Chapter 1 - Principles of Transmission

Question 1

The theory and methodology used to verify appropriate optical fiber performance are the same for both singlemode and multimode optical fibers at any wavelength.

a. True
b. False

Answer 1

a. True

p 1-106

The specifications used for each of the components (e.g., transmitter, receiver, optical fiber, connectors) must correspond to the optical fiber type and wavelength.

Question 2

The patch cord return loss test for a balanced twisted-pair permanent link requires that the patch cord be tested _____ mechanical handling to ensure that the impedance remains stable and within tight limits.

a. Before and after
b. After
c. Before

Answer 2

a. Before and after

p 1-62

The patch cord is often a weak link in a cabling system. The patch cord return loss test requires that the patch cord be tested before and after mechanical handling to ensure that the impedance remains stable and within tight limits.

Question 3

Which one of the following optical fiber transmitters is associated with a center wavelength of 850 nm and has a modulation frequency up to 10 GHz?

a. VCSEL
b. Short wavelength laser
c. Laser (LD)
d. Light-emitting diode (LED)

Answer 3

a. VCSEL

p 1-87 Table 1.24

Question 4

A maximum of ten 10BASE-T systems can share a common binder group in a multi-pair balanced twisted-pair cable having category 3 transmission characteristics.

a. True
b. False

Answer 4

b. False

p 1-72

Examples of the restrictions on shared sheaths for specific applications using binder groups in multipair cables having category 3 transmission characteristics include the following:
• No more than TWELVE (12) 10BASE-T systems can share a common binder group.

Question 5

Which of the following is a level of multiplexing used in North America?

a. DS0C
b. DS1C
c. DS2C
d. DS3C

Answer 5

b. DS1C

p 1-121

The levels of multiplexing used in North America are DS0, DS1, DS1C, DS2, and DS3.

Question 6

Echoes of voice occur at all times. In telephony, delays greater than _____ milliseconds (ms) are perceptible if they are of sufficient strength.

a. 50
b. 40
c. 30
d. 20

Answer 6

a. 50

p 1-22

For an echo to be experienced, there must be enough delay for it to be distinguishable from the original source of the sound. In telephony, delays greater than 50 ms are perceptible if they are of sufficient strength.

Question 7

The attenuation of light signals is higher for visible light (wavelengths of 400 nm to 700 nm) than for light in the near infrared region (wavelengths of 700 nm to 1600 nm)

a. True
b. False

Answer 7

a. True

p 1-101

Question 8

Which one of the following statements about loading coils is false?

a. They cut off frequencies above the voice range
b. They compensate for the capacitance of a cable pair
c. They block analog high fidelity signals
d. They improve speech transmission quality
e. They have no effect on data transmission

Answer 8

e. They have no effect on data transmission

p 1-25

Although loading coils improve speech, they adversely affect data transmission. While loading improves the loss versus frequency characteristics, it causes severe delay problems.

Question 9

E1 Level is capable of handling 30 standard (3100 Hz bandwidth) analog voice channels when standard 64 kb/s PCM is used. 60 voice channels are available if 32 kb/s ADPCM encoding is used.

a. True
b. False

Answer 9

a. True

p 1-124

Is capable of handling 30 standard (3100 Hz bandwidth) analog voice channels when standard 64 kb/s PCM is used. 60 voice channels are available if 32 kb/s ADPCM encoding is used.

Question 10

Which one of the following is not an information channel in an asymmetric digital subscriber line (ADSL) circuit?

a. A plain old telephone service (POTS) channel
b. A medium-speed duplex channel
c. A high-speed downstream channel
d. A low-speed upstream channel

Answer 10

d. A low-speed upstream channel

p 1-43

An ADSL circuit connects an ADSL modem on each end of a single balanced twisted-pair telephone line, creating three information channels
—a high-speed downstream channel,
—a medium-speed duplex channel,
—and a POTS channel.

