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DB > TDMM Chapter 1 - Part 1 > Flashcards

TDMM Chapter 1 - Part 1 Flashcards

1
Q

Amplitude

A

The maximum absolute value reached by a voltage or current waveform

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2
Q

Amplitude Modulation (AM)

A

The modulation in which the amplitude of a carrier wave is varied in accordance with some characteristic of the modulating signal

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3
Q

Analog Signal

A

A signal in the form of a wave that uses continuous variations of a physical characteristic over time (eg voltage amplitude, frequency) to transmit information

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4
Q

Attenuation

A

The ratio in decibels of the output power (or voltage) to the input power (or voltage) when the load and source impedance are matched to the characteristic impedance of the cable

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5
Q

ATM

A

Asynchronous Transfer Mode
A high speed packet switching protocol that uses fixed length packets organized into cells to carry all types of traffic. Fixed length cells allow processing to occur in hardware, reducing transit delays. ATM is designed to take advantage of high speed transmission media

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6
Q

AWG

A

American Wire Gauge
A system used to specify wire size. The greater the wire diameter, the smaller the AWG value

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7
Q

Bandwidth

A

A range of frequencies available for signaling expressed in hertz (Hz) It is used to denote the potential information handling capacity of the medium, device or system

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8
Q

Broadband Cable

A

Composite baseband video and audio signals that are amplitude and frequency modulated, respectively, with an RF carrier in accordance with the video and audio information that need to be conveyed (CATV)

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9
Q

CO

A

Central Office
A common carrier switching center office (also called public exchange) that is conveniently located in areas to serve subscriber homes and businesses.

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10
Q

Codec

A

A device that converts speech to a digital signal and its subsequent decoding to speech

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11
Q

Crosstalk

A

The signal interference between cable pairs, which may be caused by a pair picking up unwanted signals from either adjacent pairs of conductors or nearby cables

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12
Q

Decibel

A

A logarithmic unit for measuring the relative voltage, current or power of a signal. One tenth of a bel

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13
Q

Delay Skew

A

The difference in propagation delay between any pairs within the same cable sheath

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14
Q

Digital Signal

A

Information used by digital devices in the form of a sequence of discrete pulses (a binary signal with two values used to transmit the two states, 0 and 1)

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15
Q

Dispersion

A
  • The loss of signal resulting from the scattering of light pulses as they are transmitted through a medium
  • The widening or spreading out of the modes in a light pulse as it progresses along an optical fiber
  • The characteristics of the sound coverage field of a speaker
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16
Q

EMI

A

Electromagnetic Interference
Stray electrical energy radiated from electronic equipment and electronics systems (including cabling)

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17
Q

Frequency

A

The number of cycles that a periodic signal completes in a given time. If the unit of time is one second, the frequency is stated in hertz (Hz)

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18
Q

IP

A

Internet Protocol
The Open Systems Interconnection (OSI) Reference Model Layer 3 (network layer) protocol most commonly used for internetworking

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19
Q

ISDN

A

Integrated Services Digital Network
A digital communications facility designed to provide transparent end-to-end transmission of voice, data and AV across public switched telephone network (PTSN)

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20
Q

NVP

A

Nominal Velocity of Propagation
The coefficient used to determine the speed of transmission along a cable relative to the speed of light in a vacuum, typically expressed as a percentage

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21
Q

PCM

A

Pulse Code Modulation
A technique for representing an analog signal as a string of bits,

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22
Q

Phase

A
  • The relationship between two waveforms of the same frequency
  • The relationship in time between two parameters of a single waveform (eg voltage and current)
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23
Q

PoE

A

Power over Ethernet
A network subsystem that offers the ability for the LAN switching infrastructure to provide power over balanced twisted pair cabling to an endpoint device

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24
Q

Propagation Delay

A

The time required for a signal to travel from one end of the transmission path to the other end

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25
Q

QAM

A

Quadrature Amplitude Modulation
A means of encoding digital information over radio, wireline or optical fiber transmission links,

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26
Q

Sinusoid

A

An oscillating periodic signal that is completely described by three parameters:
- Amplitude
- Frequency
- Phase

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27
Q

TDM

A

Time Division Multiplexing
A process that combines binary data from several different sources into a single composite bit stream

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28
Q

What is an electrical conductor?

