User:Itpastorn/dko/ccna1-3.1-4

Cable Testing

Overview CCNA 1 - Module 4 (3.1)
 * Sine waves and square waves
 * Exponents and logarithms
 * Decibels on networking media (not audio)
 * Terminology related to time, frequency, and noise
 * Digital bandwidth and analog bandwidth
 * Noise levels
 * Attenuation and impedance mismatch
 * Define crosstalk, near-end crosstalk, far-end crosstalk, and power sum near-end crosstalk
 * Twisted pair wiring and noise
 * The ten copper cable tests defined in TIA/EIA-568-B
 * Category 5 and Category 6

Waves

 * Frequency, measured in Hz
 * Period, the inverse of frequency
 * Wavelength
 * Amplitude

Exponents and logarithms
Three important number systems:
 * Binary : Base 2
 * Decimal : Base 10
 * Hexadecimal : Base 16


 * Easier to use 109 than 1000000000.
 * "Logarithms with 10 as a base are called common logarithms."

Decibels
dB = 10 log10 (Pfinal / Pref)

dB = 20 log10 (Vfinal / Vref)

Usage in electronics

Time and frequency of signals
"Characters, words, pictures, video, or music can be represented electrically by voltage patterns on wires and in electronic devices..." "these voltage patterns can be converted to light waves or radio waves... and back"
 * Oscilloscope - "time-domain analysis"

Analog and digital signals

 * Fourier synthesis of a square wave

Noise in time and frequency
Noise = undesirable signal

Sources
 * Nearby cables
 * RFI
 * EMI (same article as RFI on Wikipedia)
 * Laser noise at the transmitter or receiver

Frequencies affected:
 * White noise = all frequencies
 * Narrowband interference = small spectrum, but usually stronger

Bandwidth

 * Digital bandwidth, measured in bits per second
 * Analog bandwidth, measured in Hz


 * Digital broadband = very high speed
 * >= 2 Mbps both upstream and downstream, according to Bredbandsutredningen
 * Only in marketing: Anything that is not a modem - which is false marketing!
 * Analog broadband, opposite of baseband

Signals over copper and fiber optic cables
Copper Fiber
 * signal ground. Important that devices to be "properly grounded"
 * Two basic types of cables (covered in the last module):
 * Shielded: Coaxial, STP, ScTP
 * Unshielded: UTP
 * Less attenuation
 * RFI and EMI is no problem
 * Grounding seldom a problem

Additional resorces (besides Wikipedia)

 * Module 4 exam questions at Learn Networking
 * The basics of Cable Testing at Learn Networking
 * A manufacturers site with cable categories
 * De-Mystifying Cabling Specifications From 5e to 7A
 * Crosstalk explained at Siemon's site
 * Guide to Alien Crosstalk in Network Cabling Systems

Navigation

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