TDMM Chapter 1 - Part 1 Flashcards
1
Q
Amplitude
A
The maximum absolute value reached by a voltage or current waveform
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
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
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
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
6
Q
AWG
A
American Wire Gauge
A system used to specify wire size. The greater the wire diameter, the smaller the AWG value
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
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)
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.
10
Q
Codec
A
A device that converts speech to a digital signal and its subsequent decoding to speech
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
12
Q
Decibel
A
A logarithmic unit for measuring the relative voltage, current or power of a signal. One tenth of a bel
13
Q
Delay Skew
A
The difference in propagation delay between any pairs within the same cable sheath
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)
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
16
Q
EMI
A
Electromagnetic Interference
Stray electrical energy radiated from electronic equipment and electronics systems (including cabling)
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)
18
Q
IP
A
Internet Protocol
The Open Systems Interconnection (OSI) Reference Model Layer 3 (network layer) protocol most commonly used for internetworking
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)
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
21
Q
PCM
A
Pulse Code Modulation
A technique for representing an analog signal as a string of bits,
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)
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
24
Q
Propagation Delay
A
The time required for a signal to travel from one end of the transmission path to the other end
25
QAM
Quadrature Amplitude Modulation
A means of encoding digital information over radio, wireline or optical fiber transmission links,
26
Sinusoid
An oscillating periodic signal that is completely described by three parameters:
- Amplitude
- Frequency
- Phase
27
TDM
Time Division Multiplexing
A process that combines binary data from several different sources into a single composite bit stream
28
What is an electrical conductor?
Any material that can carry an electric charge from one point to another
29
Name the four most common electrical conductors for ICT wire and cables
- Copper
- Copper-Covered Steel
- High-Strength Copper Alloys
- Aluminum
30
Silver and gold are good conductors, but they are not generally used for ICT wires and cables. Why?
Because of their high cost
31
Which conductor sets the standard for comparing the conductivity of other metals?
Copper
32
What type of copper is used to set the reference value?
Annealed Copper
33
What type of conductor is typically used for aerial, self-supporting drop wire?
Copper-Covered
34
How does the alloying of pure copper affect its conductivity?
The alloying of pure copper always has an adverse effect on its conductivity
35
How does the conductivity of aluminum compare to the conductivity of copper?
It has about 60% conductivity compared to copper
36
Where are aluminum conductors commonly used?
In electrical utility distribution lines
37
Which type of solid conductor has the poorest corrosion resistance?
High-Strength Alloy
38
What type of solid conductor has the poorest oxidation resistance?
Aluminum
39
Which type of solid conductor has the best tensile strength?
High-strength alloy
40
Which type of solid conductor has the best ductility?
High-Strength alloy
41
What is the conductivity for a High-Strength alloy conductor?
85% of typical
42
How are stranded conductors created?
By bundling together a number of small-gauge conductors to create a single, larger conductor
43
Name the four advantages of solid conductors
- Less costly
- Less complex termination systems
- Better transmission at high frequencies
- Less resistance
44
Name three advantages of stranded conductors
- More flexible
- Longer flex life
- Less susceptible to damage during crimp termination processes
45
What is a composite conductor?
A conductor constructed from nontraditional materials such as metallic resins or graphite
46
Name four advantages of composite conductors
- Highly flexible
- Lightweight
- Inexpensive and easy to produce
- Easily embedded into other materials
47
Name four disadvantages of composite conductors
- Poor analog transmission characteristics
- Poor digital transmission characteristics
- Easily damaged unless encased in a rigid material
- Inconsistent quality
48
Are cables with composite conductors recommended for use with modern telecommunications networks?
No, composite conductors are not recommended in a telecommunications network
49
Why is the AWG system important?
Because it provides a standard reference for comparing various conductor materials
50
What is the purpose of insulation on a cable?
To isolate the flow of current by preventing direct contact between conductors and a conductor and its environment
51
How do dielectrics reduce EM coupling between conductors?
By increasing conductor separation
52
What is the dielectric constant?
The ratio of the capacitance of an insulated conductor to the capacitance of the same conductor uninsulated in the air
53
What does dielectric strength measure?
