Chapter 3 – Physical Layer
Dr. Hussein Al-Bahadili
Chapter 3
Physical Layer
True-False Questions
The following are possible True/False questions for tests. The statement is given and the answer
is provided in square brackets. The level of difficulty (easy, moderate, difficult) and the page
number(s) relevant to the topic are also furnished.
1.
The physical layer is the only layer where two communicating nodes are directly connected.
Difficulty:
Easy
p. 74
2.
A physical circuit refers to the transmission characteristics of the connection.
3.
Difficulty:
Easy
Computers produce digital data whose values are binary: 0 or 1.
4.
5.
p.74
Difficulty:
Easy
p. 75
With modem communications, the receiving modem converts the incoming digital signal
from the telephone line into an analog signal that can be understood by the computer.
Difficulty:
Moderate
p. 75
Digital transmission produces more errors than analog transmission.
6.
Difficulty:
Easy
p. 75
Newer telephone circuits, built during the last decade, offer higher quality because they were
built using analog transmission.
7.
Difficulty:
Easy
p. 75
In a multipoint circuit configuration, each computer has a dedicated circuit between itself and
each of the other computers in the network
8.
Difficulty:
Easy
p. 76
In a multipoint circuit configuration, each computer can use the circuit at the same time.
9.
Difficulty:
Easy
p. 76
In simplex transmission, the data flows in both directions at the same time
10.
Difficulty:
Easy
An intercom is an example of half-duplex transmission.
11.
12.
p. 76
Difficulty:
Moderate
p. 76
The amount of time it takes to switch between sending and receiving in half-duplex
transmission is called the propagation delay.
Difficulty: Easy
p. 76
In full-duplex transmission, two stations can send and receive simultaneously.
Difficulty:
Easy
p. 77
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Chapter 3 – Physical Layer
Dr. Hussein Al-Bahadili
13.
The medium is the physical matter or substance that carries the voice or data transmission.
14.
Difficulty:
Easy
p. 78
Guided media refers to the type of media in which the message is broadcast through the air.
15.
Difficulty:
Easy
p. 78
Coaxial cable costs less and offers less shielding to electrical interference than twisted pair
cable.
16.
Difficulty:
Moderate
Fiber optic cable carries signals in traditional electrical form
p. 79
17.
Difficulty:
Easy
p. 79
Multimode fiber is capable of longer transmission distances than single mode fiber.
18.
Difficulty:
Easy
p. 79-81
Radio data transmission requires that each device has a radio receiver/transmitter and uses a
specific frequency.
19.
Difficulty:
Moderate
p.81
Infrared transmission uses high-frequency light waves to carry data through the air on a
direct line-of-sight path between two points.
20.
Difficulty: Moderate
p. 82
Microwave transmissions require a line of sight between any two points.
21.
Difficulty:
Easy
Propagation delay is negligible with satellite transmission.
22.
p. 82
Difficulty: Moderate
p. 83
One form of interference with satellite transmission is called raindrop attenuation in which
the transmissions are absorbed by heavy rain.
23.
Difficulty: Moderate
Fiber optic cable can only be used on LANs.
24.
Difficulty: Easy
p. 85
Radio, infrared, microwave and satellite are all examples of guided media.
25.
Difficulty: Moderate
p. 86
Of all the media available, fiber optic provides the highest transmission speeds.
26.
Difficulty: Moderate
p. 86
Coding schemes are groups of bits that translate into the “alphabet” of any given system.
27.
Difficulty: Easy
p. 86
ASCII is the least popular code for data communications.
Difficulty: Easy
p. 83
p. 86-87
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 3 – Physical Layer
Dr. Hussein Al-Bahadili
28.
ASCII is the coding scheme developed by IBM for its mainframe computers.
29.
Difficulty: Easy
p. 86-87
The predominant method of transferring information internally in a computer is via parallel
mode.
30.
Difficulty: Easy
p. 87
Serial mode transmission is much faster than parallel mode transmission.
31.
Difficulty: Easy
p. 87
Data rate refers to how often the sender can send data and is measured in bits per second
32.
