2009-7-27 P,1
Unit 8
Data Communications
Chapter Three
&Part4 Extensive Reading@ Part 1 Notes to Text
@Part5 Notes to Passage& Part 2 Word Study
@Part3 Practice on Text @Part6 Practice on Passage
2009-7-27 P,2
@ Part 1 Notes to Text
1） "External" devices are generally thought of as being
independently powered circuitry that exists beyond the
chassis of a computer or other digital message source,外部设备通常被认为是装有动力的独立电路系统，一般是安装在计算机底盘或其它数据信息源底盘之下。
注释,介词短语 as being independently powered circuitry是主语补足语。 That引导的定语从句修饰先行词 circuitry。
2） It is the aim of any communications system to provide the
highest possible transmission rate at the lowest possible
power and with the least possible noise,任何一个通信系统，
其目的就是要能够以仅最可能低的功率和最少的噪音提供最大可能的传输速度。
注释,该句的主语是不定式 to provide the highest possible
transmission rate at the lowest possible power and with the
least possible noise。
Data Communications
2009-7-27 P,3
3） The end equipment which either generates the digital
information for transmission or uses the received digital data
can be computers,printers,keyboards,CRTs,and so on,端设备可以是计算机、打印机、键盘,CRT等，它们可以生成要发送的数字信息，也可以使用所接收的数字数据。
注释,此句是典型的复合句；主语是 The end equipment；谓语动词是 can be； which 引导显然是定语从句，修饰主语。
4） Digital data,when transmitted,are in serial form,Parallel
transmission of an 8-bit word would require eight pairs of
transmission lines - not at all cost-effective,数字数据在发送时是串行的。并行发送一个 8位的字需要 8对传输线，这是不经济的。
注释,过去分次词短语 when transmitted是典型的时间状语 ；后句中的破折号省略了 which is，即应为 which is not at all cost-
effective，相当于一个非限制性定语从句，对前面作进一步说明。
2009-7-27 P,4
5） 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 lines,数据通信设备（ DCE）从 DTE接收串行数据流，并将其转换成适合于在话音线路上发送的某种模拟信号形式。
注释,该句是简单句；主语 DCE也称为数据电路终接设备 Data
Circuit-terminating Equipment；形容词短语 suitable for
transmission on voice-grade lines.修饰 form of analog signal。
6） If you transmit data by digital channel (sometimes it is called
,Digital T-carrier” ),a Pulse Code Modulation (PCM)
equipment must be used,如果使用数字信道（有时称为数字 T载波）
传输数据，则应使用脉码调制（ PCM）设备。
注释,T-carrier源于美国贝尔公司的数字通信系统，将从音频频带上来的信号转换成数字脉冲，沿金属线传送称为 T-carrier。
End
2009-7-27 P,5 End
1,chassis n,底板；机箱 11,synchronous adj,同步的
2,proportional adj,成比例的 12,multipoint adj,多点 (式 )的,多位置的
3,inversely adv,相反地 13,subscriber n,订户,用户
4,internally adv,内部地；在内部 14,exclusive adj,独一的,唯一的
5,parallel n,平行线；平行面 15,property n,资产；占有物
6,cost-effective adj,划算的 16,voice-grade adj,话音级的
7,encompass v,包含；包括 17,digital-to-analog adj,数字到模拟的
8,circuitry n,电路（系统） 18,quadrature n,正交
9,conversion n,转换,转化 19,amplitude n,振幅
10,asynchronous adj,异步的
& Part 2 Word Study
2009-7-27 P,6
Task 1,Listening training
Dictation of some key words
Directions,You will hear some key words twice,most of which are taken from
the Word Study,Then finish the Crossword Puzzle,(See you book p,)
2,Dictation of some key expressions
Directions,You will hear some key expressions twice,most of which are
taken from this text,Then you are asked to complete the missing words.
@Part3 Practice on Text
1) _____________messages
2) signal_______________
3) transmission____________
4) ________________management
5) ______________data link system
6) digital-to-analog_____________
digital
power
data link
a multipoint
lines converter
2009-7-27 P,7
Read and Reply
Directions:Students are required to read aloud the whole text after
the teacher,Then give short answers to the following questions:
a) What does data comunmunication concern?
b) What is the final purpose of data communication
system?
