with the static clock mode; AT90 RISC MCU is to enhance the structure, all static methods of work, containing the line can be Flash MCU programming, also known A VR microcontroller. PHLIPIS 51PLC Microcontroller (MCU 51): PHILIPS company's MCU is based on the 80C51 microcontroller core, embedded power-down detection, simulation and on-chip RC oscillator and other functions, which makes 51LPC in highly integrated, low cost, low power design to meet various applications performance requirements. HOLTEK SCM: Sheng Yang, Taiwan Semiconductor's single chip, cheap more categories, but less interference for consumer products. TI company microcontroller (MCU 51):Texas Instruments MSP430 provides the TMS370 and two series of general-purpose microcontroller. TMS370 MCU is the 8-bit CMOS MCU with a variety of storage mode, a variety of external interface mode, suitable for real-time control of complex situations; MSP430 MCU is a low power, high functionality integrated 16-bit low-power microcontroller, especially for applications that require low power consumption occasions Taiwan Sonix's single, mostly 8-bit machines, some with PIC 8-bit microcontroller compatible, cheap, the system clock frequency may be more options there PMW ADC internal noise filtering within the vibration. Shortcomings RAM space is too small, better anti-interference.无线通信从无线电世界到单片机世界现代计算机技术的产业革命,将世界经济从资本经济带入到知识经济时代。
计算机网络中英文对照外文翻译文献
中英文资料外文翻译计算机网络计算机网络，通常简单的被称作是一种网络，是一家集电脑和设备为一体的沟通渠道，便于用户之间的沟通交流和资源共享。
网络可以根据其多种特点来分类。
计算机网络允许资源和信息在互联设备中共享。
一．历史早期的计算机网络通信始于20世纪50年代末，包括军事雷达系统、半自动地面防空系统及其相关的商业航空订票系统、半自动商业研究环境。
1957年俄罗斯向太空发射人造卫星。
十八个月后，美国开始设立高级研究计划局(ARPA)并第一次发射人造卫星。
然后用阿帕网上的另外一台计算机分享了这个信息。
这一切的负责者是美国博士莱德里尔克。
阿帕网于来于自印度，1969年印度将其名字改为因特网。
上世纪60年代，高级研究计划局(ARPA)开始为美国国防部资助并设计高级研究计划局网(阿帕网)。
因特网的发展始于1969年，20世纪60年代起开始在此基础上设计开发，由此，阿帕网演变成现代互联网。
二．目的计算机网络可以被用于各种用途:为通信提供便利:使用网络，人们很容易通过电子邮件、即时信息、聊天室、电话、视频电话和视频会议来进行沟通和交流。
共享硬件:在网络环境下，每台计算机可以获取和使用网络硬件资源，例如打印一份文件可以通过网络打印机。
共享文件：数据和信息: 在网络环境中，授权用户可以访问存储在其他计算机上的网络数据和信息。
提供进入数据和信息共享存储设备的能力是许多网络的一个重要特征。
共享软件:用户可以连接到远程计算机的网络应用程序。
信息保存。
安全保证。
三．网络分类下面的列表显示用于网络分类：3．1连接方式计算机网络可以据硬件和软件技术分为用来连接个人设备的网络，如：光纤、局域网、无线局域网、家用网络设备、电缆通讯和G.hn（有线家庭网络标准）等等。
以太网的定义，它是由IEEE 802标准，并利用各种媒介，使设备之间进行通信的网络。
经常部署的设备包括网络集线器、交换机、网桥、路由器。
无线局域网技术是使用无线设备进行连接的。
计算机科学与技术专业无线局域网毕业论文外文文献翻译及原文
毕业设计（论文）外文文献翻译文献、资料中文题目：无线局域网文献、资料英文题目：文献、资料来源：文献、资料发表（出版）日期：院（部）：专业：计算机科学与技术专业班级：姓名：学号：指导教师：翻译日期： 2017.02.14毕业设计(论文)外文资料翻译外文出处：Chris Haseman. Android-essential(用外文写)s[M].London:Spring--Verlag,2008.8-13.附件： 1.外文资料翻译译文；2.外文原文。
指导教师评语：签名：年月日注：请将该封面与附件装订成册。
附件1：外文资料翻译译文无线局域网一、为何使用无线局域网络对于局域网络管理主要工作之一，对于铺设电缆或是检查电缆是否断线这种耗时的工作，很容易令人烦躁，也不容易在短时间内找出断线所在。
再者，由于配合企业及应用环境不断的更新与发展，原有的企业网络必须配合重新布局，需要重新安装网络线路，虽然电缆本身并不贵，可是请技术人员来配线的成本很高，尤其是老旧的大楼，配线工程费用就更高了。
因此，架设无线局域网络就成为最佳解决方案。
二、什么情形需要无线局域网络无线局域网络绝不是用来替代有限局域网络，而是用来弥补有线局域网络之不足，以达到网络延伸之目的，下列情形可能须要无线局域网络。
●无固定工作场所的使用者●有线局域网络架设受环境限制●作为有线局域网络的备用系统三、无线局域网络存取技术目前厂商在设计无线局域网络产品时，有相当多种存取设计方式，大致可分为三大类：窄频微波技术、展频(Spread Spectrum)技术、及红外线(Infrared)技术，每种技术皆有其优缺点、限制及比较，接下来是这些技术方法的详细探讨。
1.技术要求由于无线局域网需要支持高速、突发的数据业务，在室内使用还需要解决多径衰落以及各子网间串扰等问题。
具体来说，无线局域网必须实现以下技术要求：1)可靠性：无线局域网的系统分组丢失率应该低于10-5，误码率应该低于10-8。
网络的分类名词解释英文
网络的分类名词解释英文随着科技的进步和互联网的普及，网络已经成为人们日常生活中不可或缺的一部分。
网络不仅仅是人们获取信息、交流和娱乐的工具，也是连接全球的桥梁。
不同类型的网络在实现不同功能和目标方面有着不同的用途和命名分类。
本文将介绍一些常见的网络分类，并提供相关英文解释。
1. 局域网（Local Area Network，缩写为LAN）局域网是指在一个较小范围内以计算机网络为基础建立的网络。
它主要用于办公室、学校和家庭等局限空间内的计算机之间的数据传输和资源共享。
LAN通常由一组相互连接的计算机、服务器、打印机和其他网络设备组成。
它可以通过有线或无线连接来实现，并通常由路由器或交换机进行控制和管理。
2. 广域网（Wide Area Network，缩写为WAN）广域网是指跨越较大地理范围的计算机网络。
它可以连接不同城市、国家甚至是全球范围内的计算机和网络设备。
WAN通过使用公共或专用的传输线路、卫星链路或电话网络来连接不同地点的计算机。
常见的例子包括互联网和公司间的专用网络。
3. 无线局域网（Wireless Local Area Network，缩写为WLAN）无线局域网是指使用无线通信技术构建的局域网。
它使用无线电波或红外线信号来传输数据，使得设备可以无线连接到局域网并进行通信。
WLAN通常由无线路由器、无线适配器和移动设备组成。
它广泛应用于家庭、办公室、机场、图书馆等场所，为用户提供无线上网和移动性。
4. 全球性网络（Internet）全球性网络，即互联网，是连接世界上所有计算机网络的网络。
它是一个开放的、去中心化的网络，使全球各地的计算机能够互相通信和传输数据。
互联网使用标准的互联网协议（TCP/IP）进行数据传输，通过因特网服务提供商（ISP）连接到互联网。
它提供了无限的资源和信息，涵盖了各种服务和应用，如电子邮件、搜索引擎、社交媒体和在线购物等。
5. 虚拟专用网（Virtual Private Network，缩写为VPN）虚拟专用网是一种通过公共网络（如互联网）创建的安全连接。
无线网络_外文翻译_外文文献_英文文献_无线局域网技术
毕业外文翻译无线局域网技术最近几年，无线局域网开始在市场中独霸一方。
越来越多的机构发现无线局域网是传统有线局域网不可缺少的好帮手,它可以满足人们对移动、布局变动和自组网络的需求，并能覆盖难以铺设有线网络的地域。
无线局域网是利用无线传输媒体的局域网。
就在前几年，人们还很少使用无线局域网.原因包括成本高、数据率低、职业安全方面的顾虑以及需要许可证。
随着这些问题的逐步解决,无线局域网很快就开始流行起来了.无线局域网的应用局域网的扩展在20世纪80年代后期出现的无线局域网早期产品都是作为传统有线局域网替代品而问世的。
无线局域网可以节省局域网缆线的安装费用，简化重新布局和其他对网络结构改动的任务。
但是，无线局域网的这个动机被以下一系列的事件打消。
首先，随着人们越来越清楚地认识到局域网的重要性，建筑师在设计新建筑时就包括了大量用于数据应用的预先埋设好的线路.其次，随着数据传输技术的发展，人们越来越依赖于双绞线连接的局域网。
特别是3类和5类非屏蔽双绞线。
大多数老建筑中已经铺设了足够的3类电缆，而许多新建筑里则预埋了5类电缆。
因此，用无线局域网取代有线局域网的事情从来没有发生过。
但是,在有些环境中无线局域网确实起着有线局域网替代品的作用。
例如，象生产车间、股票交易所的交易大厅以及仓库这样有大型开阔场地的建筑；没有足够双绞线对，但又禁止打洞铺设新线路的有历史价值的建筑;从经济角度考虑,安装和维护有线局域网划不来的小型办公室。
在以上这些情况下，无线局域网向人们提供了一个有效且更具吸引力的选择.其中大多数情况下，拥有无线局域网的机构同时也拥有支持服务器和某些固定工作站的有线局域网。
因此，无线局域网通常会链接到同样建筑群内的有线局域网上。
所以我们将此类应用领域成为局域网的扩展。
建筑物的互连无线局域网技术的另一种用途是邻楼局域网之间的连接，这些局域网可以是无线的也可以是有线的。
在这种情况下，两个楼之间采用点对点的无线链接.被链接的设备通常是网桥或路由器。
计算机网络中英文互译,DOC
欢迎共阅计算机网络中英翻译ACK(ACKnowledgement)确认帧ADSL(AsymmetricDigitalSubscriberLine)非对称数字用户线AN(AccessNetwork）接入网ANSI(AmericanNationalStandardsInstitute)美国国家标准协会AP(AccessPoint)接入点API(ApplicationProgrammingInterface)应用编程接口APNIC(AsiaPacificNetworkInformationCenter)亚太网络信息中心ARP（AddressResolutionProtocol）地址解析协议AWT（BNACBR（CCPCSMA/CD(CarrierSenseMultipleAccess／CollisionDetection)载波监听多点接入/碰撞检测CSU/DSU（ChannelServiceUnit/DataServiceUnit)信道服务单元／数据服务单元CTD(CellTransferDelay)信元传送时延DACS(DigitalAccessandCross-connectSystem)数字交接系统DCA数据通信体系结构DCE(DataCircuit-terminatingEquipment)数据电路端接设备DE(DiscardEligibility)丢弃指示DES(DataEncryptionStandard)数据加密标准DHCP(DynamicHostConfigurationProtocol)动态主机配置协议DLCI(DataLinkConnectionIdentifier)数据链路连接标识符DMT(DiscreteMulti-Tone)离散多音（调制）DNS(DomainNameSystem)域名系统DNA数据网络系统结构DSL(DigitalSubscriberLine)数字用户线DSLAM(DSLAccessMultiplexer)数字用户线接入复用器DSSS(DirectSequenceSpreadSpectrum)直接序列扩频DTE(DataTerminalEquipment)数据终端设备DVMRP(DistanceVectorMulticastRoutingProtocol)距离向量多播路由选择协议DWDM(DenseWDM)密集波分复用EGP(ExternalGatewayProtocol)外部网关协议EIA(ElectronicIndustriesAssociation）美国电子工业协会ESS伍FCS(FrameFIFO（FR(FrameGFC（HDSL(HighspeedDSL)高速数字用户线HEC(HeaderErrorControl)首部差错控制HFC(HybridFiberCoax)光纤同轴混合（网）HTML(HyperTextMarkupLanguage)超文本置标语言HTTP(HyperTextTransferProtocol)超文本传送协议IAB(InternetArchitectureBoard)因特网体系结构委员会IAC（InterpretAsCommand）作为命令解释IAHC(InternetInternationalAdHocCommittee）因特网国际特别委员会ICMP（InternetControlMessageProtocol）因特网控制报文协议IDEA(InternationalDataEncryptionAlgorithm)国际数据加密算法IEEE电气和电子工程师协会IESG(InternetEngineeringSteeringGroup)因特网工程指导小组IETF(InternetEngineeringTaskForce)因特网工程部IFS(Inter Frame Space)帧间间隔IGMP(InternetGroupManagementProtocol)因特网组管理协议IGP(InteriorGatewayProtocol)内部网关协议IM(InstantMessaging)即时传信IMAP(InternetMessageAccessProtocol)因特网报文存取协议IMP（InterfaceMessageProcessor)接口报文处理机IP(InternetProtocol）网际协议IR(InfraRed）红外技术IRTF（ISO（ISP（ITU（ITU-T（MIB(ManagementInformationBase)管理信息库MIME(MultipurposeInternetMailExtensions)通用因特网邮件扩充modem调制解调器MOTIF(MessageOrientedTextInterchangeSystem)面向报文的电文交换系统MPEG(MotionPictureExpertsGroup)活动图像专家组标准MPOA(MultiProtocolOverATM)多协议在ATM上运行MPLS(MultiProtocolLabelSwitching)多协议标记交换MRU(MaximumReceiveUnit)最大接收单元MSS(MaximumSegmentSize)最长报文段MTU(MaximumTransferUnit)最大传送单元NAK(NegativeAcKnowlegement)否认帧NAP（NetworkAccessPoint)网络接入点N.ISDN(Narrowband-ISDN)窄带综合业务数字网NAT(NetworkAddressTranslation）网络地址转换NAV(NetworkAl location Vector)网络分配向量NCP(NetworkControlProtocol)网络控制协议NFS(NetworkFileSystem)网络文件系统NGI下一代因特网计划NIA网络适配器NIC(NetworkInterfaceCard)网络接口卡、网卡NII(NationalInformationInfrastructure)国家信息基础结构，国家信息基础设施ODBC（OSF（OSI（PBX（PCR（PCSPDHPDAPDNPDUPERPIRPLCPPLRPMDPPPPPTPPRMPRNPSN分组交换节点PacketSwitchNodePSTN公用电话交换网PublicSwitchedTelephoneNetworkRARP逆向地址解析协议ReverseAddressResolutionProtocolRAS远程访问服务器RFC请求评注RequestforCommentsRMON远程网络管理Router路由器RPC远程过程调用RemoteProcedureCallRSVP资源重复利用协议RTP接收和发送端口RTS往返样本RoundTripSampleRTS剩余时间标签SAP业务接入点ServiceAccessPointSAP服务公告协议ServiceAdvertisingProtocolSAR分段和重组(子层)SegmentationandReassemblySDH同步数字系列SynchronousDigitalHierarchySDLC同步数据链路控制(协议)AdvancedDataCommunicationControlProcedure SDTV标准数字电视SDU业务数据单元ServiceDataUnitSIPP增强的简单因特网协议SimpleInternetProtocolPlusSLIP串行线路IPSerialLineInterfaceProtocolSMDSSMFSMTSMTPSNASNMPSNRSONETSTMSTPSTSSVCTCPTDMTFTPVCC虚信道连接VirtualChannelConnectionVLAN虚拟局域网VirtualLANVLSI超大规模集成电路VOD点播图像VideoonDemandVPC虚路径连接VirtualPathConnectionVPI虚路径标识virtualpathidentifierVPN虚拟专用网络VirtualPrivateNetworkVRML虚拟现实造型语言VirtualRealityModelingLanguageVTP虚拟隧道协议WAN广域网WideAreaNetworkWDM波分多路复用WavelengthDivisionMultiplexing WWW万维网WorldWideWeb。
计算机 毕业论文 外文文献翻译 中英文：IEEE802.11 媒体接入控制
英文资料与中文翻译IEEE 802.11 MEDIUM ACCESS CONTROLThe IEEE 802.11 MAC layer covers three functional areas：reliable data delivery, medium access control, and security. This section covers the first two topics.Reliable Data DeliveryAs with any wireless network, a wireless LAN using the IEEE 802.11 physical and MAC layers is subject to considerable unreliability. Noise, interference, and other propagation effects result in the loss of a significant number of frames. Even with error-correction codes, a number of MAC frames may not successfully be received. This situation can be dealt with by reliability mechanisms at a higher layer. such as TCP. However, timers used for retransmission at higher layers are typically on the order of seconds. It is therefore more efficient to deal with errors at the MAC level. For this purpose, IEEE 802.11 includes a frame exchange protocol. When a station receives a data frame from another station. It returns an acknowledgment (ACK) frame to the source station. This exchange is treated as an atomic unit, not to be interrupted by a transmission from any other station. If the source does not receive an ACK within a short period of time, either because its data frame was damaged or because the returning ACK was damaged, the source retransmits the frame.Thus, the basic data transfer mechanism in IEEE802.11 involves an exchange of two frames. To further enhance reliability, a four-frame exchange may be used. In this scheme, a source first issues a request to send (RTS) frame to the destination. The destination then responds with a clear to send (CTS). After receiving the CTS, the source transmits the data frame, and the destination responds with an ACK. The RTS alerts all stations that are within reception range of the source that an exchange is under way; these stations refrain from transmission in order to avoid a collision between two frames transmitted at the same time. Similarly, the CTS alerts all stations that are within reception range of the destination that an exchange is under way. The RTS/CTS portion of the exchange is a required function of the MAC but may be disabled.Medium Access ControlThe 802.11 working group considered two types of proposals for a MAC algorithm: distributed access protocols, which, like Ethernet, distribute the decision to transmit over all the nodes using a carrier-sense mechanism; and centralized access protocols, which involve regulation of transmission by a centralized decision maker. A distributed access protocol makes sense for an ad hoc network of peer workstations (typically an IBSS) and may also be attractive in other wireless LAN configurations that consist primarily of burst traffic. A centralized access protocol is natural for configurations in which a umber of wireless stations are interconnected with each other and some sort of base station that attaches to a backbone wired LAN: it is especially useful if some of the data is time sensitive or high priority.The end result for 802.11 is a MAC algorithm called DFWMAC (distributed foundation wireless MAC) that provides a distributed access control mechanism with an optional centralized control built on top of that. Figure 14.5 illustrates the architecture. The lower sub-layer of the MAC layer is the distributed coordination function (DCF). DCF uses a contention algorithm to provide access to all traffic. Ordinary asynchronous traffic