Data Communications and Computer Networks A Business User's Approach 8e Curt White

Data Communications and Computer Networks A Business User’s Approach 8e Curt White 

 

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Sample Questions Are Posted Below

 

Chapter 5: Making Connections Efficient: Multiplexing and Compression

 

TRUE/FALSE

 

1. Multiplexing is a technique typically performed at the network access layer of the TCP/IP protocol suite.

 

ANS:  T                    PTS:   1                    REF:   120

 

2. One way to make a connection between two devices more efficient is to compress the data that transfers over the connection.

 

ANS:  T                    PTS:   1                    REF:   120

 

3. Frequency division multiplexing is the latest multiplexing technique.

 

ANS:  F                    PTS:   1                    REF:   120

 

4. In frequency division multiplexing, the combined signals are digital.

 

ANS:  F                    PTS:   1                    REF:   121

 

5. Cell phones are an example of dynamically assigned channels.

 

ANS:  T                    PTS:   1                    REF:   121

 

6. Time division multiplexing (TDM) allows only one user at a time to transmit.

 

ANS:  T                    PTS:   1                    REF:   123

 

7. As with a simple connection between one sending device and one receiving device, maintaining synchronization across a multiplexed link is important.

 

ANS:  T                    PTS:   1                    REF:   124

 

8. The T-1’s original purpose was to provide a high-speed connection between AT&T’s switching centers.

 

ANS:  T                    PTS:   1                    REF:   125

 

9. The T-1 system is a classic application of frequency division multiplexing.

 

ANS:  F                    PTS:   1                    REF:   125

 

10. A T-1 system sends the equivalent of 24 voice grade telephone lines over one line.

 

ANS:  T                    PTS:   1                    REF:   125

 

11. A T-1 system continuously sends a signal, even if there is no real data to transmit.

 

ANS:  T                    PTS:   1                    REF:   125

 

12. SONET is a more modern term for the older T-1 system.

 

ANS:  F                    PTS:   1                    REF:   126

 

13. SDH was developed in Europe by ITU-T.

 

ANS:  T                    PTS:   1                    REF:   126

 

14. SONET and SDH are able to multiplex varying speed streams of data onto one fiber connection.

 

ANS:  T                    PTS:   1                    REF:   127

 

15. The data rate of OC-3 is exactly thirty times the rate of OC-1.

 

ANS:  F                    PTS:   1                    REF:   127

 

16. The STS multiplexor in a SONET network can accept electrical signals from copper-based media.

 

ANS:  T                    PTS:   1                    REF:   127

 

17. Both frequency division multiplexing and synchronous time division multiplexing can waste unused transmission space.

 

ANS:  T                    PTS:   1                    REF:   128

 

18. Wavelength division multiplexing (WDM) is, in essence, a time division multiplexing technique.

 

ANS:  F                    PTS:   1                    REF:   129

 

19. WDM supports multiple lambdas.

 

ANS:  T                    PTS:   1                    REF:   130

 

20. Dense wavelength division multiplexing is an expensive way to transmit signals from multiple devices due to the high number of differently colored lasers required in one unit.

 

ANS:  T                    PTS:   1                    REF:   130

 

21. DSL is capable of achieving speeds into the millions of bits per second.

 

ANS:  T                    PTS:   1                    REF:   131

 

22. Code division multiplexing is based upon a class of modulation techniques known as spread spectrum technology.

 

ANS:  T                    PTS:   1                    REF:   132

 

23. The big advantage of frequency division multiplexing over synchronous TDM is the lower noise due to the use of digital signals during transmission.

 

ANS:  F                    PTS:   1                    REF:   134

 

24. Synchronous time division multiplexing does not require as high-speed a line as statistical time division multiplexing does.

 

ANS:  F                    PTS:   1                    REF:   134

 

25. Code division multiplexing, while using a fairly wide bandwidth of frequencies and a complex technology, is scalable like WDM.