Task 2,Read,Write and Translate
Data Communications concerns the transmission of digital
messages to devices external to the message source,
To provide the highest possible transmission rate at the
lowest possible power and with the least possible noise,
A Pulse Code Modulation (PCM) equipment must be used.
c) What device must be used when one transmits data by a
digital channel?
2009-7-27 P,8
( )1),The maximum permissible transmission rate of a
message” means that a message is allowed to be transmitted at
top speed.
( )2) Digital data are in serial form in any state,
( )3) We have several ways to transmit digital data,such as with
help of satellite communication system,voice-grade lines and the
serial data stream form,
( )4) Computers,printers,keyboards,all can receive digital data
and digita information,
( )5) Data terminal equipment (DTE) is a general phrase
containing all of the circuitry necessary to carry out parallel-to-
serial and serial-to-parallel conversions for transmission and
reception respectively and for data link management,
Read and Judge
End
T
F
T
F
T
2009-7-27 P,9
Directions:Read the following short passage,Complete it by filling in the missing words.
A,from B,which C,digital D,transmission E,signals
F,concerned G,feet H,Except I,chip J,circuit
The distance over 1)________data moves within a computer may
vary 2)________a few thousandths of an inch,as is the case within a
single IC 3)________,to as much as several 4)________along the
backplane of the main 5)________board,Over such small distances,
6)________data may be transmitted as direct,two-level electrical
7)________over simple copper conductors,8)________for the fastest
computers,circuit designers are not very 9)________about the shape
of the conductor or the analog characteristics of signal10)________.
Read and Complete
End
B
A
I G
J
C
E H
F
D
2009-7-27 P,10
1）这个项目将给失业工人创造出许多新的就业机会。（ generate）
2) 你必须明白，代价将会与你所花费的时间成正比。 (be
proportional to )
3) 为了让使自己美丽和动人，露丝每天花大量的时间打扮自己。
(make up)
4) 这座美丽的城市座落在由群山环抱的大峡谷中。 (encompass，
the Grand Canyon)
5) 出乎家长们的意料，所有的孩子在这次期末考试中考得非常好。
(perform)
Read and Translate
Directions:Put the following sentences into English,using the words or phrases given.
End
This program will generate a lot of new jobs for
the unimployed workers.
You have to know that the pay will be directly proportional to
the amount of time you put in,
She spends a lot of time making herself up every day in
order to be pretty and attractive.
This beautiful city is located
in the Grand Canyon encompassed by moutains,
Out of the parents’ expectation,all the
children
performed very well in the final-term examinations,
2009-7-27 P,11
Signals
One of the major concerns of the physical layer lies in moving
data in the form of electromagnetic signals across a
transmission medium,Whether you are collecting numerical
statistics from another computer,sending animated pictures(动画 )from a design workstation,or causing a bell to ring at a
distant control center,you are working with the transmission
of data across network connections.
Generally,the data usable to a person or application are not in
a form that can be transmitted over a network,For example,
you cannot roll up(卷起 )a photograph,insert it into a wire,and
transmit it across town,You can,however,transmit an
encoded(编码器 )description of the photograph,Instead of
sending the actual photograph,you can use an encoder to
create a stream of 1s and 0s that tells the receiving device how
to reconstruct the image of the photograph.
&Part4 Extensive Reading
2009-7-27 P,12
But even 1s and 0s cannot be sent as such across network links,
They must be further converted to a form that transmission media
can accept,Transmission media work by conducting energy along
a physical path,So a data stream of 1s and 0s must be turned into
energy in the form of electromagnetic signals.
Analog and Digital Data
Data can be analog or digital,An example of analog data is the
human voice,When someone speaks,an analog wave is created
in the air,This can be captured by a microphone and converted to
an analog signal or sampled(采样 )later and converted to a digital
signal.