Difficulty: Easy
Non-return-to-zero is a type of unipolar signaling
33.
34.
p. 88
Difficulty: Moderate
p. 88
With non return to zero signaling, the voltage alternates between zero and a positive or
negative voltage.
Difficulty: Easy
p. 88
Ethernet, a common LAN technology, uses Manchester encoding..
35.
Difficulty: Easy
p. 89
Manchester encoding is a special type of bipolar signaling in which the signal is changed
from high to low or from low to high in the middle of the signal.
36.
Difficulty: Moderate
p. 89-90
Digital transmission occurs when the signal sent over the transmission media constantly
varies among an infinite number of states.
37.
Difficulty: Easy
p. 90
Frequency is the number of cycles per second and is expressed in Hertz.
38.
Difficulty: Easy
p. 90
Amplitude, frequency and phase are all characteristics of a sound wave.
39.
Difficulty: Easy
p. 90-91
Frequency modulation refers to the changing of the height of the sound wave.
40.
Difficulty: Moderate
Baud rate is the number of bits transmitted per second.
41.
Difficulty: Easy
p. 93
Bandwidth is the difference between the highest and lowest frequencies in a band.
42.
Difficulty: Easy
p. 94
Demodulation is the conversation of an analog signal into a digital signal.
Difficulty: Moderate
p. 90-91
p. 95
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 3 – Physical Layer
43.
44.
45.
46.
47.
Dr. Hussein Al-Bahadili
“Handshaking” refers the testing of the circuit to determine the optimum combination of
symbol rate and modulation technique that will produce the highest data transmission rates.
Difficulty: Moderate
p. 95
Data compression can increase the throughput of a communication link.
Difficulty: Easy
p. 95
A codec converts an incoming digital signal to an analog signal for transmission over an
analog network.
Difficulty: Moderate
p. 96
One way to reduce quantizing errors is to increase the sampling rate of the analog signal.
Difficulty: Moderate
p. 96-97
The “local loop” refers to the wires that run from the customer premises to the telephone
switch of the telephone company.
48.
Difficulty: Moderate
p. 98
Multiplexing increases the cost of provisioning network circuits.
49.
Difficulty: Moderate
p. 101
Frequency division multiplexing divides the circuit into a set of different time slots.
50.
Difficulty: Moderate
p. 101
Time division multiplexing is more efficient that frequency division multiplexing because the
guardbands used in the frequency division multiplexing or not needed.
51.
Difficulty: Moderate
p. 102
Statistical time division multiplexing does not require the capacity of the circuit to be equal
to the sum of the combined circuits.
52.
Difficulty: Moderate
p. 102-103
Wavelength division multiplexing can only used with copper cables.
Difficulty: Easy
p. 104
MULTIPLE CHOICE
The following are possible multiple-choice questions for tests. The question is posed and the
answer is provided under the choices. The level of difficulty (easy, moderate, difficult) and the
page number(s) relevant to the topic is also furnished.
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
(4/20)
Chapter 3 – Physical Layer
1.
2.
3.
4.
5.
6.
Data is
layer.
a.
b.
c.
d.
e.
Dr. Hussein Al-Bahadili
physically transmitted from one computer or terminal to another in the ________
physical
transport
application
terminal
data link
Difficulty: Easy
p. 74
____________ refers to the transmission characteristics of the circuit.
a. handshaking
b. virtual circuit
c. bonding
d. logical circuit
e. physical circuit
Difficulty: Easy
Two fundamentally different types of data are:
a. DSL and ADSL
b. asymmetric and symmetric
c. Microsoft and IBM
d. digital and analog
e. local area and wide area
p. 74
Difficulty: Easy
p. 75
In general, networks designed to transmit primarily computer data are likely to be ________,
while networks designed to transmit voice data are likely to be ________.
a. slow, fast
b. level 1, level 2
c. numeric, musical
d. direct, indirect
e. digital, analog
Difficulty: Easy
p. 75
Which of the following is not a key advantage of digital transmission?
a. It permits only low transmission rates.
b. It is more efficient.
c. It is simpler to integrate voice, video, and data on the same circuit.
d. It is more secure.
e. It produces fewer errors.