Question 11

Composite conductors have poor analog transmission characteristics, especially above 4000 Hz.

a. True
b. False

Answer 11

a. True

p 1-5

Disadvantages of composite conductors include the following:
• Poor analog transmission characteristics, including high attenuation, especially above 4000 Hz
• Poor digital transmission characteristics
• Easily damaged unless encased in a rigid material
• Inconsistent quality

Question 12

Optical fiber spectral width is usually given as the range of wavelengths emitted with an intensity level greater than or equal to:

a. One half of the peak intensity level
b. The peak intensity level
c. The central wavelength
d. Twice the peak intensity level

Answer 12

a. One half of the peak intensity level

p 1-81

Spectral width is usually given as the range of wavelengths emitted with an intensity level greater than or equal to one half of the peak intensity level, referred to as the FWHM spectral width. See Figure 1.25

Question 13

If 32 kb/s (32,000 b/s) ADPCM encoding is used, a DS1 circuit is capable of simultaneously transporting ___ analog voice channels.

a. 24
b. 48
c. 96
d. 128

Answer 13

b. 48

p 1-121

Is capable of handling 24 standard (3100 Hz bandwidth) analog voice channels when standard 64,000 b/s PCM is used. Forty-eight voice channels are available if 32,000 b/s ADPCM encoding is used.

Question 14

The characteristics impedance of telephone cable pairs is approximately _____ for 26 AWG cables.

a. 900 ohms
b. 600 ohms
c. 300 ohms

Answer 14

a. 900 ohms

p 1-24

The characteristic impedance of telephone cable pairs is approximately 600 ohms for 22 AWG cables and 900 ohms for 26 AWG cables.

Question 15

An analog signal is in the form of a wave that uses continuous variations in time (e.g., voltage amplitude or frequency variations) to transmit information.

a. True
b. False

Answer 15

a. True

p 1-17

Question 16

Series inductance is related to the:

a. Dimensions and separation of conductors and to the dielectric constant of the insulation and jacket materials
b. Dimensions and separation of conductors
c. Dielectric loss of the insulation and jacket materials

Answer 16

b. Dimensions and separation of conductors

p 1-51

The series inductance L, expressed in H, is the loop inductance of a pair of conductors for an incremental length (Δ×). Series inductance is related to the dimensions and separation of conductors.

Question 17

There is an inverse relationship between insulation resistance and cable length.

a. True
b. False

Answer 17

a. True

p 1-8

There is an inverse relationship between insulation resistance and cable length (i.e., as the cable length increases, the insulation resistance becomes smaller).

Question 18

When compared to copper, high-strength conductors such as cadmium-chromium copper and zirconium copper have a conductivity rating of approximately:

a. 90%
b. 85%
c. 75%
d. 60%
e. 50%

Answer 18

b. 85%

p 1-3

Note, aluminum has about 60% conductivity compared with copper

Question 19

ISDN B channels are assigned for:

a. Signaling and packet data
b. Voice and data

Answer 19

b. Voice and data

p 1-41

Basic rate ISDN:
• Is intended for residential and small business users.
• Uses a digital signal consisting of two 64 kb/s B channels (assigned for voice and data) and one 16 kb/s D channel (assigned for signaling and packet data).

Question 20

Drain wires are sometimes applied in place of a shield to provide an easier means for grounding (earthing) the shield and to ensure shield continuity for metallic shields.

a. True
b. False

Answer 20

b. False

p 1-16

Key word is “in addition”, not “in place”.

Drain wires are sometimes applied in addition to a shield to provide an easier means for grounding (earthing) the shield and to ensure shield continuity for metallic foil shields. A drain wire running the length of the cable next to the shield provides ample grounding (earthing).

Question 21

Three power source equipment options for PoE are available. A(n) _____ is a PoE switch that can provide power to the PD via the structured cabling system.

a. Midspan device
b. Endspan device

Answer 21

b. Endspan device

p 1-77

Endspan devices, a PoE switch can provide power to PD via the structured cabling system.

Question 22

“The insulation’s ability to resist the flow of current through it” is the definition of:

a. Insulation resistance
b. Dissipation factor
c. Dielectric strength
d. Dielectric constant

Answer 22

a. Insulation resistance

p 1-8

The insulation’s ability to resist the flow of current through it. For inside conductors, IR is typically expressed in megohm•km or megohm•1000 ft.

Question 23

Practical attenuation measurements yield values that are higher than the attenuation, depending on the degree of mismatch.

a. True
b. False

Answer 23

a. True

p 1-53

Question 24

The magnitude of the reflection is given by the reflection coefficient (ρ). If Zt < Zo, then the polarity of the reflected wave is inverted

a. True
b. False

Answer 24

a. True

p 1-55

If Zt > Zo, then the polarity of the reflected wave is
not inverted.

Reflection coefficient (ρ) = (Zt – Zo)/(Zt + Zo)

Question 25

Mutual capacitance is related to the:

a. Dimensions and separation of conductors and to the dielectric constant of the insulation and jacket materials
b. Dimensions and separation of conductors
c. Dielectric loss of the insulation and jacket materials

Answer 25

a. Dimensions and separation of conductors and to the dielectric constant of the insulation and jacket materials

p 1-51

The mutual capacitance C, expressed in F, is capacitance between a pair of conductors for an incremental length (Δ×). Mutual capacitance is related to the dimensions and separation of conductors and to the dielectric constant of the insulation and jacket materials.