An example of digital data is data stored in the memory of a
computer in the form of 0s and 1s,It can be converted to a digital
signal when it is transferred from one position to another inside or
outside the computer or modulated into an analog signal and then
sent through a transmission medium to another computer.
2009-7-27 P,13
Analog and Digital Signals
Like the data they represent,signals can be either analog or digital,
An analog signal has infinitely(无限地 )many levels of intensity over a
period of time,As the wave moves from value A to value B,it
passes through and includes an infinite number of values along its
path,A digital signal,on the other hand,can have only a limited
number of defined values,often as simple as 1 and 0.
The simplest way to show signals is by plotting(在图上标出位置 )them on
a pair of perpendicular axes(垂直的轴 ).
The vertical axis(纵轴 ) represents the value or strength of a signal,
The horizontal axis(横轴 ) represents the passage of time,The curve(曲线 )representing the analog signal is passing through an infinite
number of points,The vertical lines of the digital signal,however,
demonstrate(显示 )the sudden jump the signal makes from value to
value.
Signals can be analog or digital,Analog signals can have an infinite
number of values in a range; digital signals can have only a limited
number of values.
End
2009-7-27 P,14
@Part5 Notes to Passage
1) One of the major concerns of the physical layer lies in moving
data in the form of electromagnetic signals across a
transmission medium.物理层中令人关注的一大重点就是将电磁信号形式的数据通过一种传输媒体来移动。
注释,动词短语 lie in意思是“在于”；介词短语 in the form of是定语，
修饰 data；注意 move sth across sth的结构。
2) Instead of sending the actual photograph,you can use an
encoder to create a stream of 1s and 0s that tells the receiving
device how to reconstruct the image of the photograph.无需发送真正的照片，你可以利用编码器编写出一连串的 0和 1，这些代码可以指示接受装置怎样重构原图。
注释,编码器（ encoder）是把角位移或直线位移转换成电信号的一种装置．前者成为码盘，后者称码尺．按照读出方式编码器可以分为接触式和非接触式两种．接触式采用电刷输出，一电刷接触导电区或绝缘区来表示代码的状态是“１”还是“０”；非接触式的接受敏感元件是光敏元件或磁敏元件，采用光敏元件时以透光区和不透光区来表示代码的状态是“１”还是“０”。
2009-7-27 P,15 End
3) This can be captured by a microphone and converted to an
analog signal or sampled later and converted to a digital
signal.这可以通过麦克风就能获得，并转变成模拟信号或再变为脉冲信号，过后转换为数字信号。
注释,该句是个简单句。一个主语，谓语动词却有四个,captured、
converted,sampled和 converted；主语 This指上文的 an analog
wave。
4) It can be converted to a digital signal when it is transferred
from one position to another inside or outside the computer
or modulated into an analog signal and then sent through a
transmission medium to another computer,可以它转化为数字信号，一旦它从电脑的内部或外部的某个位置传递到另一个位置，
或被调制成模拟信号，就可以通过传输媒介将它发送到另一台电脑。
注释,It指代前文中的 0s and 1s；连词 when在此处相当于 as soon
as；动词短语 modulate into意思是“将 … 调制成 …,。
2009-7-27 P,16
1.Listening Challenge
Spot Dictation
Directions,The following passage will be heard 3 times,During the second time,you
are required to put the missing words or phrases in the numbered blanks according to
what you hear,The third time is for you to check your answers,Now the passage
begins.
Frequently,however,data must be sent 1)_________the local
circuitry that constitutes a 2)______________,In many cases,the
distances 3)____________may be enormous,Unfortunately,as the
distance between the 4)________of a message and its destination
increases,accurate 5)_____________becomes increasingly difficult.
This 6)________from the electrical distortion of signals traveling
through long conductors,and from noise added to the
7)________as it propagates through a transmission medium.
Although some precautions 8)_________________for data exchange
within a computer,9)_______________________occur when data is
transferred to devices outside the computer's circuitry,In this case,
distortion and noise can become10)___________________________.
