EST
問題一覧
1
The first service provided by the data-link layer is _____.
Framing
2
In a ____ protocol, frames are sent from one node to the next without any relationship between the frames; each frame is independent.
Connectionless
3
For a series-resonant circuit, if the circuit is resonant at a point above the generator frequency (the generator frequency is too low), then the circuit acts
Capacitively
4
When light waves, which travel in straight lines, encounter any substance, they are either:
Transmitted, refracted, reflected, or absorbed
5
The gain of a collinear antenna is greatest when the elements are spaced from ______ wavelength apart or when the number of elements is increased.
0.4 to 0.5
6
In circular waveguides, the second subscript indicates the number of _______.
half-wave patterns across the diameter
7
The denser the medium, the higher the speed of sound. The denser the medium, the _____ the speed of light.
lesser
8
The color of light depends on its ______.
frequency, not its wavelength
9
What refers to the bends, twists, and joints necessary to install waveguides. E bends, H bends, and twists must have a radius greater than two wavelengths?
waveguide plumbing
10
What type of waveguide bend where the magnetic fields are distorted when a waveguide is bent in this manner?
H bend
11
In wave propagation, if either the source or the receiver or both move toward the other, the receiver will perceive a ______ frequency sound.
higher
12
In a _____ code, if a codeword is cyclically shifted (rotated), the result is another codeword.
Cyclic
13
To guarantee the detection of up to s errors in all cases, the minimum Hamming distance in a block code must be ______.
dmin=s+1
14
In antennas, the exact value of radiation resistance depends on the ______.
height of the antenna above the ground
15
A twisted-pair cable can pass a wide range of frequencies. Increasing frequency, the attenuation, measured in decibels per kilometer (dB/km), sharply increases with frequencies above ______.
100kHz
16
In antennas, the points of minimum current and minimum voltage are known as current and voltage ____.
nodes
17
In wave propagation, as the angle of incidence increases, the amount of wave energy reflected _____.
increases
18
In _____ propagation, radio waves travel through the lowest portion of the atmosphere, hugging the earth.
ground
19
What is the most common UP connector, which is a keyed connector, meaning the connector can be inserted in only one way?
RJ45
20
In wave propagation, the reflected energy is the greatest when the wave is ______ to the reflecting surface.
nearly parallel
21
The frequency range of any system using waveguides is limited by the _____ of the waveguides.
physical dimensions
22
In ____ TDM, the data rate of the link is n times faster, and the unit duration is n times shorter.
synchronous
23
What signals can be used for short-range communication in a closed area using line-of-sight propagation?
Infrared
24
The field associated with the energy stored in the antenna is the _____ field.
induction
25
In what mode, each station can both transmit and receive, but not at the same time?
Half-duplex
26
The narrowest dimension determines the
maximum frequency ________ of the waveguide and is called the "b" dimension.
power-handling capability of the line
27
In a multipoint environment, the capacity of the channel is shared. If several devices can use the link temporally, it is a ____ connection.
time shared
28
What technique uses M different carrier frequencies that are modulated by the source signal? At one moment, the signal modulates one carrier frequency; at the next moment, the signal modulates another carrier frequency.
frequency hopping and spread spectrum
29
What deals with procedures for communication between two adjacent nodes-node-to-node communication-no matter whether the link is dedicated or broadcast?
data link control
30
Today, the prevalent coding system is called _____ which uses 32 bits to represent a symbol or character used in any language in the world.
unicode
31
In ______ propagation, higher frequency radio waves radiate upward into the ionosphere (the layer of atmosphere where particles exist as ions) where they are reflected back to earth.
sky
32
The cutoff wavelength of a circular guide is_____ times the diameter of the waveguide.
1.71
33
For transmission over bodies of water, _______ polarization is much better for antennas at the lower heights.
vertical
34
What technique also expands the bandwidth of the original signal, but the process is different? In this technique, we replace each data bit with n bits using a spreading code.
direct sequence spread spectrum
35
Substances that transmit almost all the light waves that fall upon them are said to be _____.
transparent
36
At medium and low frequencies,______ polarization cannot be used at these frequencies because the electric lines of force are parallel to and touch the
earth.
horizontal
37
The effectiveness of a data communications system depends on what four fundamental characteristics?
delivery, accuracy, timeliness and jitter
38
Single-mode uses _____ fiber and a highly focused source of light that limits beams to a small range of angles, all close to the horizontal.
step-index
39
Graded index fiber optic cable is one with varying densities. Density is _____ at the center of the curve.
highest
40
Changing the frequencies of a cavity is known as ______.
tuning
41
To connect coaxial cable to devices, we need coaxial connectors. The most common type of connector used today is the _____.
bayonett neill-concelman
42
What is the process of adding one extra 0 whenever five consecutive 1s follow a 0 in the data, so that the receiver does not mistake the pattern 0111110 for a flag?
bit stuffing
43
What is the process of adding one extra byte whenever there is a flag or escape character in the text?
byte stuffing
44
On an open-ended resonant line, and at all even ¼-wavelength points, the voltage is _____, the current is ______ and the impedance is maximum.
maximum, minimum
45
In a circuit-switched network, a dedicated connection, called a _______, is always available between the two end systems; the switch can only make it active or inactive.
circuit
46
A parity-check code can detect an ____ number of errors.
odd
47
In sound propagation, a denser material (such as lead) passes sound ______.
slower
48
In the reflection of waves, if the reflecting surface is smooth and polished, the angle between the incident ray and the normal will be ____ the angle between the reflected ray and the normal.
the same as
49
In antenna radiation, a _____ is the area of a radiation pattern that has minimum radiation.
null
50
The diameter of an equivalent circular waveguide must be _____ times the "a" dimension of a rectangular waveguide.