Difficulty: Moderate
_________ is the basic layout of the circuit.
a. point-to-point configuration
b. configuration
c. circuit configuration
d. circuit design
e. circuit plan
Difficulty: Moderate
p. 75
p. 76
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 3 – Physical Layer
7.
8.
9.
10.
11.
Dr. Hussein Al-Bahadili
A(n) __________ circuit is another name for a multipoint configuration.
a. analog
b. dedicated
c. point-to-point
d. shared
e. simplex
Difficulty: Moderate
p. 76
Which is not true about point-to-point circuits?
a. point-to-point circuits are dedicated to the use of the two computers.
b. point-to-point circuits are more expensive than multipoint circuits.
c. point-to-point circuits are called dedicated circuits.
d. point-to-point circuits reduce the amount of cable required and use the circuit more
efficiently than multipoint circuits.
e. Point-to-point circuits are used when the computers generate enough traffic to fill the
capacity of the communication circuit.
Difficulty: Moderate
p. 76
Having a conversation with someone using a cellular phone is an example of _________
transmission.
a. simplex
b. full-duplex
c. half-duplex
d. analog
e. digital
Difficulty: Easy
p.76-77
The ability to transmit in both directions, but only in one direction at a time is an example of
_______________ transmission.
a. simplex
b. full-duplex
c. half-duplex
d. analog
e. digital
Difficulty: Easy
The two basic types of media are:
a. statistical and frequency
b. guided and wireless (radiated)
c. local and wide area
d. attenuator and Gaussian
e. duplexed and non-duplexed
Difficulty: Easy
p. 14
p. 78
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
(6/20)
Chapter 3 – Physical Layer
12.
13.
14.
15.
16.
Dr. Hussein Al-Bahadili
Which of the following would be considered a type of wireless media?
a. unshielded twisted pair
b. shielded twisted pair
c. coaxial cable
d. microwave
e. fiber optics
Difficulty: Moderate
p. 78
The type of media usually installed on homes and businesses by the telephone company is
called ____________.
a. fiber optic cable
b. coaxial cable
c. twisted pair
d. phone cable
e. phone wire
Difficulty: Easy
The earliest type of fiber optic systems were:
a. Graded index multimode
b. Attenuated
c. Multimode
d. Single mode
e. Step mode
p. 78
Difficulty: Easy
Another term for the weakening of a signal over distance is:
a. turnaround time
b. propagation delay
c. dispersion
d. insulation
e. attenuation
p. 79
Difficulty: Moderate
p. 79
___________ refers to the spreading of the signal that different parts of the signal arrive at
different times at the destination.
a.
b.
c.
d.
e.
turnaround time
propagation delay
dispersion
insulation
attenuation
Difficulty: Moderate
p. 79
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
(7/20)
Chapter 3 – Physical Layer
17.
18.
19.
20.
21.
22.
Dr. Hussein Al-Bahadili
Which of the following media can best withstand harsh environmental conditions?
a. shielded twisted pair
b. unshielded twisted pair
c. Cat 5 twisted pair
d. coaxial cable
e. fiber optic cable
Difficulty: Moderate
__________ is a line-of-sight type of wireless media.
a. coaxial cable
b. microwave
c. radio
d. twisted pair
e. fiber optic
p. 81
Difficulty: Moderate
p. 82
____________ transmission is prone to interference from smoke, heavy rain and fog and
requires line-of-sight.
a. microwave
b. radio
c. infrared
d. fiber optic
e. led
Difficulty: Moderate
Microwave transmission:
a. is a type of high frequency radio communication
b. requires a clear line-of-sight path
c. is typically used for long distance data transmission
d. does not require the laying of any cable
e. all of the above
p. 82
Difficulty: Easy
p. 82-83
______________ refers to the time it takes for a signal to travel from sender to recipient
(highly exaggerated with satellite transmission).
a. Line-of-sight effect
b. Multimode index
c. Saturation effect
d. Raindrop attenuation
e. Propagation delay
Difficulty: Moderate
p. 83
Which of the following is not an important factor to consider when selecting media to be
used in a network?
a. prestige value of the type of media
b. type of network
c. cost
d. transmission distance
e. security
Difficulty: Moderate
p. 85
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
(8/20)
Chapter 3 – Physical Layer
23.