@Part6 Practice on Passage
End
beyond
computer
involved
source
transmission
results
signal
must be taken
the biggest problems
so severe that information is lost
2009-7-27 P,17
End of this Unit
Unit 8
Data Communications
Chapter Three
&Part4 Extensive Reading@ Part 1 Notes to Text
@Part5 Notes to Passage& Part 2 Word Study
@Part3 Practice on Text @Part6 Practice on Passage
2009-7-27 P,2
@ Part 1 Notes to Text
1） "External" devices are generally thought of as being
independently powered circuitry that exists beyond the
chassis of a computer or other digital message source,外部设备通常被认为是装有动力的独立电路系统，一般是安装在计算机底盘或其它数据信息源底盘之下。
注释,介词短语 as being independently powered circuitry是主语补足语。 That引导的定语从句修饰先行词 circuitry。
2） It is the aim of any communications system to provide the
highest possible transmission rate at the lowest possible
power and with the least possible noise,任何一个通信系统，
其目的就是要能够以仅最可能低的功率和最少的噪音提供最大可能的传输速度。
注释,该句的主语是不定式 to provide the highest possible
transmission rate at the lowest possible power and with the
least possible noise。
Data Communications
2009-7-27 P,3
3） The end equipment which either generates the digital
information for transmission or uses the received digital data
can be computers,printers,keyboards,CRTs,and so on,端设备可以是计算机、打印机、键盘,CRT等，它们可以生成要发送的数字信息，也可以使用所接收的数字数据。
注释,此句是典型的复合句；主语是 The end equipment；谓语动词是 can be； which 引导显然是定语从句，修饰主语。
4） Digital data,when transmitted,are in serial form,Parallel
transmission of an 8-bit word would require eight pairs of
transmission lines - not at all cost-effective,数字数据在发送时是串行的。并行发送一个 8位的字需要 8对传输线，这是不经济的。
注释,过去分次词短语 when transmitted是典型的时间状语 ；后句中的破折号省略了 which is，即应为 which is not at all cost-
effective，相当于一个非限制性定语从句，对前面作进一步说明。
2009-7-27 P,4
5） 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 lines,数据通信设备（ DCE）从 DTE接收串行数据流，并将其转换成适合于在话音线路上发送的某种模拟信号形式。
注释,该句是简单句；主语 DCE也称为数据电路终接设备 Data
Circuit-terminating Equipment；形容词短语 suitable for
transmission on voice-grade lines.修饰 form of analog signal。
6） If you transmit data by digital channel (sometimes it is called
,Digital T-carrier” ),a Pulse Code Modulation (PCM)
equipment must be used,如果使用数字信道（有时称为数字 T载波）
传输数据，则应使用脉码调制（ PCM）设备。
注释,T-carrier源于美国贝尔公司的数字通信系统，将从音频频带上来的信号转换成数字脉冲，沿金属线传送称为 T-carrier。
End
2009-7-27 P,5 End
1,chassis n,底板；机箱 11,synchronous adj,同步的
2,proportional adj,成比例的 12,multipoint adj,多点 (式 )的,多位置的
3,inversely adv,相反地 13,subscriber n,订户,用户
4,internally adv,内部地；在内部 14,exclusive adj,独一的,唯一的
5,parallel n,平行线；平行面 15,property n,资产；占有物
6,cost-effective adj,划算的 16,voice-grade adj,话音级的
7,encompass v,包含；包括 17,digital-to-analog adj,数字到模拟的
8,circuitry n,电路（系统） 18,quadrature n,正交
9,conversion n,转换,转化 19,amplitude n,振幅
10,asynchronous adj,异步的
& Part 2 Word Study
2009-7-27 P,6
Task 1,Listening training
Dictation of some key words
Directions,You will hear some key words twice,most of which are taken from
the Word Study,Then finish the Crossword Puzzle,(See you book p,)
2,Dictation of some key expressions
Directions,You will hear some key expressions twice,most of which are
taken from this text,Then you are asked to complete the missing words.
@Part3 Practice on Text
1) _____________messages
2) signal_______________
3) transmission____________
4) ________________management
5) ______________data link system
6) digital-to-analog_____________
digital
power
data link
a multipoint
lines converter
2009-7-27 P,7
Read and Reply
Directions:Students are required to read aloud the whole text after
the teacher,Then give short answers to the following questions:
a) What does data comunmunication concern?
b) What is the final purpose of data communication
system?
