TDMM Chapter 1 - Part 2 Flashcards
1
Q
Name the three types of transmission circuits
A
- Simplex
- Half-Duplex
- Full-Duplex
2
Q
What is simplex transmission?
A
The transmission of signals in one direction only
3
Q
What is half-duplex transmission?
A
The transmission of signals in either direction, but in one direction at a time
4
Q
What is full-duplex transmission?
A
The transmission of signals in both directions at the same time
5
Q
Why is asynchronous transmission a popular method of telecommunications among microcomputer users?
A
Because of a common standardized interface and protocol between machines
6
Q
Why is asynchronous transmission less efficient than synchronous transmission?
A
Because it requires the addition of some combination of start and stop bits to the data stream
7
Q
How is synchronous transmission performed?
A
By synchronizing the data bits in phase or in unison with equally spaced clock signals or pulses
8
Q
What is used to prevent confusion of the characters in the data stream
A
Clocking pulses
9
Q
Who are the intended users of basic rate ISDN?
A
Residential and small business users
10
Q
What is the total information capacity of basic rate ISDN?
A
144 kb/s (line rate = 160 kb/s)
11
Q
Who are the intended users of primary rate ISDN North America?
A
Large Business Users
12
Q
What is the total information capacity of primary rate ISDN North America?
A
1.536 Mb/s (line rate = 1.544 Mb/s)
13
Q
Delay Skew
A
The difference in propagation delay between any pairs within the same cable sheath
14
Q
What is the total information capacity of primary rate ISDN Europe?
A
1.92 Mb/s (line rate = 2.048 Mb/s)
15
Q
Dispersion
A
The loss of signal resulting from the scattering of light pulses as they are transmitted through a medium
16
Q
HDSL requires no repeaters on lines less than __ for 24AWG
A
~3600m (11,811ft)
17
Q
What has effectively replaced HDSL?
A
SDSL and other xDSL technologies
18
Q
What is SDSL?
A
A single-pair version of HDSL, transmitting up to DS1 rate signals over a single balanced twisted pair
19
Q
What is distance limitations for SDSL?
A
~3000m (9842ft)
20
Q
What does asymmetric describe about ADSL technologies?
A
That they allow more bandwidth downstream (server to client) than they do upstream (client to server)
21
Q
What down-to-upstream ratio is required for good Internet performance?
A
At least 10:1
22
Q
What do ADSL modems use to reduce errors caused by impulse noise?
A
Forward Error Correction (FEC)
23
Q
What does RADSL allow the Access Provider (AP) to adjust?
A
The bandwidth of the DSL link to fit the need of the application and to account for the length and quality of the line
24
Q
How does RADSL increase the percentage of users served by DSL services?
A
By extending the possible distance from the subscriber to the Access Provider (AP) facility
25
What are the target ranges of VDSL downstream rates?
- 12.6 to 13.8 Mb/s
- 25.92 to 27.6 Mb/s
- 51.84 to 55.2 Mb/s
26
What are the general ranges of VDSL upstream rates?
- 1.6 to 2.3 Mb/s
- 19.2 Mb/s
- Equal to downstream
27
How much delay is introduced by interleaving?
In the order of 40 times the maximum length correctable impulse
28
What is a baseband analog video signal?
A baseband analog video signal is a continuous varying signal whose magnitude and frequency represent the video content. A baseband video signal contains all the necessary information to reproduce a picture, but it does not modulate an RF carrier
29
Name two types of baseband signalling
- Composite
- Component
30
What information is contained in a composite format analog signal?
All the components necessary to construct a monochrome or color picture but no audio information
31
What colors are used to create a color video picture?
Red, Green, Blue (RGB)
32
How does a component video keep the three color components of an image seperate?
With three cables
33
Why is the RGB signal separated from the luminance signal in a component video?
To minimize crosstalk and permit higher resolution
34
How is RGB signaling typically used?
For high-end graphic workstations where the need for higher-quality imaging is required
35
What does an RF carrier represent?
TV Channel
36
Which categories of balanced twisted-pair cabling support baseband composite signaling?
Category 3/Class C or higher
(in excess of ~100M (328ft))
37
Which categories of balanced twisted-pair cabling support RGB composite signaling?
Category 3/Class C or higher
(for a minimum of ~100M (328ft) using passive media adapters)
38
Which categories of balanced twisted-pair cabling support broadband analog CATV signaling?
