02-2 2.2 Data Communications Channels.pptx

第1页：2.2 生词表

第2页：2.2 生词表（续）

第3页：2.2 生词表（续）

第4页：2.2 常用短语

第5页：数据为了传递，必须通过一些东西

Togetheretothere,data must move through something. A telephone line,cable,or the atmosphere are all transmission media or channels. But before the data can be communicated,it must be converted into a form suitable for communication.数据为了传递，必须通过一些东西：电话线、电缆或空气都是传输介质，即信道。但是，数据在传送前必须被转化成适于通信的形式。

第6页：数据通信线路可以以两种配置方式连接：点到

数据通信线路可以以两种配置方式连接：点到点和多点线路连接。点到点线路直接连接发送设备和接收设备，多点线路连接多个设备而不仅一个发送设备和一个接收设备。Data communications lines can be connected in two types of configurations:point-to-point and multi drop. A point-to-point line directly connects the sending and the receiving devices,and a multi drop line connects many devices,not just one sending device and one receiving device.

第7页：微型机之间以及与其他设备的连接有通过电缆

微型机之间以及与其他设备的连接有通过电缆和通过空气两种方法。数据可以被转化为用于通信的三种基本形式：电脉冲或电荷、电磁波和光波。Thetwowaysof connecting microcomputers with eachother and with other equipments are through the cable and through the air. There are three basic forms into which data can be converted for communication:electrical pulses or charges,electromagnetic waves,and pulses of light.

第8页：具体来说

Specifically,five kinds of technology are used to transmit data. They are telephone lines(twistedpair),coaxialcable,fiber-opticcable,microwave and satellite.具体来说，有五种技术可用来传送数据。它们是电话线（双绞线）、同轴电缆、光缆、微波和卫星。

第9页：2.2 数据通信信道 课文要点

TelephoneLines[1]Inexpensive,multiple-conductor cable comprised of one or more pairs of 18 to 24 gauge copper strands. The strands are twisted to improve protection against electromagnetic and radiofrequency interference. The cable,which maybe either shielded or unshielded,is used in low-speed communications,as telephone cable. Itisusedonly in baseband networks because of its narrow bandwidth.分析：这句话实际上是个名词解释，过去分词短语comprisedof…作定语，修饰cable。电话线由一对或多对18到24规格的铜线组成的便宜的多重导体电缆。铜线绞合着以提高防止电磁和无线电频率干扰的能力。这些电缆，可以是屏敝的或非屏敝的，作为电话线用于低速通信中。由于其窄的带宽，它仅被用于基带网络中。

第10页：你看到的架在电线杆上的绝大多数电话线是双

Most telephone lines you see strung on poles that consist of cables made up of hundreds of copper wires are twisted pairs. Twistedpairs are susceptible to a variety of types of electrical interference(noise),which limits the practical distance that data can be transmitted without being garbled. Twistedpairs have been used for years for voice and data transmission,however they are now being phased out by more technically advanced and reliable media.你看到的架在电线杆上的绝大多数电话线是双绞线，它们是由数以百计的铜线组成的电缆。双绞线对于各类电的干扰很敏感，这就限制了数据不被窜改而传送的实际距离。双绞线被用于传递声音和数据已有好多年了，然而它们正被技术更先进和可靠的介质逐步代替。

第11页：同轴电缆同轴电缆

Coaxial Cable Coaxialcable is a type of thickly insulated copper wire that can carry a larger volume of data—about 100 million bits per second,the insulation is composed of a nonconductive material covered by a layer of wovenwiremesh and heavy-duty rubber or plastic.同轴电缆同轴电缆是一种有厚绝缘层的铜线，可以携带大量的数据——大约每秒100万位。这个绝缘层由覆盖有一层金属筛网的绝缘材料和厚的橡胶或塑料组成。