Task 2,Read,Write and Translate
Data Communications concerns the transmission of digital
messages to devices external to the message source,
To provide the highest possible transmission rate at the
lowest possible power and with the least possible noise,
A Pulse Code Modulation (PCM) equipment must be used.
c) What device must be used when one transmits data by a
digital channel?
2009-7-27 P,8
( )1),The maximum permissible transmission rate of a
message” means that a message is allowed to be transmitted at
top speed.
( )2) Digital data are in serial form in any state,
( )3) We have several ways to transmit digital data,such as with
help of satellite communication system,voice-grade lines and the
serial data stream form,
( )4) Computers,printers,keyboards,all can receive digital data
and digita information,
( )5) Data terminal equipment (DTE) is a general phrase
containing all of the circuitry necessary to carry out parallel-to-
serial and serial-to-parallel conversions for transmission and
reception respectively and for data link management,
Read and Judge
End
T
F
T
F
T
2009-7-27 P,9
Directions:Read the following short passage,Complete it by filling in the missing words.
A,from B,which C,digital D,transmission E,signals
F,concerned G,feet H,Except I,chip J,circuit
The distance over 1)________data moves within a computer may
vary 2)________a few thousandths of an inch,as is the case within a
single IC 3)________,to as much as several 4)________along the
backplane of the main 5)________board,Over such small distances,
6)________data may be transmitted as direct,two-level electrical
7)________over simple copper conductors,8)________for the fastest
computers,circuit designers are not very 9)________about the shape
of the conductor or the analog characteristics of signal10)________.
Read and Complete
End
B
A
I G
J
C
E H
F
D
2009-7-27 P,10
1）这个项目将给失业工人创造出许多新的就业机会。（ generate）
2) 你必须明白，代价将会与你所花费的时间成正比。 (be
proportional to )
3) 为了让使自己美丽和动人，露丝每天花大量的时间打扮自己。
(make up)
4) 这座美丽的城市座落在由群山环抱的大峡谷中。 (encompass，
the Grand Canyon)
5) 出乎家长们的意料，所有的孩子在这次期末考试中考得非常好。
(perform)
Read and Translate
Directions:Put the following sentences into English,using the words or phrases given.
End
This program will generate a lot of new jobs for
the unimployed workers.
You have to know that the pay will be directly proportional to
the amount of time you put in,
She spends a lot of time making herself up every day in
order to be pretty and attractive.
This beautiful city is located
in the Grand Canyon encompassed by moutains,
Out of the parents’ expectation,all the
children
performed very well in the final-term examinations,
2009-7-27 P,11
Signals
One of the major concerns of the physical layer lies in moving
data in the form of electromagnetic signals across a
transmission medium,Whether you are collecting numerical
statistics from another computer,sending animated pictures(动画 )from a design workstation,or causing a bell to ring at a
distant control center,you are working with the transmission
of data across network connections.
Generally,the data usable to a person or application are not in
a form that can be transmitted over a network,For example,
you cannot roll up(卷起 )a photograph,insert it into a wire,and
transmit it across town,You can,however,transmit an
encoded(编码器 )description of the photograph,Instead of
sending the actual photograph,you can use an encoder to
create a stream of 1s and 0s that tells the receiving device how
to reconstruct the image of the photograph.
&Part4 Extensive Reading
2009-7-27 P,12
But even 1s and 0s cannot be sent as such across network links,
They must be further converted to a form that transmission media
can accept,Transmission media work by conducting energy along
a physical path,So a data stream of 1s and 0s must be turned into
energy in the form of electromagnetic signals.
Analog and Digital Data
Data can be analog or digital,An example of analog data is the
human voice,When someone speaks,an analog wave is created
in the air,This can be captured by a microphone and converted to
an analog signal or sampled(采样 )later and converted to a digital
signal.