directly uses DCE. The point coordination function (PCF) is a centralized MAC algorithm used to provide contention-free service. PCF is built on top of DCF and exploits features of DCF to assure access for its users. Let us consider these two sub-layers in turn.MAClayerFigure 14.5 IEEE 802.11 Protocol ArchitectureDistributed Coordination FunctionThe DCF sub-layer makes use of a simple CSMA (carrier sense multiple access) algorithm, which functions as follows. If a station has a MAC frame to transmit, it listens to the medium. If the medium is idle, the station may transmit; otherwise the station must wait until the current transmission is complete before transmitting. The DCF does not include a collision detection function (i.e. CSMA/CD) because collision detection is not practical on a wireless network. The dynamic range of the signals on the medium is very large, so that a transmitting station cannot effectively distinguish incoming weak signals from noise and the effects of its own transmission.To ensure the smooth and fair functioning of this algorithm, DCF includes a set of delays that amounts to a priority scheme. Let us start by considering a single delay known as an inter-frame space (IFS). In fact, there are three different IFS values, but the algorithm is best explained by initially ignoring this detail. Using an IFS, the rules for CSMA access are as follows (Figure 14.6):Figure 14.6 IEEE 802.11 Medium Access Control Logic1. A station with a frame to transmit senses the medium. If the medium is idle. It waits to see if the medium remains idle for a time equal to IFS. If so , the station may transmit immediately.2. If the medium is busy (either because the station initially finds the medium busy or because the medium becomes busy during the IFS idle time), the station defers transmission and continues to monitor the medium until the current transmission is over.3. Once the current transmission is over, the station delays another IFS. If the medium remains idle for this period, then the station backs off a random amount of time and again senses the medium. If the medium is still idle, the station may transmit. During the back-off time, if the medium becomes busy, the back-off timer is halted and resumes when the medium becomes idle.4. If the transmission is unsuccessful, which is determined by the absence of an acknowledgement, then it is assumed that a collision has occurred.To ensure that back-off maintains stability, a technique known as binary exponential back-off is used. A station will attempt to transmit repeatedly in the face of repeated collisions, but after each collision, the mean value of the random delay is doubled up to some maximum value. The binary exponential back-off provides a means of handling a heavy load. Repeated failed attempts to transmit result in longer and longer back-off times, which helps to smooth out the load. Without such a back-off, the following situation could occur. Two or more stations attempt to transmit at the same time, causing a collision. These stations then immediately attempt to retransmit, causing a new collision.The preceding scheme is refined for DCF to provide priority-based access by the simple expedient of using three values for IFS:●SIFS (short IFS):The shortest IFS, used for all immediate responseactions，as explained in the following discussion●PIFS (point coordination function IFS):A mid-length IFS, used by thecentralized controller in the PCF scheme when issuing polls●DIFS (distributed coordination function IFS): The longest IFS, used as aminimum delay for asynchronous frames contending for access Figure 14.7a illustrates the use of these time values. Consider first the SIFS.Any station using SIFS to determine transmission opportunity has, in effect, the highest priority, because it will always gain access in preference to a stationwaiting an amount of time equal to PIFS or DIFS. The SIFS is used in the following circumstances：●Acknowledgment (ACK): When a station receives a frame addressed onlyto itself (not multicast or broadcast) it responds with an ACK frame after, waiting on1y for an SIFS gap. This has two desirable effects. First, because collision detection IS not used, the likelihood of collisions is greater than with CSMA/CD, and the MAC-level ACK provides for efficient collision recovery. Second, the SIFS can be used to provide efficient delivery of an LLC protocol data unit (PDU) that requires multiple MAC frames. In this case, the following scenario occurs. A station with a multi-frame LLC PDU to transmit sends out the MAC frames one at a time. Each frame is acknowledged after SIFS by the recipient. When the source receives an ACK, it immediately (after SIFS) sends the next frame in the sequence. The result is that once a station has contended for the channel, it will maintain control of the channel until it has sent all of the fragments of an LLC PDU.●Clear to Send (CTS):A station can ensure that its data frame will getthrough by first issuing a small. Request to Send (RTS) frame. The station to which this frame is addressed should immediately respond with a CTS frame if it is ready to receive. All other stations receive the RTS and defer using the medium.●Poll response: This is explained in the following discussion of PCF.longer than DIFS(a) Basic access methoddefers(b) PCF super-frame constructionFigure 14.7 IEEE 802.11 MAC TimingThe next longest IFS interval is the: PIFS. This is used by the centralized controller in issuing polls and takes precedence over normal contention traffic. However, those frames transmitted using SIFS have precedence over a PCF poll.Finally, the DIFS interval is used for all ordinary asynchronous traffic.Point C00rdination Function PCF is an alternative access method implemented on top of the DCE. The operation consists of polling by the centralized polling master (point coordinator). The point coordinator makes use of PIFS when issuing polls. Because PI FS is smaller than DIFS, the point coordinator call seize the medium and lock out all asynchronous traffic while it issues polls and receives responses.As an extreme, consider the following possible scenario. A wireless network is configured so that a number of stations with time, sensitive traffic are controlled by the point coordinator while remaining traffic contends for access using CSMA. The point coordinator could issue polls in a round—robin fashion to all stations configured for polling. When a poll is issued, the polled station may respond using SIFS. If the point coordinator receives a response, it issues another poll using PIFS. If no response is received during the expected turnaround time, the coordinator issues a poll．If the discipline of the preceding paragraph were implemented, the point coordinator would lock out all asynchronous traffic by repeatedly issuing polls. To prevent this, an interval known as the super-frame is defined. During the first part of this interval, the point coordinator issues polls in a round, robin fashion to all stations configured for polling. The point coordinator then idles for the remainder of the super-frame, allowing a contention period for asynchronous access.Figure l4.7 b illustrates the use of the super-frame. At the beginning of a super-frame, the point coordinator may optionally seize control and issues polls for a give period of time. This interval varies because of the variable frame size issued by responding stations. The remainder of the super-frame is available for contention based access. At the end of the super-frame interval, the point coordinator contends for access to the medium using PIFS. If the medium is idle. the point coordinator gains immediate access and a full super-frame period follows. However, the medium may be busy at the end of a super-frame. In this case, the point coordinator must wait until the medium is idle to gain access: this result in a foreshortened super-frame period for the next cycle.OctetsFC=frame control SC=sequence controlD/I=duration/connection ID FCS=frame check sequence（a ） MAC frameBitsDS=distribution systemMD=more data MF=more fragmentsW=wired equivalent privacy RT=retryO=orderPM=power management (b) Frame control filedFigure 14.8 IEEE 802.11 MAC Frame FormatMAC FrameFigure 14.8a shows the 802.11 frame format when no security features are used. This general format is used for all data and control frames, but not all fields are used in all contexts. The fields are as follows:● Frame Control: Indicates the type of frame and provides contr01information, as explained presently.● Duration/Connection ID: If used as a duration field, indicates the time(in-microseconds) the channel will be allocated for successful transmission of a MAC frame. In some control frames, this field contains an association, or connection, identifier.●Addresses: The number and meaning of the 48-bit address fields dependon context. The transmitter address and receiver address are the MAC addresses of stations joined to the BSS that are transmitting and receiving frames over the wireless LAN. The service set ID (SSID) identifies the wireless LAN over which a frame is transmitted. For an IBSS, the SSID isa random number generated at the time the network is formed. For awireless LAN that is part of a larger configuration the SSID identifies the BSS over which the frame is transmitted: specifically, the SSID is the MAC-level address of the AP for this BSS (Figure 14.4). Finally the source address and destination address are the MAC addresses of stations, wireless or otherwise, that are the ultimate source and destination of this frame. The source address may be identical to the transmitter address and the destination address may be identical to the receiver address.●Sequence Control: Contains a 4-bit fragment number subfield used forfragmentation and reassembly, and a l2-bit sequence number used to number frames sent between a given transmitter and receiver.●Frame Body: Contains an MSDU or a fragment of an MSDU. The MSDUis a LLC protocol data unit or MAC control information.●Frame Check Sequence: A 32-bit cyclic redundancy check. The framecontrol filed, shown in Figure 14.8b, consists of the following fields.●Protocol Version: 802.11 version, current version 0.●Type: Identifies the frame as control, management, or data.●Subtype: Further identifies the function of frame. Table 14.4 defines thevalid combinations of type and subtype.●To DS: The MAC coordination sets this bit to 1 in a frame destined to thedistribution system.●From DS: The MAC coordination sets this bit to 1 in a frame leaving thedistribution system.●More Fragments: Set to 1 if more fragments follow this one.●Retry: Set to 1 if this is a retransmission of a previous frame.●Power Management: Set to]if the transmitting station is in a sleep mode.●More Data: Indicates that a station has additional data to send. Each blockof data may be sent as one frame or a group of fragments in multiple frames.●WEP：Set to 1 if the optional wired equivalent protocol is implemented.WEP is used in the exchange of encryption keys for secure data exchange.This bit also is set if the newer WPA security mechanism is employed, as described in Section 14.6.●Order：Set to 1 in any data frame sent using the Strictly Ordered service,which tells the receiving station that frames must be processed in order. We now look at the various MAC frame types.Control Frames Control frames assist in the reliable delivery of data frames. There are six control frame subtypes:●Power Save-Poll (PS-Poll): This frame is sent by any station to the stationthat includes the AP (access point). Its purpose is to request that the AP transmit a frame that has been buffered for this station while the station was in power saving mode.