A

Any material that can carry an electric charge from one point to another

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29
Q

Name the four most common electrical conductors for ICT wire and cables

A
  • Copper
  • Copper-Covered Steel
  • High-Strength Copper Alloys
  • Aluminum
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30
Q

Silver and gold are good conductors, but they are not generally used for ICT wires and cables. Why?

A

Because of their high cost

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31
Q

Which conductor sets the standard for comparing the conductivity of other metals?

A

Copper

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32
Q

What type of copper is used to set the reference value?

A

Annealed Copper

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33
Q

What type of conductor is typically used for aerial, self-supporting drop wire?

A

Copper-Covered

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34
Q

How does the alloying of pure copper affect its conductivity?

A

The alloying of pure copper always has an adverse effect on its conductivity

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35
Q

How does the conductivity of aluminum compare to the conductivity of copper?

A

It has about 60% conductivity compared to copper

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36
Q

Where are aluminum conductors commonly used?

A

In electrical utility distribution lines

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37
Q

Which type of solid conductor has the poorest corrosion resistance?

A

High-Strength Alloy

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38
Q

What type of solid conductor has the poorest oxidation resistance?

A

Aluminum

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39
Q

Which type of solid conductor has the best tensile strength?

A

High-strength alloy

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40
Q

Which type of solid conductor has the best ductility?

A

High-Strength alloy

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41
Q

What is the conductivity for a High-Strength alloy conductor?

A

85% of typical

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42
Q

How are stranded conductors created?

A

By bundling together a number of small-gauge conductors to create a single, larger conductor

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43
Q

Name the four advantages of solid conductors

A
  • Less costly
  • Less complex termination systems
  • Better transmission at high frequencies
  • Less resistance
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44
Q

Name three advantages of stranded conductors

A
  • More flexible
  • Longer flex life
  • Less susceptible to damage during crimp termination processes
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45
Q

What is a composite conductor?

A

A conductor constructed from nontraditional materials such as metallic resins or graphite

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46
Q

Name four advantages of composite conductors

A
  • Highly flexible
  • Lightweight
  • Inexpensive and easy to produce
  • Easily embedded into other materials
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47
Q

Name four disadvantages of composite conductors

A
  • Poor analog transmission characteristics
  • Poor digital transmission characteristics
  • Easily damaged unless encased in a rigid material
  • Inconsistent quality
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48
Q

Are cables with composite conductors recommended for use with modern telecommunications networks?

A

No, composite conductors are not recommended in a telecommunications network

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49
Q

Why is the AWG system important?

A

Because it provides a standard reference for comparing various conductor materials

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50
Q

What is the purpose of insulation on a cable?

A

To isolate the flow of current by preventing direct contact between conductors and a conductor and its environment

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51
Q

How do dielectrics reduce EM coupling between conductors?

A

By increasing conductor separation

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52
Q

What is the dielectric constant?

A

The ratio of the capacitance of an insulated conductor to the capacitance of the same conductor uninsulated in the air

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53
Q

What does dielectric strength measure?

A

The maximum voltage that an insulation can withstand without breakdown

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54
Q

What is dissipation factor?

A

The relative power loss in the insulation due to molecular excitement and subsequent kinetic and thermal energy losses

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55
Q

What is insulation resistance?

A

The insulations ability to resist the flow of current through it

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56
Q

How is insulation resistance typically expressed?

A

In megaohmkm or megaohm1000ft

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57
Q

How does cable length affect cable resistance?

A

As the cable length increases, the insulation resistance becomes smaller

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58
Q

What is the main reason for twisting conductor pairs?

A

To minimize crosstalk and noise by decreasing capacitance unbalance and mutual inductance coupling between pairs

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59
Q

What does pair-to-pair capacitance unbalance measure?

A

The electric field coupling between two pairs if a differential voltage is applied on one pair and a differential noise voltage is measured on another pair in close proximity

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60
Q

What is mutual inductance?

A

A measure of the magnetic field coupling between two pairs if a differential current is applied on one pair and a differential noise current is measured on another pair in close proximity

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61
Q

How is crosstalk within a multipair cable minimized?

A

By giving each pair a different twist length within a standard range

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62
Q

What type of twist is generally used for voice and low-frequency data cables?

A

A counterclockwise twist length between ~50mm and ~150mm (1.97in and 6in)

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63
Q

What is tight twisting?

A

Creating pair twist lengths that are less than ~12.7 mm (0.50in)

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64
Q

Where is tight twisting commonly used?

A

Within and between computers and other date processing equipment

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65
Q

Which cable categories employ tight twisting for optimum transmission performance?