The maximum voltage that an insulation can withstand without breakdown
54
What is dissipation factor?
The relative power loss in the insulation due to molecular excitement and subsequent kinetic and thermal energy losses
55
What is insulation resistance?
The insulations ability to resist the flow of current through it
56
How is insulation resistance typically expressed?
In megaohm*km or megaohm*1000ft
57
How does cable length affect cable resistance?
As the cable length increases, the insulation resistance becomes smaller
58
What is the main reason for twisting conductor pairs?
To minimize crosstalk and noise by decreasing capacitance unbalance and mutual inductance coupling between pairs
59
What does pair-to-pair capacitance unbalance measure?
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
60
What is mutual inductance?
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
61
How is crosstalk within a multipair cable minimized?
By giving each pair a different twist length within a standard range
62
What type of twist is generally used for voice and low-frequency data cables?
A counterclockwise twist length between ~50mm and ~150mm (1.97in and 6in)
63
What is tight twisting?
Creating pair twist lengths that are less than ~12.7 mm (0.50in)
64
Where is tight twisting commonly used?
Within and between computers and other date processing equipment
65
Which cable categories employ tight twisting for optimum transmission performance?
Category 5e, 6, 6A and higher
66
What term is used to refer to stray electrical radiated from electrical equipment and electronics systems?
Electromagnetic Interference (EMI)
67
At what temperature does attenuation increase in balanced twisted-pair cables?
Above 20*C (68*F)
68
What temperature reference is cited in cabling standards for all twisted-pair cables?
20*C +/- 3*C (68*F +/- 5.4*F)
69
What is a cable shield?
A metallic covering or envelope enclosing an insulated conductor, individual group of conductors within a core and cable core
70
Name three potential benefits of using a cable shield if it is properly terminated, bonded and grounded
- 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
71
Name three factors that can affect a shields effectiveness
- Type and thickness of the shield material
- Number and size of openings in the shield
- Effectiveness of the bonding connection to ground
72
How is shield effectiveness determind?
By measuring the surface transfer impedance
73
What is surface transfer impedance?
The ratio of the conductor-to-shield voltage per unit length to the shield current
74
Why are solid metal tubes inappropriate for most cable applications?
Because of their rigid nature
75
Name the four primary criteria for selecting cable shields
- 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
What type of cable shield has poor tensile strength?
Foil (Foil and Braid)
77
Which type of cable shield is the least effective for radio frequency?
Flexible Conduit
78
What type of cable shield has a poor fatigue life?
Solid Conduit
79
Which cable shields have excellent tensile strength?
- Single-Layer Braid
- Multiple-Layer Braid
- Solid Conduit
80
What is permeability?
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
Name two reasons for using a drain wire
- To provide an easier means for grounding the shield
- To ensure shield continuity for metallic foil shields
82
How are drain wires typically applied?
Longitudinally next to the metallic part of the shield for the length of the cables
83
What is an analog signal?
A wave that used continuous variations in time to transmit information
84
What is the most fundamental concept of an analog signal?
Sinusoid
85
Name the three parameters used to describe a sinusoid
- Amplitude
- Frequency
- Phase
86
What is the standard unit of frequency measurement?
Hertz (Hz)
87
What formula is used to represent the relationship between cycle time and frequency?
f = 1/T
88
What is the typical range of frequencies that humans can hear?
20Hz to 20,000Hz
89
What range of frequencies is typically used for voice circuits?
300Hz to 3400Hz
90
What is a phase?
A description of the reference time
t = 0
91
How many degrees are in a cycle?
360 degrees
92
What is a signals spectrum?
A sum of sinusoidal signals that differ in amplitude, frequency and phase
93
What is necessary for the received signal to be an exact duplicate of the transmitted signal?
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
What defined the analog signals bandwidth?
The frequency range of the sinusoidal signals needed to describe an analog signal
95
What is the frequency range of the very low frequency (VLF) band?
3kHz to 30kHz
96
What is the frequency of the low frequency (LF) band?
30kHz to 300kHz
97
What is the frequency of the medium frequency (MF) band?