Category 5e/Class D or higher
39
What are the components of an idealized transmission line?
Two conductors separated by a dielectric material uniformly spaced over the line's length
40
What was the basis of the earliest functional model of a transmission line?
Resistive loss
41
How can a transmission line be represented?
By an electrical circuit containing only passive components that are arranged in a ladder network
42
Name the four primary transmission line parameters
- Series resistance
- Series inductance
- Mutual capacitance
- Mutual conductance
43
What is series resistance?
The loop resistance of a pair of conductors for an incremental length
44
What unit of measure is used to express series resistance?
Ohms
45
What is series inductance?
The loop inductance of a pair of conductors for an incremental length
46
What unit of measure is used to express series inductance?
Henries (H)
47
What is mutual capacitance?
The capacitance between a pair of conductors for an incremental length
48
What unit of measure is used to express mutual inductance?
Farads (F)
49
How can the secondary parameters of a transmission line be determined?
The conductance between a pair of conductors for an incremental length
50
What unit of measure is used to express mutual conductance?
Siemens (S)
51
What forms the foundation of EM wave theory?
Maxwell's equations
52
How can the secondary parameters of a transmission line be determined?
- By calculating the primary parameters
- By direct measurement
53
When is maximum power transferred from the source to the load?
When the source impedance (Zs) and the terminating impedance (Zt) are equal to the complex conjugate of the transmission line characteristic impedance (Zo)
54
What term refers to the ratio of output to input power (or voltage) where the terminations are perfectly matched?
Attenuation
55
What term describes signal interference between cable pairs?
Crosstalk
56
How is NVP for balanced twisted-pair cables expressed?
As a percentage of the speed of light
57
What is the range of typical NVP values for 100 ohm balanced twisted-pair cables?
.56c to .74c
58
What term is used to describe the difference in propagation delay between any pairs within the same cable sheath?
Delay Skew
59
What term describes the ratio between the transmitted power and the reflected power?
Return Loss
60
What is the signal-to-noise ratio (SNR)?
The ratio between the level of the received signal at the receiver end and the level or transmitted signal
61
How is attenuation-to-crosstalk ratio (ACR) obtained?
By subtracting the attenuation (dB) from near-end crosstalk (NEXT) (dB)
62
How is ACR normally stated?
At a given frequency
63
What is power sum attenuation-to-crosstalk ratio (PSACR)?
A ratio in decibels determined by subtracting the attenuation from PSNEXT loss
64
What is power sum attenuation-to-alien crosstalk ratio at the near end (PSAACRN)?
A ratio in decibels determined by subtracting the attenuation from PSANEXT loss between cables or channels in close proximity
65
What is power sum attenuation-to-alien crosstalk ratio at the far end (PSAACRF)?
A ratio in decibels determined by subtracting the attenuation from the PSAFEXT loss between cables or channels in close proximity
66
How do cabling standards define a channel?
All cables, cords and connectors from an equipment connection at one end to the equipment connection at the other end
67
What is the nominal characteristic impedance of balanced-twisted pair cables?
100ohms at 100MHz
68
What is the nominal characteristic impedance of balanced twisted-pair cables?
100ohms at 100MHz
69
Name the three most important parameters that affect the performance of balanced twisted-pair network cabling
- Insertion Loss
- PSNEXT Loss
- Return Loss
70
What is channel insertion loss?
The sum of the attenuation of the various components in the test channel, plus all the mismatch losses at cable and connector interfaces, and the increase in attenuation adjusted for temperature
71
What is NEXT loss in a channel?
The vector sum of crosstalk induced in the cable, connectors and patch cords
72
What is power sum equal level far-end crosstalk (PSELFEXT)
A computation of the unwanted signal coupling from multiple transmitters at the near end into a pair measured at the far end
73
What determines the available channel bandwidth for a specified channel?
The range of frequencies that can be successfully transmitted for a given distance
74
What is the dominant noise source for most LAN systems today?
NEXT interference between all transmit pairs and a receive pair
75
How much horizontal cabling may be used in a permanent link?
Up to ~90m (295ft)
76
True or False
The transmission categories of all components used in the same cabling system must be matched
True
77
What category/class of balanced twisted pair cable provides the minimum acceptable performance level for network cabling?