第12页：根据电话连接的数目

Intermsof number of telephone connections,a coaxial cable has over 80 times the transmission capacity of twisted pair. Coaxial cables are most often used as the primary communications medium for local connected network in which all computer communication is within a limited geographic area,such as in the same building. Coaxialcable is also used for undersea telephone lines.根据电话连接的数目，同轴电缆的传输容量是双绞线的80多倍。同轴电缆是局域网最常用的主要的通信介质，而局域网中所有计算机间的通信是局限在有限的地理区域（比如一座大楼内）。同轴电缆也用于海底电话线。

第13页：光缆由金属包裹层和外层保护层包裹着的中央

语言点分析：此句是一个名词解释，过去分词短语composedof…作定语，修饰medium,过去分词短语surroundedby…作定语，修饰cable。

Fiber-Optic Cable[2]A transmission medium composed of a central glass optical fiber cable surrounded by cladding and an outer protective sheath. Ittransmits digital signals in the form of modulated light from a laser or LED (light-emitting diode). Infiber-optic cable, data is transmitted as pulses of light through tubes of glass. Intermsof number of telephone connections, fiber-optic cable has 20,000 times the transmission capacity of twisted pair. However, it is significantly smaller.

光缆由金属包裹层和外层保护层包裹着的中央玻璃光学纤维绳组成的一种传输介质。光缆以调制的从激光或光发射二板管中发射的光的形式来传递数字信号。在光缆中，当光脉冲通过玻璃管时数据就被传送。根据可连接的电话数目，光缆的传输容量是双绞线的2万多倍，然而它的体积却非常小。

第14页：光缆管的直径仅仅

实际上，光缆管的直径仅仅是人的头发丝的一半。尽管传送信息的距离有限，光缆还是具有一些优点。光缆不受电子的干扰，这就使得它们更安全。它们比同轴电缆轻、便宜，而且传输数据更可靠。光缆用光束以光的速度而不是电脉冲的速度传输数据，这就使得通过光缆传输比通过铜缆传输快得多。光缆正迅速地取代双绞线电话线。

Indeed, a fiber-optic tube can behalf the diameter of a human hair. Although limited in the distance they can carry information, fiber-optic cables have several advantages. Suchcables are immune to electronic interference, which makes them more secure. They are also lighter and less expensive than coaxial cable and are more reliable at transmitting data. They transmit information using beams of light at light speeds instead of pulses of electricity, making them far faster than copper cable. Fiber-optic cable is rapidly replacing twisted-pair telephone lines.

第15页：微波不使用电线或电缆

微波不使用电线或电缆，微波系统使用大气作为传输介质传送信号。微波是以直线穿过空气的高频率的无线电波。由于微波不能随地球表面的弯曲度弯曲，所以只能传送很短的距离。

Microwave Instead of using wire or cables, microwave systems can use the atmosphere as the medium through which to transmit signals. Microwaves are high-frequency radiowaves that travel in straight lines through the air. Because the waves cannot bend with the curvature of the earth, they can be transmitted only over short distances.

第16页：这样，对于一个城市中或者

这样，对于一个城市中或者是一个大学校园内的大楼之间，微波是很好的传送数据的介质。对于较长距离，微波必须通过“盘子”（即天线）放大。这些天线可以被安装在塔上、高楼上、以及山顶上。每个塔的设备接收进来的信号，增强信号的强度，然后将信号发送给下一站。

Thus, microwave is a good medium for sending data between buildings in acityorona large college campus. For longer distances, the waves must be relayed by means of"dishes", or antennas. Thesecanbe installed on towers, high buildings and mountaintops. Eachtower facility receives incoming traffic, boosts the signal strength, and sends the signal to the next station.

第17页：卫星卫星通信指的

语言点分析：本句为简单句，句中referto意思是“指的是”。例如：Loosely,theterm"job"is sometimes used to refer to a representation of a job.习惯上说，“作业”这个术语通常指的是作业的一种表述。

卫星卫星通信指的是利用轨道通信卫星将从一个地面站发来的信息传送到另外一个或多个地面站。

Satellites[3]Satellite communications refers to the utilization of geostationary orbiting satellites to relay the transmission received from one earth station to one or more earth stations.

