4, 5, 12

Question 1

Which of the following is a better indicator of what outside influences are affecting an RF signal at a specific moment in time?

A. RSSI
B. SNR
C. EIRP
D. SINR

Answer 1

D. SINR

The signal-to-interference-plus-noise ratio (SINR) compares the primary signal to both interference and noise.

Question 2

A point source that radiates RF signal equally in all directions is known as what?

A. Omnidirectional signal generator
B. Omnidirectional antenna
C. Intentional radiator
D. Nondirectional transmitter
E. Isotropic radiator

Answer 2

E. Isotropic radiator

An isotropic radiator is also known as a point source.

Question 3

When calculating the link budget and system operating margin of a point-to-point outdoor WLAN bridge link, which factors should be taken into account? (Choose all that apply.)

A. Distance
B. Receive sensitivity
C. Transmit amplitude
D. Antenna height
E. Cable loss
F. Frequency

Answer 3

A. Distance, B. Receive sensitivity, C. Transmit amplitude, E. Cable loss, F. Frequency

All but antenna height

When radio communications are deployed, a link budget is the sum of all gains and losses from the transmitting radio, through the RF medium, to the receiver radio.

Question 4

The sum of all the components from the transmitter to the antenna, not including the antenna, is known as what? (Choose two.)

A. IR
B. Isotropic radiator
C. EIRP
D. Intentional radiator

Answer 4

A. IR, D. Intentional radiator

IR is the abbreviation for intentional radiator. The components making up the IR include the transmitter, all cables and connectors, and any other equipment (grounding, lightning arrestors, amplifiers, attenuators, and so forth) between the transmitter and the antenna. The power of the IR is measured at the connecter that provides the input to the antenna.

Question 5

Which term is used to describe the amount of RF power emitted from the head of an antenna?

A. Equivalent isotropically radiated power
B. Transmit antenna radiated power
C. Total radiated power
D. Antenna radiated power

Answer 5

A. Equivalent isotropically radiated power

Equivalent isotropically radiated power, also known as EIRP, is a measure of the strongest signal that is radiated from an antenna

Question 6

Select the absolute units of power. (Choose all that apply.)

A. Watt
B. Milliwatt
C. Decibel
D. dBm
E. Bel

Answer 6

A. Watt, B. Milliwatt, D. dBm

Bel doesn’t belong here.

Watts, milliwatts, and dBms are all absolute power measurements. One watt is equal to 1 ampere (amp) of current flowing at 1 volt. A milliwatt is 1/1,000 of 1 watt. dBm is deci-bels relative to 1 milliwatt.

Question 7

Select the units of comparison (relative). (Choose all that apply.)

A. dBm
B. dBi
C. Decibel
D. dBd
E. Bel

Answer 7

B. dBi, C. Decibel, D. dBd, E. Bel

The unit of measurement known as a bel is a relative expression and a measurement of change in power. A decibel (dB) is equal to one-tenth of a bel. Antenna gain measurements of dBi and dBd are relative measurements. dBi is defined as decibels relative to an isotropic radiator. dBd is defined as decibels relative to a dipole antenna.

Question 8

2 dBd is equal to how many dBi?

A. 5 dBi
B. 4.41 dBi
C. 4.14 dBi
D. 2 dBi

Answer 8

C. 4.14 dBi

To convert any dBd value to dBi, simply add 2.14 to the dBd value.

Question 9

23 dBm is equal to how many mW?

A. 200 mW
B. 14 mW
C. 20 mW
D. 23 mW
E. 400 mW

Answer 9

A. 200 mW

To convert dBm to mW, first calculate how many 10s and 3s are needed to add up to 23, starting at 0 dBm is 0 + 10 + 10 + 3. To calculate the mW, starting at 1mw, you must multiply 1 × 10 × 10 × 2, which calculates to 200 mW.

Question 10

A wireless bridge is configured to transmit at 100 mW. The antenna cable and connectors produce a 3 dB loss and are connected to a 16 dBi antenna. What is the EIRP?

A. 20 mW
B. 30 dBm
C. 2,000 mW
D. 36 dBm
E. 8 W

Answer 10

100 > 2,000
C. 2,000 mW

To reach 100 mW, you can use 10s and 2s along with multiplication and division.

