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Physical Layer (Guide transmission media (Fibre Optics (Cables (Single…
Physical Layer
Guide transmission media
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Twisted Pairs
Two insulated copper wire, helical (DNA) form, twisted reduce radiance from effectively parallel antennae, distance < 5KM
Carry either analogue or digital signals, bandwidth dependent on distance, wire quality / density
Link terminology
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Half-duplex link: both direction, but not at the same time
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Coaxial Cable
Better shielding than twisted pair = high speed over greater distance, brandwidth approach 1Ghz
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Power lines
Wires: convenient to use, but horrible for sending data
Fibre Optics
3 components: light source, transmission medium, detector
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Cables
Single-mode
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Use with laser for long distance, eg 100KM
Multi-mode
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Used with LED, cheap and shorter distance
Scalable network medium: LAN, WAN, long haul
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Wireless transmission
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Microwave: LANs and 3G, 4G
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