A

Category 5e, 6, 6A and higher

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66
Q

What term is used to refer to stray electrical radiated from electrical equipment and electronics systems?

A

Electromagnetic Interference (EMI)

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67
Q

At what temperature does attenuation increase in balanced twisted-pair cables?

A

Above 20C (68F)

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68
Q

What temperature reference is cited in cabling standards for all twisted-pair cables?

A

20C +/- 3C (68F +/- 5.4F)

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69
Q

What is a cable shield?

A

A metallic covering or envelope enclosing an insulated conductor, individual group of conductors within a core and cable core

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70
Q

Name three potential benefits of using a cable shield if it is properly terminated, bonded and grounded

A
  • Reduces the radiated signal from the cable
  • reduces the effects of electrical hazards
  • Minimizes the effect of external EMI on the conductors within the shielded cable
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71
Q

Name three factors that can affect a shields effectiveness

A
  • Type and thickness of the shield material
  • Number and size of openings in the shield
  • Effectiveness of the bonding connection to ground
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72
Q

How is shield effectiveness determind?

A

By measuring the surface transfer impedance

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73
Q

What is surface transfer impedance?

A

The ratio of the conductor-to-shield voltage per unit length to the shield current

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74
Q

Why are solid metal tubes inappropriate for most cable applications?

A

Because of their rigid nature

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75
Q

Name the four primary criteria for selecting cable shields

A
  • Nature of the signal to be transmitted
  • magnitude of the EM fields through which the cable will run
  • EMC regulations
  • Physical environment and specific mechanical requirements
76
Q

What type of cable shield has poor tensile strength?

A

Foil (Foil and Braid)

77
Q

Which type of cable shield is the least effective for radio frequency?

A

Flexible Conduit

78
Q

What type of cable shield has a poor fatigue life?

A

Solid Conduit

79
Q

Which cable shields have excellent tensile strength?

A
  • Single-Layer Braid
  • Multiple-Layer Braid
  • Solid Conduit
80
Q

What is permeability?

A

The property of a magnetic substance that determines the degree in which it modifies the magnetic flux in the region occupied by it in a magnetic field

81
Q

Name two reasons for using a drain wire

A
  • To provide an easier means for grounding the shield
  • To ensure shield continuity for metallic foil shields
82
Q

How are drain wires typically applied?

A

Longitudinally next to the metallic part of the shield for the length of the cables

83
Q

What is an analog signal?

A

A wave that used continuous variations in time to transmit information

84
Q

What is the most fundamental concept of an analog signal?

85
Q

Name the three parameters used to describe a sinusoid

A
  • Amplitude
  • Frequency
  • Phase
86
Q

What is the standard unit of frequency measurement?

A

Hertz (Hz)

87
Q

What formula is used to represent the relationship between cycle time and frequency?

88
Q

What is the typical range of frequencies that humans can hear?

A

20Hz to 20,000Hz

89
Q

What range of frequencies is typically used for voice circuits?

A

300Hz to 3400Hz

90
Q

What is a phase?

A

A description of the reference time
t = 0

91
Q

How many degrees are in a cycle?

A

360 degrees

92
Q

What is a signals spectrum?

A

A sum of sinusoidal signals that differ in amplitude, frequency and phase

93
Q

What is necessary for the received signal to be an exact duplicate of the transmitted signal?

A

The transmission system must not change the frequency of any signal components, and the relative amplitude and phases of all components must be maintained

94
Q

What defined the analog signals bandwidth?

A

The frequency range of the sinusoidal signals needed to describe an analog signal

95
Q

What is the frequency range of the very low frequency (VLF) band?

A

3kHz to 30kHz

96
Q

What is the frequency of the low frequency (LF) band?

A

30kHz to 300kHz

97
Q

What is the frequency of the medium frequency (MF) band?

A

300kHz to 3000kHz

98
Q

What is the frequency range of the high frequency (HF) band?

A

3MHz to 30MHz

99
Q

What is the frequency range of the very high frequency (VHF) band?

A

30MHz to 300MHz

100
Q

What is the frequency range of the ultra high frequency (UHF) band?

A

300MHz to 3000MHz

101
Q

What is the frequency range of the community antenna TV (CATV) band?

A

54MHz to 1002MHz

102
Q

What is the frequency range of the super high frequency (SHF) band?

A

3GHz to 30GHz

103
Q

What is the frequency range of the extremely high (EHF) band?

