CCNA1 Cable Testing

8/9/2019 CCNA1 Cable Testing

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CCNA Semester1

Module 4

Cable Test ing

Objectives

Basic definitions regarding cable testing

Issues relating to the testing of media


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Background for StudyingFrequency-Based Cable

Testing

Waves

A wave is energy traveling from one place toanother.

Networking professionals are specifically

interested in voltage waves on copper media,light waves in optical fiber, and alternatingelectric and magnetic fields calledelectromagnetic waves.


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Analog signals

Continuous voltage

Voltage varies as time progresses

Typical of things in nature

Many encodings possible

Digital signals

Discret, not continuous

Can only have one or two voltage states

Voltage jumps between 2 levels

Made up of particular sine waves


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Decibels

The decibel (dB) is a measurement unit important indescribing networking signals.

There are two formulas for calculating decibels:

dB = 10 log10 (Pfinal / Pref)

dB = 20 log10 (Vfinal / Vreference)

dB measures the loss or gain of the power of a wave.

Typically, light waves on optical fiber and radio waves inthe air are measured using the power formula.Electromagnetic waves on copper cables are measuredusing the voltage formula.

Viewing signals in time and frequency

Analyzing signals using an oscilloscope iscalled time-domain analysis

Graphs voltage over time

X-axis represents T, Y-axis represents V, mayobserve and compare 2 waves at once


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Fourier synthesis

Noise

Nearby cable carrying electricsignal

Radio frequency interference(RFI), which is noise fromother signals being transmitted

nearby

Electromagnetic interference(EMI), which is noise fromnearby sources such asmotors and lights

Laser noise at the transmitteror receiver of an optical signal


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Narrowband Interference and white noise

Noise that affects all transmission frequenciesequally is called white noise.

Noise that only affects small ranges of

frequencies is called narrowband interference.

Bandwidth

Bandwidth is an extremely important concept incommunications systems. Two ways ofconsidering bandwidth that are important for thestudy of LANs are analog bandwidth and digital

bandwidth. Analog bandwidth typically refers to the

frequency range of an analog electronic system.

Digital bandwidth measures how muchinformation can flow from one place to anotherin a given amount of time.


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Signals and Noise

Signaling over copper and fiber optic cabling

On copper cable, data signals are represented byvoltage levels that represent binary ones and zeros.

The voltage levels are measured with respect to areference level of ground volt at both the transmitter and

the receiver. Fiber optic cable is used to transmit data signals by

increasing and decreasing the intensity of light torepresent binary ones and zeros.

In order for the LAN to operate properly, the receivingdevice must be able to accurately interpret the binaryones and zeros transmitted as signal levels.


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Attenuation loss on copper media

Attenuation is the decrease in signal amplitude over the length of alink.

Long cable lengths and high signal frequencies contribute to greater signalattenuation.

The resistance of the copper cable converts some of the electrical energy ofthe signal to heat.

Signal energy is also lost when it leaks through the insulation of the cableand by impedance caused by defective connectors.

Impedance Discontinuity

If a connector is improperly installed on Cat5, it will havea different impedance value than the cable. This is calledan impedance discontinuity or an impedance mismatch.

Impedance mismatch cause attenuation and jitter as a

portion of signal will be reflected back to thetransmitting device.

The combination of the effects of signal attenuation andimpedance discontinuities is called insertion loss.


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Types of crosstalk

Near-end Crosstalk(NEXT)

Far-end Crosstalk (FEXT)

Power Sum Near-endCrosstalk (PSNEXT)

Cable testing standards

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 Standard

Wiring Fault


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Other test parameters

Testing optical fiber

Fiber links are subject to the optical equivalentof UTP impedance discontinuities.

The main concern with a fiber link is the

strength of the light signal that arrives at thereceiver.


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A new standard

On June 20, 2002, the Category 6 (or Cat 6)addition to the TIA-568 standard was published,called ANSI/TIA/EIA-568-B.2-1.

This new standard specifies the original set ofperformance parameters that need to be testedfor Ethernet cabling as well as the passingscores for each of these tests.

Lab Companion

3.1.9 UTP Cable Construction

4.2.1 Fluke 620 Cable Tester


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Summary

Sine waves and square waves

Analog bandwidth and digital bandwidth

Signals over copper and fiber optic

Attenuation loss, impedence discontinuty,crosstalk

Wiring faults

Cable testing standards

Documents

CCNA1 Cable Testing