Chapter 4 – Data Link Layer
Dr. Hussein Al-Bahadili
Chapter 4
Data Link 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.
Media access controls refer to the need to control when computers transmit.
2.
Difficulty: Easy
p.115
The data link layer accepts messages from the network layer and controls the hardware that
transmits them.
3.
Difficulty: Moderate
p. 115
Only the sender of a data transmission needs to be concerned about the rules or protocols that
govern how it communicates with the receiver
4.
Difficulty: Easy
p. 115
Most computer networks managed by a host mainframe computer use contention media
access control.
5.
Difficulty: Moderate
p. 116
Polling is the process of permitting all clients to transmit or receive at any time.
6.
Difficulty: Moderate
p. 116
With roll call polling, a server polls clients in a consecutive, pre-arranged priority list.
7.
Difficulty: Easy
p. 116
Token passing is a term that refers to hub polling, in which one computer starts a poll and
passes it to the next computer on a multipoint circuit.
8.
Difficulty: Easy
p. 116-117
With contention, a computer does not have to wait before it can transmit. A computer can
transmit at anytime.
9.
Difficulty: Moderate
Contention is commonly used with Ethernet local area networks.
10.
Difficulty: Easy
p. 117
Controlled access MAC approaches work better in a large network with high usage.
11.
p. 117
Difficulty: Easy
p. 117
In a network, the type of errors caused during data transmission can be controlled by the
network hardware and software.
Difficulty: Easy
p. 117
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 4 – Data Link Layer
Dr. Hussein Al-Bahadili
12.
The two categories of network errors are: lost data and delimited data.
13.
Difficulty: Easy
p. 118
If a computer transmits a message containing “ABC” and the destination computer receives
“abc” as the message, the message is corrupted.
Difficulty: Moderate
In data transmission, data errors are uniformly distributed in time.
p. 118
14.
Difficulty: Easy
Private dedicated lines are more prone to error than dialup lines.
p. 118
15.
16.
Difficulty: Moderate
p 118
Undesirable stray electrical voltage can cause data communication errors.
p. 119
17.
Difficulty: Moderate
Gaussian noise is a special type of attenuation.
Difficulty: Moderate
Impulse noise is caused by the thermal agitation of electrons.
p.119
18.
19.
20.
21.
22.
Difficulty: Easy
p. 119
Crosstalk occurs when the signal transmitted on one circuit or channel of a transmission
system creates an undesired effect in another circuit or channel.
Difficulty: Moderate
Attenuation refers to the loss of signal strength.
p. 120
Difficulty: Easy
p 120
When the signals from two circuits combine to form a new signal that falls into a frequency
band reserved for another signal, this is called, intermodulation noise.
Difficulty: Moderate
p. 120
Eliminating jitter to generate a pure carrier signal in an analog circuit is impossible
23.
Difficulty: Easy
p. 120
The distance between repeaters or amplifiers on a telephone circuit is determined by the
amount of power gained per unit length of the transmission.
24.
Difficulty: Moderate
p. 121
When we amplify the signal on an analog circuit, we also amplify any noise that is present on
the circuit.
25.
Difficulty: Easy
p. 121
A conditioned circuit is more expensive than a regular telephone circuit because it has been
certified by the carrier to experience fewer errors.
Difficulty: Moderate
p.122
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 4 – Data Link Layer
Dr. Hussein Al-Bahadili
26.
For effective error detection and correction, extra error detection “data” must be included
with each message
27.
Difficulty: Moderate
p. 122
In an odd parity-checking scheme, the parity bit is set to make the total number of ones in the
byte (including the parity bit) an even number.
28.
Difficulty: Easy
p. 122-123
Parity checking can only detect an error when an even number of bits are switched.
29.
Difficulty: Moderate
p. 123
Cyclical redundancy check is the most popular polynomial error-checking scheme.
30.
Difficulty: Easy
The simplest method for error correction is retransmission.
31.
Difficulty: Easy
Another term for stop-and-wait ARQ is sliding window.
p. 124
p.124
32.
Difficulty: Easy
One type of forward error correction is the Hamming code.
33.
Difficulty: Moderate
p. 126-127
Forward error correction is commonly used in satellite transmission.
Difficulty: Easy
HDLC is very similar to the SDLC synchronous data link protocol.
p. 126
34.