A

30GHz to 300GHz

104
Q

What unit of measure is often used to express the strength of a signal?

A

Decibel (dB)

105
Q

What decibel (dB) change occurs when the power is doubled?

106
Q

What decibel (dB) change occurs when the power is reduced by half?

107
Q

True or False
Decibel (dB) levels are used to express power ratios of all types of analog and digital signals, regardless of the medium?

108
Q

In telephony, which delays are perceptible?

A

Delays greater than 50ms if they are of sufficient strength

109
Q

Name the three basic components of a telecommunications transmission system

A
  • Source of energy
  • Medium to carry the energy
  • Receiving device
110
Q

What is the purpose of an analog telephone?

A

To convert sound waves into electrical and analog signals that can be transmitted over much longer distances than the sound can travel

111
Q

True or False
Early telephones were designed to match the frequencies used in human speech, from 50Hz to 12kHz

A

False
Although speech contains frequencies from 50Hz to 12kHz, quality intelligibility was only in the range of 300Hz to 3400Hz

112
Q

What type of devices converts electrical energy back into sound energy?

113
Q

When does the maximum transmission of electrical power occur in a telephone line?

A

When a transmitting device and a receiving device have the same load resistance or the same impedance

114
Q

How does impedance differ from resistance?

A

Both are measured in ohms, but impedance has both a magnitude and a phase component

115
Q

What is the preferred impedance for private line circuits and trunks?

116
Q

What is the preferred impedance for CO switching system line circuits?

117
Q

When is an echo perceptible during a long-distance phone call?

A

When part of the transmitted signal is sent or reflected back to the originating end

118
Q

What causes part of a signal to be sent back or reflected to the originating end?

A

Impedance mismatch between the transmission line and the receiver

119
Q

What principal elements contribute to loss and phase distortion at voice frequencies?

A
  • Conductor resistance
  • Mutual capacitance of the cable pair
120
Q

How does increasing the frequency affect the speed of transmission through cable pairs?

A

Increasing the frequency increases the speed of transmission

121
Q

True of False
Increasing the frequency to increase the speed of transmission does not noticeably affect speech intelligibility

122
Q

What is the purpose of placing load coils along a cable?

A

To improve speech transmission quality

123
Q

How do load coils improve the quality of speech transmission?

A
  • By compensating for the capacitance of a cable pair
  • By reducing the capacitive current loading in the range of audio frequencies
124
Q

What is the most common distance between loading points for D loading?

A

~1.37km (4495ft)

125
Q

What is the most common distance between loading points for H loading?

A

~1.83km (6004ft)

126
Q

What types of signals are blocked by loading coils?

A

Analog high fidelity and digital signals

127
Q

How do loading coils affect data transmission?

A

Load coils adversely affect data transmission

128
Q

What determines the upper cutoff frequency of a loading coil?

A

Loading coil spacing determines the upper cutoff frequency

129
Q

Name three common interface options for IP Telephony

A
  • IP Telephone
  • Computer with IP Telephony software and a microphone/speaker or USB handset
  • Multifunctional devices with a wireless receiver
130
Q

True or False
IP telephony software is only operational when the computer is running

131
Q

Name three common implementation options for IP telephony architecture

A
  • Separate lines
  • One line for everything using a dual port IP telephone or a soft telephone
  • Wireless connection using APs to connect the IP telephone
132
Q

Although using a dual-port telephone or softphone may sound like an attractive option, what are the possible drawbacks?

A

A single cable carrying all information reduces flexibility and redundancy

133
Q

How many telecommunications outlets or connectors are recommended for each individual work area?

134
Q

True or False
Both horizontal cables at the work area location should be considered cables that support data applications

A

True
While one cable may be associated with voice and the other data, both should be considered data cables

135
Q

What is used to provide uninterrupted power to the telephone set?

A

Power over Ethernet (PoE)

136
Q

What is the most significant property of a digital signal?

A

The most significant property of a digital signal is that at any time it can take on only a value from a discrete set of values

137
Q

What three steps are used to convert an analog signal to a digital signal?

A
  • Filtering
  • Sampling
  • Quantizing/Companding
138
Q

Why is the analog filtered before it is sampled?

A

To limit its frequency content

139
Q

What sampling rate is used to faithfully reproduce the analog signal during the conversion process?

A

A rate that is at least twice the highest frequency component of the analog signal

140
Q

What is quantizing?

