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。
l 无固定工作场所的使用者
l 有线局域网络架设受环境限制
l 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
l 应用程序框架：支持组件的重用与替换
l Dalvik虚拟机：专门为移动设备做了优化
l 内部集成浏览器：该浏览器基于开源的WebKit引擎
l 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）
l #SQLite：用作结构化的数据存储
l 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）
l GSM电话（依赖于硬件）
l 蓝牙Bluetooth，EDGE，3G和WiFi（依赖于硬件）
l 照相机，GPS，指南针和加速度计（依赖于硬件）
l 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：
l 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
l 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。
l 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）。
l 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。
l 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。
外文原文
Chris Haseman. Android-essentials[M].London:Spring--Verlag,2008.8-13.
WLAN
Why use WLAN
For 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 WLAN
WLAN 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.
l no fixed workplace users
l wired local area network set up by the environmental constraints
l As a wired local area network backup system
WLAN access technology
Currently 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 requirements
As 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 as possible with the existing wired LAN network operating system and network software compatible.
3) Data rate: In order to meet the needs of local area network traffic, wireless LAN data transfer rate should be more than 1Mbps.
4) The confidentiality of communications: As the data transmitted in the air via wireless media, wireless local area networks at different levels must take effective 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 the machine is in sleep mode, when activated again when the data transceiver to achieve the savings in power consumption.
7) small size and low price: This is the key to the popularity of wireless local area network can be.
8) Electromagnetic environment: wireless LAN should consider the humanbodyand the surrounding electromagnetic environment effects.
Android
Google 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: 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
l application framework to support component reuse and replacement
l Dalvik virtual machine specifically for mobile devices is optimized
l Internal integrated browser, the browser-based open-source WebKit engine
l optimization of 2D and 3D graphics library includes graphics library, 3D graphics library based on OpenGL ES 1.0 (hardware-accelerated optional)
l # SQLite for structured data storage
l Multimedia support includes the common audio, video and static image file formats (such as MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)
l GSM phone (depending on hardware)
l Bluetooth Bluetooth, EDGE, 3G, and WiFi (hardware dependent)
l Camera, GPS, compass, and accelerometer (hardware dependent)
l Rich development environment including a device emulator, debugger, memory and performance analysis charts, and the Eclipse integrated development environment plug-ins
Applications
A 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 JAVA.
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:
l 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.
l Content Manager (Content Providers) allows applications to access data from another application program (such as the contact database), or to share their own data.
l A resource manager (Resource Manager) to provide access to non-code resources, such as local strings, graphics, and hierarchical file (layout files).
l A notification manager (Notification Manager) allows applications to customers in the status bar display notification information.
l An activity class Manager (Activity Manager) to manage the application life cycle and provides common navigation rollback feature.
Ordering the system
Ordering 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 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.