300kHz to 3000kHz
98
What is the frequency range of the high frequency (HF) band?
3MHz to 30MHz
99
What is the frequency range of the very high frequency (VHF) band?
30MHz to 300MHz
100
What is the frequency range of the ultra high frequency (UHF) band?
300MHz to 3000MHz
101
What is the frequency range of the community antenna TV (CATV) band?
54MHz to 1002MHz
102
What is the frequency range of the super high frequency (SHF) band?
3GHz to 30GHz
103
What is the frequency range of the extremely high (EHF) band?
30GHz to 300GHz
104
What unit of measure is often used to express the strength of a signal?
Decibel (dB)
105
What decibel (dB) change occurs when the power is doubled?
+3 dB
106
What decibel (dB) change occurs when the power is reduced by half?
-3dB
107
True or False
Decibel (dB) levels are used to express power ratios of all types of analog and digital signals, regardless of the medium?
True
108
In telephony, which delays are perceptible?
Delays greater than 50ms if they are of sufficient strength
109
Name the three basic components of a telecommunications transmission system
- Source of energy
- Medium to carry the energy
- Receiving device
110
What is the purpose of an analog telephone?
To convert sound waves into electrical and analog signals that can be transmitted over much longer distances than the sound can travel
111
True or False
Early telephones were designed to match the frequencies used in human speech, from 50Hz to 12kHz
False
Although speech contains frequencies from 50Hz to 12kHz, quality intelligibility was only in the range of 300Hz to 3400Hz
112
What type of devices converts electrical energy back into sound energy?
Receiver
113
When does the maximum transmission of electrical power occur in a telephone line?
When a transmitting device and a receiving device have the same load resistance or the same impedance
114
How does impedance differ from resistance?
Both are measured in ohms, but impedance has both a magnitude and a phase component
115
What is the preferred impedance for private line circuits and trunks?
600 ohms
116
What is the preferred impedance for CO switching system line circuits?
900 ohms
117
When is an echo perceptible during a long-distance phone call?
When part of the transmitted signal is sent or reflected back to the originating end
118
What causes part of a signal to be sent back or reflected to the originating end?
Impedance mismatch between the transmission line and the receiver
119
What principal elements contribute to loss and phase distortion at voice frequencies?
- Conductor resistance
- Mutual capacitance of the cable pair
120
How does increasing the frequency affect the speed of transmission through cable pairs?
Increasing the frequency increases the speed of transmission
121
True of False
Increasing the frequency to increase the speed of transmission does not noticeably affect speech intelligibility
True
122
What is the purpose of placing load coils along a cable?
To improve speech transmission quality
123
How do load coils improve the quality of speech transmission?
- By compensating for the capacitance of a cable pair
- By reducing the capacitive current loading in the range of audio frequencies
124
What is the most common distance between loading points for D loading?
~1.37km (4495ft)
125
What is the most common distance between loading points for H loading?
~1.83km (6004ft)
126
What types of signals are blocked by loading coils?
Analog high fidelity and digital signals
127
How do loading coils affect data transmission?
Load coils adversely affect data transmission
128
What determines the upper cutoff frequency of a loading coil?
Loading coil spacing determines the upper cutoff frequency
129
Name three common interface options for IP Telephony
- IP Telephone
- Computer with IP Telephony software and a microphone/speaker or USB handset
- Multifunctional devices with a wireless receiver
130
True or False
IP telephony software is only operational when the computer is running
True
131
Name three common implementation options for IP telephony architecture
- 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
Although using a dual-port telephone or softphone may sound like an attractive option, what are the possible drawbacks?
A single cable carrying all information reduces flexibility and redundancy
133
How many telecommunications outlets or connectors are recommended for each individual work area?
Two
134
True or False
Both horizontal cables at the work area location should be considered cables that support data applications
True
While one cable may be associated with voice and the other data, both should be considered data cables
135
What is used to provide uninterrupted power to the telephone set?
Power over Ethernet (PoE)
136
What is the most significant property of a digital signal?
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
What three steps are used to convert an analog signal to a digital signal?
- Filtering
- Sampling
- Quantizing/Companding
138
Why is the analog filtered before it is sampled?