Question 11

A WLAN transmitter that emits a 400 mW signal is connected to a cable with 9 dB of loss. If the cable is connected to an antenna with 19 dBi of gain, what is the EIRP?

A. 4 W
B. 3,000 mW
C. 3,500 mW
D. 2 W

Answer 11

A. 4 W

If the original transmit power is 400 mW and cabling induces 9 dB of loss, the power at the opposite end of the cable would be 50 mW.

Question 12

WLAN vendors use RSSI thresholds to trigger which radio card behaviors? (Choose all that apply.)

A. Receive sensitivity
B. Roaming
C. Retransmissions
D. Dynamic rate switching

Answer 12

B. Roaming, D. Dynamic rate switching

Received signal strength indicator (RSSI) thresholds are a key factor for clients when they initiate the roaming handoff. RSSI thresholds are also used by vendors to implement dynamic rate switching, which is a process used by 802.11 radios to shift between data rates.

Question 13

Received signal strength indicator (RSSI) metrics are used by 802.11 radios to define which RF characteristics?

A. Signal strength
B. Phase
C. Frequency
D. Modulation

Answer 13

A. Signal strength

The received signal strength indicator (RSSI) is a metric used by 802.11 radio cards to measure signal strength (amplitude).

Question 14

dBi is a measure of what?

A. The output of the transmitter
B. The signal increase caused by the antenna
C. The signal increase of the intentional transmitter
D. The comparison between an isotropic radiator and the transceiver
E. The strength of the intentional radiator

Answer 14

B. The signal increase caused by the antenna

dBi is defined as “decibel gain referenced to an isotropic radiator” or “change in power relative to an antenna.” dBi is the most common measurement of antenna gain.

Question 15

Which of the following are valid calculations when using the rule of 10s and 3s? (Choose all that apply.)

A. For every 3 dB of gain (relative), double the absolute power (mW).
B. For every 10 dB of loss (relative), divide the absolute power (mW) by a factor of 2.
C. For every 10 dB of loss (absolute), divide the relative power (mW) by a factor of 3.
D. For every 10 mW of loss (relative), multiply the absolute power (dB) by a factor of 10.
E. For every 10 dB of loss (relative), halve the absolute power (mW).
F. For every 10 dB of loss (relative), divide the absolute power (mW) by a factor of 10.

Answer 15

A. For every 3 dB of gain (relative), double the absolute power (mW).
F. For every 10 dB of loss (relative), divide the absolute power (mW) by a factor of 10.

The four rules of the 10s and 3s are as follows: For every 3 dB of gain (relative), double the absolute power (mW). For every 3 dB of loss (relative), halve the absolute power (mW). For every 10 dB of gain (relative), multiply the absolute power (mW) by a factor of 10. For every 10 dB of loss (relative), divide the absolute power (mW) by a factor of 10.

Question 16

A WLAN transmitter that emits a 100 mW signal is connected to a cable with a 3 dB loss. If the cable were connected to an antenna with 7 dBi of gain, what would be the EIRP at the antenna element?

A. 200 mW
B. 250 mW
C. 300 mW
D. 400 mW

Answer 16

B. 250 mW

Question 17

In a normal wireless bridged network, the greatest loss of signal is caused by what component of the link?

A. Receive sensitivity
B. Antenna cable loss
C. Lightning arrestor
D. Free space path loss

Answer 17

D. Free space path loss

A distance of as little as 100 meters will cause free space path loss (FSPL) of 80 dB, far greater than any other component. RF components such as connectors, lightning arrestors, and cabling all introduce insertion loss. However, FSPL will always be the reason for the greatest amount of loss.

Question 18

To double the effective distance of a signal at a specific power level, the EIRP must be increased by how many dBs?

A. 3 dB
B. 6 dB
C. 10 dB
D. 20 dB

Answer 18

B. 6 dB

The 6 dB rule states that increasing the amplitude by 6 decibels doubles the usable distance of an RF signal. The 6 dB rule is very useful for understanding antenna gain because every 6 dBi of extra antenna gain will double the usable distance of an RF signal.

Question 19

During a site survey of a point-to-point link between buildings at a manufacturing plant, the WLAN engineer determines that the noise floor is extremely high because of all the machinery that is operating in the buildings. The engineer is worried about the ambient noise from inside the building affecting the outdoor bridge link. What is a suggested best practice to deal with this scenario?

