SUNY UlsterSUNY Ulster

Cisco Semester 1 Cisco Semester 1

Unit 4 – Cable TestingUnit 4 – Cable Testing

K. Wick CCAIK. Wick CCAI

BackgroundBackground

Signals and NoiseSignals and Noise

Note to instructor: Have Note to instructor: Have curriculum opencurriculum open

Sine WavesSine Waves

ShapeShape AmplitudeAmplitude FrequencyFrequency WavelengthWavelength Period = 1/fPeriod = 1/f Objective 4.1.1 has a nice demo of Objective 4.1.1 has a nice demo of

sinusoidal waves.sinusoidal waves.

Square WavesSquare Waves

Objective 4.1.2 does NOT show a Objective 4.1.2 does NOT show a pure square wave. pure square wave.

It shows a square wave with a DC It shows a square wave with a DC component. (Wave is offset from component. (Wave is offset from zero)zero)

Square wave vs Periodic Pulse vs Square wave vs Periodic Pulse vs PulsePulse

LogarithmsLogarithms

Logarithms are a way to express Logarithms are a way to express differences between numbers that are differences between numbers that are orders of magnitude apart.orders of magnitude apart.

If we ask “To what power do we raise If we ask “To what power do we raise ten to be equal to a number in ten to be equal to a number in question”, that is the logarithm of the question”, that is the logarithm of the number.number.

Log 1 = 0 because 10Log 1 = 0 because 1000 = 1 = 1 Log 8 = 0.9031 because 10Log 8 = 0.9031 because 100..90310..9031 = 8 = 8

LogarithmsLogarithms

Run interactive activities in 4.1.3Run interactive activities in 4.1.3

The logarithm of ten raised to any The logarithm of ten raised to any power is the power itself.power is the power itself.

Log 1000 = log 10Log 1000 = log 1033 = 3 = 3 Log 1,000,000 = log 10Log 1,000,000 = log 1066 = 6 = 6

DecibelsDecibels

Cisco says, “There are two Cisco says, “There are two formulas for calculating decibels”: formulas for calculating decibels”:

dB = 10 log10 (Pfinal / Pref) dB = 10 log10 (Pfinal / Pref) dB = 20 log10 (Vfinal / Vreference) dB = 20 log10 (Vfinal / Vreference) They are partially correct.They are partially correct. These formulas depend on equal These formulas depend on equal

input and output impedance.input and output impedance.

DecibelsDecibels

Answers to examples in 4.1.4Answers to examples in 4.1.4

• -30 decibels. A loss-30 decibels. A loss• 1.7 microwatts1.7 microwatts• -113.9 decibels. A major loss.-113.9 decibels. A major loss.

Measuring DevicesMeasuring Devices

A multimeter or digital A multimeter or digital multimeter (DMM) measures multimeter (DMM) measures voltage, current, resistance, voltage, current, resistance, continuity and sometimes continuity and sometimes other parameters.other parameters.

An oscilloscope gives a visual An oscilloscope gives a visual display of voltage versus time.display of voltage versus time.

– A Cable meter will test a A Cable meter will test a cable for correct wiringcable for correct wiring

Fourier Analysis ????Fourier Analysis ????

Cisco is insane!Cisco is insane! OK here is a basic:OK here is a basic: Every complex waveform can be Every complex waveform can be

made by adding a series of sinusoids made by adding a series of sinusoids of proper frequency and amplitude.of proper frequency and amplitude.

A square wave is the sum of the seriesA square wave is the sum of the series A * sin(x) + A/3 * sin(3x) + A/5 * A * sin(x) + A/3 * sin(3x) + A/5 *

sin(5x) …sin(5x) …

Building a Square WaveBuilding a Square Wave

Measuring DevicesMeasuring Devices

Spectrum Analyzer.Spectrum Analyzer.

Gives a bar graph representing all Gives a bar graph representing all frequencies and amplitudes frequencies and amplitudes present in a waveform.present in a waveform.

Measuring DevicesMeasuring Devices

Time Delay ReflectometerTime Delay Reflectometer Because the wires inside the cable Because the wires inside the cable

are twisted, signals actually travel are twisted, signals actually travel farther than the physical length of the farther than the physical length of the cable. cable.

