gphywchannel - I1070/T2000 Intro to Telecom Physical Layer...

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I1070/T2000 Intro to Telecom Physical Layer - channels Dr. Richard A. Thompson Telecommunications Program University of Pittsburgh
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Overview Channel’s characteristics & quality determined by medium & signal Guided – wire & fiber medium is more important Although signal (line code) helps a lot Unguided – wireless bandwidth produced by the antenna is more important Key concerns are data rate & distance
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Design Factors Bandwidth Higher bandwidth gives higher data rate Transmission impairments Attenuation & various distortions Interference Noise & 2 kinds of crosstalk Number of receivers (guided media) More receivers (multi-point) more attenuation
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Electromagnetic Spectrum
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Guided Transmission Media Twisted Pair Coaxial cable Optical fiber
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Transmission Characteristics of Guided Media   Frequency  Range Typical  Attenuation Typical Delay Repeater  Spacing Twisted pair  (with loading) 0 to 3.5 kHz 0.2 dB/km @  1 kHz 50  µ s/km 2 km Twisted pairs  (multi-pair  cables) 0 to 1 MHz 0.7 dB/km @  1 kHz µ s/km 2 km Coaxial cable 0 to 500 MHz 7 dB/km @ 10  MHz µ s/km 1 to 9 km Optical fiber 186 to 370  THz 0.2 to 0.5  dB/km µ s/km 40 km
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Twisted Pair
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Twisted Pair - Applications Most common medium Telephone network Between house and local exchange (subscriber loop) Within buildings To private branch exchange (PBX) For local area networks (LAN) 10Mbps or 100Mbps
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Twisted Pair - Pros & Cons Cheap Easy to work with Low data rate Short range
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Twisted Pair – Transmission Characteristics Analog Amplifiers every 5km to 6km Digital Use either analog or digital signals repeater every 2km or 3km Limited: distance bandwidth (1MHz), data rate (100MHz) Susceptible to interference and noise Depends on cable category
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Near End Crosstalk Coupling of signal from one pair to another Coupling takes place when transmit signal entering the link couples back to receiving pair i.e. near transmitted signal is picked up by near receiving pair
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Unshielded & Shielded TP Unshielded Twisted Pair (UTP) Ordinary telephone wire Cheapest Easiest to install Suffers from external EM interference Shielded Twisted Pair (STP) Metal braid or sheathing reduces interference More expensive Harder to handle (thick, heavy)
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UTP Categories Cat 3 up to 16MHz Voice grade found in most offices Twist length of 7.5 cm to 10 cm Cat 4
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