A. Increase the WLAN bridge access points’ transmission amplitude 5–10 dB.
B. Mount the WLAN bridge access points higher.
C. Double the distance of the WLAN bridge AP signal with 6 dBi of antenna gain.
D. Plan for received amplitude with a 5–10 dB fade margin.

Answer 19

D. Plan for received amplitude with a 5-10 dB fade margin.

In a high multipath or noisy environment, a common best practice is to add a 5–10 dB fade margin when designing for a WLAN bridge link based on a vendor’s recommended received signal strength or the noise floor, whichever is louder.

Question 20

Which value should not be used to compare wireless network radios manufactured by different WLAN vendors?

A. Maximum data rates
B. Maximum transmit power
C. Antenna gain
D. Received signal strength indicator

Answer 20

D. Received signal strength indicator

WLAN vendors execute received signal strength indicator (RSSI) metrics in a proprietary manner. The actual range of the RSSI value is from 0 to a maximum value (less than or equal to 255) that each vendor can choose on its own (known as RSSI_Max).

Question 21

Which of the following refers to the polar chart of an antenna as viewed from above the antenna? (Choose all that apply.)

A. Horizontal view
B. Vertical view
C. H-plane
D. E-plane
E. Elevation chart
F. Azimuth chart

Answer 21

A. Horizontal view, C. H-plane, F. Azimuth chart

The azimuth chart is the top-down view of an antenna’s radiation pattern, also known as the H-plane, or horizontal. The side view is known as the elevation chart, vertical view, or E-plane.

Question 22

The azimuth chart represents a view of an antenna’s radiation pattern from which direction?

A. Top
B. Side
C. Front
D. Both top and side

Answer 22

A. Top

The azimuth is the top-down view of an antenna’s radiation pattern, also known as the H-plane.

Question 23

What is the definition of the horizontal beamwidth of an antenna?

A. The measurement of the angle of the main lobe as represented on the azimuth chart
B. The distance between the two points on the horizontal axis where the signal decreases by a third. This distance is measured in degrees.
C. The distance between the two –3 dB power points on the horizontal axis, measured in degrees
D. The distance between the peak power and the point where the signal decreases by half. This distance is measured in degrees.

Answer 23

C. The distance between the two –3 dB power points on the horizontal axis, measured in degrees

The beamwidth is the distance in degrees between the –3 dB (half-power) point on one side of the main signal and the –3 dB point on the other side of the main signal, measured along the horizontal axis. These are also known as half-power points.

Question 24

Which antennas are highly directional? (Choose all that apply. There’s two!)

A. Patch
B. Panel
C. Parabolic dish
D. Grid
E. Sector

Answer 24

C. Parabolic dish, D. Grid

A parabolic dish and a grid are highly directional. The rest of the antennas are semidi-rectional, and the sector antenna is a special type of semidirectional antenna.

Question 25

Semidirectional antennas are often used for which of the following purposes? (Choose all that apply. There are three!)

A. To provide short-distance point-to-point outdoor communications
B. To provide long-distance point-to-point outdoor communications
C. To provide unidirectional coverage from an access point to clients in an indoor environment
D. To provide focused or sector coverage in a high-density environment.

Answer 25

A. To provide short-distance point-to-point outdoor communications
C. To provide unidirectional coverage from an access point to clients in an indoor environment
D. To provide focused or sector coverage in a high-density environment.

Everything but long distance!

Semidirectional antennas provide too wide a beamwidth to support long-distance communications but will work for short distances. They are also useful for providing unidirectional coverage from the access point to clients in an indoor environment. They are also used to provide focused coverage in a high-density environment.

Question 26

The Fresnel zone should not be blocked by more than what percentage to maintain a reliable communications link?

A. 20 percent
B. 40 percent
C. 50 percent
D. 60 percent

Answer 26

B. 40 percent

Any more than 40 percent encroachment into the Fresnel zone is likely to make a link unreliable. The clearer the Fresnel zone, the better. Ideally the Fresnel zone should not be blocked at all.

Question 27

The size of the Fresnel zone is controlled by which factors? (Choose all that apply.)

A. Antenna beamwidth
B. RF line of sight
C. Distance
D. Frequency

Answer 27

C. Distance, D. Frequency

The distance and frequency determine the size of the Fresnel zone; these are the only variables in the Fresnel zone formula.
r1max = √(c * D / (4 * f))

Question 28

When a long-distance point-to-point link is installed, earth bulge should be considered beyond what distance?