An example of digital data is data stored in the memory of a
computer in the form of 0s and 1s,It can be converted to a digital
signal when it is transferred from one position to another inside or
outside the computer or modulated into an analog signal and then
sent through a transmission medium to another computer.
2009-7-27 P,13
Analog and Digital Signals
Like the data they represent,signals can be either analog or digital,
An analog signal has infinitely(无限地 )many levels of intensity over a
period of time,As the wave moves from value A to value B,it
passes through and includes an infinite number of values along its
path,A digital signal,on the other hand,can have only a limited
number of defined values,often as simple as 1 and 0.
The simplest way to show signals is by plotting(在图上标出位置 )them on
a pair of perpendicular axes(垂直的轴 ).
The vertical axis(纵轴 ) represents the value or strength of a signal,
The horizontal axis(横轴 ) represents the passage of time,The curve(曲线 )representing the analog signal is passing through an infinite
number of points,The vertical lines of the digital signal,however,
demonstrate(显示 )the sudden jump the signal makes from value to
value.
Signals can be analog or digital,Analog signals can have an infinite
number of values in a range; digital signals can have only a limited
number of values.
End
2009-7-27 P,14
@Part5 Notes to Passage
1) One of the major concerns of the physical layer lies in moving
data in the form of electromagnetic signals across a
transmission medium.物理层中令人关注的一大重点就是将电磁信号形式的数据通过一种传输媒体来移动。
注释,动词短语 lie in意思是“在于”；介词短语 in the form of是定语，
修饰 data；注意 move sth across sth的结构。
2) Instead of sending the actual photograph,you can use an
encoder to create a stream of 1s and 0s that tells the receiving
device how to reconstruct the image of the photograph.无需发送真正的照片，你可以利用编码器编写出一连串的 0和 1，这些代码可以指示接受装置怎样重构原图。
注释,编码器（ encoder）是把角位移或直线位移转换成电信号的一种装置．前者成为码盘，后者称码尺．按照读出方式编码器可以分为接触式和非接触式两种．接触式采用电刷输出，一电刷接触导电区或绝缘区来表示代码的状态是“１”还是“０”；非接触式的接受敏感元件是光敏元件或磁敏元件，采用光敏元件时以透光区和不透光区来表示代码的状态是“１”还是“０”。
2009-7-27 P,15 End
3) This can be captured by a microphone and converted to an
analog signal or sampled later and converted to a digital
signal.这可以通过麦克风就能获得，并转变成模拟信号或再变为脉冲信号，过后转换为数字信号。
注释,该句是个简单句。一个主语，谓语动词却有四个,captured、
converted,sampled和 converted；主语 This指上文的 an analog
wave。
4) It can be converted to a digital signal when it is transferred
from one position to another inside or outside the computer
or modulated into an analog signal and then sent through a
transmission medium to another computer,可以它转化为数字信号，一旦它从电脑的内部或外部的某个位置传递到另一个位置，
或被调制成模拟信号，就可以通过传输媒介将它发送到另一台电脑。
注释,It指代前文中的 0s and 1s；连词 when在此处相当于 as soon
as；动词短语 modulate into意思是“将 … 调制成 …,。
2009-7-27 P,16
1.Listening Challenge
Spot Dictation
Directions,The following passage will be heard 3 times,During the second time,you
are required to put the missing words or phrases in the numbered blanks according to
what you hear,The third time is for you to check your answers,Now the passage
begins.
Frequently,however,data must be sent 1)_________the local
circuitry that constitutes a 2)______________,In many cases,the
distances 3)____________may be enormous,Unfortunately,as the
distance between the 4)________of a message and its destination
increases,accurate 5)_____________becomes increasingly difficult.
This 6)________from the electrical distortion of signals traveling
through long conductors,and from noise added to the
7)________as it propagates through a transmission medium.
Although some precautions 8)_________________for data exchange
within a computer,9)_______________________occur when data is
transferred to devices outside the computer's circuitry,In this case,
distortion and noise can become10)___________________________.
@Part6 Practice on Passage
End
beyond
computer
involved
source
transmission
results
signal
must be taken
the biggest problems
so severe that information is lost
2009-7-27 P,17
End of this Unit
