京剧四大名旦-陕西中考时间

Unit 8 Computer Network and Networked Control
计算机网络和网络控制

8.1 Introduction to Computer network
A computer network is a group of computers connected to each other electronically. This
means that the computers can
information to the others. A computer network allows user to exchange data quickly, access and
share resources including equipments, application software, and information.
Data communications systems are the electronic systems that transmit data over
communications lines from one location to another. You might use data communications through
your microcomputer to send information to a friend using another computer. You might work for
an organization whose computer system is spread throughout a building, or even throughout the
country or world. That is, all the parts—input and output units, processor, and storage
devices—are in different places and linked by communications. Or you might use
telecommunications lines—telephone lines—to tap into information located in an outside data
bank. You could then transmit it to your microcomputer for your own reworking and analysis.
To attach to a network, a special-purpose hardware component is used to handle all the
transmission. The hardware is called a network adapter card or network interface card (NIC), it is
a printed circuit board plugged into a computer's bus, and a cable connects it to a network
medium.
Communications networks differ in geographical size. There are three important types: Local
Area Networks (LANs), Metropolitan Area Networks (MANs), and Wide Area Networks
(WANs).
（1）Local Area Networks (LANs)
Networks with computers and peripheral devices in close physical proximity—within the same
building, for instance—are called local area networks (LANs). Linked by cable-telephone, coaxial,
or fiber optic. LANs often use a bus form organization. In a LANs, people can share different
equipments, which lower the cost of equipments. LANs may be linked to other LANs or to larger
networks by using a network gateway. With the gateway, one LANs may be connected to the
LANs of another LANs of another office group. It may also be connected to others in the wide
world, even if their configurations are different. Alternatively, a network bridge would be
used to connect networks with the same configurations.


There is a newly development for LANs: WLAN. A wireless LANs (WLANs) is a flexible
data communication system implemented as an extension to, or as an alternative for, a wired
LANs within a building or campus. Using electromagnetic waves, WLANs transmit and receive
data over the air, minimizing the need for wired connections. Thus, WLANs combine data
connectivity with user mobility, and, through simplified configuration, enable movable LANs.
Over the recent several years, WLANs have gained strong popularity in a number of vertical
markets, including the health-care, retail, manufacturing, warehousing, and academic arenas.

These industries have profited from the productivity gains of using hand-held terminals and
notebook computers to transmit real-time information to centralized hosts for processing. Today
WLANs are becoming more widely recognized as a general-purpose connectivity alternative for a
broad range of business customers.
Wireless LANs frequently augment rather than replace wired LAN networks—often
providing the final few meters of connectivity between a backbone network and the mobile
user. The following list describes some of the many applications made possible through the
①
②

power and flexibility of wireless LANs:

Doctors and nurses in hospitals are more productive because hand-held or notebook
computers with wireless LANs capability deliver patient information instantly.

Consulting or accounting audit engagement teams or small workgroups increase productivity
with quick network setup.

Network managers in dynamic environments minimize the overhead of moves, adds, and
changes with wireless LANs, thereby reducing the cost of LANs ownership.
 Training sites at corporations and students at universities use wireless connectivity to
facilitate access to information, information exchanges, and learning.
 Network managers installing networked computers in older buildings find that wireless
LANs are a cost-effective network infrastructure solution.
 Retail store owners use wireless networks to simply frequent network reconfiguration.
 Trade show and branch office workers minimize setup requirements by installing
preconfigured wireless LANs needing no local MIS support.
 Warehouse workers use wireless LANs to exchange information with central databases and
increase their productivity.
 Network managers implement wireless LANs to provide backup for mission-critical
applications running on wired networks.

Senior executives in conference rooms make quicker decisions because they have real-time
information at their fingertips.
The increasingly mobile user also becomes a clear candidate for a wireless LANs. Portable
access to wireless networks can be achieved using laptop computers and wireless NICs. This
enables the user to travel to various locations–meeting rooms, hallways, lobbies, cafeterias,
classrooms, etc.–and still have access to their networked data. Without wireless access, the user
would have to carry clumsy cabling and find a network tap to plug into.
(2) Metropolitan Area Networks (MANs)
These networks are used as links between office buildings in a city. Cellular phone systems
expand the flexibility of MAN by allowing links to car phones and portable phones.
(3) Wide Area Networks(WANs)
Wide area networks are countrywide and worldwide networks. Among other kinds of
channels, they use microwave relays and satellites to reach users over long distances. One of the
most widely used WANs is Internet, which allows users to connect to other users and facilities
worldwide.

New Words and Expressions
alternatively adv. 二中择一，换句话说
attach v. 附上，连接
audit v. 审计，会计检查，查账，核查
augment v. 增大，增加
backbone n. 构架，中心，中枢，主干线
cafeteria n. 自助食堂
candidate n. 选择物，候选人
clumsy adj. 笨拙的
engagement n. 约定

exchange v. 交换，调换
facilitate v. 易于，便于，助长
cost-effective adj. 划算的
gateway n. 网关
halfway adj. 中途的，一半的长度的
implement v. 履行
infrastructure n. 下部结构，永久性基地，基础
lobby n. 门廊，休息室
metropolitan adj. 大城市的
mission n. 使命，任务，代表团 v. 派遣
mobility n. 灵活性，移动性，可动性
overhead adj. 过顶的，头上的，经常的
peripheral n. 外部设备，辅助设备
plug n. 插头，插塞
profit v. 有利于，获益
proximity n. 接近，近似，近程
retail n. 零售
warehouse n. 仓库
LAN (Local Area Network) 局域网
MAN (Metropolitan Area Network) 城域网
MIS (Management Information System) 管理信息系统
NIC (Network Interface Card) 网络接口卡
WAN (Wide Area Network) 广域网
WLAN (Wireless Local Area Network) 无线局域网