A. 5 miles
B. 7 miles
C. 10 miles
D. 30 miles

Answer 28

B. 7 miles

The distance when the curvature of the earth should be considered when installing a point-to-point link is 7 miles.

Question 29

A network administrator replaced some coaxial cabling used in an outdoor bridge deployment after water damaged the cabling. After replacing the cabling, the network administrator noticed that the EIRP increased drastically and is possibly violating the maximum EIRP power regulation mandate. What are the possible causes of the increased amplitude? (Choose all that apply.)

A. The administrator installed a shorter cable.
B. The administrator installed a lower-grade cable.
C. The administrator installed a higher-grade cable.
D. The administrator installed a longer cable.
E. The administrator used a different-color cable.

Answer 29

A. The administrator installed a shorter cable.
C. The administrator installed a higher-grade cable.

Installing a shorter cable of the same grade will result in less loss and thus more amplitude being transmitted out the antenna. A higher-grade cable rated for less dB loss will have the same result.

Question 30

Which of the following is true for MIMO transmissions?

A. The transceiver can only receive from one antenna at a time.
B. Transceivers can transmit from multiple antennas at the same time.
C. The transceiver samples multiple antennas and chooses the best received signal from one antenna.
D. Transceivers can transmit from only one antenna at a time.

Answer 30

B. Transceivers can transmit from multiple antennas at the same time.

A MIMO transceiver can transmit from multiple antennas at the same time, if it is operating using multiple radio chains.

Question 31

To establish a four-mile point-to-point bridge link in the 5 GHz U-NII-3 band, what factors should be taken under consideration? (Choose all that apply.)

A. Fresnel zone clearance
B. Earth bulge calculations
C. Outdoor power regulations
D. Proper choice of semidirectional antennas
E. Proper choice of highly directional antennas

Answer 31

A. Fresnel zone clearance
C. Outdoor power regulations
D. Proper choice of semidirectional antennas

Point-to-point bridge links require a minimum Fresnel zone clearance of 60 percent, although 100 percent clearance is ideal. Semidirectional antennas such as patch antennas or Yagi antennas are used for short-to-medium-distance bridge links. Highly directional antennas are used for long-distance bridge links. Compensating for earth bulge is generally not a factor until 7 miles. Every nation has specific outdoor power regulations that must also be respected.

Question 32

The ratio between the maximum peak voltage and minimum voltage on a line is known as what?

A. Signal flux
B. Return loss
C. VSWR
D. Signal incidents

Answer 32

C. VSWR
Voltage standing wave ratio (VSWR) is the difference between these voltages and is represented as a ratio, such as 1.5:1.

Question 33

What are some of the possible negative effects of an impendence mismatch? (Choose all that apply.)

A. Voltage reflection
B. Blockage of the Fresnel zone
C. Erratic signal strength
D. Decreased signal amplitude
E. Amplifier/transmitter failure

Answer 33

A. Voltage reflection
C. Erratic signal strength
D. Decreased signal amplitude
E. Amplifier/transmitter failure

All but Fresnel zone blockage

The reflected voltage caused by an impedance mismatch can result in a decrease in power or amplitude (loss) of the signal that is supposed to be transmitted. If the transmitter is not protected from excessive reflected power or large voltage peaks, it can overheat and fail. Understand that VSWR may cause decreased signal strength, erratic signal strength, or even transmitter failure.

Question 34

When you are determining the mounting height of a long-distance point-to-point antenna, which of the following should you consider? (Choose all that apply.)
A. Frequency
B. Distance
C. Visual line of sight
D. Earth bulge
E. Antenna beamwidth
F. RF line of sight

Answer 34

A. Frequency
B. Distance
D. Earth bulge
F. RF line of sight

All but visual line of sight (C) and antenna beamwidth (E)

Frequency and distance are needed to determine the Fresnel zone. Visual line of sight is not needed as long as you have RF line of sight. You may not be able to see the antenna because of fog, but the fog will not prevent RF line of sight. Earth bulge will need to be considered. The beamwidth is not needed to determine the height, although it is useful when aiming the antenna.

Question 35

Which of the following are true about cables? (Choose all that apply.)