 

ANS:  T                    PTS:   1                    REF:   134

 

26. The basic way to perform compression is to look for some common pattern in the data and replace each data pattern with a symbol or symbols that will consume less space during transmission or storage.

 

ANS:  T                    PTS:   1                    REF:   135

 

27. The Lempel-Ziv algorithm can be fairly effective in compressing data.

 

ANS:  T                    PTS:   1                    REF:   137

 

28. The human ear can hear sounds only within a certain range, which for an average person is 10 Hz to 40 kHz (40,000 Hz).

 

ANS:  F                    PTS:   1                    REF:   138

 

29. The MP3 encoder produces a data stream that has a much faster data rate than that of conventional CD-quality music.

 

ANS:  F                    PTS:   1                    REF:   138

 

30. A video device displays multiple (typically 30) frames per second.

 

ANS:  T                    PTS:   1                    REF:   141

 

MULTIPLE CHOICE

 

1. Presently, a medium can be divided in three basic ways: a division of ____, a division of time, and a division of transmission codes.

a.	frequencies	c.	wavelength
b.	amplitudes	d.	direction

 

 

ANS:  A                    PTS:   1                    REF:   120

 

2. ____ is the assignment of nonoverlapping frequency ranges to each “user” of a medium.

a.	Time division multiplexing (TDM)	c.	Amplitude division multiplexing (ADM)
b.	Transmission code multiplexing (TCM)	d.	Frequency division multiplexing (FDM)

 

 

ANS:  D                    PTS:   1                    REF:   120

 

3. To allow multiple users to share a single medium, FDM assigns each user a separate ____.

a.	time slot	c.	channel
b.	transmission code	d.	amplitude

 

 

ANS:  C                    PTS:   1                    REF:   120

 

4. First-generation cellular telephone systems allocated channels using frequency ranges within the 800 to ____ megahertz (MHz) spectrum.

a.	830	c.	930
b.	900	d.	960

 

 

ANS:  B                    PTS:   1                    REF:   121

 

5. The device that is attached to the receiving end of the medium and splits off each signal to deliver it to the appropriate receiver is called the second multiplexor, or ____.

a.	multiplexor	c.	splitxor
b.	endplexor	d.	demultiplexor

 

 

ANS:  D                    PTS:   1                    REF:   122

 

6. In FDM, ____ take up frequencies that might be used for other data channels, thus introducing a certain level of wastefulness.

a.	guard bands	c.	multiplexors
b.	channels	d.	demultiplexors

 

 

ANS:  A                    PTS:   1                    REF:   122

 

7. Since time division multiplexing was introduced, it has split into two roughly parallel but separate technologies: synchronous time division multiplexing and ____ time division multiplexing.

a.	fixed	c.	inverse
b.	statistical	d.	empirical

 

 

ANS:  B                    PTS:   1                    REF:   123

 

8. ____ gives each incoming source signal a turn to be transmitted, proceeding through the sources in round-robin fashion.

a.	Statistical time division multiplexing (Stat TDM)
b.	Empirical time division multiplexing (ETDM)
c.	Synchronous time division multiplexing (Sync TDM)
d.	Fixed time division multiplexing (FTDM)

 

 

ANS:  C                    PTS:   1                    REF:   123

 

9. Under normal circumstances, the synchronous time division multiplexor maintains a simple ____ sampling order of the input devices.

a.	round-robin	c.	LIFO
b.	FIFO	d.	FILO

 

 

ANS:  A                    PTS:   1                    REF:   123

 

10. Three types of synchronous time division multiplexing that are popular today are T-1 multiplexing, ____ multiplexing, and SDH.

a.	EIA-232F	c.	SONET
b.	IPS/SPX	d.	RS-232

 

 

ANS:  C                    PTS:   1                    REF:   125

 

11. In the 1960s, AT&T created a service known as ____, which multiplexed digital data and digitized voice onto a high-speed telephone line with a data rate of 1.544 megabits per second.