Difficulty: Moderate
Ethernet is a character-oriented data link protocol
p.131-132
35.
Difficulty: Easy
Point-to-point Protocol is a byte-count-oriented protocol.
p. 132-133
36.
37.
38.
p. 124-125
Difficulty: Easy
p. 133
Overhead bits are used for error checking and marking the start and end of characters and
packets.
Difficulty: Easy
p. 134
Transmission efficiency refers to the percentage of bits transmitted without errors.
Difficulty: Moderate
p. 135
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Chapter 4 – Data Link Layer
Dr. Hussein Al-Bahadili
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.
1.
2.
3.
4.
As part of the five-layer network model used in this textbook, the data link layer sits directly
between:
a. the physical and the application layers
b. the network and the application layers
c. the network and transport layers
d. the physical and the application layers
e. the physical and the network layers
Difficulty: Easy
p. 115
Which of the following is true with respect to the data link layer?
a. It accepts streams of bits from the application layer.
b. It is responsible for getting a message from one computer to another (one node to
another) without errors.
c. It accepts messages from the physical layer.
d. It performs routing functions.
e. It organizes data from the physical layer and passes these coherent messages to the
application layer.
Difficulty: Moderate
____________ is not a function of a data link protocol.
a. Media access control
b. Message delineation
c. Amplitude shift keying
d. Indicating when a message starts and stops
e. Error control
f. 802.11g
p. 115
Difficulty: Moderate
p. 115
Media access control:
a. is not very important in point-to-point with full duplex configuration
b. is not very important in local area networks
c. is not very important in a point-to-point with a half duplex configuration
d. is not very important in a multipoint configuration
e. does not control when computers transmit
Difficulty: Easy
p.115
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Chapter 4 – Data Link Layer
5.
Dr. Hussein Al-Bahadili
Which of the following is not a controlled access method of media access control?
a. Token access
b. CSMA/CD
c. polling
d. roll call polling
e. hub polling
Difficulty: Easy
6.
7.
8.
9.
p. 116
________ is the process of sending a signal to a client that gives its permission to transmit or
asks it to receive.
a. Contention
b. Polling
c. Pooling
d. Carrier sense
e. CRC
Difficulty: Moderate
116
Which of the following is true about roll call polling?
a. It can not be modified to increase priority of clients or terminals.
b. It does not require a server or host or special device that performs the polling.
c. It is also called token passing.
d. It is a type of contention approach to media access control.
e. It typically involves some waiting because the front-end processor or server has to
wait for a response from the polled client or terminal.
Difficulty: Moderate
p. 116
With contention:
a. computers wait until the circuit is free before they send data
b. the server or front end processor works consecutively through a list of clients to
determine who should have access to the media
c. the front end processor must wait for a response from the polled client or terminal
d. one computer starts the poll and passes it to the next computer on the multipoint
circuit
e. there is never a chance for “collision,” or two computers trying to send data at the
same time
Difficulty: Easy
p.117
In general, controlled approaches:
a. work better than contention approaches for small networks that have low usage
b. work better than contention approaches for large networks that have high usage
c. work better than contention approaches for all sizes of networks
d. do not require a host, server, or active monitor to assign media access control
e. have many collisions
Difficulty: Moderate
p. 117
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 4 – Data Link Layer
10.
11.
12.
13.
14.
15.
Dr. Hussein Al-Bahadili
In a _________ , more than one data bit is changed by the error-causing condition.
a. burst error
b. data rate shift
c. Trellis-coded modulation
d. uniform distribution
e. amplitude key shift
Difficulty: Moderate
Errors on a network can occur:
a. only on dial-up type of circuits
b. because of noise on the line
c. only on poorly maintained networks
d. only due to Gaussian noise
e. only due to lightning strikes
p. 118
Difficulty: Moderate
p. 118
In a dial-up network:
a. the error rate will vary because the circuits will change with each dial-up
b. the network is less prone to errors than private dedicated lines
c. users might try to transmit the data at a higher speed to decrease the error rate
d. constant transmission conditions will always create a constant error rate
e. users might try to transmit the data at a lower speed to speed up the data transmission
Difficulty: Moderate
Which of the following media is least susceptible to noise?
a. fiber optic cable
b. coaxial cable
c. twisted pair
d. unshielded twisted pair
e. shielded twisted pair
p. 118-119
Difficulty: Easy
p. 119
Optical media is:
a. more likely to suffer from noise than electrical media
b. has about the same likelihood of suffering from noise as electrical media
c. has about the same likelihood of suffering from noise as coaxial cable
d. less likely to suffer from noise than electrical media
e. more prone to noise than twisted pair media
Difficulty: Moderate
p. 119
____________ refers to bits that have been changed, in error, from 1 to 0, or vice versa, in a
data transmission.
a. Contracted bits
b. Polled bits
c. Inverse multiplexed bits
d. Flipped bits
e. Bit delineation
Difficulty: Moderate
p. 119
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Chapter 4 – Data Link Layer
16.