A TDR measurement sends a pulse A TDR measurement sends a pulse signal down a wire pair and measures signal down a wire pair and measures the amount of time required for the the amount of time required for the pulse to return on the same wire pair. pulse to return on the same wire pair.

Measuring DevicesMeasuring Devices

Time Delay ReflectometerTime Delay Reflectometer Also used to identify the distance to Also used to identify the distance to

wiring faults such as shorts and wiring faults such as shorts and opens.opens.

This presumes that we know the This presumes that we know the propagation speed of the specific propagation speed of the specific wire type.wire type.

Ten tests for Category 5 Ten tests for Category 5 cablecable

Wire map Wire map Insertion loss Insertion loss Near-end crosstalk (NEXT) Near-end crosstalk (NEXT) Power sum near-end crosstalk (PSNEXT) Power sum near-end crosstalk (PSNEXT) Equal-level far-end crosstalk (ELFEXT) Equal-level far-end crosstalk (ELFEXT) Power sum equal-level far-end crosstalk Power sum equal-level far-end crosstalk

(PSELFEXT) (PSELFEXT) Return loss Return loss Propagation delay Propagation delay Cable length Cable length Delay skew Delay skew

Types of Signal Types of Signal DegradationDegradation

Propagation and DelayPropagation and Delay

Propagation means travel of a signalPropagation means travel of a signal Propagation Propagation DelayDelay is the time it takes a is the time it takes a

signal to travel from point to point.signal to travel from point to point. It is measured in hundreths of It is measured in hundreths of

nanoseconds.nanoseconds. Skew: The difference in delay between Skew: The difference in delay between

pairs.pairs. Read CISCO questions carefully, watch the Read CISCO questions carefully, watch the

exact wording!exact wording!

AttenuationAttenuation

Attenuation means loss of signal Attenuation means loss of signal amplitudeamplitude

If a signal gets too small, it can not If a signal gets too small, it can not be decoded at the receiving endbe decoded at the receiving end

ReflectionReflection

Sometimes on a physical medium a signal Sometimes on a physical medium a signal travels to the end of the medium and part of travels to the end of the medium and part of the signal reflects back toward the source. the signal reflects back toward the source.

This reflection can interfere with the original This reflection can interfere with the original signal.signal.

Reflections are especially bad with Reflections are especially bad with impedance mismatches in the physical impedance mismatches in the physical layer.layer.

(Caused by wrong media or bad (Caused by wrong media or bad connections)connections)

Nominal Z for Cat 5 cable is 100 ohmsNominal Z for Cat 5 cable is 100 ohms

Attenuation (signal deterioration) and Attenuation (signal deterioration) and noise (signal interference) cause noise (signal interference) cause problems in networks because the data problems in networks because the data is not recognizable when it is received. is not recognizable when it is received.

Proper attachment of cable connectors Proper attachment of cable connectors and proper cable installation are and proper cable installation are important. If standards are followed in important. If standards are followed in these areas, attenuation and noise these areas, attenuation and noise levels are minimized. levels are minimized.

Noise – Where are the 1’s Noise – Where are the 1’s and 0’s?and 0’s?

5 volts

Analog vs Digital Analog vs Digital BandwidthBandwidth

Analog bandwidth typically refers to the Analog bandwidth typically refers to the frequency range of an analog electronic frequency range of an analog electronic system. system.

The units of measurement for analog The units of measurement for analog bandwidth is Hertz, the same as the unit of bandwidth is Hertz, the same as the unit of frequency. frequency.

Examples of analog bandwidth values are 3 Examples of analog bandwidth values are 3 kHz for telephony, 20 kHz for audible kHz for telephony, 20 kHz for audible signals, 5 kHz for AM radio stations, and 200 signals, 5 kHz for AM radio stations, and 200 MHz for FM radio stations. MHz for FM radio stations.

Analog vs Digital Analog vs Digital BandwidthBandwidth

Digital bandwidth measures how much Digital bandwidth measures how much information can flow from one place to information can flow from one place to another in a given amount of time. another in a given amount of time.

The fundamental unit of measurement for The fundamental unit of measurement for digital bandwidth is bits per second (bps). digital bandwidth is bits per second (bps).