a.	ISDN	c.	SONET
b.	T-1	d.	SDH

 

 

ANS:  B                    PTS:   1                    REF:   125

 

12. ____ multiplexing is the multiplexing technique used to support SONET.

a.	FDM	c.	Frequency division
b.	ADM	d.	Synchronous time division

 

 

ANS:  D                    PTS:   1                    REF:   126

 

13. A ____ multiplexes 24 input channels together onto one high-speed telephone line.

a.	T-1 system	c.	SDH system
b.	SONET system	d.	congruent system

 

 

ANS:  A                    PTS:   1                    REF:   126

 

14. A T-1 system multiplexes _______ into each frame.

a.	a single ASCII character	c.	a single SYNC bit
b.	a single LENGTH byte	d.	a single SYNC byte

 

 

ANS:  C                    PTS:   1                    REF:   125

 

15. SONET was developed in the United States by ____.

a.	ISO	c.	IEEE
b.	ANSI	d.	IETF

 

 

ANS:  B                    PTS:   1                    REF:   126

 

16. SONET and SDH are both ____ multiplexing techniques.

a.	synchronous	c.	empirical
b.	statistical	d.	random

 

 

ANS:  A                    PTS:   1                    REF:   126

 

17. SONET defines a hierarchy of signaling levels, or data transmission rates, called ____.

a.	statistical transport signals (StatTS)	c.	asynchronous transport signals (ATS)
b.	empirical transport signals (ETS)	d.	synchronous transport signals (STS)

 

 

ANS:  D                    PTS:   1                    REF:   126

 

18. It is relatively simple to multiplex four STS-12 signals into one ____ signal.

a.	STS-8	c.	STS-32
b.	STS-16	d.	STS-48

 

 

ANS:  D                    PTS:   1                    REF:   126-127

 

19. The STS-1 signaling level supports ____ frames per second.

a.	8000	c.	32000
b.	16000	d.	64000

 

 

ANS:  A                    PTS:   1                    REF:   127

 

20. Statistical time division multiplexing is sometimes called ____ time division multiplexing.

a.	empirical	c.	asynchronous
b.	random	d.	synchronous

 

 

ANS:  C                    PTS:   1                    REF:   128

 

21. ____ multiplexes multiple data streams onto a single fiber-optic line.

a.	Statistical time division multiplexing (Stat TDM)
b.	Wavelength division multiplexing (WDM)
c.	Time division multiplexing (TDM)
d.	Channel division multiplexing (CDM)

 

 

ANS:  B                    PTS:   1                    REF:   129

 

22. ____ uses different wavelength (frequency) lasers to transmit multiple signals at the same time over a single medium.

a.	Wave division multiplexing	c.	Channel division multiplexing
b.	Statistical time division multiplexing	d.	Time division multiplexing

 

 

ANS:  A                    PTS:   1                    REF:   130

 

23. ____ is designed for short-distance connections and has only a few lambdas, with a greater space between lambdas.

a.	Dense wavelength division multiplexing (DWDM)
b.	Fixed wavelength division multiplexing (FWDM)
c.	Coarse wavelength division multiplexing (CWDM)
d.	Inverse wavelength division multiplexing (IWDM)

 

 

ANS:  C                    PTS:   1                    REF:   130

 

24. ____ is the technology behind the popular digital subscriber line (DSL) system.

a.	Time division	c.	Wavelength division
b.	Amplitude division	d.	Discrete multitone

 

 

ANS:  D                    PTS:   1                    REF:   131

 

25. ____ is a technology that allows a high-speed data signal to traverse a standard copper-based telephone line.

a.	DSL	c.	EIA-232F
b.	RS-232	d.	FireWire

 

 

ANS:  A                    PTS:   1                    REF:   131

 

26. Chip spreading codes are ____ bits in length.

a.	32	c.	128
b.	64	d.	256

 

 