Category 3/Class C
78
What category/class of balanced twisted-pair cable is recommended as the minimum by most standards?
Category 5e/Class D
79
What category/class of balanced twisted-pair cable represents BICSI best practices for network cabling?
Category 6/Class E
80
What frequency is supported by Category 3/Class C cable?
16MHz
81
What frequency is supported by Category 5/Class D cable?
100MHz
82
What frequency is supported by Category 6/Class E cable?
250MHz
83
How many 10BASE-T systems can share a binder group?
No more than 12
84
Name the three advantages of media conversion to balanced twisted-pair
- It can be a cost effective solution
- Moves can be simpler to implement
- Less space in risers or conduits is required
85
Name the three main categories of terminal interfaces
- Impedance-matching devices
- Signal converters
- Media filters
86
How are baluns used?
To adapt the balanced impedance of twisted-pairs to the unbalanced impedance of coaxial cables
87
Where are baluns required?
Wherever a transition is made from twisted-pair to coaxial or from coaxial to twisted-pair
88
What is a signal converter?
An electronic device that receives one type of signal and outputs another type of signal
89
Name two advantages of signal converters
- Decrease the risk of transmission and EMI problems
- Extend the unbalanced signal reach of a DTE
90
What is the purpose of a media filter?
To eliminate unwanted frequencies affecting link performance that could radiate from the balanced twisted-pair cable
91
What is a transceiver?
A radio frequency device capable of sending and receiving radio frequencies
92
Name the four benefits of combining power and data onto a single cable
- Eliminating the need to provide ac electrical outlets at the same location
- Faster installation times
- Detecting loss of power to a device
- Backup power to network devices
93
What is the maximum power output for Type 1 POE?
15.4W
94
What is the maximum power output for Type 2 POE?
30W
95
What is the maximum power output for Type 3 POE?
60W
96
What is the maximum power output for Type 4 POE?
90W
97
What is link layer discovery protocol (LLDP)?
Type 3 or 4 PSE power classification information exchanged during initial negotiation
98
Name three practical power sourcing equipment (PSE) options for POE
- Endspan devices
- Midspan devices
- Local power sources
99
Name the three elements of a simple telecommunications system
- transmitter
- receiver
- medium
100
What is the purpose of an optical transmitter?
To convert electrical signals to optical signals for transmission over an optical fiber cable
101
What are the four nominal wavelengths of optical fiber transmitters?
- 850nm
- 1300nm
- 1310nm
- 1550nm
102
What term refers to the range of wavelengths over which the total power emitted by a transmitter is distributed?
Spectral Width
103
What unit of measure is typically used to specify spectral width?
Nanometer (nm)
104
How do wide spectral widths affect the dispersion of light pulses?
Wide spectral widths lead to increased dispersion of light pulses as the light pulses propagate through an optical fiber
105
What is the average power of a transmitter?
The mean level of power output of a given light source during modulation
106
What is the modulation frequency of a transmitter?
The rate at which the transmission changes in intensity
107
Name the three major types of transmitter light sources
- LED
- VCSEL
- LD
108
What center wavelength ranges are typical for LEDs?
- 800 to 900 nm
- 1259 to 1350 nm
109
What is the modulation frequency of most LEDs?
Under 200 MHz
110
What is the average launched optical power level of LEDs?
-10 to -30 dBm into multimode fiber
111
What is the center wavelength for short wavelength lasers?
780 nm
112
How does the modulation frequency of short wavelength lasers compare to that of LEDs?
It is higher than LEDs (can exceed 1 GHz)
113
What is the average launched optical power level of short wavelength lasers?
+1 to -8 decibels per mW (dBm)
114
What are the center wavelengths used for VCSELs?
- 850 nm
- 1300 nm
115
How does the modulation frequency for VCSELs compare to that of LEDs?
It is much higher than LEDs, allowing up to 56GHz
116
What is the average launched power level of VCELs?
-1 to -8 decibels per milliwatt into multimode fiber
117
What is the predominate center wavelength for laser diodes (LDs)?
1310 nm
118
How does the spectral width for LDs compare to that of LEDs?
Narrow in comparison
119
Whereare typical LD sources used?
Almost exclusively in singlemode optical fiber links
120
What is the average launched optical power level of LDs?
Common values of +4 to -9 power level decibels per milliwatt into singlemode optical fibers
121
Which type of transmitter is the most expensive: LED, VCSEL or LD?