24.
25.
26.
27.
28.
Dr. Hussein Al-Bahadili
Which of the following media is the least secure?
a. coaxial cable
b. unshielded twisted pair
c. shielded twisted pair
d. fiber optic cable
e. infrared
Difficulty: Moderate
p. 86
Which of the following media has the lowest error rates and the highest transmission speeds?
a. coaxial cable
b. unshielded twisted pair
c. shielded twisted pair
d. fiber optic cable
e. infrared
Difficulty: Moderate
p. 86
Transmission speeds:
a. are the same among all media
b. are not a factor in selecting a media because all media have more than enough speed
to serve current communication demands
c. are a constant, 56Kbps, for all media types
d. differ widely among media
e. always have a direct correlation with security
Difficulty: Moderate
p. 86
A coding scheme that uses 10 bits to represent each character is capable of representing
_________ different characters.
a. 256
b. 20
c. 200
d. 512
e. 1024
Difficulty: Moderate
p. 86
____________ is one of the most commonly used coding schemes used in data transmission.
a. ASCII
b. ISDN
c. MAU
d. ATM
e. FDM
Difficulty: Easy
p. 86
The representation of the character A by the group of 8 bits, 10000001, is an example of:
a. digital coding
b. phase modulation
c. binary modulation
d. analog transmission
e. pitch variation
Difficulty: Moderate
p. 86
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 3 – Physical Layer
29.
30.
31.
32.
33.
Dr. Hussein Al-Bahadili
When all bits of a character are transferred one after another, the bits are transferred in
___________ mode.
a. serial
b. frequency division
c. multiplexing
d. parallel
e. full complex
Difficulty: Moderate
p. 87
Which of the following statements is correct?
a. Parallel transmission is most often used for sending data on a circuit that is made up
of one wire.
b. Parallel transmission is distinguished from serial transmission by the fact that the
transmitting device sends a single bit, then a second bit, and so on, until all the bits
are transmitted.
c. Parallel transmission is only used for analog data.
d. Serial transmission is slower than parallel transmission.
e. Parallel transmission is the same as serial transmission.
Difficulty: Moderate
___________ is not a type of digital signaling technique.
a. Non-return-to-zero signaling
b. Unipolar signaling
c. Manchester encoding
d. Return-to-zero signaling
e. Data rate signaling
p. 87
Difficulty: Moderate
p. 88
With which type of digital signaling does the signal always return to zero volts after each bit?
a. Non-return-to-zero signaling
b. Unipolar signaling
c. Return-to-zero signaling
d. Data rate signaling
e. Huffman encoding signal
Difficulty: Easy
p.88
Which type of digital signaling would experience fewer errors because it has more distinct
signals?
a. unipolar
b. serial
c. bipolar
d. attenuation
e. Huffman encoding signal
Difficulty: Difficult
p. 88
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
(10/20)
Chapter 3 – Physical Layer
34.
35.
36.
37.
38.
39.
Dr. Hussein Al-Bahadili
Which of the following is a characteristic of sound waves that can be modulated to convert
digital data into analog signals?
a. phase
b. attenuation
c. bipolar
d. bandwidth
e. codec
Difficulty: Moderate
The direction in which the sound wave begins is known as:
a. amplitude, which our ears detect as loudness
b. frequency, which our ears detect as pitch
c. phase
d. bandwidth
e. furlong
p. 90-91
Difficulty: Moderate
The height of a sound wave is called its:
a. frequency
b. phase
c. amplitude
d. bandwidth
e. furlong
p. 90-91
Difficulty: Easy
90
_____________ is not a form of modulation used to transform digital data into analog
signals.
a. synchronous time division
b. amplitude shift keying
c. amplitude modulation
d. frequency modulation
e. phase modulation
Difficulty: Moderate
91-92
____________ refers to changing the shape of the sound wave in different ways to represent
a 1 or a 0.
a. digitizing.
b. sampling
c. modulation
d. demodulation
e. shaping
Difficulty: Moderate
91
With respect to converting digital data into analog signals, AM stands for:
a. Asynchronous Manchester
b. Analog Multimode
c. Amplitude Modulation
d. Anomaly Multiplexing
e. Analytical Mosaic
Difficulty: Moderate
p. 91
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 3 – Physical Layer
40.