17.
18.
19.
20.
21.
Dr. Hussein Al-Bahadili
Another term for impulse noise is:
a. Gaussian noise
b. spikes
c. attenuation
d. cross-talk
e. intermodulation noise
Difficulty: Moderate
p.119
The familiar background static on radios and telephones is called:
a. echoes
b. intermodulation noise
c. line outages
d. cross-talk
e. white noise
Difficulty: Moderate
The primary source of error in data communications is:
a. echoes
b. intermodulation noise
c. spikes
d. jitter
e. cross-talk
p. 119
Difficulty: Moderate
p. 119
__________can obliterate a group of bits, causing a burst error.
a. Crosstalk
b. Attenuation
c. Impulse noise
d. Intermodulation noise
e. Jitter
Difficulty: Moderate
p.120
Cross-talk:
a. occurs when one circuit picks up signals in another
b. is always bothersome because it has a high signal strength
c. decreases with increased proximity of two wires
d. decreases during wet or damp weather
e. increases with lower frequency signals
Difficulty: Moderate
p.120
When a signal is reflected back to the transmitting equipment, it is called a(n) _________.
a. jitter
b. echo
c. crosstalk
d. attenuation
e. impulse noise
Difficulty: Moderate
p.120
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Chapter 4 – Data Link Layer
22.
23.
24.
25.
26.
Dr. Hussein Al-Bahadili
The loss of power a signal suffers as it travels from the transmitting computer to a receiving
computer is:
a. jitter
b. spiking
c. attenuation
d. intermodulation noise
e. echo
Difficulty: Moderate
p. 120
If a signal with a frequency of 500 MHz combines with a another signal of 1500 MHz and
they form a new signal of 2000 MHz; this is an example of:
a. intermodulation noise
b. attenuation
c. echo
d. jitter
e. harmonic distortion
Difficulty: Moderate
p. 120
When the output signal from an amplifier on a circuit is different from the input signal, this is
called _________________.
a. intermodulation noise
b. attenuation
c. echo
d. jitter
e. harmonic distortion
Difficulty: Moderate
A phase hit is likely to be:
a. spikes
b. a short term shift out of phase
c. intermodulation noise
d. white noise
e. Gaussian noise
120
Difficulty: Moderate
p. 120
_____________ is an effective way to prevent impulse noise, cross talk, and intermodulation
noise.
a. Shielding wires
b. Adding fluorescent lights
c. Adding repeaters to a circuit
d. Adding amplifiers to a circuit
e. Shorting a circuit
Difficulty: Easy
120-121
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Chapter 4 – Data Link Layer
27.
28.
29.
30.
31.
Dr. Hussein Al-Bahadili
_____________ is an effective way to prevent attenuation.
a. Shielding wires
b. Adding fluorescent lights
c. Adding repeaters or amplifiers to a circuit
d. Changing multiplexing techniques
e. Shorting a circuit
Difficulty: Moderate
121
Which of the following is way to reduce or eliminate crosstalk on a circuit,
a. changing multiplexing techniques
b. adding repeaters or amplifiers to a circuit
c. reducing the length of the cable
d. adding fluorescent lights
e. shorting a circuit
Difficulty: Moderate
p.121
On digital circuits, we use _________ to increase the strength of the signal and prevent
attenuation.
a. amplifiers
b. repeaters
c. multiplexers
d. digitizers
e. modems
Difficulty: Moderate
p. 121
Which of the following is not an error detection method used in the data link layer?
a. parity checking
b. cyclic redundancy checking
c. CRC-32
d. pulse code checking
e. polynomial checking
Difficulty: Moderate
p. 122-124
With odd parity (assume that the parity bit (in bold) has been placed at the end of each of the
following) and a 7-bit ASCII code, which of the following is incorrect?
a.
b.
c.
d.
e.