A

Assigning each sampled value a discrete level that approximates the analog signal at the sampling instant

141
Q

What is companding?

A

Non-uniform mapping between the analog sampled value to an assigned digital level

142
Q

Name the two forms of companding that are in current use

A
  • A-Law
  • Mu-Law
143
Q

What type of companding is used in the United States, Canada and Japan

A

Mu-Law
( μ-law )

144
Q

What type of companding is used in Europe?

145
Q

True or False
A-Law and Mu-Law are compatible

A

False
Although the perform similar functions, they are not compatible

146
Q

What term is used to describe the three step process for converting an analog signal into a digital signal

A

Pulse Code Modulation (PCM)

147
Q

What is used to encode speech signals at data rates lower than 64 kb/s?

A

Data signal processing

148
Q

What data rates can be used by ADPCM?

A

40, 32, 24 and 16 kb/s

149
Q

What device is used to convert speech to a digital signal and its subsequent decoding to speech?

150
Q

At what rates can vocoders transmit speech?

A

8 to 2.4 kbs

151
Q

What do lower bit rates typically imply about a signal’s quality?

A

That the signal quality is degraded

152
Q

What process involves combining binary data from several different sources into a single composite bit stream?

A

Time Division Multiplexing (TDM)

153
Q

What is the purpose of Time Division Multiplexing (TDM)?

A

To increase the information-carrying capacity of the digital telecommunications channel

154
Q

How is Time Division Multiplexing (TDM) accomplished?

A

By predetermined (deterministic) interleaving of samples from different voice channels along with one or more bits for control purposed to make up a frame

155
Q

What is the most popular form of Time Division Multiplexing (TDM)

A

Statistical TDM

156
Q

In the DS1 format, the digital data from ___ speech channels is combined for transmission over a signal transmission channel

A

24 speech channels

157
Q

What is the data rate for the DS1 format?

A

1.544 Mb/s

158
Q

Describe the CEPT PCM-30 format

A

In the CEPT PCM-30 format, the digital data from 30 speech channels is combined for transmission over a single transmission channel

159
Q

What is the data rate for the CEPT PCM-30 format?

A

2.048 Mb/s

160
Q

What term is used to describe the process of reconstituting the individual channels from the composite signal?

A

Demultiplexing

161
Q

What is a channel blank?

A

Multiplexing and demultiplexing equipment

162
Q

What stages of multiplexing contain A/D conversion?

A

Only the first order multiplexing stage (T1 and E1)

163
Q

In the United States, how many T1 frames are needed to create a superframe?

164
Q

In Europe, how many E1 frames are needed to create a multiframe?

165
Q

What is the basic unit of digital data?

166
Q

True of False
A sequence of binary pulses consisting of 1s and 0s is the optimum format for transmitting digital data over balanced-twisted pair cables

167
Q

What is the final step in the encoding process?

A

The modification of the shape and pattern of pulses to achieve more efficient transmission

168
Q

What is the line-encoding technique designed to do?

A
  • Eliminate the dc component
  • Improve timing recovery
169
Q

What encoding technique is used for T1 carriers?

A

Bipolar Alternate Mark Inversion (AMI)

170
Q

What type of encoding allows signal transition to occur in the middle of every bit interval?

A

Manchester encoding

171
Q

What term is used to describe the rate at which a signal can change states?

172
Q

What transmission method is used for ISDN (basic rate)?

173
Q

What transmission method is used for ISDN (primary rate)?

174
Q

What transmission method is used for HDSL?

175
Q

What transmission method is used for 10BASE-T?

A

Manchester

176
Q

What is the encoding rate for ISDN (basic rate)?

177
Q

What is the encoding rate for ISDN (primary rate)?

A

1.544 Mb/s

178
Q

What is the encoding rate for HDSL?

A

2 x 784 kb/s

179
Q

What is the encoding rate for 10BASE-T?

180
Q

What is a QAM signal?

A

A signal composed of two sinusoidal carriers, each having the same frequency but differing in phase by one quarter of a cycle

181
Q

Which QAM sinusoid is the equivalent of a sine wave?

182
Q

Which QAM sinusoid is the equivalent of a cosine wave?

183
Q

What type of modulation does DMT use?

A

Multicarrier modulation

184
Q

How can data rates be adjusted with DMT?

A

By increasing the number of sub-bands and by varying the number of bits carried in each sub-band

185
Q

Which line application uses 8B/1Q4 PAM 5 encoding?

DB (19 decks)

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