To limit its frequency content
139
What sampling rate is used to faithfully reproduce the analog signal during the conversion process?
A rate that is at least twice the highest frequency component of the analog signal
140
What is quantizing?
Assigning each sampled value a discrete level that approximates the analog signal at the sampling instant
141
What is companding?
Non-uniform mapping between the analog sampled value to an assigned digital level
142
Name the two forms of companding that are in current use
- A-Law
- Mu-Law
143
What type of companding is used in the United States, Canada and Japan
Mu-Law
( μ-law )
144
What type of companding is used in Europe?
A-Law
145
True or False
A-Law and Mu-Law are compatible
False
Although the perform similar functions, they are not compatible
146
What term is used to describe the three step process for converting an analog signal into a digital signal
Pulse Code Modulation (PCM)
147
What is used to encode speech signals at data rates lower than 64 kb/s?
Data signal processing
148
What data rates can be used by ADPCM?
40, 32, 24 and 16 kb/s
149
What device is used to convert speech to a digital signal and its subsequent decoding to speech?
Codec
150
At what rates can vocoders transmit speech?
8 to 2.4 kbs
151
What do lower bit rates typically imply about a signal's quality?
That the signal quality is degraded
152
What process involves combining binary data from several different sources into a single composite bit stream?
Time Division Multiplexing (TDM)
153
What is the purpose of Time Division Multiplexing (TDM)?
To increase the information-carrying capacity of the digital telecommunications channel
154
How is Time Division Multiplexing (TDM) accomplished?
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
What is the most popular form of Time Division Multiplexing (TDM)
Statistical TDM
156
In the DS1 format, the digital data from ___ speech channels is combined for transmission over a signal transmission channel
24 speech channels
157
What is the data rate for the DS1 format?
1.544 Mb/s
158
Describe the CEPT PCM-30 format
In the CEPT PCM-30 format, the digital data from 30 speech channels is combined for transmission over a single transmission channel
159
What is the data rate for the CEPT PCM-30 format?
2.048 Mb/s
160
What term is used to describe the process of reconstituting the individual channels from the composite signal?
Demultiplexing
161
What is a channel blank?
Multiplexing and demultiplexing equipment
162
What stages of multiplexing contain A/D conversion?
Only the first order multiplexing stage (T1 and E1)
163
In the United States, how many T1 frames are needed to create a superframe?
12
164
In Europe, how many E1 frames are needed to create a multiframe?
16
165
What is the basic unit of digital data?
Bit
166
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
False
167
What is the final step in the encoding process?
The modification of the shape and pattern of pulses to achieve more efficient transmission
168
What is the line-encoding technique designed to do?
- Eliminate the dc component
- Improve timing recovery
169
What encoding technique is used for T1 carriers?
Bipolar Alternate Mark Inversion (AMI)
170
What type of encoding allows signal transition to occur in the middle of every bit interval?
Manchester encoding
171
What term is used to describe the rate at which a signal can change states?
Baud
172
What transmission method is used for ISDN (basic rate)?
2B1Q
173
What transmission method is used for ISDN (primary rate)?
Bipolar
174
What transmission method is used for HDSL?
2B1Q
175
What transmission method is used for 10BASE-T?
Manchester
176
What is the encoding rate for ISDN (basic rate)?
160 kb/s
177
What is the encoding rate for ISDN (primary rate)?
1.544 Mb/s
178
What is the encoding rate for HDSL?
2 x 784 kb/s
179
What is the encoding rate for 10BASE-T?
10 Mb/s
180
What is a QAM signal?
A signal composed of two sinusoidal carriers, each having the same frequency but differing in phase by one quarter of a cycle
181
Which QAM sinusoid is the equivalent of a sine wave?
I signal
182
Which QAM sinusoid is the equivalent of a cosine wave?
Q signal
183
What type of modulation does DMT use?
Multicarrier modulation
184
How can data rates be adjusted with DMT?
By increasing the number of sub-bands and by varying the number of bits carried in each sub-band
185
Which line application uses 8B/1Q4 PAM 5 encoding?
100BASE-T
