CCNA1_M4_Cable_Testing (1130692)

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CCNA – Semester1Module 4Cable TestingObjectives• Basic definitions regarding cable testing• Issues relating to the testing of mediaBackground for StudyingFrequency-Based CableTestingWaves• A wave is energy traveling from one place toanother.• Networking professionals are specificallyinterested in voltage waves on copper media,light waves in optical fiber, and alternatingelectric and magnetic fields calledelectromagnetic waves.Analog signals••••Continuous voltageVoltage varies as time progressesTypical of things in natureMany encodings possibleDigital signals••••Discret, not continuousCan only have one or two voltage statesVoltage jumps between 2 levelsMade up of particular sine wavesDecibels• 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 onceFourier synthesisNoise••••Nearby cable carrying electricsignalRadio frequency interference(RFI), which is noise fromother signals being transmittednearbyElectromagnetic interference(EMI), which is noise fromnearby sources such asmotors and lightsLaser noise at the transmitteror receiver of an optical signalNarrowband Interference and white noise• Noise that affects all transmission frequenciesequally is called white noise.• Noise that only affects small ranges offrequencies 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 digitalbandwidth.• Analog bandwidth typically refers to thefrequency range of an analog electronic system.• Digital bandwidth measures how muchinformation can flow from one place to anotherin a given amount of time.Signals and NoiseSignaling 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 andthe receiver.• Fiber optic cable is used to transmit data signals byincreasing 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.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 aportion of signal will be reflected back to thetransmitting device.• The combination of the effects of signal attenuation andimpedance discontinuities is called insertion loss.Types of crosstalk• Near-end Crosstalk(NEXT)• Far-end Crosstalk (FEXT)• Power Sum Near-endCrosstalk (PSNEXT)Cable testing standards••••••••••Wire mapInsertion lossNear-end crosstalk (NEXT)Power sum near-end crosstalk (PSNEXT)Equal-level far-end crosstalk (ELFEXT)Power sum equal-level far-end crosstalk (PSELFEXT)Return lossPropagation delayCable lengthDelay skewCable Testing StandardWiring FaultOther test parametersTesting optical fiber• Fiber links are subject to the optical equivalentof UTP impedance discontinuities.• The main concern with a fiber link is thestrength of the light signal that arrives at thereceiver.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 TesterSummary••••Sine waves and square wavesAnalog bandwidth and digital bandwidthSignals over copper and fiber opticAttenuation loss, impedence discontinuty,crosstalk• Wiring faults• Cable testing standards.

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