41.
42.
Dr. Hussein Al-Bahadili
In which type of modulation is a 1 distinguished from a 0 by shifting the direction in which
the wave begins?
a. bandwidth modulation
b. amplitude modulation
c. frequency modulation
d. phase modulation
e. codec modulation
Difficulty: Moderate
p. 92
When sending four bits at a time using frequency modulation, the number of different
frequency levels that would be needed would be _______.
a. 24
b. 16
c. 2
d. 8
e. 4
Difficulty: Moderate
p. 92
____________ is a modulation technique that combines two different amplitude
combinations with eight different phase combinations modulation to send four bits per wave,
or symbol.
a. quadrature amplitude modulation
b. time division multiplexing
c. synchronous digital line control
d. pulse code modulation
e. baseband signaling
Difficulty: Moderate
43.
44.
p. 93
__________ is a unit of signaling speed that indicates how often the signal changes on a
communication circuit.
a. bits per second rate
b. phase rate
c. symbol rate
d. attenuation rate
e. trellis rate
Difficulty: Moderate
The _____________ of a circuit determines a circuit’s capacity.
a. frequency
b. bandwidth
c. phase
d. amplitude
e. loudness
Difficulty: Moderate
p. 93
93
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
(12/20)
Chapter 3 – Physical Layer
45.
46.
47.
48.
49.
Dr. Hussein Al-Bahadili
The typical range of human hearing is:
a. 0 to 4,000 Hz
b. 0 to 1,200 Hz
c. 20 to 14,000 Hz
d. 0 to 300 Hz
e. 0 to 56,000 Hz
Difficulty: Easy
p. 94
If the highest frequency of a circuit is 10KHZ and the lowest frequency is 900 Hz, the
bandwidth available for this circuit is :
a. 890 Hz
b. 8900 HZ
c. 9100 Hz
d. 9Khz
e. 890 KHz
Difficulty: Difficult
p. 94
To get more “bandwidth” in a digital transmission, you must:
a. increase the range of frequencies available for a transmission
b. increase the loudness per transmission
c. decrease the bits per second transmission speed
d. increase the phase shifts per transmission
e. increase the baud rate per transmission
Difficulty: Moderate
p. 94
Which of the following statements is true?
a. the longer the distance of a telephone wire between sender and recipient, the lower
the bandwidth across that wire
b. the shorter the distance of a telephone wire between sender and recipient, the lower
the bandwidth across that wire
c. bandwidth is constant across any wire, therefore distance is not relevant to its
capacity
d. the longer the distance of a telephone wire between sender and recipient, the higher
the bandwidth across that wire
e. bandwidth is not a term that can be used when discussing telephone transmissions
Difficulty: Difficult
p. 94
Using TCM that sends 6 bits per each signal and a voice grade line with a bandwidth of 3000
Hz (assume: no noise on the line), the data capacity would be ___________ bits per second.
a. 56K
b. 6
c. 24,000
d. 500
e. 18,000
Difficulty: Moderate
p. 94-95
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
(13/20)
Chapter 3 – Physical Layer
50.
51.
52.
