Transcript CCNA1 Module 4 Powerpoint

Cable Testing
CCNA 1 v3 – Module 4
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Waves
1.
2.
3.
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5.
period
The _________
of the waves is the amount of
time between each wave, measured in seconds.
frequency is the number of waves per
The _________
second, (or cycle per second) measured in Hertz.
amplitude of an electrical signal
The __________
represents height, measured in volts.
A disturbance that is deliberately caused of fixed,
pulse
predictable duration is called a ________.
Pulses determine the value of the data being
_______
transmitted.
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Sine Waves and Square Waves
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Sine waves are periodic, continuously varying,
representation of natural occurrences. Analog waves.
Square waves are periodic, do not continuously vary.
Hold one value and then suddenly change to a different
value. Digital signals, or pulses.
Analyzing signals using an oscilloscope is called timedomain analysis, because the x-axis or domain of the
mathematical function represents time
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Decibels
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log (109) equals 9, log (10-3) = -3
The decibel is related to exponents and logarithms
dB measures the loss or gain of the power of a wave
There are two formulas for calculating decibels:
1.
2.
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dB = 10 log10 (Pfinal / Pref)
Light waves on optical fiber and radio waves in the air are
measured using the Power formula. (P = Watts)
dB = 20 log10 (Vfinal / Vreference)
Electromagnetic waves on copper cables are measured using
the Voltage formula.
Usually -ve value, representing a loss in power
Can also be +ve value if the signal is amplified
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Digital Signal and Electrical Noise
Possible sources of noise:
 Nearby cables
 RFI
 EMI
 Laser noise
White Noise affects all transmission frequencies equally.
Narrowband Interference affects a small ranges of frequencies.
Bandwidth
Analog bandwidth refers to the frequency range of analog electronic systems
Digital bandwidth measures how much information can flow
During cable testing, analog bandwidth is used to determine the digital
bandwidth of a copper cable
Media that will support higher analog bandwidths without high degrees of
attenuation will also support higher digital bandwidths.
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Signaling over Copper and Fiber Optic Cabling
2.
On copper cable, data signals are represented by voltage levels
zero volts
compared to a reference level of ________
signal ground
This reference level is called the ____________
3.
Shielded and Unshielded
Two basic types of copper cable: ______________________
1.
4.
5.
6.
7.
8.
9.
Coaxial cable’s shielding is electrically grounded to protect the inner
external noise
conductor from ______________
shielding also helps eliminate signal loss by keeping the
The _________
transmitted signal confined to the cable.
noisy more __________
expensive and more
Coaxial is less _____,
difficult to install than other copper cabling.
___________________
Fiber optic transmitters increase and decrease the intensity of light to
represent
binary ones and zeros
_____________________________
electrical noise
Optical signals are not affected by _______________
Optical
fiber does not need to be grounded.
___________
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Attenuation and Insertion Loss on Copper Media
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Attenuation is the decrease in signal amplitude over the
length of a link measured in dB using -ve numbers.
Smaller -ve dB values indicate better link performance
Impedance is a measurement of the resistance to AC,
measured in ohms (Cat 5 impedance = 100 Ohms)
Improperly installed connectors cause impedance
discontinuity
Impedance discontinuities cause attenuation because a
portion of a transmitted signal is reflected back
The combination of the effects of signal attenuation and
impedance discontinuities is called insertion loss
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Sources of Noise on Copper Media
1.
2.
3.
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5.
6.
7.
Noise
________
is any electrical energy on the transmission cable
that makes it difficult for a receiver to interpret data.
Crosstalk
_________ involves the transmission of signals from one wire
to a nearby wire.
When crosstalk is caused by a signal on another cable, it is
alien crosstalk
called _____________
higher transmission
Crosstalk is more destructive at _________
frequencies.
Cable testing instruments apply a test signal to one wire pair
and measure the amplitude of the crosstalk on the
other wire pairs
________________
Twisted-pair cable takes advantage of the effects of
crosstalk in order to minimize noise.
__________
more twists on each wire
Higher categories of UTP require ____________
pair in the cable to minimize crosstalk at high transmission
frequencies.
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Types of Crosstalk
There are three distinct types of crosstalk:
1.
Near-end Crosstalk (NEXT)
The ratio of voltage amplitude between the test signal and the
crosstalk signal when measured from the same end
2.
Far-end Crosstalk (FEXT)
Crosstalk occurring further away from the transmitter
3.
Power Sum Near-end Crosstalk (PSNEXT)
The cumulative effect of NEXT from all wire pairs in cable
Cable testing standards include the following:
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Equal-level far-end crosstalk (ELFEXT)
Pair-to-pair ELFEXT is the difference between the FEXT and the
insertion loss of the wire pair whose signal is disturbed by the FEXT
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Power sum equal-level far-end crosstalk (PSELFEXT)
the combined effect of ELFEXT from all wire pairs
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Cable testing standards
Ten primary tests for a cable to meet TIA/EIA standards are:
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Wire map
Insertion loss
Near-end crosstalk (NEXT)
Power sum near-end crosstalk (PSNEXT)
Equal-level far-end crosstalk (ELFEXT)
Power sum equal-level far-end crosstalk (PSELFEXT)
Return loss
Propagation delay
Cable length
Delay skew
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Cable testing standards
1.
2.
3.
4.
5.
6.
Wire
map
___________
test verifies that all wires are connected to the
correct pins on both ends of the cable
Insertion
loss is the combination of signal attenuation and
_____________
impedance discontinuities, measured in decibels at the far
end of the cable
Return
loss
_____________
is a measure in decibels of reflections
caused by impedance discontinuities along the link
Propagation
delay is a simple measurement of how long it
_________________
takes for a signal to travel along the cable being tested
Cable
length
______________
– a cable tester makes a TDR
measurement by sending a signal down a wire pair and
measuring the time required for the signal to return
Delay
skew
____________
is the delay difference between pairs
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Cable testing standards
Open
Good Wiremap
Short
Wiring Faults
Correct Wiring
Reversed-Pair
Split-Pair
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Transposed-Pair
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Testing optical fiber
1.
2.
3.
4.
5.
6.
7.
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two separate fibers.
A fiber link consists of _____
EMI problems.
There are no crosstalk
________ and no external _____
Attenuation
__________ occurs to a much lesser extent than on copper.
When light hits an _____________________,
some of the light is
optical discontinuity
reflected back .
light arriving at the receiver make signal
Reduced amounts of ______
recognition difficult.
Improperly installed connectors are the main cause of light
______________________________
reflection and signal strength loss.
Testing fiber optic cable involves shining light down the fiber and
receiver .
measuring how much light reaches the ___________
optical link loss budget is the acceptable amount of signal
The ______________________
power loss that can occur without dropping below the requirements of the
receiver
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