●Request to Send (RTS):This is the first frame in the four-way frameexchange discussed under the subsection on reliable data delivery at the beginning of Section 14.3.The station sending this message is alerting a potential destination, and all other stations within reception range, that it intends to send a data frame to that destination.●Clear to Send (CTS): This is the second frame in the four-way exchange.It is sent by the destination station to the source station to grant permission to send a data frame.●Acknowledgment:Provides an acknowledgment from the destination tothe source that the immediately preceding data, management, or PS-Poll frame was received correctly.●Contention-Free (CF)-End: Announces the end of a contention-freeperiod that is part of the point coordination function.●CF-End+CF-Ack:Acknowledges the CF-End. This frame ends thecontention-free period and releases stations from the restrictions associated with that period.Data Frames There are eight data frame subtypes, organized into two groups. The first four subtypes define frames that carry upper-level data from the source station to the destination station. The four data-carrying frames are as follows: ●Data: This is the simplest data frame. It may be used in both a contentionperiod and a contention-free period.●Data+CF-Ack: May only be sent during a contention-free period. Inaddition to carrying data, this frame acknowledges previously received data.●Data+CF-Poll: Used by a point coordinator to deliver data to a mobilestation and also to request that the mobile station send a data frame that it may have buffered.●Data+CF-Ack+CF-Poll: Combines the functions of the Data+CF-Ack andData+CF-Poll into a single frame.The remaining four subtypes of data frames do not in fact carry any user data. The Null Function data frame carries no data, polls, or acknowledgments. It is used only to carry the power management bit in the frame control field to the AP, to indicate that the station is changing to a low-power operating state. The remaining three frames (CF-Ack, CF-Poll,CF-Ack+CF-Poll) have the same functionality as the corresponding data frame subtypes in the preceding list (Data+CF-Ack, Data+CF-Poll, Data+CF-Ack+CF-Poll) but withotit the data. Management FramesManagement frames are used to manage communications between stations and APs. The following subtypes are included:●Association Request：Sent by a station to an AP to request an association,with this BSS. This frame includes capability information, such as whether encryption is to be used and whether this station is pollable.●Association Response:Returned by the AP to the station to indicatewhether it is accepting this association request.●Reassociation Request: Sent by a station when it moves from one BSS toanother and needs to make an association with tire AP in the new BSS. The station uses reassociation rather than simply association so that the new AP knows to negotiate with the old AP for the forwarding of data frames.●Reassociation Response:Returned by the AP to the station to indicatewhether it is accepting this reassociation request.●Probe Request: Used by a station to obtain information from anotherstation or AP. This frame is used to locate an IEEE 802.11 BSS.●Probe Response: Response to a probe request.●Beacon: Transmitted periodically to allow mobile stations to locate andidentify a BSS.●Announcement Traffic Indication Message: Sent by a mobile station toalert other mobile stations that may have been in low power mode that this station has frames buffered and waiting to be delivered to the station addressed in this frame.●Dissociation: Used by a station to terminate an association.●Authentication：Multiple authentication frames are used in an exchange toauthenticate one station to another.●Deauthentication:Sent by a station to another station or AP to indicatethat it is terminating secure communications.IEEE802.11 媒体接入控制IEEE 802．11 MAC层覆盖了三个功能区：可靠的数据传送、接入控制以及安全。
计算机专业外文翻译-----无线局域网技术
WIRELESS LANIn just the past few years, wireless LANs have come to occupy a significant niche in the local area network market. Increasingly, organizations are finding that wireless LANs are an indispensable adjunct to traditional wired LANs, as they satisfy requirements for mobility, relocation, ad hoc networking, and coverage of locationsdifficult to wire. As the name suggests, a wireless LAN is one that makes use of a wireless transmission medium. Until relatively recently, wireless LANs were little used; the reasons for this included high prices, low data rates, occupational safety concerns, and licensing requirements. As these problems have been addressed, the popularity of wireless LANs has grown rapidly.In this section, we first look at the requirements for and advantages of wireless LANs, and then preview the key approaches to wireless LAN implementation.Wireless LANs ApplicationsThere are four application areas for wireless LANs: LAN extension, crossbuilding interconnect, nomadic access, and ad hoc networks. Let us consider each of these in turn.LAN ExtensionEarly wireless LAN products, introduced in the late 1980s, were marketed as substitutes for traditional wired LANs. A wireless LAN saves the cost of the installation of LAN cabling and eases the task of relocation and other modifications to network structure. However, this motivation for wireless LANs was overtaken by events. First, as awareness of the need for LAN became greater, architects designed new buildings to include extensive prewiring for data applications. Second, with advances in data transmission technology, there has been an increasing reliance on twisted pair cabling for LANs and, in particular, Category 3 unshielded twisted pair. Most older building are already wired with an abundance of Category 3 cable. Thus, the use of a wireless LAN to replace wired LANs has not happened to any great extent.However, in a number of environments, there is a role for the wireless LAN as an alternative to a wired LAN. Examples include buildings with large open areas, such as manufacturing plants, stock exchange trading floors, and warehouses; historical buildings with insufficient twisted pair and in which drilling holes for new wiring is prohibited; and small offices where installation and maintenance of wired LANs is not economical. In all of these cases, a wireless LAN provides an effective and more attractive alternative. In most of these cases, an organization will also have a wired LAN to support servers and some stationary workstations. For example, a manufacturing facility typically has an office area that is separate from the factory floor but which must be linked to it for networking purposes. Therefore, typically, a wireless LAN will be linked into a wired LAN on the same premises. Thus, this application area is referred to as LAN extension.Cross-Building InterconnectAnother use of wireless LAN technology is to connect LANs in nearby buildings, be they wired or wireless LANs. In this case, a point-to-point wireless link is used between two buildings. The devices so connected are typically bridges or routers. This single point-to-point link is not a LAN per se, but it is usual to include this application under the heading of wireless LAN.Nomadic AccessNomadic access provides a wireless link between a LAN hub and a mobile data terminal equipped with an antenna, such as a laptop computer or notepad computer. One example of the utility of such a connection is to enable an employee returning from a trip to transfer data from a personalportable computer to a server in the office. Nomadic access is also useful in an extended environment such as a campus or a business operating out of a cluster of buildings. In both of these cases, users may move around with their portable computers and may wish access to the servers on a wired LAN from various locations.Ad Hoc NetworkingAn ad hoc network is a peer-to-peer network (no centralized server) set up temporarily to meet some immediate need. For example, a group of employees, each with a laptop or palmtop computer, may convene in a conference room for a business or classroom meeting. The employees link their computers in a temporary network just for the duration of the meeting.Wireless LAN RequirementsA wireless LAN must meet the same sort of requirements typical of any LAN, including high capacity, ability to cover short distances, full connectivity among attached stations, and broadcast capability. In addition, there are a number of requirements specific to the wireless LAN environment. The following are among the most important requirements for wireless LANs: Throughput. The medium access control protocol should make as efficient use as possible of the wireless medium to maximize capacity.Number of nodes. Wireless LANs may need to support hundreds of nodes across multiple cells. Connection to backbone LAN. In most cases, interconnection with stations on a wired backbone LAN is required. For infrastructure wireless LANs, this is easily accomplished through the use of control modules that connect to both types of LANs. There may also need to be accommodation for mobile users and ad hoc wireless networks.Service area. A typical coverage area for a wireless LAN may be up to a 300 to 1000 foot diameter.Battery power consumption. Mobile workers use battery-powered workstations that need to have a long battery life when used with wireless adapters. This suggests that a MAC protocol that requires mobile nodes to constantlymonitor access points or to engage in frequent handshakes with a base stationis inappropriate.Transmission robustness and security. Unless properly designed, a wireless LAN may be interference-prone and easily eavesdropped upon. The design of a wireless LAN must permit reliable transmission even in a noisy environment and should provide some level of security from eavesdropping.Collocated network operation. As wireless LANs become more popular, it is quite likely for two of them to operate in the same area or in some area where interference between the LANs is possible. Such interference may thwart the normal operation of a MAC algorithm and may allow unauthorized access to a particular LAN.License-free operation. Users would prefer to buy and operate wireless LAN products without having to secure a license for the frequency band used by the LAN.HandoWroaming. The MAC protocol used in the wireless LAN should enable mobile stations to move from one cell to another.Dynamic configuration. The MAC addressing and network management aspects of the LAN should permit dynamic and automated addition, deletion, and relocation of end systems without disruption to other users.Physical Medium SpecificationThree physical media are defined in the current 802.11 standard:Infrared at 1 Mbps and 2 Mbps operating at a wavelength between 850 and 950 nm.Direct-sequence spread spectrum operating in the 2.4-GHz ISM band. Up to 7 channels, each with a data rate of 1 Mbps or 2 Mbps, can be used.Frequency-hopping spread spectrum operating in the 2.4-GHz ISM band. The details of this option are for further study.Wireless LAN TechnologyWireless LANs are generally categorized according to the transmission techniquethat is used. All current wireless LAN products fall into one of the following categories:Infrared (IR) LANs. An individual cell of an IR LAN is limited to a single room, as infrared light does not penetrate opaque walls.Spread Spectrum LANs. This type of LAN makes use of spread spectrum transmission technology. In most cases, these LANs operate in the ISM (Industrial, Scientific, and Medical) bands, so that no FCC licensing is required for their use in the U.S.Narrowband Microwave. These LANs operate at microwave frequencies but do not use spread spectrum. Some of these products operate at frequencies that require FCC licensing, while others use one of the unlicensed