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Cable Testing CCNA 1 v3 – Module 4 NESCOT CATC 1 Waves 1. 2. 3. 4. 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. NESCOT CATC 2 Sine Waves and Square Waves 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 NESCOT CATC 3 Decibels 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. 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 NESCOT CATC 4 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. NESCOT CATC 5 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. ___________ NESCOT CATC 6 Attenuation and Insertion Loss on Copper Media 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 NESCOT CATC 7 Sources of Noise on Copper Media 1. 2. 3. 4. 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. NESCOT CATC 8 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: 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 Power sum equal-level far-end crosstalk (PSELFEXT) the combined effect of ELFEXT from all wire pairs NESCOT CATC 9 Cable testing standards Ten primary tests for a cable to meet TIA/EIA standards are: 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 NESCOT CATC 10 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 NESCOT CATC 11 Cable testing standards Open Good Wiremap Short Wiring Faults Correct Wiring Reversed-Pair Split-Pair NESCOT CATC Transposed-Pair 12 Testing optical fiber 1. 2. 3. 4. 5. 6. 7. 8. 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 NESCOT CATC 13