LD
122
What is the primary type of optical fiber used with LD transmitters?
Singlemode
123
Name the three characteristic parameters of optical fiber receivers
- Sensitivity
- Bit Error Rate (BER)
- Dynamic Range
124
Define sensitivity in terms of optical fiber receivers
The minimum power level an incoming signal must have to achieve an acceptable level of performance
125
What is bit error rate (BER)?
The fractional number of errors allowed to occur between the transmitter and receiver
126
What happens to the BER (bite error rate) if the power of the incoming signal falls below the receiver sensitivity?
The number of bit errors will increase beyond the maximum BER specified for the receive
127
What is dynamic range?
The range of power that a receiver can process at a specified bit error rate (BER)
128
Name the three key factors that are used to determine which optical fiber to use in a given application
- Active equipment
- Distance
- Bandwidth (data rate)
129
Which classes of multimode cable are recognized for use in new installations?
- OM3
- OM4
- OM5
130
Name the two essential determinants of the end to end bandwidth for an optical fiber system
- Transmitter
- Optical Fiber
131
What is rise time?
The time it takes transmitters to change from a low poweer state (logical 0) to a high power state (logical 1)
132
How does dispersion affect a light pulse?
It causes the light pulse to broaden in duration as it travels through the optical fiber
133
What is often used in place of bandwidth to define system capacity in singlemode systems?
Maximum Pulse Distortion
134
Name the three effects that are combined to calculate and predict the bandwidth requirements for a multimode system
- Transmitter rise time
- Optical fiber modal dispersion
- Chromatic Dispersion
135
What type of dispersion occurs when the wider range of wavelengths in each pulse travels at a wider range of individual speeds?
Chromatic Dispersion
136
What is modal dispersion?
An event that occurs when a pulse of light, which consists of hundreds of modes in a multimode optical fiber, broadens in time as it travels through the optical fiber
137
What are the two major classifications of optical fiber cable?
- Singlemode
- Multimode
138
What are the two popular sizes of multimode optical fiber cables?
-62.5/125 um
- 50/125 um
139
What are the most common wavelength windows for optical fiber cables?
- 850 nm
- 1300 nm
- 1550 nm
140
What is the characteristic core diameter for singlemode optical fiber?
Between 8 and 9 um
141
What is the diameter of the cladding on a singlemode optical fiber cable?
125 um
142
What is the bandwidth for singlemode optical fiber?
Greater than 20 GHz
143
What are the operating wavelengths for singlemode optical fiber?
- 1310 nm
- 1550 nm
144
What establishes the maximum supportable distance for optical fiber cables?
The application standards
145
What establishes maximum channel attenuation?
The difference between the minimum transmitter output power coupled into the optical fiber and the receiver sensitivity, less any power penalties established
146
What is the maximum attenuation value for 50/125 um multimode cable at 850 nm?
3.5 dB/km
147
What is the maximum attenuation value for 62.5/125 um multimode cable at 1300 nm?
1.5 dB/km
148
What is the maximum attenuation value for singlemode inside plant cable at 1310 nm?
1.0 dB/km
149
What is the maximum attenuation value for singlemode outside plant cable at 1550 nm?
0.4 dB/km
150
How is optical fiber cable bandwidth validated?
Through the manufacturers specification and quality checking of the product specification sheets with the installed components
151
What determines the maximum permissible end to end system attenuation in a given link?
The average transmitter power and the receiver sensitivtiy
152
What connector loss value should be used for 0 to 4 connector pairs?
The maximum value
153
What connector loss value should be used for 5 or more connector pairs?
The typical value
154
What is the recommended loss value for optical fiber cable connectors?
0.75 dB
155
What is the average splice loss for fusion splice in multimode cabling?
0.05 dB
156
What is the average splice loss for a mechanical splice in singlemode cabling?
0.10 dB
157
What is the maximum splice loss for mechanical and fusion splices in multimode cabling?
0.3 dB
158
How is the minimum required system loss calculated?
By subtracting the receivers dynamic range from the system gain
159
What device can be used to add additional loss to an optical fiber system?
Attenuator
160
Name the two standards that have been established for optical fiber carrier transmissions
- Synchronous Optical Network (SONET) - North America
- Synchronous Digital Hierarchy (SDH) - International