01101011
00011011
00100101
10110110
11111110
Difficulty: Moderate
p. 123
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 4 – Data Link Layer
32.
33.
Dr. Hussein Al-Bahadili
The probability of detecting an error, given that one has occurred, using parity checking is
about:
a. 100%
b. 0%
c. 50%
d. 75%
e. 98%
Difficulty: Easy
p. 123
Using parity, the probability for detecting an error, given that one has occurred, is:
a. about 50% for either even or odd parity
b. about 70% for even parity and 30% for odd parity
c. about 30% for even parity and 70% for odd parity
d. about 0% for either even or odd parity
e. about 100% for either even or odd parity
Difficulty: Moderate
34.
35.
36.
p. 123
The probability of detecting an error, provided that one has occurred, using cyclic
redundancy checking is about:
a. 75%
b. 0%
c. exactly 100%
d. 50%
e. > 99%
Difficulty: Easy
p. 124
ARQ means that:
a. a receiver that detects an error in a message simply asks the sender to retransmit the
message until it is received without error
b. the common carrier Automatically Returns Queries to the subscriber upon receipt of
such queries
c. a sender is using a data link protocol called Asynchronous Repeating reQuest
d. a fiber optic cable meets the American Registered Quality, a certification standard
for use in high-quality data communication transmission lines
e. a sender is using a parity scheme called Array Resource Quality
Difficulty: Moderate
p. 124
In ARQ, a NAK:
a. is sent by the recipient if the message was received without error
b. is sent by the sender at the same time as it sends a data packet
c. is sent by the recipient if the message contains an error
d. refers to non-asynchronous Kermit technique
e. means that the sender should continue with sending the next message
Difficulty: Moderate
p. 124-125
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 4 – Data Link Layer
37.
38.
39.
40.
41.
42.
Dr. Hussein Al-Bahadili
Stop-and-wait ARQ uses ___________ type of data flow.
a. full simplex
b. half complex
c. full duplex
d. half duplex
e. full complex
Difficulty: Moderate
124
With __________ ARQ, the sender pauses for a response from the receiver to alter each
message or packet of data.
a. open window
b. halt and be recognized (HBR)
c. sliding window
d. stop and wait
e. continuous
Difficulty: Moderate
124
With __________ ARQ, the sender immediately sends the next message or packet of data.
a. continuous
b. immediate
c. open window
d. stop-and-wait
e. halt and be recognized (HBR)
Difficulty: Moderate
124-125
______________ controls errors by detecting and correcting them at the receiving end
without retransmission of the original message.
a. Hamming code
b. Huffman encoding
c. Front end processing
d. Wave division multiplexing
e. Hub polling
Difficulty: Moderate
p. 127
Asynchronous transmission:
a. is used to transmit each character simultaneously with all other characters
b. has a pre-determined, fixed time between sending characters
c. is typically used on multipoint half duplex circuits
d. uses a continuous series of start bits as an idle signal
e. is also known as start-stop transmission
Difficulty: Moderate
p.128
Which of the following is not a type of asynchronous file transfer protocol?
a. XMODEM-CRC
b. OSCAR
c. XMODEM
d. XMODEM-1K
e. ZMODEM
Difficulty: Moderate
p.130-131
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 4 – Data Link Layer
43.
44.
45.
46.
47.
48.
Dr. Hussein Al-Bahadili
Synchronous transmission:
a. cannot be used on multipoint circuits
b. is used to send one character at a time
c. uses start bits before each character to be sent
d. uses stop bits after each character to be sent
e. is used to transmit a “frame” or “packet” of data at a time
Difficulty: Moderate
p.131
Which of the following is true about the data link protocol, SDLC:
a. It is a client-server protocol developed by Compaq in 1996
b. It is a byte-count-oriented protocol
c. It uses a special bit pattern called a flag at the beginning and end of every frame (or
packet)
d. It uses a contention media access control protocol
e. It does not have a problem with transparency
Difficulty: Moderate
p.131-132
Which of the following is true about the data link protocol, Ethernet (IEEE 802.3)?
a. it is a byte-oriented protocol
b. it is a bit-oriented protocol
c. it uses block check characters for error detection
d. it is a byte-count oriented protocol
e. it uses parity bits for error detection
Difficulty: Moderate
p.132
Which of the following is true about the data link protocol, PPP?