Since LANs are capable of speeds of Since LANs are capable of speeds of millions of bits per second, measurement millions of bits per second, measurement is expressed in kilobits per second (Kbps) is expressed in kilobits per second (Kbps) or megabits per second (Mbps).or megabits per second (Mbps).

Analog vs Digital Analog vs Digital BandwidthBandwidth

During cable testing, analog bandwidth is During cable testing, analog bandwidth is used to determine the digital bandwidth of used to determine the digital bandwidth of a copper cable. a copper cable.

Analog frequencies are transmitted from Analog frequencies are transmitted from one end and received on the opposite end.one end and received on the opposite end.

The two signals are then compared, and The two signals are then compared, and the amount of attenuation of the signal at the amount of attenuation of the signal at each frequency is calculated. each frequency is calculated.

In general, media that will support higher In general, media that will support higher analog bandwidths without high degrees of analog bandwidths without high degrees of attenuation will also support higher digital attenuation will also support higher digital bandwidths. bandwidths.

Noise PickupNoise Pickup

ExternalExternal• ImpulseImpulse• Radio - EMI RFIRadio - EMI RFI• Line to groundLine to ground• MotorMotor

Crosstalk - NEXTCrosstalk - NEXT Twisted Pairs minimize noise pickupTwisted Pairs minimize noise pickup

Crosstalk and other evilsCrosstalk and other evils

CrosstalkCrosstalk

Near End – at near end of link.Near End – at near end of link. Far EndFar End Power Sum – cumulative effect of Power Sum – cumulative effect of

crosstalk on all pairs in the cable.crosstalk on all pairs in the cable.

For all – Larger negative numbers For all – Larger negative numbers mean LESS crosstalk. (-30dB vs -mean LESS crosstalk. (-30dB vs -20dB).20dB).

Some testers leave out the minus sign.Some testers leave out the minus sign.

Wiring Errors (Fluke Wiring Errors (Fluke Tester)Tester)

Or Crossover Cable

Fiber Optic Cable TestingFiber Optic Cable Testing

Remember that a fiber link consists of Remember that a fiber link consists of two separate glass fibers functioning as two separate glass fibers functioning as independent data pathways. independent data pathways.

Fiber optic cable does not suffer from Fiber optic cable does not suffer from crosstalk or noise pickup.crosstalk or noise pickup.

Attenuation does occur on fiber links, but Attenuation does occur on fiber links, but to a lesser extent than on copper cabling.to a lesser extent than on copper cabling.

Fiber links are subject to the optical Fiber links are subject to the optical equivalent of UTP impedance equivalent of UTP impedance discontinuities. discontinuities.

Fiber Optic Cable TestingFiber Optic Cable Testing

Just as with UTP cable, improperly installed Just as with UTP cable, improperly installed connectors are the main cause of light connectors are the main cause of light reflection and signal strength loss in optical reflection and signal strength loss in optical fiber. fiber.

If attenuation weakens the light signal at the If attenuation weakens the light signal at the receiver, then data errors will result. Testing receiver, then data errors will result. Testing fiber optic cable primarily involves shining a fiber optic cable primarily involves shining a light down the fiber and measuring whether light down the fiber and measuring whether a sufficient amount of light reaches the a sufficient amount of light reaches the receiver. receiver.

If the fiber fails the test, the cable test If the fiber fails the test, the cable test instrument should indicate where the optical instrument should indicate where the optical discontinuities occur along the length of the discontinuities occur along the length of the cable link. cable link.

Category 6 UTP and STPCategory 6 UTP and STP

Cables certified as Cat 6 cable must Cables certified as Cat 6 cable must pass the same ten tests as Cat 5 pass the same ten tests as Cat 5 cable.cable.

Cat 6 cable must pass these tests with Cat 6 cable must pass these tests with higher scores to be certified. higher scores to be certified.

It must be capable of carrying It must be capable of carrying frequencies up to 250 MHz (vs 100 frequencies up to 250 MHz (vs 100 MHz) and must have lower levels of MHz) and must have lower levels of crosstalk and return loss. crosstalk and return loss.

End of Chapter 4End of Chapter 4