A. They cause impedance on the signal.
B. They work regardless of the frequency.
C. Attenuation decreases as frequency increases.
D. They add loss to the signal.

Answer 35

A. They cause impedance on the signal.
D. They add loss to the signal.

Cables must be selected that support the frequency you are using. Attenuation actually increases with frequency.

Question 36

Amplifiers can be purchased with which of the following features? (Choose all that apply.)

A. Bidirectional amplification
B. Unidirectional amplification
C. Fixed gain
D. Fixed output

Answer 36

A, B, C, D.
All of the above

Question 37

The signal between the transceiver and the antenna will be reduced by which of the following methods? (Choose all that apply.)

A. Adding an attenuator
B. Increasing the length of the cable
C. Shortening the length of the cable
D. Using cheaper-quality cable

Answer 37

A. Adding an attenuator
B. Increasing the length of the cable
D. Using cheaper-quality cable

Only shortening the cable will have no effect.

Adding an attenuator is an intentional act to add loss to the signal. Since cable adds loss, increasing the length will add more loss, whereas shortening the length will reduce the loss. Better-quality cables produce less signal loss.

Question 38

Lightning arrestors will defend against which of the following?

A. Direct lightning strikes
B. Power surges
C. Transient currents
D. Improper common grounding

Answer 38

C. Transient currents

Lightning arrestors will not stand up to a direct lightning strike, only transient currents caused by nearby lightning strikes.

Question 39

The radius of the first Fresnel zone is __________. (Choose all that apply.) 2

A. The outermost point of the area where the signal is out of phase with the point source
B. The outermost point of the area where the signal is in phase with the point source
C. Dependent on the gain of the directional antenna
D. Smaller than the second Fresnel zone

Answer 39

B. The outermost point of the area where the signal is in phase with the point source
D. Smaller than the second Fresnel zone

The area within the radius of the first Fresnel zone is in phase with the point source. The radius of the first Fresnel zone is the point where the second Fresnel zone begins and is where the signal transitions from being in phase with the point source to being out of phase. Because the second Fresnel zone begins where the first Fresnel zone ends, the radius of the second Fresnel zone is larger than the radius of the first Fresnel zone. The size of the Fresnel is dependent on the frequency and distance of the link. The gain of the antenna has no bearing on the size of the Fresnel zone.

Question 40

While aligning a directional antenna, you notice that the signal drops as you turn the antenna away from the other antenna, but then it increases a little. This increase in signal is most likely caused by what?

A. Signal reflection
B. Frequency harmonic
C. Side band
D. Side lobe

Answer 40

D. Side lobe

Side lobes are areas of antenna coverage (other than the coverage provided by the main signal) that have a stronger signal than would be expected when compared with the areas around them. Side lobes are best seen on an azimuth chart. Side bands and frequency harmonics have nothing to do with antenna coverage.

Question 41

The IEEE 802.3af and 802.3at amendments have been incorporated into the IEEE Std 802.3-2018 revised standard and are defined in which clause?

A. Clause 15
B. Clause 17
C. Clause 19
D. Clause 33
E. Clause 43

Answer 41

D. Clause 33

Even when 802.3af and 802.3at were amendments, PoE was defined in Clause 33. When an amendment is incorporated into a revised standard, the clause numbering remains the same. It is important to remember the clause number, as it is commonly referenced when discussing PoE. The new 802.3bt amendment defines PoE over 4-pair Ethernet in Clause 145.

Question 42

If a classification signature is not provided, the device is considered to be in what class?

A. 0
B. 1
C. 2
D. 3
E. 4

Answer 42

A. 0

Any device that does not provide a classification signature (which is optional) is automatically considered a Class 0 device, and the PSE will provide 15.4 watts of power to that device.

Question 43

Which types of PoE devices are defined by the standard? (Choose all that apply.)

A. PSE
B. PPE
C. PD
D. PT

Answer 43

A. PSE
C. PD

The Power over Ethernet (PoE) standard defines two types of devices: powered devices (PDs) and power-sourcing equipment (PSE).

Question 44

A powered device (PD) must be capable of accepting up to how many volts from either the data lines or the unused pairs of the Ethernet cable?

A. 14.5 volts
B. 20.5 volts
C. 48 volts
D. 57 volts

Answer 44

D. 57 volts

The power supplied to the powered device (PD) is at a nominal 48 volts; however, the PD must be capable of accepting up to 57 volts.