Dr. Hussein Al-Bahadili
The acronym, Modem, stands for _________________.
a. multiplexing/demultiplexing
b. more/demote
c. Mode-M technique
d. modulator/demodulator
e. Mod emulation technique
Difficulty: Easy
p. 95
Which statement is false about modems?
a. modems are usually used in pairs (2 at a time)
b. a receiving modem demodulates and a sending modem modulates
c. most modems support several modem standards so that they can communicate with a
variety of modems
d. modems may operate at a lower speed that that for which they are rated, especially if
they detect noise in the communication line
e. modems must always be internal to the computer
Difficulty: Moderate
p. 95-96
______ is a modem standard that uses Lempel-Ziv encoding to compress data.
a. V.22
b. V.44
c. V.32bis
d. V.34
e. RS 232
Difficulty: Moderate
53.
54.
p.95
Equipment used to transform analog voice signals to digital signals and digital signals to
analog signals.
a. voice converter
b. modem
c. codec
d. multiplexer
e. demodulator
Difficulty: Moderate
p. 96
_____________ refers to the difference between the original analog data and the
approximation of that data using the techniques for translating from analog data to digital
signals.
a. quantizing error
b. handshaking phase
c. modulating frequency
d. POTS anomaly
e. amplitude Trellis effect
Difficulty: Moderate
p. 96
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
(14/20)
Chapter 3 – Physical Layer
55.
56.
Dr. Hussein Al-Bahadili
When converting analog voice data to digital signals, Pulse Code Modulation samples the
incoming voice signal _______ times per second.
a. 8,000
b. 8
c. 18,000
d. 64
e. 256
Difficulty: Moderate
p. 97
How many bits are required to sample an incoming signal 4000 times per second using 64
different amplitude levels?
a. 64
b. 32
c. 16
d. 8
e. 6
Difficulty: Moderate
57.
58.
59.
p. 98
If each sample uses 16 bits and the number of samples taken each second is 8000; then the
transmission speed on the circuit is?
a. 128 Kbps
b. 64 Kbps
c. 12800 bps
d. 96 Kbps
e. 32000 bps
Difficulty: Moderate
p. 98-99
A(n) ___________ divides one high-speed communication circuit into several lower speed
circuits for the primary reason of saving communication line costs.
a. transponder
b. multiplexer
c. inverse multiplexer
d. codec
e. intelligent terminal
Difficulty: Moderate
p. 98-99
____________ is used by IM and other applications that provide voice services over lowerspeed digital circuits.
a.
b.
c.
d.
e.
pulse code modulation
adaptive differential pulse code modulation
Voice conversation
code modulation
phase modulation
Difficulty: Moderate
p. 99
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
(15/20)
Chapter 3 – Physical Layer
60.
61.
62.
63.
64.
Dr. Hussein Al-Bahadili
The type of multiplexer that divides the circuit horizontally into different light frequencies
that are transmitted simultaneously across many channels is a:
a. wave division multiplexer
b. time division multiplexer
c. statistical time division multiplexer
d. frequency division multiplexer
e. statistical frequency division multiplexer
Difficulty: Moderate
p.101
Frequency division multiplexing:
a. operates by statistically time slicing the signal
b. operates by dividing the signal into different frequencies
c. uses a codec that divides signals into different channels
d. operates by time slicing the signal
e. operates by light dividing the signal
Difficulty: Easy
p. 101
________________ separate channels to reduce interference between channels in frequency
division multiplexing.
a. Channel blockers
b. Statistical dividers
c. Attenuators
d. Guardbands
e. Adaptive differential processors
Difficulty: Moderate
p. 101
Time (non-statistical) division multiplexing differs from frequency division multiplexing
because it:
a. does not share a communication circuit
b. splits the communication circuit vertically (with time slots) instead of horizontally
c. increases the wavelength and phase angles of the baseband frequency used for
transmission
d. moves the baseband of a circuit by shifting it to a higher frequency
e. reduces baseband signal velocity more than frequency division multiplexing
Difficulty: Moderate
p. 102
Inverse multiplexing means:
a. combining several low speed circuits to enable them to be transmitted across one
high speed circuit
b. multiplexing from the terminal to the host, rather than from the host to the terminal
c. combining high speed circuits to enable them to be transmitted across one low speed
circuit
d. inverting the frequencies used for transmission across a low speed circuit for
switching to a digital circuit
e. multiplexing to a codec, rather than to a modem
Difficulty: Moderate
p105-106
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 3 – Physical Layer
65.
