Computer Network and Infrastructure Transmission Media

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Computer Network and InfrastructureTransmission
Media

• Dr. E.C. Kulasekere

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Section Objectives

• Understand the principles behind media selection.
• The different types of guided media
• The different types of unguided media
• Understand the uses and applications of such
  media.

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Transmission Media

• The characteristics and quality of a data
  transmission is determine by both the
  characteristics of the medium and the
  characteristics of the signal.
• The key concerns of transmission
• Data rate
• Distance of tx.

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Media Design Factors

• Bandwidth
• Higher bandwidth gives higher data rate
• Transmission impairments
• Attenuation limits the distance of transmission
• Interference
• Particularly for unguided media with overlapping
  frequencies.
• Number of receivers
• In guided media
• More receivers (multi-point) introduce more
  attenuation

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Classification of Media

• Guided Transmission Media
• Conductive Metal
• Glass or Plastic
• Wireless Transmission Media
• Ground wave
• Sky wave
• Line-of-sight

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Electromagnetic Spectrum
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Guided Transmission MediaConductive Metal

• Twisted Pair Cables (TP)
• Shielded Twisted Pair (STP)
• Unshielded Twisted Pair (UTP)
• UTP Data Transmission Categories
• Category 3 (up to 16 MHz)
• Category 4 (up to 20 MHz)
• Category 5 (up to 100 MHz)

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Conductive MetalTwisted Pair Cables
UTP STP
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Conductive MetalShielded Twisted Pair Cables
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Conductive MetalTwisted Pair

• The twisting is done to reduce cross talk.
• Neighboring pairs may have different twist
  lengths.

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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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Conductive MetalCoaxial Cables

• Functionally Grouped into
• Baseband cable dedicated for only one channel
• Broadband cable can carry several analog signals
  (at different frequencies) simultaneously.

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Conductive MetalCoaxial Cable Physical Layout
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Coaxial Cable Applications

• Most versatile medium
• Television distribution
• Ariel to TV
• Cable TV
• Long distance telephone transmission
• Can carry 10,000 voice calls simultaneously
• Being replaced by fiber optic
• Short distance computer systems links
• Local area networks

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Optical Fiber
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Optical Fiber - Benefits

• Greater capacity
• Data rates of hundreds of Gbps
• Smaller size weight
• Lower attenuation
• Electromagnetic isolation
• Greater repeater spacing
• 10s of km at least

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Wireless Transmission

• Unguided media
• Transmission and reception via antenna
• Directional
• Focused beam
• Careful alignment required
• Omnidirectional
• Signal spreads in all directions
• Can be received by many antennae

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Wireless Transmission MediaTerrestrial Microwave
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Wireless Transmission MediaSatellites
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Wireless Transmission MediaGeostationary
Satellites
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Wireless Transmission MediaOther Media

• Broadcast Radio
• Covers VHF and part of the UHF
• Covers FM radio and UHF television
• Infrared
• Line of sight
• Omni directional
• Lasers

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Review Questions

• What are some major advantages and disadvantages
  of microwave transmission?
• Point-to-point microwave transmission has a high
  data rate and less attenuation than twisted pair
  or coaxial cable. It is affected by rainfall,
  however, especially above 10 GHz. It is also
  requires line of sight and is subject to
  interference from other microwave transmission,
  which can be intense in some places.

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Review Questions

• Why must a satellite have distinct uplink and
  downlink frequencies?
• In order to avoid interference from the uplink
  and downlink signals
• Indicate some significant differences between
  broadcast radio and microwave.
• Broadcast is omnidirectional, does not require
  dish shaped antennas, and the antennas do not
  have to be rigidly mounted in precise alignment.

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Review Problems

• Given a 100W power source, what is the maximum
  allowable length for the following transmission
  media if a signal of 1W is to be received?
• 24-gauge (0.5mm) twisted wire operating at 300kHz
• 24-gauge (0.5mm) twisted wire operating at 1MHz
• 0.375in (9.5mm) coaxial cable operating at 1MHz
• 0.375in (9.5mm) coaxial cable operating at 25MHz
• Optical fiber operating at its optimal frequency.

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Review Problems
The allowable power loss is 10 log 100 20
dB a. From Figure in next page, the attenuation
is about 13 dB per km. Length (20 dB)/(13 dB
per km) 1.5 km b. Length (20 dB)/(20 dB per
km) 1 km c. Length (20 dB)/(2.5 dB per km)
8 km d. Length (20 dB)/(10 dB per km) 2
km e. Length (20 dB)/(0.2 dB per km) 100 km
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