ANS:  B                    PTS:   1                    REF:   133

 

27. ____ division multiplexing is a good choice for connecting a number of lower-speed devices that do not transmit data on a continuous basis to a remote computer system.

a.	Statistical time	c.	Discrete tone
b.	Time	d.	Frequency

 

 

ANS:  A                    PTS:   1                    REF:   134

 

28. ____ division multiplexing is a good technique for transmitting multiple concurrent signals over a fiber-optic line.

a.	Statistical time	c.	Frequency
b.	Synchronous time	d.	Wavelength

 

 

ANS:  D                    PTS:   1                    REF:   134

 

29. ____ technology is a unique form of multiplexing in that all the subchannels multiplexed together are intended for one user.

a.	Time division	c.	Frequency division
b.	Discrete multitone	d.	Code division

 

 

ANS:  B                    PTS:   1                    REF:   134

 

30. Code division multiplexing can produce system capacities that are ____ times those of frequency division multiplexing systems.

a.	2 to 4	c.	4 to 8
b.	3 to 6	d.	8 to 10

 

 

ANS:  D                    PTS:   1                    REF:   135

 

31. If a compression technique does lose some of the data as a result of the compression process, then it is referred to as a ____ compression technique.

a.	complete	c.	lossy
b.	random	d.	lossless

 

 

ANS:  C                    PTS:   1                    REF:   136

 

32. ____ replaces any repetitions of the same bit or byte that occur in a sequence of data with a single occurrence of the bit/byte and a run count, or simply with a run count.

a.	Run-length encoding	c.	Random compression
b.	Lossy compression	d.	Full encoding

 

 

ANS:  A                    PTS:   1                    REF:   136

 

33. A technique that can be used to compress data when a ____ compression is necessary is the Lempel-Ziv technique.

a.	random	c.	lossy
b.	run-length	d.	lossless

 

 

ANS:  D                    PTS:   1                    REF:   137

 

34. ____, which is an abbreviation for MPEG (Moving Picture Experts Group) Audio Layer-3, is a common form of audio compression.

a.	MPEG	c.	MP3
b.	GIF	d.	JPEG

 

 

ANS:  C                    PTS:   1                    REF:   138

 

35. ______ is a technique that is very commonly used to compress video images.

a.	JPEG	c.	MP3
b.	MPEG	d.	AAA

 

 

ANS:  A                    PTS:   1                    REF:   138

 

36. MPEG-1 and MPEG-2—or simply MPEG—are common examples of ____ compression.

a.	wavelength encoding	c.	code division
b.	differential encoding	d.	frequency encoding

 

 

ANS:  B                    PTS:   1                    REF:   138

 

37. Discrete multitone (DMT) is a multiplexing techinque commonly found in _______ systems.

a.	TDM	c.	ATM
b.	DSL	d.	microwave

 

 

ANS:  B                    PTS:   1                    REF:   131

 

COMPLETION

 

1. The technique of transmitting multiple signals over a single medium is ____________________.

 

ANS:  multiplexing

 

PTS:   1                    REF:   120

 

2. A(n) ____________________ is an assigned set of frequencies that is used to transmit the user’s signal.

 

ANS:  channel

 

PTS:   1                    REF:   121

 

3. In general, the device that accepts input from one or more users is called the ____________________.

 

ANS:  multiplexor

 

PTS:   1                    REF:   122

 

4. To keep one signal from interfering with another signal, a set of unused frequencies called a(n) ____________________ is usually inserted between the two signals, to provide a form of insulation.

 

ANS:  guard band

 

PTS:   1                    REF:   122

 

5. In ____________________, the sharing of the medium is accomplished by dividing available transmission time among users.

 

ANS:

time division multiplexing (TDM)

time division multiplexing

TDM

 

PTS:   1                    REF:   123

 

6. In ____________________ multiplexing, the frames of the multiplexor’s output stream are divided into 24 separate digitized voice/data channels of 64 kbps each.