第18页：卫星通信是通信领域的研究成果

卫星通信是通信领域的研究成果，其目的就是以尽可能少的代价获得不断增加的范围和容量。卫星在地球表面22 000英里的轨道上以精确位置和速度旋转着。这就使得它们看起来是静止的，因此可以将一个地面站转发器发送来的信息放大和传送到下一站。

They are the outcome of research in the area of communications whose objective is to achieve ever-increasing ranges and capacities with the lowest possible costs. Orbiting about 22,000 miles above the earth, satellites rotate at a precise point and speed above the earth. This makes them appear stationary so they can amplify and relay microwave signals from one transmitter on the ground to another.

第19页：通信卫星的主要优点

通信卫星的主要优点是一个卫星可以覆盖的面积的数量。它还具有其他的特点：远距离通信、转发站的费用独立于通信距离、以广播方式运作、易于多路访问、承受大量的信息、能够传送不同类型的服务、独立的发送、接收和监控。

The primary advantage of satellite communication is the amount of area that can be covered by a single satellite. Italsohas other features: long communication distance, and the cost of station building is independent of the communication distance, operating in broadcasting mode, easy for multiple access, sustaining heavy traffic, able to transport different types of service, independent sending and receiving, and monitoring.

第20页：在特定轨道放置三颗卫星就可覆盖整个地球表

在特定轨道放置三颗卫星就可覆盖整个地球表面，而且还有些重叠。其惟一缺点是恶劣的天气有时可影响数据的传送。

Three satellites placed in particular orbits can cover the entire surface of the earth, with some overlap. Their only drawback is that bad weather can sometimes interrupt the flow of data.

第21页：习题2.2 一 判断正误

习题2.2 一 判断正误：根据课文内容判断下列说法正误。

Put“true”or“false”in the brackets for the following statements according to the passage.

1. ()Aircanbeused to transmit data.
2. ()Point-to-point and multi drop are two types of configuration for communications lines connecting.
3. ()Twistedpairs are susceptible to noise, which limits the practical distance they can transmit.
4. ()Coaxialcable and twisted pairs are all high-frequency transmission cables.
5. ()Optic-fiber cables can transmit both electrical and light signals.
6. ()Optic-fiber cables are more secure because they are not susceptible to electrical interference.
7. ()Microwave can transmit data over long distances.
8. ()The primary advantage of satellite communication is the long distance a single satellite can cover.

第22页：习题2.2 二 练习

习题2.2 二 练习：根据课文内容完成下列练习。

Fillinthe blanks according to the passage.

1. Thetwowaysof connecting microcomputers with eachother and with other equipments are through the______and through the____.
2. Data communications lines can be connected in two types of configurations:__________and__________.
3. Twistedpairs are____________to a variety of types of electrical interference (noise), which limits the practical distance that data can be transmitted without being________.
4. ___________transmits digital signals in the form of modulated light from a laser or LED.
5. ___________systems can use the atmosphere as the medium through which to transmit signals.
6. Microwaves cannot bend with the__________of the earth, they can be transmitted only over short distances.
7. Satellite communications refers to the___________of geostationary orbiting satellites to__________the transmission received from one earth station to one or more earth stations.
8. Three satellites placed in particular orbits can cover the entire surface of the earth, with some__________.

第23页：习题2.2 三 翻译

习题2.2 三 翻译：将下列单词和短语译成中文。

Translate the following words and expressions into Chinese.

1. communications channels
2. multiple-conductor
3. facility
4. stationary
5. transmission capacity
6. electromagnetic waves
7. pulses of light
8. light-emitting diode
9. a solid wire conductor
10. electrical interference