Question 45

To qualify as compliant with the 802.3at amendment (now part of the 802.3 standard), a powered device (PD) must do which of the following? (Choose all that apply.)

A. Be able to accept power over the unused data pairs
B. Reply to the PSE with a detection signature
C. Accept power with either polarity from the PSE
D. Reply to the PSE with a classification signature

Answer 45

A. Be able to accept power over the unused data pairs
B. Reply to the PSE with a detection signature
C. Accept power with either polarity from the PSE

.
Does not need to reply with a class signature.
.

The powered device (PD) must be able to accept power over either the data pairs or the unused pairs if it is a 10BaseT or 100BaseTX device, and over the 1–2, 3–6 data pairs or the 4–5, 7–8 data pairs if it is a 1000BaseT device. The PD must also reply to the power-sourcing equipment (PSE) with a detection signature. The PD must accept power with either polarity. Replying to the PSE with a classification signature is optional.

Question 46

A VoIP telephone is connected to a 24-port PoE midspan PSE. If the telephone does not provide a classification signature, how much power will the PSE provide to the telephone?

A. 12.95 watts
B. 4.0 watts
C. 7.0 watts
D. 15.4 watts

Answer 46

D. 15.4 watts

Providing a classification signature is optional for the powered device (PD). If the PD does not provide a classification signature, the device is considered a Class 0 device, and the power-sourcing equipment (PSE) will allocate the maximum power, or 15.4 watts.

Question 47

Which amendment introduced the support of PoE over four pairs of Ethernet?

A. 802.3af
B. 802.3at
C. 802.3bt
D. 802.11 clause 33
E. All PoE uses two pairs of Ethernet

Answer 47

C. 802.3bt

Prior to 802.3bt, PoE was only provided using 2-pairs of Ethernet. With the introduction of 802.3bt, PSE equipment providing 45 W, 60 W, 75 W, or 90 W uses 4-pairs of Ethernet for both endpoint PoE and midspan PoE.

Question 48

What is the range of maximum power used by a Class 4 PD?

A. 0.44–12.95 watts
B. 3.84–6.49 watts
C. 6.49–12.95 watts
D. 12.95–25.5 watts
E. 15–30 watts

Answer 48

D. 12.95–25.5 watts

Class 4 devices are defined in the 802.3at amendment. The maximum power that a Class 4 powered device (PD) requires is between 12.95 and 25.5 watts.

Question 49

At maximum power requirements, a 24-port 802.3at-compliant PoE Ethernet switch must be able to provide about how many total watts of power to PoE devices on all ports?

A. 15.4 watts
B. 370 watts
C. 720 watts
D. 1,000 watts
E. Not enough information is provided to answer the question.

Answer 49

C. 720 watts

At maximum power, each Power over Ethernet (PoE) device will be provided with 30 watts of power from the power-sourcing equipment (PSE). If all 24 ports have powered devices (PDs) connected to them, then a total of just under 720 watts (30 watts × 24 ports = 720 watts) is needed.

Question 50

If an 802.3bt-compliant AP is equipped with two radios and requires 35 watts of power, how much power will the PSE provide to it?
A. 35 watts
B. 40 watts
C. 45 watts
D. 60 watts
E. 90 watts

Answer 50

C. 45 watts

Question 51

The PSE provides power within a range of __________ volts, with a nominal value of __________ volts.

A. 14.5–20.5, 18
B. 6.49–12.95, 10.1
C. 12–19, 15.4
D. 44–57, 48

Answer 51

D. 44–57, 48

The power-sourcing equipment (PSE) provides power within a range of 44 volts to 57 volts, with a nominal power of 48 volts.

Question 52

John has installed an Ethernet switch that is compliant with 802.3at. He is having problems with his APs randomly rebooting. Which of the following could be causing his problems?

A. Many PoE VoIP telephones are connected to the same Ethernet switch.
B. Most of the Ethernet cables running from the switch to the APs are 90 meters long.
C. The Ethernet cables are only CAT 5e.
D. The switch is capable of 1000BaseT, which is not compatible with VoIP telephones.