 

ANS:  T-1

 

PTS:   1                    REF:   125

 

7. Synchronous Optical Network (SONET) and ____________________, are powerful standards for multiplexing data streams over a single medium.

 

ANS:

Synchronous Digital Hierarchy (SDH)

Synchronous Digital Hierarchy

SDH

 

PTS:   1                    REF:   126

 

8. ____________________, and Synchronous Digital Hierarchy (SDH) are two almost identical standards for the high-bandwidth transmission of a wide range of data types over fiber-optic cable.

 

ANS:

Synchronous Optical Network (SONET)

Synchronous Optical Network

SONET

 

PTS:   1                    REF:   126

 

9. A T-1 telecommunications line uses a multiplexing technique termed ____________________, which provides for the multiplexing of up to 24 separate channels at a total speed of 1.544 Mbps.

 

ANS:  DS-1 signaling

 

PTS:   1                    REF:   126

 

10. Each STS level supports a particular data rate and is supported by a physical specification called a(n) ____________________.

 

ANS:

optical carrier (OC)

optical carrier

OC

 

PTS:   1                    REF:   126

 

11. ____________________, transmits data only from active users and does not transmit empty time slots.

 

ANS:

Statistical time division multiplexing (Stat TDM)

Statistical time division multiplexing

Stat TDM

 

PTS:   1                    REF:   128

 

12. In Stat TDM, the ____________________, provides information that the receiving multiplexor can use to detect transmission errors within the frame.

 

ANS:

frame check sequence (FCS)

frame check sequence

FCS

 

PTS:   1                    REF:   129

 

13. The inability of a single fiber-optic line to meet users’ needs is called ____________________.

 

ANS:  fiber exhaust

 

PTS:   1                    REF:   129

 

14. In WDM, the wavelength of each differently colored laser is called the ____________________.

 

ANS:  lambda

 

PTS:   1                    REF:   130

 

15. When WDM can support a large number of lambdas, it is often called ____________________.

 

ANS:

dense wavelength division multiplexing (DWDM)

dense wavelength division multiplexing

DWDM

 

PTS:   1                    REF:   130

 

16. ____________________ is a multiplexing technique commonly found in digital subscriber line (DSL) systems.

 

ANS:

Discrete multitone (DMT)

Discrete multitone

DMT

 

PTS:   1                    REF:   131

 

17. ____________________ is a modulation technique that involves a four-bit code in which eight phase angles have a single amplitude, and four phase angles have double amplitudes.

 

ANS:

Quadrature amplitude modulation (QAM)

Quadrature amplitude modulation

QAM

 

PTS:   1                    REF:   131

 

18. ____________________ is a relatively new technology that has been used extensively by both the military and cellular telephone companies.

 

ANS:

Code division multiplexing (CDM)

Code division multiplexing

CDM

 

PTS:   1                    REF:   132

 

19. Code division multiplexing uses ____________________ spread spectrum technology.

 

ANS:  direct sequence

 

PTS:   1                    REF:   132

 

20. ____________________ are the codes assigned to users in CDM.

 

ANS:  Chip spreading codes

 

PTS:   1                    REF:   133

 

21. ____________________ is the process of taking data and somehow packing more of it into the same space.

 

ANS:  Compression

 

PTS:   1                    REF:   134

 

22. With a(n) ____________________ compression technique, no data is lost due to compression.

 

ANS:  lossless

 

PTS:   1                    REF:   134

 

23. One of the more common and simpler examples of lossless compression is ____________________-length encoding.

 

ANS:  run

 

PTS:   1                    REF:   136

 

24. Audio engineers compress music through techniques called perceptual noise shaping, or ____________________.

 

ANS:  perceptual encoding

 

PTS:   1                    REF:   138

 

ESSAY

 

1. What is the difference between a multiplexor and a demultiplexor?

 

ANS:

In general, the device that accepts input from one or more users is called the multiplexor. The device that is attached to the receiving end of the medium and splits off each signal to deliver it to the appropriate receiver is called the second multiplexor, or demultiplexor. In all frequency division multiplexing systems, the multiplexor accepts input from the user(s), converts the data streams to analog signals using either fixed or dynamically assigned frequencies, and transmits the combined  analog signals over a medium that has a wide enough bandwidth  to support the total range of all the assigned frequencies. The demultiplexor then accepts the combined analog signals, separates out one or more of the individual analog signals, and delivers these to the appropriate user(s).