ISM bands.A set of wireless LAN standards has been developed by the IEEE 802.11 committee. The terminology and some of the specific features of 802.11 are unique to this standard and are not reflected in all commercial products. However, it is useful to be familiar with the standard as its features are representative of required wireless LAN capabilities.The smallest building block of a wireless LAN is a basic service set (BSS), which consists of some number of stations executing the same MAC protocol and competing for access to the same shared medium. A basic service set may be isolated, or it may connect to a backbone distribution system through an access point. The access point functions as a bridge. The MAC protocol may be fully distributed or controlled by a central coordination function housed in the access point. The basic service set generally corresponds to what is referred to as a cell in the literature. An extended service set (ESS) consists of two or more basic service sets interconnected by a distribution system. Typically, the distribution system is a wired backbone LAN. The extended service set appears as a single logical LAN to the logical link control (LLC) level. The standard defines three types of stations, based on mobility:No-transition. A station of this type is either stationary or moves only within the direct communication range of the communicating stations of a single BSS.BSS-transition. This is defined as a station movement from one BSS to another BSS within the same ESS. In this case, delivery of data to the station requires that the addressing capability be able to recognize the new location of the station.ESS-transition. This is defined as a station movement from a BSS in one ESS to a BSS within another ESS. This case is supported only in the sense that the station can move. Maintenance of upper-layer connections supported by 802.11 cannot be guaranteed. In fact, disruption of service is likely to occur. details of this option are for further study.The 802.11 working group considered two types of proposals for a MAC algorithm: distributed-access protocols which, like CSMAICD, distributed the decision to transmit over all the nodes using a carrier-sense mechanism; and centralized access protocols, which involve regulation of transmission by a centralized decision maker. A distributed access protocol makes sense of an ad hoc network of peer workstations and may also be attractive in other wireless LANconfigurations that consist primarily of bursty traffic. A centralized access protocol is natural for configurations in which a number of wireless stations are interconnected with each other and with some sort of base station that attaches to a backbone wired LAN; it is especially useful if some of the data is time-sensitive or high priority.The end result of the 802.11 is a MAC algorithm called DFWMAC (distributed foundation wireless MAC) that provides a distributed access-control mechanism with an optional centralized control built on top of that. Figure 13.20 illustrates the architecture. The lower sublayer of the MAC layer is the distributed coordination function (DCF). DCF uses a contention algorithm to provide access to all traffic. Ordinary asynchronous traffic directly uses DCF. The point coordination function (PCF) is a centralized MAC algorithm used to provide contention-free service. PCF is built on top of DCF and exploits features of DCF to assure access for its users. Let us consider these two sublayers in turn.Distributed Coordination FunctionThe DCF sublayer makes use of a simple CSMA algorithm. If a station has a MAC frame to transmit, it listens to the medium. If the medium is idle, the station may transmit; otherwise, the station must wait until the current transmission is complete before transmitting. The DCF does not include a collision-detection function (i.e., CSMAICD) because collision detection is not practical on a wireless network. The dynamic range of the signals on the medium is very large, so that a transmitting station cannot effectively distinguish incoming weak signals from noise and the effects of its own transmission. To ensure the smooth and fair functioning of this algorithm, DCF includes a set of delays that amounts to a priority scheme. Let us start by considering a single delay known as an interframe space (IFS). In fact, there are three different IFS values, but the algorithm is best explained by initially ignoring this detail. Using an IFS, the rules for CSMA access are as follows:I. A station with a frame to transmit senses the medium. If the medium is idle, the station waits to see if the medium remains idle for a time equal to IFS, and, if this is so, the station may immediately transmit.2. If the medium is busy (either because the station initially finds the medium busy or because the medium becomes busy during the IFS idle time), the station defers transmission and continues to monitor the medium until the current transmission is over.3. Once the current transmission is over, the station delays another IFS. If the medium remains idle for this period, then the station backs off using a binary exponential backoff scheme and again senses the medium. If the medium is still idle, the station may transmit.Point Coordination FunctionPCF is an alternative access method implemented on top of the DCF. The operation consists of polling with the centralized polling master (point coordinator). The point coordinator makes use of PIFS when issuing polls. Because PIFS is smaller than DIFS, the point coordinator can seize the medium and lock out all asynchronous traffic while it issues polls and receives responses.As an extreme, consider the following possible scenario. A wireless network is configured so that a number of stations with time-sensitive traffic are controlled by the point coordinator while remaining traffic, using CSMA, contends for access.The point coordinator could issue polls in a round-robin fashion to all stations configured for polling. When a poll is issued, the polled station may respond using SIFS. If the point coordinator receives a response, it issues another poll using PIFS. If no response is received during theexpected turnaround time, the coordinator issues a poll. If the discipline of the preceding paragraph were implemented, the point coordinator would lock out all asynchronous traffic by repeatedly issuing polls. To prevent this situation, an interval known as the superframe is defined. During the first part of this interval, the point coordinator issues polls in a round-robin fashion to all stations configured for polling. The point coordinator then idles for the remainder of the superframe, allowing a contention period for asynchronous access.At the beginning of a superframe, the point coordinator may optionally seize control and issue polls fora give period of time. This interval varies because of the variable frame size issued by responding stations. The remainder of the superframe is available for contention-based access. At the end of the superframe interval, the point coordinator contends for access to the medium using PIFS. If the medium is idle, the point coordinator gains immediate access, and a full superframe period follows. However, the medium may be busy at the end of a superframe. In this case, the point coordinator must wait until the medium is idle to gain access; this results in a foreshortened superframe period for the next cycle.无线局域网技术最近几年，无线局域网开始在市场中独霸一方。
无线局域网是什么意思
无线局域网是什么意思无线局域网是什么意思你知道吗?无线局域网是用无线通信技术将终端设备互联起来，构成可以互相通信和实现资源共享的局域网络体系。
一起来看看无线局域网是什么意思，欢迎查阅!无线局域网是什么无线局域网英文名称：wireless LAN WLAN，与我们一般采用交换机或路由器组建的局域网络类似，只是采用的是无线技术，它利用射频(Radio Frequency RF)的技术，取代旧式碍手碍脚的双绞铜线(Coaxial)所构成的局域网络，使得无线局域网络能利用简单的存取架构让用户透过它，达到的理想境界。
猜你喜欢：无线路由器传输速度150M或300M是什么意思?无线局域网设备示意图无线局域网一、网络组建篇一个无线局域网可当作有线局域网的扩展来使用，也可以独立作为有线局域网的替代设施，因此无线局域网提供了很强的组网灵活性。
虽然这样，但在网络的组建中仍有不少问题需要考虑，总结起来，有以下方面：1. 设备选购早准备关于设备的选购方面，笔者一直认为注重产品的一致性比较重要，也就是说选择同一厂商、同一速率的产品，这样可以获得最好的兼容性与稳定的速度。
大家注意看产品包装说明，支持802.11b的产品只支持到11M的无线速度，显得稍慢但价格非常实惠。
目前支持802.11g的产品多数是54M产品，也是目前的主流速度，其技术支持以及相关资料也很齐全，是选购的重点参考;而802.11g+一般都为108支持的速率为108M，这是未来一年内的主流传输速率，如果你的无线网络对速度有一定的要求，选购这类产品比较合适，其实价格也不是想象中的那么贵，无线设备麻，肯定要比有线设备稍贵一些。
2. 拓扑结构不能乱。
网络结构已平面拓扑为基础，在任何网络搭建之初，都应该考虑实际网络环境。
wifi上网是什么意思有线无线共存环境：如果已经存在一个有线网络，要在此基础上搭建无线网络，那么应综合考虑有线与无线的设备兼容，本着用最少的投资办最多的事的原则进行;一般家庭有线网络都是ADSL Modem+宽带路由器的结构，最简单的办法就是添加一台无线AP用作无线信号中转，然后在计算机中配置一块无线网卡即可;由于无线AP并不具有虚拟拨号功能，因此应将其与宽带路由器相连，近而用宽带路由器来统一管理有线与无线网络，并实现两类网络的互访(不过这类管理配置起来较麻烦)。
计算机毕业论文外文文献翻译中英文：IEEE802.11媒体接入控制
计算机毕业论⽂外⽂⽂献翻译中英⽂：IEEE802.11媒体接⼊控制英⽂资料与中⽂翻译IEEE 802.11 MEDIUM ACCESS CONTROLThe IEEE 802.11 MAC layer covers three functional areas：reliable data delivery, medium access control, and security. This section covers the first two topics.Reliable Data DeliveryAs with any wireless network, a wireless LAN using the IEEE 802.11 physical and MAC layers is subject to considerable unreliability. Noise, interference, and other propagation effects result in the loss of a significant number of frames. Even with error-correction codes, a number of MAC frames may not successfully be received. This situation can be dealt with by reliability mechanisms at a higher layer. such as TCP. However, timers used for retransmission at higher layers are typically on the order of seconds. It is therefore more efficient to deal with errors at the MAC level. For this purpose, IEEE 802.11 includes a frame exchange protocol. When a station receives a data frame from another station. It returns an acknowledgment (ACK) frame to the source station. This exchange is treated as an atomic unit, not to be interrupted by a transmission from any other station. If the source does not receive an ACK within a short period of time, either because its data frame was damaged or because the returning ACK was damaged, the source retransmits the frame.Thus, the basic data transfer mechanism in IEEE802.11 involves an exchange of two frames. To further enhance reliability, a four-frame exchange may be used. In this scheme, a source first issues a request to send (RTS) frame to the destination. The destination then responds with a clear to send (CTS). After receiving the CTS, the source transmits the data frame, and the destination responds with an ACK. The RTS alerts all stations that are within reception range of the source that an exchange is under way; these stations refrain from transmission in order to avoid a collision between two frames transmitted at the same time. Similarly, the CTS alerts all stations that are within reception range of the destination that an exchange is under way. The RTS/CTS portion of the exchange is a required function of the MAC but may be disabled.Medium Access ControlThe 802.11 working group considered two types of proposals for a MAC algorithm: distributed access protocols, which, like Ethernet, distribute the decision to transmit over all the nodes using a carrier-sense mechanism; and centralized access protocols, which involve regulation of transmission by a centralized decision maker. A distributed access protocol makes sense for an ad hoc network of peer workstations (typically an IBSS) and may also be attractive in other wireless LAN configurations that consist primarily of burst traffic. A centralized access protocol is natural for configurations in which a umber of wireless stations are interconnected with each other and some sort of base station that attaches to a backbone wired LAN: it is especially useful if some of the data is time sensitive or high priority.The end result for 802.11 is a MAC algorithm called DFWMAC (distributed foundation wireless MAC) that provides a distributed access control mechanism with an optional centralized control built on top of that. Figure 14.5 illustrates the architecture. The lower sub-layer of the MAC layer is the distributed