Cable Testing

1. Cable Testing CCNA 1 v3 – Module 4 NESCOT CATC

2. Waves period • The _________ of the waves is the amount of time between each wave, measured in seconds. • The _________ is the number of waves per second, (or cycle per second) measured in Hertz. • The __________ of an electrical signal represents height, measured in volts. • A disturbance that is deliberately caused of fixed, predictable duration is called a ________. • _______ determine the value of the data being transmitted. frequency amplitude pulse Pulses NESCOT CATC

3. 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 time-domain analysis, because the x-axis or domain of the mathematical function represents time NESCOT CATC

4. 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: • 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

5. 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

6. Signaling over Copper and Fiber Optic Cabling zero volts signal ground Shielded and Unshielded • On copper cable, data signals are represented by voltage levels compared to a reference level of ________ • This reference level is called the ____________ • Two basic types of copper cable: ______________________ • Coaxial cable’s shielding is electrically grounded to protect the inner conductor from ______________ • The _________ also helps eliminate signal loss by keeping the transmitted signal confined to the cable. • Coaxial is less _____, more __________ and more ___________________ than other copper cabling. • Fiber optic transmitters increase and decrease the intensity of light to _____________________________ • Optical signals are not affected by _______________ • ___________ does not need to be grounded. external noise shielding noisy expensive difficult to install represent binary ones and zeros electrical noise Optical fiber NESCOT CATC

7. 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

8. Sources of Noise on Copper Media Noise Crosstalk • ________ is any electrical energy on the transmission cable that makes it difficult for a receiver to interpret data. • _________ involves the transmission of signals from one wire to a nearby wire. • When crosstalk is caused by a signal on another cable, it is called _____________ • Crosstalk is more destructive at _________ transmission frequencies. • Cable testing instruments apply a test signal to one wire pair and measure the amplitude of the crosstalk on the ________________ • Twisted-pair cable takes advantage of the effects of __________ in order to minimize noise. • Higher categories of UTP require ____________ on each wire pair in the cable to minimize crosstalk at high transmission frequencies. alien crosstalk higher other wire pairs crosstalk more twists NESCOT CATC

9. Types of Crosstalk There are three distinct types of crosstalk: • Near-end Crosstalk (NEXT) The ratio of voltage amplitude between the test signal and the crosstalk signal when measured from the same end • Far-end Crosstalk (FEXT) Crosstalk occurring further away from the transmitter • 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

10. 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

11. Cable testing standards Wire map Insertion loss • ___________ test verifies that all wires are connected to the correct pins on both ends of the cable • _____________ is the combination of signal attenuation and impedance discontinuities, measured in decibels at the far end of the cable • _____________ is a measure in decibels of reflections caused by impedance discontinuities along the link • _________________ is a simple measurement of how long it takes for a signal to travel along the cable being tested • ______________ – 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 • ____________ is the delay difference between pairs Return loss Propagation delay Cable length Delay skew NESCOT CATC

12. Cable testing standards Open Good Wiremap Short Wiring Faults Correct Wiring Reversed-Pair Split-Pair Transposed-Pair NESCOT CATC

13. Testing optical fiber two EMI crosstalk Attenuation • A fiber link consists of _____ separate fibers. • There are no ________ and no external _____ problems. • __________ occurs to a much lesser extent than on copper. • When light hits an _____________________, some of the light is reflected back . • Reduced amounts of ______ arriving at the receiver make signal recognition difficult. • ______________________________ are the main cause of light reflection and signal strength loss. • Testing fiber optic cable involves shining light down the fiber and measuring how much light reaches the ___________ . • The ______________________ is the acceptable amount of signal power loss that can occur without dropping below the requirements of the receiver optical discontinuity light Improperly installed connectors receiver optical link loss budget NESCOT CATC