Question 26

Rise time is usually measured from ___ percent to ___ percent power level. In simplified discussions, the rise time is assumed to be zero. At high data rates, the rise time becomes significant.

a. 0 , 100
b. 10, 90
c. 20, 85
d. 25, 75

Answer 26

b. 10, 90

p 1-92

Transmitters have bandwidth limitations because they take time to change from a low-power state (logical 0) to a high-power state (logical 1). This period is called the rise time.

Rise time is usually measured from 10 percent to 90 percent power level. In simplified discussions, the rise time is assumed to be zero. At high data rates, the rise time becomes significant.

Question 27

What is the maximum power output from the PSE for Type 2 PoE?

a. 30 W
b. 25.5 W
c. 15.4 W
d. 12.95 W

Answer 27

a. 30 W

p 1-75

802.3at defines a Type 2 maximum power output of 30W from the PSE and up to 25.5 W to the PD.

Question 28

Which one of the following types of insulation has the smallest dielectric constant?

a. PVC
b. XL polyolefin
c. ECTFE
d. PE
e. FEP

Answer 28

e. FEP

p 1-7 Table 1.3

Question 29

In an optical fiber system, _____ is the difference between the transmitter average power and the receiver sensitivity.

a. Operating margin
b. System gain
c. Link loss budget
d. Bandwidth

Answer 29

b. System gain

p 1-110

System gain is the difference between the transmitter average power and the receiver sensitivity.

Question 30

The sensitivity of an optical fiber receiver specifies the maximum power level an incoming signal must have.

a. True
b. False

Answer 30

b. False

p 1-88

The sensitivity of a receiver specifies the MINIMUM power level an incoming signal must have to achieve an acceptable level of performance, which is usually specified as a BER.

Question 31

Historically, polyvinyl chloride insulated conductors were commonly used for outside plant cables.

a. True
b. False

Answer 31

b. False

p 1-6

Historically, telecommunications cable conductors were insulated with PVC and PE. PVC-insulated conductors were commonly used for inside plant cables, and PE-insulated conductors were commonly used for OSP cables.

Question 32

The numerical aperture of a 62.5/125 µm multimode optical fiber is approximately:

a. 0.10
b. 0.20
c. 0.275
d. 0.325

Answer 32

c. 0.275

p 1-82 Figure 1.26

Question 33

A DS2 circuit multiplexes ____ DS1 channels.

a. 2
b. 4
c. 7
d. 24

Answer 33

b. 4

p 1-122

The second full level of multiplexing is DS2, which:
• Typically handles four DS1 channels, for a total of 96 voice channels.
• Employs a 6.312 Mb/s pulse stream.

Also se Table 1.39

Question 34

When calculating the power penalties for an optical fiber system, if the manufacturer does not specify the operating margin, then use a value of ___ for LEDs.

a. 3 dB
b. 0.5 dB
c. 1 dB
d. 2 dB

Answer 34

d. 2 dB

p 1-111

Variations in the component temperature within the operating range of the system. If the system manufacturer does not specify the operating margin, use value of:
• 2 dB for LEDs.
• 3 dB for lasers.

Question 35

Which one of the following types of cable shields get a shield effectiveness rating of “poor” for fatigue life?

a. Foil / foil + braid
b. Single-layer braid
c. Multiple-layer braid
d. Flexible conduit
e. Solid conduit

Answer 35

e. Solid conduit

p 1-15 Table 1.5

Question 36

Dispersion in singlemode optical fiber systems is a function of:

a. Transmitter rise time
b. Spectral width
c. Wavelength

Answer 36

c. Wavelength

p 1-94

Dispersion in singlemode systems is a function of wavelength. It is important that the optical fiber dispersion specification coincides with the operating wavelength range of the transmitter.