Notes
[1] It may also be connected to others in the wide world, even if their configurations are different.
Alternatively, a network bridge would be used to connect networks with the same configurations.
译文：它也可以连接到世界范围的其他局域网上，即使它们的配置不同。另外一种方法是用
网桥 来连接具有相同配置的网络。
解析：even if引导让步状语从句，Alternatively为插入语，may also be connected和would be used
均为被动语态，介词短语with the same configurations using作方式状语，修饰谓语would be
used。
[2] Wireless LANs frequently augment rather than replace wired LAN networks—often providing
the final few meters of connectivity between a backbone network and the mobile user.
译文：无线局域网通常是增加，而不是代替有线局域网的功能，通常是在中 枢网络和移动用
户之间提供几米的连接。
解析：…rather than…意思是“是… …,而不是……”，现在分词短语providing…作状语，介
词短语between…and…作 后置定语，修饰connectivity。


参考译文：
第八单元 计算机网络与网络控制
8.1计算机网络简介

计算机 网络是一组相互连接的电子计算机。这意味着计算机可以相互―谈话‖，在网络中
的每台计算机彼此可以 将信息发送给其他人。计算机网络允许用户快速地交换数据，访问和
共享包括设备、应用软件和信息在内 的资源。
数据通信系统是通过通信 线路将数据从一个地方传送到另一个地方的电子系统。你可
以使用数据通信，用微机将信息发送给使用另一台机器的朋友。你有可能在为一家公司工作，
其计算机 系统遍布一座大楼，或者甚至是全国乃至全世界。也就是说，所有的组成部分——
输入输出单元、处理器 以及存储设备——都在不同的地方，是通过通信连接起来的。或者你
可以使用远程通信线——电话线—— 接受位于外部单元的信息，然后你可能将信息传送到自
己的微机上，进行重新工作和分析。
为 了连接到网络上，需要使用特殊用途的硬件部件来处理所有的信息传送。这种硬件被
称为网络适配卡或网 络接口卡，他是插入到计算机总线上的印刷电路板，由电缆将它连接到
网络介质。
由于通信网络所占据的地理范围大小不同，可分为三种重要的类型：局域网、城域网和
广域网。
（1） 局域网
计算机和外部设备在很近的物理范围内的网络被称为局域网。如在一座大楼内 ，由电缆
连接——电话线、同轴电缆或光缆。局域网同城使用总线型的结构。在局域网中，人们可以共享不同的设备，这样可以降低设备的费用。局域网可以通过使用网关连接到另外一个局域
网或者更 大的网络。使用网关，可以把一个局域网连接到另一个办公团体的局域网上。它也
可以连接到世界范围的 其他局域网上，即使它们的配置不同。另外一种方法是用网桥来连接
具有相同配置的网络。
有 一种新开发的局域网——无线局域网。无线局域网是一种灵活的数据传输系统，它可
以实现大楼或校园内 有线局域网的延伸或替换。无线局域网使用电磁波，通过空气传送和接
收数据，最低限度地减少了有线连 接。这样，无线局域网把数据可连接性与用户的可移动性
结合起来，通过简化的配置，形成了移动的局域 网。
随着近几年的发展，无线局域网在一些市场领域已经获得了广泛的普及，其中包括健康
保 健、零售业、制造业、仓储业和学术界等。这些领域通过手提终端和笔记本电脑将实时信
息传送到中央主 机进行处理，所获得的生产率说明受益非浅。如今，对于大多数的商业客户
而言，无线局域网正成为公认 的通用连接的替代品。
无线局域网通常是增加而不是替代有线局域网的功能——通常是在中枢网络和移 动用
户间提供最后几米的连接。通过使用无线局域网的灵活性和功能，可以实现如下一些应用：
 医院的医生和护士利用手提或笔记本电脑与无线局域网连接的性能，及时传递患者的
信息， 提高了工作效率。
 顾问或会计审计事务组或一些小的工作组使用快速搭建的网络，可以提高工作效率。
 在动态环境下 的网络管理者使用无线局域网最大限度地减少经常的移动、添加和修改
工作，从而降低局域网使用者的费 用。
 公司的培训点和大学的学生使用无线连接便于访问信息，进行信息交换和学习。
 在旧建筑物内安装网络计算机的网络管理员发现，无线局域网是划算的网络基础结构
解决方案。
 零售店的老板使用无线局域网简化经常性的网络重新配置（问题）。
 贸易展览部门工 作人员通过安装预先设置的无线局域网，最大限度地减低配置需求，
而不需要当地信息管理系统的支持。
 仓储工人使用无线局域网和中心数据库交换信息提高生产率。
 网络管理员使用无线局域网提供运行在有线网络上的关键应用程序的备份。

 在会议室的高级行政官员因为手头有实时信息可供使用，因此可以做出快速的决策。
日益 增长的移动用户也成为无线局域网的坚实后备力量。使用膝上电脑和无线网络接
口卡，就可以实现移动访 问无线局域网，这就使得用户可以在不同的地方穿梭——会议室、
门厅、休息室、自助食堂、教室等地方 ——仍然可以访问器网络数据。加入没有无线局域网，
用户就不得不携带笨重的电缆寻找网络插头。
（2） 城域网
这些网路用于一个城市内的建筑物之间的连接。移动电话系统通过允许将汽车 电话和移
动电话接入而扩展了大城市网的灵活性。
（3） 广域网
广域网是国家和 世界范围内的网络。在其他的信道种类中，广域网使用微波中继和卫星
通信远距离到达用户。使用的最广 泛的广域网是Internet，它允许在世界范围内用户和用户
及设备的连接