coordination function (DCF). DCF uses a contention algorithm to provide access to all traffic. Ordinary asynchronous traffic directly uses DCE. The point coordination function (PCF) is a centralized MAC algorithm used to provide contention-free service. PCF is built on top of DCF and exploits features of DCF to assure access for its users. Let us consider these two sub-layers in turn.MAClayerFigure 14.5 IEEE 802.11 Protocol ArchitectureDistributed Coordination FunctionThe DCF sub-layer makes use of a simple CSMA (carrier sense multiple access) algorithm, which functions as follows. If a station has a MAC frame to transmit, it listens to the medium. If the medium is idle, the station may transmit; otherwise the station must wait until the current transmission is complete before transmitting. The DCF does not include a collision detection function (i.e. CSMA/CD) because collision detection is not practical on a wireless network. The dynamic range ofthe signals on the medium is very large, so that a transmitting station cannot effectively distinguish incoming weak signals from noise and the effects of its own transmission.To ensure the smooth and fair functioning of this algorithm, DCF includes a set of delays that amounts to a priority scheme. Let us start by considering a single delay known as an inter-frame space (IFS). In fact, there are three different IFS values, but the algorithm is best explained by initially ignoring this detail. Using an IFS, the rules for CSMA access are as follows (Figure 14.6):Figure 14.6 IEEE 802.11 Medium Access Control Logic1. A station with a frame to transmit senses the medium. If the medium is idle. It waits to see if the medium remains idle for a time equal to IFS. If so , the station may transmit immediately.2. If the medium is busy (either because the station initially finds the medium busy or because the medium becomes busy during the IFS idle time), the station defers transmission and continues to monitor the medium until the current transmission is over.3. Once the current transmission is over, the station delays another IFS. If the medium remains idle for this period, then the station backs off a random amount of time and again senses the medium. If the medium is still idle, the station may transmit. During the back-off time, if the medium becomes busy, the back-off timer is halted and resumes when the medium becomes idle.4. If the transmission is unsuccessful, which is determined by the absence of an acknowledgement, then it is assumed that a collision has occurred.To ensure that back-off maintains stability, a technique known as binary exponential back-off is used. A station will attempt to transmit repeatedly in the face of repeated collisions, but after each collision, the mean value of the random delay is doubled up to some maximum value. The binary exponential back-off provides a means of handling a heavy load. Repeated failed attempts to transmit result in longer and longer back-off times, which helps to smooth out the load. Without such a back-off, the following situation could occur. Two or more stations attempt to transmit at the same time, causing a collision. These stations then immediately attempt to retransmit, causing a new collision.The preceding scheme is refined for DCF to provide priority-based access by the simple expedient of using three values for IFS:●SIFS (short IFS):The shortest IFS, used for all immediate responseactions，as explained in the following discussion●PIFS (point coordination function IFS):A mid-length IFS, used by thecentralized controller in the PCF scheme when issuing polls●DIFS (distributed coordination function IFS): The longest IFS, used as aminimum delay for asynchronous frames contending for access Figure 14.7a illustrates the use of these time values. Consider first the SIFS.Any station using SIFS to determine transmission opportunity has, in effect, the highest priority, because it will always gain access in preference to a stationwaiting an amount of time equal to PIFS or DIFS. The SIFS is used in the following circumstances：●Acknowledgment (ACK): When a station receives a frame addressed onlyto itself (not multicast or broadcast) it responds with an ACK frame after, waiting on1y for an SIFS gap. This has two desirable effects. First, because collision detection IS not used, the likelihood of collisions is greater than with CSMA/CD, and the MAC-level ACK provides for efficient collision recovery. Second, the SIFS can be used to provide efficient delivery of an LLC protocol data unit (PDU) that requires multiple MAC frames. In this case, the following scenario occurs. A station with a multi-frame LLC PDU to transmit sends out the MAC frames one at a time. Each frame is acknowledged after SIFS by the recipient. When the source receives an ACK, it immediately (after SIFS) sends the next frame in the sequence. The result is that once a station has contended for the channel, it will maintain control of the channel until it has sent all of the fragments of an LLC PDU.●Clear to Send (CTS):A station can ensure that its data frame will getthrough by first issuing a small. Request to Send (RTS) frame. The station to which this frame is addressed should immediately respond with a CTS frame if it is ready to receive. All other stations receive the RTS and defer using the medium.●Poll response: This is explained in the following discussion of PCF.longer than DIFS(a) Basic access methoddefers(b) PCF super-frame constructionFigure 14.7 IEEE 802.11 MAC TimingThe next longest IFS interval is the: PIFS. This is used by the centralized controller in issuing polls and takes precedence over normal contention traffic. However, those frames transmitted using SIFS have precedence over a PCF poll.Finally, the DIFS interval is used for all ordinary asynchronous traffic.Point C00rdination Function PCF is an alternative access method implemented on top of the DCE. The operation consists of polling by the centralized polling master (point coordinator). The point coordinator makes use of PIFS when issuing polls. Because PI FS is smaller than DIFS, the point coordinator call seize the medium and lock out all asynchronous traffic while it issues polls and receives responses.As an extreme, consider the following possible scenario. A wireless network is configured so that a number of stations with time, sensitive traffic are controlled by the point coordinator while remaining traffic contends for access using CSMA. The point coordinator could issue polls in a round—robin fashion to all stations configured for polling. When a poll is issued, the polled station may respond using SIFS. If the point coordinator receives a response, it issues another poll using PIFS. If no response is received during the expected turnaround time, the coordinator issues a poll．If the discipline of the preceding paragraph were implemented, the point coordinator would lock out all asynchronous traffic by repeatedly issuing polls. To prevent this, an interval known as the super-frame is defined. During the first part of this interval, the point coordinator issues polls in a round, robin fashion to all stations configured for polling. The point coordinator then idles for the remainder of the super-frame, allowing a contention period for asynchronous access.Figure l4.7 b illustrates the use of the super-frame. At the beginning of a super-frame, the point coordinator may optionally seize control and issues polls for a give period of time. This interval varies because of the variable frame size issued by responding stations. The remainder of the super-frame is available for contention based access. At the end of the super-frame interval, the point coordinator contends for access to the medium using PIFS. If the medium is idle. the point coordinator gains immediate access and a full super-frame period follows. However, the medium may be busy at the end of a super-frame. In this case, the point coordinator must wait until the medium is idle to gain access: this result in a foreshortened super-frame period for the next cycle.OctetsFC=frame control SC=sequence controlD/I=duration/connection ID FCS=frame check sequence（a ） MAC frameBitsDS=distribution systemMD=more data MF=more fragmentsW=wired equivalent privacy RT=retryO=orderPM=power management (b) Frame control filedFigure 14.8 IEEE 802.11 MAC Frame FormatMAC FrameFigure 14.8a shows the 802.11 frame format when no security features are used. This general format is used for all data and control frames, but not all fields are used in all contexts. The fields are as follows:● Frame Control: Indicates the type of frame and provides contr01information, as explained presently.● Duration/Connection ID: If used as a duration field, indicates the time(in-microseconds) the channel will be allocated for successful transmission of a MAC frame. In some control frames, this field contains an association, or connection, identifier.●Addresses: The number and meaning of the 48-bit address fields dependon context. The transmitter address and receiver address are the MAC addresses of stations joined to the BSS that are transmitting and receiving frames over the wireless LAN. The service set ID (SSID) identifies the wireless LAN over which a frame is transmitted. For an IBSS, the SSID isa random number generated at the time the network is formed. For awireless LAN that is part of a larger configuration the SSID identifies the BSS over which the frame is transmitted: specifically, the SSID is the MAC-level address of the AP for this BSS (Figure 14.4). Finally the source address and destination address are the MAC addresses of stations, wireless or otherwise, that are the ultimate source and destination of this frame. The source address may be identical to the transmitter address and the destination address may be identical to the receiver address.●Sequence Control: Contains a 4-bit fragment number subfield used forfragmentation and reassembly, and a l2-bit sequence number used to number frames sent between a given transmitter and receiver.●Frame Body: Contains an MSDU or a fragment of an MSDU. The MSDUis a LLC protocol data unit or MAC control information.●Frame Check Sequence: A 32-bit cyclic redundancy check. The framecontrol filed, shown in Figure 14.8b, consists of the following fields.●Protocol Version: 802.11 version, current version 0.●Type: Identifies the frame as control, management, or data.●Subtype: Further identifies the function of frame. Table 14.4 defines thevalid combinations of type and subtype.●To DS: The MAC coordination sets this bit to 1 in a frame destined to thedistribution system.●From DS: The MAC coordination sets this bit to 1 in a frame leaving thedistribution system.●More Fragments: Set to 1 if more fragments follow this one.●Retry: Set to 1 if this is a retransmission of a previous frame.●Power Management: Set to]if the transmitting station is in a sleep mode.●More Data: Indicates that a station has additional data to send. Each blockof data may be sent as one frame or a group of fragments in multiple frames.●WEP：Set to 1 if the optional wired equivalent protocol is implemented.WEP is used in the exchange of encryption keys for secure data exchange.This bit also is set if the newer WPA security mechanism is employed, as described in Section 14.6.●Order：Set to 1 in any data frame sent using the Strictly Ordered service,which tells the receiving station that frames must be processed in order. We now look at the various MAC frame types. Control Frames Control frames assist in the reliable delivery of data frames. There are six control frame subtypes:●Power Save-Poll (PS-Poll): This frame is sent by any station to the stationthat includes the AP (access point). Its purpose is to request that the AP transmit a frame that has been buffered for this station while the station was in power saving mode.