Answer 52

A. Many PoE VoIP telephones are connected to the same Ethernet switch.

The maximum distance of 100 meters is an Ethernet limitation, not a Power over Ether-net (PoE) limitation. At 90 meters, this is not an issue. Although not specifically mentioned in the PoE standard, CAT 5e cables support 1000BaseT communications and are therefore capable of also providing PoE. The large number of PoE VoIP telephones could be requiring more power than the switch is capable of providing, thus causing the access points (APs) to reboot randomly.

Question 53

Ann is designing an 802.3at-compliant network and is installing a 24-port Ethernet switch to support 10 Class 1 VoIP phones and 10 Class 0 APs. The switch requires 500 watts to per-form its basic switching functions. How much total power will be needed?

A. 500 watts
B. 694 watts
C. 808 watts
D. 1,000 watts

Answer 53

B. 694 watts

The switch will provide the Class 0 devices with 15.4 watts of power each and the Class 1 devices with 4.0 watts of power each. So the 10 VoIP phones will require 40 watts of power, the 10 access points (APs) will require 154 watts of power, and the switch will need 500 watts of power—for a total of 694 watts (40 W + 154 W + 500 W).

Question 54

George is designing an 802.3at-capable network and is installing a 24-port Ethernet switch to support 10 Class 2 cameras and 10 Class 3 APs. The switch requires 1,000 watts to per-form its basic switching functions. How much total power will be needed?

A. 1,080 watts
B. 1,224 watts
C. 1,308 watts
D. 1,500 watts

Answer 54

B. 1,224 watts

The switch will provide the Class 2 devices with 7.0 watts of power each and the Class 3 devices with 15.4 watts of power each. So the 10 cameras will require 70 watts of power, the 10 access points (APs) will require 154 watts of power, and the switch will need 1,000 watts of power—for a total of 1,224 watts (70 W + 154 W + 1,000 W).

Question 55

When a PoE network is installed, what is the maximum distance from the PSE to the PD, as defined in the standard? (Choose all that apply.)

A. 90 meters
B. 100 meters
C. 300 feet
D. 328 feet
E. 328 meters

Answer 55

B. 100 meters
D. 328 feet

Implementing Power over Ethernet (PoE) does not affect the distances supported by Ethernet, which is 100 meters or 328 feet.

Question 56

What is the maximum power draw of an 802.3bt PD?

A. 12.95 watts
B. 15 watts
C. 60 watts
D. 51 watts
E. 90 watts
F. 71.3 watts

Answer 56

F. 71.3 watts

An 802.3bt powered device (PD) will draw up to 71.3 watts of power.

Question 57

What is the maximum power used by a PD Class 0 device?

A. 3.84 watts
B. 6.49 watts
C. 12.95 watts
D. 15.4 watts

Answer 57

C. 12.95 watts

The maximum power used by a Class 0 powered device (PD) is 12.95 watts. The power-sourcing equipment (PSE) provides 15.4 watts to account for a worst-case scenario, in which there may be power loss due to the cables and connectors between the PSE and the PD.

Question 58

The PSE will apply a voltage of between 14.5 and 20.5 and measure the resulting current to determine the class of the device. Which current range represents Class 2 devices?

A. 0–4 mA
B. 5–8 mA
C. 9–12 mA
D. 13–16 mA
E. 17–20 mA

Answer 58

E. 17–20 mA

Question 59

A PD must be capable of accepting power with either polarity from the power supply. Using Alternative A, on which conductors/wires does the PD accept power?

A. 1, 2, 3, 4
B. 5, 6, 7, 8
C. 1, 2, 3, 6
D. 4, 5, 7, 8

Answer 59

C. 1, 2, 3, 6

Alternative A uses 2-pairs of the Ethernet for PoE, and accepts power with either polarity from the power supply on wires 1, 2, 3, and 6. With alternative B, the wires used are 4, 5, 7, and 8.

Question 60

A Type 4 PSE will perform a two-event Physical layer classification or Data-Link layer classification. If mutual identification cannot be completed, what does the Type 4 device do?

A. It defaults as a Category 0 device.
B. It operates as a Type 2 device.
C. It operates as a Type 1 device.
D. It provides 15.4 watts of power using Alternative A.

Answer 60

C. It operates as a Type 1 device.

Type 2, 3, or 4 devices will perform a two-event Physical layer classification or Data-Link layer classification, which allows the device to identify whether it is connected to a Type 1 or a Type 2, 3, or 4 PSE. If mutual identification cannot be completed, then the device can only operate as a Type 1 device.