 

PTS:   1                    REF:   122

 

2. How does time division multiplexing work?

 

ANS:

Suppose an instructor in a classroom poses a controversial question to students. In response, a number of hands shoot up, and the instructor calls on each student, one at a time. It is the instructor’s responsibility to make sure that only one student talks at any given moment, so that each individual’s response is heard. In a relatively crude way, the instructor is a time division multiplexor, giving each user (student) a moment in time to transmit data (express an opinion to the rest of the class). In a similar fashion, a time division multiplexor calls on one input device after another, giving each device a turn at transmitting its data over a high-speed line. Suppose two users, A and B, wish to transmit data over a shared medium to a distant computer. We can create a rather simple time division multiplexing scheme by allowing user A to transmit during the first second, then user B during the following second, followed again by user A during the third second, and so on.

 

PTS:   1                    REF:   123

 

3. How does T-1 multiplexing work?

 

ANS:

In T-1 multiplexing, the frames of the T-1 multiplexor’s output stream are divided into 24 separate digitized voice/data channels of 64 kbps each. Users who wish to use all 24 channels are using a full T-1, while other users who need to use only part of the 24 channels may request a fractional T-1. The T-1 multiplexed stream is a continuous repetition of frames. Each frame consists of 1 byte from each of the 24 channels (users) plus 1 synchronization bit. Thus, data from the first user is followed by the data from the second user, and so on, until data from the 24th user is once again followed by data from the first user. If one of the 24 input sources has no data to transmit, the space within the frame is still allocated to that input source. The input data from a maximum of 24 devices is assigned to fixed intervals. Each device can transmit only during that fixed interval. If a device has no significant data to transmit, the time slot is still assigned to that device, and data such as blanks or zeros are transmitted.

 

PTS:   1                    REF:   125

 

4. How does Wavelength division multiplexing work?

 

ANS:

The technique assigns a uniquely colored laser to each input source and combines the multiple optical signals of the input sources so that they can be amplified as a group and transported over a single fiber. It is interesting to note that because of the properties of the signals and glass fiber, plus the nature of light itself, each signal carried on the fiber can be transmitted at a different rate from the other signals. This means that a single fiber-optic line can support simultaneous transmission speeds such as 51.84 Mbps, 155.52 Mbps, 622.08 Mbps, and 2.488 Gbps (which, incidentally, are multiples of T-1 speeds and are defined as OC-1, OC-3, OC-12, and OC-48, the optical carrier specifications for high-speed fiber-optic lines). In addition, a single fiber-optic line can support a number of different transmission formats such as SONET, Asynchronous Transfer Mode (ATM), and others, in various combinations.

 

PTS:   1                    REF:   129

 

5. What are the major disadvantages of frequency division multiplexing?

 

ANS:

Frequency division multiplexing suffers from two major disadvantages. The first disadvantage is found in computer-based systems that multiplex multiple channels over a single medium. Because the frequencies are usually statically assigned, devices that do not have anything to transmit are still assigned frequencies, and thus bandwidth is wasted. The second disadvantage of frequency division multiplexing is due to the fact that the technique uses analog signals, and analog signals are more susceptible to noise disruption than digital signals. Nonetheless, many different types of applications (such as television and radio) use frequency division multiplexing because of its simplicity, and the technique is probably going to be with us for a long time.

 

PTS:   1                    REF:   134