●Request to Send (RTS):This is the first frame in the four-way frameexchange discussed under the subsection on reliable data delivery at the beginning of Section 14.3.The station sending this message is alerting a potential destination, and all other stations within reception range, that it intends to send a data frame to that destination.●Clear to Send (CTS): This is the second frame in the four-way exchange.It is sent by the destination station to the source station to grant permission to send a data frame.●Acknowledgment:Provides an acknowledgment from the destination tothe source that the immediately preceding data, management, or PS-Poll frame was received correctly.●Contention-Free (CF)-End: Announces the end of a contention-freeperiod that is part of the point coordination function.●CF-End+CF-Ack:Acknowledges the CF-End. This frame ends thecontention-free period and releases stations from the restrictions associated with that period.Data Frames There are eight data frame subtypes, organized into two groups. The first four subtypes define frames that carry upper-level data from the source station to the destination station. The four data-carrying frames are as follows: ●Data: This is the simplest data frame. It may be used in both a contentionperiod and a contention-free period.●Data+CF-Ack: May only be sent during a contention-free period. Inaddition to carrying data, this frame acknowledges previously received data.●Data+CF-Poll: Used by a point coordinator to deliver data to a mobilestation and also to request that the mobile station send a data frame that it may have buffered.●Data+CF-Ack+CF-Poll: Combines the functions of the Data+CF-Ack andData+CF-Poll into a single frame.The remaining four subtypes of data frames do not in fact carry any user data. The Null Function data frame carries no data, polls, or acknowledgments. It is used only to carry the power management bit in the frame control field to the AP, to indicate that the station is changing to a low-power operating state. The remaining three frames (CF-Ack, CF-Poll,CF-Ack+CF-Poll) have the same functionality as the corresponding data frame subtypes in the preceding list (Data+CF-Ack, Data+CF-Poll,Data+CF-Ack+CF-Poll) but withotit the data. Management FramesManagement frames are used to manage communications between stations and APs. The following subtypes are included:●Association Request：Sent by a station to an AP to request an association,with this BSS. This frame includes capability information, such as whether encryption is to be used and whether this station is pollable.●Association Response:Returned by the AP to the station to indicatewhether it is accepting this association request.●Reassociation Request: Sent by a station when it moves from one BSS toanother and needs to make an association with tire AP in the new BSS. The station uses reassociation rather than simply association so that the new AP knows to negotiate with the old AP for the forwarding of data frames.●Reassociation Response:Returned by the AP to the station to indicatewhether it is accepting this reassociation request.●Probe Request: Used by a station to obtain information from anotherstation or AP. This frame is used to locate an IEEE 802.11 BSS.●Probe Response: Response to a probe request.●Beacon: Transmitted periodically to allow mobile stations to locate andidentify a BSS.●Announcement Traffic Indication Message: Sent by a mobile station toalert other mobile stations that may have been in low power mode that this station has frames buffered and waiting to be delivered to the station addressed in this frame.●Dissociation: Used by a station to terminate an association.●Authentication：Multiple authentication frames are used in an exchange toauthenticate one station to another.●Deauthentication:Sent by a station to another station or AP to indicatethat it is terminating secure communications.IEEE802.11 媒体接⼊控制IEEE 802．11 MAC层覆盖了三个功能区：可靠的数据传送、接⼊控制以及安全。
网络工程局域网中英文对照外文翻译文献
中英文对照外文翻译(文档含英文原文和中文翻译)PUTER NETWORKSDATE COMMUNICATIONSThe end equipment which either generates the digital information for transmission or uses the received digital data can be computer ,printers ,keyboards, CRTs, and so on. This equipment generally manipulates digital information internally in word units—all the bits that make up a word in a particular piece of equipment are transferred in parallel. Digital data, when transmitted, are in serial form. Parallel transmission of an 8-bit word require eight pairs of transmission lines—not at all cost-effective. Data terminal (DTE) is a general phrase encompassing all of the circuitry necessary to perform parallel-to-serial and serial-to-parallel conversions for transmission and reception respectively and for data link management. The UART (Universal Asynchronous Receiver/Transmitter) and USART (Universal Asynchronous/Asynchronous Receiver/Transmitter) are the devices that perform the parallel-to-serial and serial-to-parallel conversions. The primary DTE includes a line control unit (LCU or LinCo) which controls the flow of information in a multipoint data link system. A station controller (STACO) is the corresponding that belonged to the subscriber in a data link system. Between the DTEs, starting with the modems, was communications equipment owned and maintained by Telco property.Data communications equipment (DCE) accepts the serial data stream from the DTE and converts it to some form of analog signal suitable for transmission on voice-grade lined. At the receive end, the DCE performs the reverse function of converting the received analog signal to a serial digital data stream. The simplest form of DCE is a modem (modulator/demodulator) or data set. At the transmit end, the modem can be considered a form of digital-to-analog converter, while at the receive end, it can considered a form of analog-to-digital converter. The most common of modulation by modems are frequency shift keying (FSK), phase shift keying (PSK), and quadrature amplitude modulation (QAM). This is a typically data transmission mode using the analog telephone lines. If you transmit data by digital channel (sometimes it is called “Digital T-carrier”), a pulse Code Modulation (PCM) equipment must be used. A microwave transmission system can also be used for the data communication. Finally, you can use the satellite communication system for data transmission.If the cables and signal levels used to interconnect the DTE and DCE were left unregulated, the variations generated would probably be proportional to the number of manufacturers. Electronics industries Association (EIA),an organization of manufactures with establishing the DTE and modem. This is a 25-pincable whose pins have designated functions and specified signal levels. The RS-232C is anticipated to be replaced by an update standard.2.ARCHITECTURE OF COMPUTER NETWORKSComputer network is a complex consisting of two or more conned computing units, it is used for the purpose of data communication and resource resource sharing. Design of a network and its logical structure should comply with a set of design principles, including the organization of functions and the description of data formats and procedure. This is the network architecture and so called as a set of layers and protocols, because the architecture is a layer-based.In the next two sections we will discuss two important network architectures, the OSI reference model and the TCP/IP reference model.1.The OSI Reference ModelThe OSI model is shown in Fig.14-2(minus the physical medium). This model is based on a proposal developed by the International Standards Organizations (OSI) as the first step toward international standardization of the protocols used in the various layers. The model is called the ISO OSI (Open System Interconnection) Reference Model because it deals with connecting open systems--that is, systems that are open for communication with other systems, We will usually just call it the OSI model for short.The OSI model has seven has seven layers. Note that the OSI model itself is not a network architecture because it does not specify the exact services and protocols to be used in each layer. It just tells what each layer should do. However , However, ISO has also produced standards for all the layers, although these are not part of the reference model itself. Each one has been published as a separate international standard.2.The TCP/IP Reference ModelThe TCP/IP reference model is an early transport protocol which was designed by the US Department of Defence (DOD) around in 1978. It is often claimed that it gave rise the OSI “connectionless”mode of operation. TCP/IP is still usedextensively and is called as a industrial standard of internet work in fact, TCP/IP has two parts: TCP and IP. TCP means it is on the transport layer and IP means it is on the network layer separately.1.There are two end-to-end protocols in the transport layer, one of which is TCP (Transmission Control Protocol) , another is UDP (User Datagram Protocol). TCP is a connection-oriented protocol that allows a byte stream originating on one machine to be delivered without error on any other machine in the internet. UDP is an unreliable, connectionless protocol for application that do not want TCP’s sequencing of flows control flow control and wish to provide their own.2.The network layer defines an official packet format and protocol called IP (Internet protocol). The job of the network layer is to deliver IP packets where they are supposed to go.The TCP/IP Reference Model is shown in Fig.14.3. On top of the transport layer is the application layer, It contains all the higher-level protocols. The early ones included virtual terminal (TELNET), file transfer (FTP), electronic mail (SMTP) and domain name service(DNS).3.WIDE AREA NETWORKA wide area network, or WAN, spans a large geographical area, often a country or continent . It contains a collection of machines intended for running user (i. e. , application) programs. We will follow traditional usage and call these machines hosts. By a communication subnet, or just subnet for short. The job of the subnet is to carry messages from host to host, just as the telephone system carries words from speaker to listener. By separating the pure communication aspects of the network (the subnet) from the application aspects (the hosts), the complete network design is greatly simplified. Relation between hosts and the subnet is shown in Fig.14-4.One of many methods that can be used to categorize wide area networks is with respect to the flow of information on a transmission facility. If we use this method to categorize wide area networks, we can group them into three basic types: circuit switched, leased line and packet switched.1.CIRCUIT SWITCHED NETWORKSThe most popular type of network and the one almost all readers use on a daily basis is a circuit switched network. The public switched telephone network, however,is not limited to the telephone company, By purchasing appropriate switching equipment, any organization can construct their own internal circuit switched network and, if desired, provide one or more interfaces to the public switched network to allow voice and data transmission to flow between the public network and their private internal network2．