Dr. Hussein Al-Bahadili
Digital Subscriber Line:
a. is a fairly recent approach to provide higher data transmission rates across traditional
voice circuits in the local loop
b. combines analog transmission and frequency division multiplexing
c. involves the use of a customer premises equipment (CPE)
d. uses a combination of amplitude and phase modulation
e. all of the above
Difficulty: Moderate
p. 107
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Chapter 3 – Physical Layer
Dr. Hussein Al-Bahadili
Essay and Short Answer Questions
1. Define analog, and then describe the conversion from analog to digital using a four
step method (sampling, measuring, quantizing and coding), and present a detailed
diagram like the one which in the slides. What is quantizing error and how can it
be lessened in some situations? Draw a sketch of quantizing error in your model.
2. Describe the three types of data flows, and discuss why some are applicable in
some situations and vice versa.
3. Describe three types of guided media. Give an example, describe what it looks
like and how it works, and why it might be used in a scenario of a network.
4. Describe four types of radiated media. Give an example, describe what it looks
like and how it works, and why it might be used in a scenario of a network.
5. What is the term used to describe the placing of two or more signals on a single
circuit?
6. What is the function of a front end processor?
7. What is the purpose of multiplexing? How does it work? Multiplexing usually is
done in multiples of _______ ? Of the different types of multiplexing, what
distinguishes
a.
Frequency division multiplexing (FDM)? (describe and draw a sketch of
this)
b.
Time division multiplexing (TDM)? (describe and draw a sketch of this)
c.
Statistical time division multiplexing (STDM)? (describe and draw a sketch
of this)
d.
Wavelength division multiplexing (WDM)? (describe)
8. What is the function of inverse multiplexing? What is an inverse multiplexer?
Why would you put one on a network?
9. If you were buying a multiplexer, why would you choose either TDM or FDM?
10. Describe two ways in which Statistical Time Division Multiplexing (STDM)
differs from Time Division Multiplexing (TDM).
11. Compare and contrast Frequency Division Multiplexing (FDM) and Wavelength
Division Multiplexing (WDM).
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 3 – Physical Layer
Dr. Hussein Al-Bahadili
12. Under what circumstances would you use a microwave circuit rather than a
satellite circuit?
13. Explain two reasons why the use of twisted pair cable is becoming more common
than the use of coax cable?
14. How does analog data differ from digital data?
15. Clearly explain the differences between analog data, analog transmission, digital
data, and digital transmission.
16. Define digital data and draw a picture of it as compared to a picture of analog
data. Explain why most networks are now digital. Why is digital transmission
superior to analog? Give five reasons.
17. What is coding? Briefly describe the two most important coding schemes.
18. How is data transmitted in parallel? What feature distinguishes serial mode from
parallel mode?
19. How does bipolar signaling differ from unipolar signaling? Why is Manchester
encoding more popular than either? What kind of signaling is used in Ethernet?
20. What are the three important characteristics of a sound wave?
21. Describe how data could be transmitted using amplitude modulation. Draw this.
22. Describe how data could be transmitted using frequency modulation. Draw this.
23. Describe how data could be transmitted using phase modulation. Draw this.
24. Describe how data could be transmitted using a combination of modulation
techniques.
25. Is the bit rate the same as the symbol rate? Explain.
26. What is a modem? How does a modem send digital data on an analog network?
Draw a schematic or diagram of this, explaining the process step by step.
27. Describe two common modem standards.
28. Why is data compression so useful? Describe how it works.
29. What is the typical sampling network in telephony? Why is a higher sampling
rate more effective for sound quality?
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 3 – Physical Layer
Dr. Hussein Al-Bahadili
30. How does PCM differ from PAM? Explain this question with details and
diagrams.
31. What is the difference between multiplexing and modulation? Why are each
important? Draw a picture that shows a sample of multiplexing at work (a specific
kind) and modulation at work (a specific kind).
32. Compare and contrast data rate (i.e., bits per second) and symbol rate (also called
baud rate) by giving two concrete, different examples.
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