Question 37

Which one of the following types of cable shield get a shield effectiveness rating of poor for tensile strength?

a. Flexible conduit
b. Foil/foil + braid
c. Solid conduit
d. Single-layer braid
e. Multiple-layer braid

Answer 37

b. Foil/foil + braid

p 1-15 See table 1.5

Question 38

Stranded conductors are less costly than solid conductors.

a. True
b. False

Answer 38

b. False

p 1-4

Advantages of solid conductors include the following:
• Less costly
• Less complex termination systems
• Better transmission performance at high frequencies
• Less resistance
Advantages of stranded conductors include the following:
• More flexible
• Longer flex life
• Less susceptible to damage during crimp termination processes

Question 39

Cables with a lower dielectric constant and dissipation factor have better transmission performance.

a. True
b. False

Answer 39

a. True

p 1-6

Cables with a lower dielectric constant and dissipation factor have better transmission performance, including lower attenuation characteristics and lower capacitance.

The electrical performance of balanced twisted-pair cables is inversely related to the insulation’s dielectric constant and dissipation factor

Question 40

The center wavelength of short wavelength lasers is:

a. 1310 nm
b. 1250 nm
c. 900 nm
d. 780 nm

Answer 40

d. 780 nm

p 1-84

Question 41

The _____ of an optical fiber transmitter is the rate at which the transmission changes in intensity.

a. Modulation frequency
b. Average power
c. Emission pattern
d. Spectral width

Answer 41

a. Modulation frequency

p 1-83

The modulation frequency of a transmitter is the rate at which the transmission changes in intensity.

Question 42

In general, characteristic impedance has both a(n) _____ and a(n) _____ component.

a. Inductive; resistive
b. Resistive; capacitive
c. Capacitive; inductive
d. Inductive; reactive
e. Resistive; reactive

Answer 42

e. Resistive; reactive

p 1-53

In general, the characteristic impedance has both a resistive and reactive component. Characteristic impedance is a function of the frequency of the applied signal, but it is unrelated to the cable length.

Question 43

Baseband composite video signaling can be supported over a minimum of ___ balanced twisted-pair cable in excess of ≈100 m (328 ft).

a. Category 6 / class E
b. Category 5e / class D
c. Category 3 / class C

Answer 43

c. Category 3 / class C

p 1-47

Baseband composite signaling can be supported over category 3/class C or higher cabling in excess of ≈100 m (328 ft)

Question 44

The term broadband video refers to composite baseband video and audio signals

a. True
b. False

Answer 44

a. True

p 1-47

Question 45

The shielding effectiveness of a cable shield is determined by measuring the:

a. Voltage gradient between the conductors inside the cable
b. Shield resistance
c. Effectiveness of the bonding connection to ground
d. Surface transfer impedance

Answer 45

d. Surface transfer impedance

p 1-13

The shielding effectiveness of a cable shield is determined by measuring the surface transfer impedance. The surface transfer impedance is the ratio of the conductor-to-shield voltage per unit length to the shield current.

Question 46

Which one of the following types of insulation has the largest dielectric constant?

a. ECTFE
b. PVC (plenum rated)
c. PVC (non-plenum rated)
d. PE
e. FEP

Answer 46

b. PVC (plenum rated)

p 1-7 Table 1.3

Question 47

The bandwidth of a multimode optical fiber system is a function of:

a. Central wavelength, modal dispersion, and rise time
b. Chromatic dispersion, modal dispersion, and length
c. Spectral width, chromatic dispersion, and central wavelength
d. Transmitter rise time, length, and modal dispersion

Answer 47

b. Chromatic dispersion, modal dispersion, and length

p 1-95

The bandwidth of a multimode system is a function of chromatic dispersion and modal dispersion as well as length.

Question 48

Rate-adaptive digital subscriber line (RADSL) adapts its transmission speed based on the:

a. Type of signal being transmitted and the volume of data traffic
b. Volume of data traffic and the signal quality of the line
c. Length and signal quality of the line
d. Type of signal being transmitted and the length of the line

Answer 48

c. Length and signal quality of the line

p 1-44

RADSL is the rate-adaptive variation of ADSL. Transmission speed is rate adaptive based on the length and signal quality of the line.

Question 49

The two key parameters in optical fiber cabling performance that must be verified for compatibility with the proposed electronics are:

a. Attenuation and bandwidth
b. Bandwidth and wavelength
c. Wavelength and attenuation

Answer 49

a. Attenuation and bandwidth

p 1-105

The two key parameters in optical fiber cabling performance that must be verified for compatibility with the proposed electronics are:
• Bandwidth.
• Attenuation.

Question 50

___ is the minimum performance for balanced twisted-pair network cabling according to BICSI best practices.

a. Category 6A / class EA
b. Category 6 / class E
c. Category 5e / class D
d. Category 3 / class C

Answer 50

b. Category 6 / class E

p 1-64

Category 6/class E or higher cabling represents BICSI best practices.