1.17
問題一覧
1
The first service provided by the data-link layer is _____.
Framing
2
In a ____ protocol, frames are sent from one node to the next without any relationship between the frames; each frame is independent.
Connectionless
3
For a series-resonant circuit, if the circuit is resonant at a point above the generator frequency (the generator frequency is too low), then the circuit acts
Capacitively
4
When light waves, which travel in straight lines, encounter any substance, they are either:
Transmitted, refracted, reflected, or absorbed
5
The gain of a collinear antenna is greatest when the elements are spaced from ______ wavelength apart or when the number of elements is increased.
0.4 to 0.5
6
In circular waveguides, the second subscript indicates the number of _______.
half-wave patterns across the diameter
7
The denser the medium, the higher the speed of sound. The denser the medium, the _____ the speed of light.
lesser
8
The color of light depends on its ______.
frequency, not its wavelength
9
What refers to the bends, twists, and joints necessary to install waveguides. E bends, H bends, and twists must have a radius greater than two wavelengths?
waveguide plumbing
10
What type of waveguide bend where the magnetic fields are distorted when a waveguide is bent in this manner?
H bend
11
In wave propagation, if either the source or the receiver or both move toward the other, the receiver will perceive a ______ frequency sound.
higher
12
In a _____ code, if a codeword is cyclically shifted (rotated), the result is another codeword.
Cyclic
13
To guarantee the detection of up to s errors in all cases, the minimum Hamming distance in a block code must be ______.
dmin=s+1
14
In antennas, the exact value of radiation resistance depends on the ______.
height of the antenna above the ground
15
A twisted-pair cable can pass a wide range of frequencies. Increasing frequency, the attenuation, measured in decibels per kilometer (dB/km), sharply increases with frequencies above ______.
100kHz
16
In antennas, the points of minimum current and minimum voltage are known as current and voltage ____.
nodes
17
In wave propagation, as the angle of incidence increases, the amount of wave energy reflected _____.
increases
18
In _____ propagation, radio waves travel through the lowest portion of the atmosphere, hugging the earth.
ground
19
What is the most common UP connector, which is a keyed connector, meaning the connector can be inserted in only one way?
RJ45
20
In wave propagation, the reflected energy is the greatest when the wave is ______ to the reflecting surface.
nearly parallel
21
The frequency range of any system using waveguides is limited by the _____ of the waveguides.
physical dimensions
22
In ____ TDM, the data rate of the link is n times faster, and the unit duration is n times shorter.
synchronous
23
What signals can be used for short-range communication in a closed area using line-of-sight propagation?
Infrared
24
The field associated with the energy stored in the antenna is the _____ field.
induction
25
In what mode, each station can both transmit and receive, but not at the same time?
Half-duplex
26
The narrowest dimension determines the
maximum frequency ________ of the waveguide and is called the "b" dimension.
power-handling capability of the line
27
In a multipoint environment, the capacity of the channel is shared. If several devices can use the link temporally, it is a ____ connection.
time shared
28
What technique uses M different carrier frequencies that are modulated by the source signal? At one moment, the signal modulates one carrier frequency; at the next moment, the signal modulates another carrier frequency.
frequency hopping and spread spectrum
29
What deals with procedures for communication between two adjacent nodes-node-to-node communication-no matter whether the link is dedicated or broadcast?
data link control
30
Today, the prevalent coding system is called _____ which uses 32 bits to represent a symbol or character used in any language in the world.
unicode
31
In ______ propagation, higher frequency radio waves radiate upward into the ionosphere (the layer of atmosphere where particles exist as ions) where they are reflected back to earth.
sky
32
The cutoff wavelength of a circular guide is_____ times the diameter of the waveguide.
1.71
33
For transmission over bodies of water, _______ polarization is much better for antennas at the lower heights.
vertical
34
What technique also expands the bandwidth of the original signal, but the process is different? In this technique, we replace each data bit with n bits using a spreading code.
direct sequence spread spectrum
35
Substances that transmit almost all the light waves that fall upon them are said to be _____.
transparent
36
At medium and low frequencies,______ polarization cannot be used at these frequencies because the electric lines of force are parallel to and touch the
earth.
horizontal
37
The effectiveness of a data communications system depends on what four fundamental characteristics?
delivery, accuracy, timeliness and jitter
38
Single-mode uses _____ fiber and a highly focused source of light that limits beams to a small range of angles, all close to the horizontal.
step-index
39
Graded index fiber optic cable is one with varying densities. Density is _____ at the center of the curve.
highest
40
Changing the frequencies of a cavity is known as ______.
tuning
41
To connect coaxial cable to devices, we need coaxial connectors. The most common type of connector used today is the _____.
bayonett neill-concelman
42
What is the process of adding one extra 0 whenever five consecutive 1s follow a 0 in the data, so that the receiver does not mistake the pattern 0111110 for a flag?
bit stuffing
43
What is the process of adding one extra byte whenever there is a flag or escape character in the text?
byte stuffing
44
On an open-ended resonant line, and at all even ¼-wavelength points, the voltage is _____, the current is ______ and the impedance is maximum.
maximum, minimum
45
In a circuit-switched network, a dedicated connection, called a _______, is always available between the two end systems; the switch can only make it active or inactive.
circuit
46
A parity-check code can detect an ____ number of errors.
odd
47
In sound propagation, a denser material (such as lead) passes sound ______.
slower
48
In the reflection of waves, if the reflecting surface is smooth and polished, the angle between the incident ray and the normal will be ____ the angle between the reflected ray and the normal.
the same as
49
In antenna radiation, a _____ is the area of a radiation pattern that has minimum radiation.
null
50
The diameter of an equivalent circular waveguide must be _____ times the "a" dimension of a rectangular waveguide.
1.17