LEASED LINE NETWORKSThis is a dedicated network connected by leased lines. Leased line is a communications line reserved for the exclusive use of a leasing customer without inter-exchange switching arrangements. Leased or private lines are dedicated to the user. This advantage is that the terminal or computer is a always physically connected to the line. Very short response times are met with service.3.PACKET SWITCHING NETWORKSA packet network is constructed through the use of equipment that assembles and disassembles packets, equipment that routes packet, and transmission facilities used to route packets from the originator to the destination device. Some types of data terminal equipment (DTE) can create their own packets, while other types of DTE require the conversion of their protocol into packets through the use of a packet assembler / disassemble (PAD). Packets are routed through the network by packet switches. Packet switches examine the destination of packets as they flow through the network and transfer the packets onto trunks interconnecting switches based upon the packet destination destination and network activity.Many older pubic networks follow a standard called X.25. It was developed during 1970s by CCITT to provide an interface between public packet-switched network and their customers.CCITT Recommendation X.25 controls the access from a packet mode DTE, such as a terminal device or computer system capable of forming packets, to the DCE at a packet mode. CCITT Recommendation X.28 controls the interface between non-packet mode devices that cannot interface between the PAD and the host computer. CCITT Recommendation X.3 specifies the parameter settings on the PAD and X.75 specifies the interface between packet network.4.LOCAL AREA NETWORKLocal area data network , normally referred to simply as local area network or LANs, are used to interconnect distributed communities of computer-based DTEs located within a building or localized group of building. For example, a LAN may be used to interconnect workstations distributed around offices within a single building or a group of buildings such as a university campus. Alternatively, it may be complex. Since all the equipment is located within a single establishment, however, LANs are normally installed and maintained by the organization. Hence they are also referred to as private data networks.The main difference between a communication path established using a LAN and a connection made through a public data network is that a LAN normally offers much higher date transmission rates because of the relatively short physical separations involved. In the context of the ISO Reference Model for OSI, however, this difference manifests itself only at the lower network dependent layers. In many instances the higher protocol layers in the reference model are the same for both types of network.Before describing the structure and operation of the different types of LAN, it is perhaps helpful to first identify some of the selection issues that must be considered. It should be stressed that this is only a summary; there are also many possible links between the tips of the branches associated with the figure.1.TopologyMost wide area networks, such as the PSTN, use a mesh (sometimes referred to as a network) topology. With LANs, however, the limited physical separation of the subscriber DTEs allows simpler topologies to be used. The four topologies in common use are star, bus ,ring and hub.The most widespread topology for LANs designed to function as data communication subnetworks for the interconnection of local computer-based equipment is the hub topology, which is a variation a variation of the bus and ring. Sometimes it is called hub/tree topology.2.Transmission mediaTwisted pair, coaxial cable and optical fiber are the three main type of transmission medium used for LANs.3. Medium access control methodsTwo techniques have been adopted for use of the medium access control in the LANs. They are carrier-sense-multiple-access with collision detection (CSMA/CD), for bus network topologies, and control token, for use with either bus or ring networks.CSMA/CD is used to control multiple-access networks. Each on the network “listens” before attempting to send a message, waiting for the “traffic” to clear. If two stations try to sent their messages at exactly the same time, a “collision” is detected, and both stations are required to “step back” and try later.Control token is another way of controlling access to a shared transmission medium that is by the use of a control (permission) token. This token is passed form one DTE to another according to a defined set of rules understood and adhered to by all DTEs connected to the medium. ADTE may only transmit a frame when it is in possession of the token and, after it has transmitted the frame, it passed the token on to allow another DTE to access the transmission medium.1．计算机网络数据通信端设备可以是计算机、打印机、键盘、CRT等，它们可以产生要发送的数字信息，也可使用所接收的数字数据。
无线局域网外文翻译
AbstractThis paper focuses on the development of an energy efficent street lighting remote management system making use of low-rate wireless personal area networks and the Digital Addressable Lighting Interface (DALI) protocol to get a duplex communication, necessary for checking lamp parameters like lamp status, current level ,etc.Because of the fact that two thirds of the installed street lighting systems use old and inefficient technologies there exists a huge potential to renew the street lighting and save in the energy consumption. The proposed system uses DALI protocol in street lighting increasing the maximum number of slave devices (ballasts) that can be controlled with DALI-originally it can only have 64 ballasts. Some aspects regarding the lighting control protocol and the communication system are discussed, presenting experimental results obtained from several tests.IntroductionTwo thirds of the current installed street lighting systems still use very old and inefficient technologies, that is , there exists a huge potential to renew the existing street lighting and save in the energy consumption[1]. It is estimated that nearly the 5% of the energy used in lighting applications is consumed by the street lighting, being the most important energy regarding the energy usage in a city . New industrial approaches have been develop recently in order to achieve an efficient lighting, which can be summarized in improvements in lamps' technology and electronic ballasts, soft start systems, noiseless performance and lighting automatisms.Saving energy in street lighting can be achieved with two methods,by controlling the light duration or by dimming. There also exist remote management systems that allow the user to keep an individual remote control and monitorization of every single lamp. By making use of these systems the operator can monitor the main parameters of any light point from a central or mobile unit. The obtained data are ready for processing, allowing the reckoning of statistical consumption, lamp status, voltages, anomalies,ect,decreasing the mean time to repair. Another interesting parameter could be the arc voltage level, which can mean the change of a corrective or preventive maintenance to a predictive one, saving money in the maintenance cost.In order to have an optimum control, the remote management system should allow a duplex or half/duplex communication between the user and the ballast; otherwise we could not know the lighting status. The management system is implemented using a communication system and a lighting control protocol. The communication system can be wired,such as Ethernet, optical fiber and Power Line Carrier(PLC) or wireless. Among the last group we have GSM/GPRS, RF,WiFi,WiMAX,IEEE802.15.4 and ZigBee have brought about the boom of wireless sensor networks(WSNs).A comprehensive study of the state of the art of WSNs and both standards can be found in [2] and [3].A WSN consists of tiny sensor nodes, sink nodes, an information transport network and personal computers. Usually, WSN architecture consists of three layers, the physical layer, the MAC layer and the application layer. The IEEE802.15.4 standard deals with Low-Rate Wireless Personal Area Networks(LR-WPAN); its aim is to standardize the two lower layers of OSI protocol stack, i.e.physical layer and medium access control layer. It only considers star and peer-to-peer network topologies. On the other hand , ZigBee defines the upper layers, network and application layers, its main contribution is to provide the ability of forming cluster,tree and meshnetwork topologies to IEEE802.15.4 applicationsAs regards the lighting control protocol, it can be chosen between an open protocol,like TCP/IP , BACNet, DMX512,LONWorks,X-10, 0-10 V or DALI, or proprietary.DALI stands for Digital Addressable Lighting Interface, it was defined by annex E.4 of IEC 60929 as a digital signal controller for tubular fluorescent lamp ballasts' control interface and modified by IEC 62386, which also integrates other application of DALI apart from lighting and extends the kind of lamp to high intensity discharge (HID), halogens, incandescent, LEDs,etc.This paper focuses on developing a street lighting management system by making use of wireless sensor networks and DALI ballasts, materials used in the system are described and results about tests and measurements are presented.BackgroundSeveral scientific researches have been carried out in order to take the WSN advantages to the street lighting systems. For example, reference[4] explains the development of a wireless control system based on ZigBee. Their system allows the user to control and monitor the state of the lighting , but they do not focus on the energy efficienty, just the maintenance and the removal of wires in public areas for the people safety. Reference[5] gives a more complex exemple of WSN applied to street lighting, they develop a system that consists of sensor nodes placed in streetlight poles, a sink node in transformer station which controls every sensor node placed in a pole that belongs to that transformer station. The information of any sink node is sent to the control center via GPRS. The system also has individual or bank dimming up to 60% in order to save the energy consumption. Reference[6] states the main features of a WSN to be used as a street lighting control system, they use 6LoWPAN instead of ZigBee due to ZigBee routing protocols drawbacks and the ease of adapting 6LoWPAN, which does not define routing protocols, to any specific system文摘这一张主要是关注基于无线节能局域网和DALI协议的节能型路灯的远程控制系统之间的连接，用于检查单个路灯，比如路灯的位置、路灯的电流等。
无线局域网WLAN
无线局域网编辑WLAN 即无线局域网。
无线局域网络英文全名：Wireless Local Area Networks；简写为： WLAN。
简写中文翻译名称：微览。
它是相当便利的数据传输系统，它利用射频（Radio Frequency； RF）的技术，取代旧式碍手碍脚的双绞铜线（Coaxial）所构成的局域网络，使得无线局域网络能利用简单的存取架构让用户透过它，达到“信息随身化、便利走天下”的理想境界。
中文名无线局域网外文名Wireless Local Area Networks； WLAN技术射频标准IEEE802.11需要设备无线网卡、无线路由器优点灵活性和移动性目录1简介2结构▪无线桥接▪中型WLAN▪大型可交换WLAN3应用4优点5设置▪路由器▪无线网卡▪技术要求6硬件设备7开源项目8用户管理▪ IP地址分配管理▪用户资料库▪用户注册▪用户登陆▪用户级别设置▪用户权限设置▪用户日志9展频10注意事项11中国移动即将启用收费模式12组建和优化1简介编辑局域网络管理的主要工作之一就是铺设电缆或是检查电缆是否断线这种耗时的工作，很容易令人烦躁，也不容易在短时间内找出断线所在。
再者，由于配合企业及应用环境不断的更新与发展，原有的企业网络必须配合重新布局，需要重新安装网络线路。
虽然电缆本身并不贵，可是请技术人员来配线的成本很高，尤其是老旧的大楼，配线工程费用就更高了。
因此，架设无线局域网络就成为最佳解决方案。
2结构编辑无线局域网拓扑结构概述：基于IEEE802.11标准的无线局域网允许在局域网络环境中使用可以不必授权的ISM频段中的2.4GHz或5GHz射频波段进行无线连接。
它们被广泛应用，从家庭到企业再到Internet 接入热点。
无线局域网简单的家庭无线LAN简单的家庭无线WLAN：在家庭无线局域网最通用和最便宜的例子，如图1所示，一台设备作为防火墙，路由器，交换机和无线接入点。
这些无线路由器可以提供广泛的功能，例如：保护家庭网络远离外界的入侵。
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毕业设计(论文)外文资料翻译系：信息工程学院专业：计算机科学与技术姓名：学号：外文出处：Chris Haseman. Android-essential(用外文写)s[M].London:Spring--Verlag,2008.8-13.附件： 1.外文资料翻译译文；2.外文原文。
指导教师评语：签名：年月日注：请将该封面与附件装订成册。
附件1：外文资料翻译译文无线局域网一、为何使用无线局域网络对于局域网络管理主要工作之一，对于铺设电缆或是检查电缆是否断线这种耗时的工作，很容易令人烦躁，也不容易在短时间内找出断线所在。
再者，由于配合企业及应用环境不断的更新与发展，原有的企业网络必须配合重新布局，需要重新安装网络线路，虽然电缆本身并不贵，可是请技术人员来配线的成本很高，尤其是老旧的大楼，配线工程费用就更高了。
因此，架设无线局域网络就成为最佳解决方案。
二、什么情形需要无线局域网络无线局域网络绝不是用来替代有限局域网络，而是用来弥补有线局域网络之不足，以达到网络延伸之目的，下列情形可能须要无线局域网络。
●无固定工作场所的使用者●有线局域网络架设受环境限制●作为有线局域网络的备用系统三、无线局域网络存取技术目前厂商在设计无线局域网络产品时，有相当多种存取设计方式，大致可分为三大类：窄频微波技术、展频(Spread Spectrum)技术、及红外线(Infrared)技术，每种技术皆有其优缺点、限制及比较，接下来是这些技术方法的详细探讨。
1.技术要求由于无线局域网需要支持高速、突发的数据业务，在室内使用还需要解决多径衰落以及各子网间串扰等问题。