a. it is a byte-oriented protocol
b. it is a bit-oriented protocol
c. it uses block check characters for error detection
d. it is a byte-count oriented protocol
e. it uses parity bits for error detection
Difficulty: Moderate
p.133
Which of the following is not a type of synchronous data link protocol?
a. SDLC
b. KERMIT
c. PPP
d. HDLC
e. Ethernet (IEEE 802.3)
Difficulty: Moderate
p.128-133
In communication protocols, _________ are used to convey the user’s meaning.
a. information bits
b. overhead bits
c. stop bits
d. start bits
e. flag bits
Difficulty: Moderate
p.134
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Chapter 4 – Data Link Layer
49.
50.
51.
Dr. Hussein Al-Bahadili
_________________ is defined as the total number of information bits divided by the total
number of bits in the transmission.
a. Asynchronous rate
b. Protocol percentage
c. Throughput
d. Transmission Rate of Information Bits
e. Transmission efficiency
Difficulty: Moderate
p. 135
Calculating the actual throughput of a data communication network is:
a. not normally required for synchronous networks because they are so fast
b. complex because many factors affect throughput
c. simple because packet size is the primary factor affecting throughput
d. not needed for satellite-based networks
e. far less complicated if the system operates on a contention basis
Difficulty: Easy
p.136
TRIB, an acronym that relates to throughput, stands for:
a. Throughput Reduction of Information Barriers
b. Transmission Rate of Information Bits
c. Throughput Rate of Iso-synchronous Bytes
d. Transmission Regulation for Inverse-multiplexing Bands
e. Trellis-coded Regulation of Information Bits
Difficulty: Moderate
p.137
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 4 – Data Link Layer
Dr. Hussein Al-Bahadili
Essay and Short Answer Questions
1.
What does the data link layer do? What are its primary responsibilities? Where
does the data link layer sit in terms of the simplified five layers network model?
2.
What is media access control and why is it important? What are two examples
of controlled access methods and contention based media access methods?
When might one access method be preferred over another in a network, and
why? Under what conditions do contention-based media access control
techniques outperform controlled-access techniques (i.e., have lower response
time)? Explain.
3.
Compare and contrast roll call polling, hub polling (or token passing), and
contention. Which is better, hub polling or contention? Explain.
4.
Errors normally appear in ______________________________, which is when
more than one data bit is changed by the error-causing condition. Is there any
difference in the error rates of lower speed lines and of higher speed lines?
What kinds of lines are more prone to errors?
5.
Briefly define noise. Describe five types of noise and the underlying causes of
this noise. Which type of noise is likely to pose the greatest problem to network
managers? What does error look like in a data network?
6.
How do amplifiers differ from repeaters?
7.
What are three ways of reducing errors and the types of noise they affect?
8.
Describe three approaches to detecting errors, including how they work, the
probability of detecting an error, and any other benefits or limitations.
9.
Briefly describe how even parity and odd parity work. Give an example of even
parity with a 7-bit ASCII code, for the following: 0110110, using a 0 start bit
and a 1 stop bit.
10.
How does cyclical redundancy checking work?
11.
How does forward error correction work? How is it different from other error
correction methods? Under what circumstances is forward error correction
desirable? What is one type of forward error correction by name? Given a
diagram like that in the text of forward error correction, be able to explain how
the system works.
12.
Compare and contrast stop-and-wait ARQ and continuous ARQ.
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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Chapter 4 – Data Link Layer
Dr. Hussein Al-Bahadili
13.
Describe from a high level perspective the packet layout for SDLC, ethernet,
and token ring.
14.
What is transparency?
15.
What is transmission efficiency? How do information bits differ from overhead
bits? What are three issues which might effect packet throughput rates? Which
is better for file transfer, large packet sizes or small packet sizes?
16.
What is asynchronous transmission v. synchronous transmission? Give two
protocols which use asynch and two which use synchronous transmission.
17.
Think about a recent world impact event and how useful the technologies of
communications might have been related to helping people impacted by that
event (Hurricane Katrina, Pakistan earthquakes, or some other large world
event). How might telecom have a positive role in large scale human events?
Use insight gained from the technological underpinnings provided in the course.
Be creative.
J. FitzGerald and A. Dennis. Business Data Communications and Networking, John Wiley & Sons, Inc., 9th Edition 2006.
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