具体来说，无线局域网必须实现以下技术要求：1)可靠性：无线局域网的系统分组丢失率应该低于10-5，误码率应该低于10-8。
2)兼容性：对于室内使用的无线局域网，应尽可能使其跟现有的有线局域网在网络操作系统和网络软件上相互兼容。
3)数据速率：为了满足局域网业务量的需要，无线局域网的数据传输速率应该在1Mbps以上。
4)通信保密：由于数据通过无线介质在空中传播，无线局域网必须在不同层次采取有效的措施以提高通信保密和数据安全性能。
5)移动性：支持全移动网络或半移动网络。
6)节能管理：当无数据收发时使站点机处于休眠状态，当有数据收发时再激活，从而达到节省电力消耗的目的。
7)小型化、低价格：这是无线局域网得以普及的关键。
8)电磁环境：无线局域网应考虑电磁对人体和周边环境的影响问题。
Android是Google开发的基于Linux平台的开源手机操作系统（在华注册商标名为“安致”）。
它包括操作系统、用户界面和应用程序——移动电话工作所需的全部软件，而且不存在任何以往阻碍移动产业创新的专有权障碍，号称是首个为移动终端打造的真正开放和完整的移动软件。
Google与开放手机联盟合作开发了Android，这个联盟由包括中国移动、摩托罗拉、高通和T-Mobile在内的30多家技术和无线应用的领军企业组成。
Google通过与运营商、设备制造商、开发商和其他有关各方结成深层次的合作伙伴关系，希望借助建立标准化、开放式的移动电话软件平台，在移动产业内形成一个开放式的生态系统。
它采用了软件堆层(software stack，又名软件叠层)的架构，主要分为三部分：底层以Linux核心为基础，由c语言开发，只提供基本功能。
中间层包括函数库Library和虚拟机Virtual Machine，由c++语言开发。
最上层是各种应用软件，包括通话程序，短信程序等，应用软件则由各公司自行开发，以Java 编写。
为了推广此技术，Google和其它几十个手机公司建立了开放手机联盟（Open Handset Alliance）。
2.特性●应用程序框架：支持组件的重用与替换●Dalvik虚拟机：专门为移动设备做了优化●内部集成浏览器：该浏览器基于开源的WebKit引擎●优化的图形库：包括2D和3D图形库，3D图形库基于OpenGL ES 1.0（硬件加速可选）●#SQLite：用作结构化的数据存储●多媒体支持：包括常见的音频、视频和静态印象文件格式（如MPEG4，H.264，MP3，AAC，AMR，JPG，PNG，GIF）●GSM电话（依赖于硬件）●蓝牙Bluetooth，EDGE，3G和WiFi（依赖于硬件）●照相机，GPS，指南针和加速度计（依赖于硬件）●丰富的开发环境：包括设备模拟器，调试工具，内存及性能分析图表，和Eclipse集成开发环境插件3.应用程序Android会同一个核心应用程序包一起发布，该应用程序包包括email客户端，SMS短消息程序，日历，地图，浏览器，联系人管理程序等。
所有的应用程序都是用Java编写的。
Android应用程序框架开发者也完全可以访问核心应用程序所使用的API 框架。
该应用程序架构用来简化组件软件的重用，任何一个应用程序都可以发布它的功能块并且任何其它的应用程序都可以使用其所发布的功能块（不过得遵循框架的安全性限制）。
该应用程序重用机制使得组建可以被用户替换。
以下所有的应用程序都由一系列的服务和系统组成，包括：●一个可扩展的视图（Views）可以用来建应用程序，包括列表（lists），网格（grids），文本框（text boxes），按钮（buttons），甚至包括一个可嵌入的web浏览器●内容管理器（Content Providers）使得应用程序可以访问另一个应用程序的数据（如联系人数据库），或者共享它们自己的数据。
●一个资源管理器（Resource Manager）提供非代码资源的访问，如本地字符串，图形，和分层文件（layout files）。
●一个通知管理器（Notification Manager）使得应用程序可以在状态栏中显示客户通知信息。
●一个活动类管理器（Activity Manager）用来管理应用程序生命周期并提供常用的导航回退功能。
4.点餐系统点餐系统利用软件的全自动信息化手段，实现点菜、配菜、炒菜到传菜的全部管理过程；完成点菜单计算机管理、点菜单前端收银台与各厨房的同步打印；实现菜单无纸化操作；后台经理查询；仓库进销存管理等。
除此之外，点餐系统还可以对客户资料进行有效的管理，存档和备查，杜绝酒楼“漏单”、“跑单”现象；帮助酒楼利用计算机强大的数据处理能力和流程优化能力，实现自动化管理，简化酒楼的工作流程，减少浪费及人为管理的疏漏现象，重新优化配置企业资源，把经营成本降低到最低。
功能强大的点餐系统除支持一般的单机和局域网应用之外，还支持总店/分店多级架构的远程联网应用于分店使用POS系统实现前台销售收银、即时打印销售小票、销售日结、上报销售数据和接收新菜品信息等功能。
目前点餐系统共有三种实现模式：1)触摸屏点菜模式：它利用了目前最为流行的触摸式电脑实现点菜过程，即点菜员可以根据软件的画面提示，只需用手指点击画面就可以完成整个点菜过程，方便快捷，这种模式适用于菜式和做法丰富大型的酒楼、酒家和菜馆等。
2)无线PDA点菜模式：它利用了无线WiFi技术，通过PDA显示点菜界面，使用触摸笔完成点菜过程，真正实现随时随地点菜实时响应，这种模式适用于菜式和做法较为简单的西餐厅、特色菜馆和特具情调的中高级餐厅等。
3)无线点菜宝模式：它使用了ISM频段，可以在有楼层或其它障碍物阻挡的情况下无缝覆盖达10米之远，而信号依然稳定，这是其比之无线PDA点菜模式最大的优势，这种模式适用于菜式和做法较为简单及其它要求较少的快餐店、火锅店等。
附件2：外文原文WLANWhy use WLANFor one of the main local area network management, for the laying of cables, or check the cable is disconnected this time-consuming work, it is easy to upset, not easy to break in a short time to find out where. Furthermore, for the business and application environment constantly updating and development of enterprise network must be matched with the original re-layout, need to re-install the network lines, although the cable itself is not expensive, but requested the technical staff to the high cost of wiring, especially the old building, wiring project costs even higher. Therefore, the construction of wireless local area network has become the best solution.What conditions need to use WLANWLAN is not limited to alternative local area network, but to make up for lack of wired local area networks, in order to achieve the purpose of extending the network, the following circumstances may have wireless local area network.●no fixed workplace users●wired local area network set up by the environmental constraints●As a wired local area network backup systemWLAN access technologyCurrently manufacturers in the design of wireless local area network products, there are quite a variety of access design methods can be divided into three categories: narrowband microwave, spread spectrum (Spread Spectrum) technology, and infrared have their advantages and disadvantages, limitations, and more, followed by detailed discussion of these techniques. (Infrared) technology, each technique has their advantages and disadvantages, limitations, and more, followed by detailed discussion of these techniques.Technical requirementsAs wireless local area network needs to support high-speed, burst data services, need to be addressed in the indoor use of multipath fading, as well as issues such as crosstalk subnets. Specifically, wireless local area network must achieve the following technical requirements:1)Reliability: Wireless LAN system packet loss rate should be lower than 10-5,the error rate should be lower than 10-8.2)Compatibility: For indoor use of wireless local area network, so as far aspossible with the existing wired LAN network operating system and networksoftware compatible.3)Data rate: In order to meet the needs of local area network traffic, wirelessLAN data transfer rate should be more than 1Mbps.4)The confidentiality of communications: As the data transmitted in the air viawireless media, wireless local area networks at different levels must takeeffective measures to improve communication security and data security.5)Mobility: support for all mobile networks or semi-mobile network.6)Energy Management: When receiving or sending data to the site when themachine is in sleep mode, when activated again when the data transceiver toachieve the savings in power consumption.7)small size and low price: This is the key to the popularity of wireless local areanetwork can be.8)Electromagnetic environment: wireless LAN should consider thehumanbodyand the surrounding electromagnetic environment effects.AndroidGoogle Android is a Linux-based platform for developing open-source phone operating system (registered trademark in China called "Achi;). It includes operating systems, user interface and applications - mobile phone work required by the software, but there is no past, the exclusive right to impede innovation and barriers to mobile industry, called mobile terminal is the first to create a truly open and complete mobile software. Google and Open Handset Alliance to develop the Android, the allianceby including China Mobile, Motorola, Qualcomm and T-Mobile, including more than 30 technology and the composition of a leader in wireless applications. Google with operators, equipment manufacturers, developers and other interested parties to form deep-level partnerships, hoping to establish a standardized, open software platform for mobile phones in the mobile industry to form an open ecosystem .It uses software stack layers (software stack, also known as the software stack) architecture, is divided into three parts: the core of the underlying Linux-based language developed by the c, only basic functions. Middle layer consists of library. Library and Virtual Machine Virtual Machine, developed by the C +. At the top are a variety of applications, including the call procedures, SMS procedures, application software is developed by the companies themselves to write java.To promote this technology, Google, and dozens of other phone company has established the Open Handset Alliance (Open Handset Alliance).Characteristic●application framework to support component reuse and replacement●Dalvik virtual machine specifically for mobile devices is optimized●Internal integrated browser, the browser-based open-source WebKit engine●optimization of 2D and 3D graphics library includes graphics library, 3Dgraphics library based on OpenGL ES 1.0 (hardware-accelerated optional)●# SQLite for structured data storage●Multimedia support includes the common audio, video and static image fileformats (such as MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)●GSM phone (depending on hardware)●Bluetooth Bluetooth, EDGE, 3G, and WiFi (hardware dependent)●Camera, GPS, compass, and accelerometer (hardware dependent)●Rich development environment including a device emulator, debugger,memory and performance analysis charts, and the Eclipse integrateddevelopment environment plug-insApplicationsA core Android application package together with the release of the applicationpackage, including email client, SMS short messaging program, calendar, maps, browser, contact management procedures. A ll applications are written using JA V A.Android Application Framework Developers have full access to core applications used by the API framework. The application framework designed to simplify the reuse of software components; any application can publish its functional blocks and any other applications can use the function block its release (but must follow the framework of security restrictions). Reuse mechanism allows the application form can be user replaced.All of the following applications by the composition of a range of services and systems, including:●an expanded view (Views) can be used to build applications, including a list of(lists), grid (grids), text boxes (text boxes), buttons (buttons), and even an embeddable web browser.●Content Manager (Content Providers) allows applications to access data fromanother application program (such as the contact database), or to share their own data.● A resource manager (Resource Manager) to provide access to non-coderesources, such as local strings, graphics, and hierarchical file (layout files).● A notification manager (Notification Manager) allows applications to customersin the status bar display notification information.●An activity class Manager (Activity Manager) to manage the application lifecycle and provides common navigation rollback feature.Ordering the systemOrdering the system information using automated software tools to achieve la carte, side dishes, stir fry vegetables to the transfer of all management processes; completion point, the computer management menu, point the menu and the kitchen, front-end checkout synchronization print; achieved without the menu paper-based operation; backstage manager of inquiry; warehouse inventory management and so on.In addition, ordering the system can also effectively manage customer data, archiving and future reference, put an end to the restaurant "leakage List", "run list" phenomenon; help restaurants using computer data processing capability and powerfulability to process optimization to achieve automated management, streamline workflow restaurant, reduce waste and man-made phenomenon of management oversight, re-optimal allocation of corporate resources, the operating costs to a minimum.Powerful addition to ordering the system to support the general application of stand-alone and LAN in addition to support head office / branch of multi-level framework used for remote network using the POS system to achieve front store sales cashier, sales of small-ticket instantly print sales day-end, reporting sales data and receive information of new features dishes.There are three currently ordering the system to achieve mode:First, the touch screen a la carte model: It uses the currently most popular touch-computer ordering process to achieve that members can to order the software screen prompts, simply click on the screen with your fingers can complete the entire ordering process and convenient This model applies to the practice of rich dishes and large restaurants, restaurants, and restaurant, etc..Second,the wireless PDA ordering mode: it uses a wireless WiFi technology, a la carte interface by PDA display, use touch pen to complete the ordering process, virtually anywhere, anytime to order real-time response, this model is more suitable for dishes and practices simple restaurant, features a restaurant and special mood of senior restaurants.Third, the wireless ordering Po mode: it uses the ISM band, can be a floor or other obstruction in the case of seamless coverage up to 10 meters away, while the signal remained stable, which is the ratio of the wireless PDA ordering model's greatest strength, this model applies to simple dishes and practices and other requirements with fewer fast food restaurants, pot shops.。