Transmission Media

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Transmission Media

• Lesson 04
• NETS2150/2850

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Lesson Outline

• Wired or guided Media
• Electromagnetics waves are guided along a solid
  medium
• Wireless or unguided media
• Transmission occurs through atmosphere, outer
  space or water
• Understand media characteristics and typical
  applications

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Classes of transmission media
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Electromagnetic Spectrum
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Twisted-pair cable
Note Single pair represents one communication
link Twisting reduces crosstalk interference
between pairs
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UTP and STP
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Categories of unshielded twisted-pair cables
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UTP connector
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Twisted Pair - Applications

• Most common medium
• Unshielded Twisted Pair (UTP)
• Cheapest
• Easiest to install
• Voice Grade Telephone wire (Cat 3)
• Data Grade Better quality (Cat 5)
• For LAN, 100 Mbps over 100 m possible
• Shielded Twisted Pair (STP)
• Metal braid reduces interference
• More expensive
• Harder to handle (thick, heavy)

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Coaxial Cable
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Coaxial Cable Applications

• Most versatile medium
• Television distribution
• Arial to TV
• Cable TV
• Short distance computer systems links
• Local area networks

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Bending of light ray for transmission
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Optical Fibre
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Figure 7.12 Propagation modes
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Figure 7.13 Modes
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Optical Fibre - Benefits

• Great for noisy environments!
• Tremendous bandwidth
• Data rates of hundreds of Gbps
• Smaller size weight
• Lower attenuation
• Greater amplifier spacing
• 40-60 km at least before amplification required
  for SMF
• Used in backbone and high traffic inter-city or
  inter continent links (submarine cables -
  undersea)

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Wireless transmission waves
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Wireless Spectrum
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Wireless Transmission

• 30MHz to 1GHz
• Suitable for Omnidirectional
• Broadcast radio
• 2GHz to 40GHz
• Microwave range
• Highly directional
• Point to point
• 3 x 1011 to 2 x 1014 Hz
• Infrared range
• Used within confined areas

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Broadcast Radio

• Omnidirectional
• FM radio
• UHF and VHF television
• Requires line of sight

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Omnidirectional antennas
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Radio waves are used for broadcast
communications, such as radio and television, and
paging systems.
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Terrestrial Microwave

• Uses parabolic dish as antenna
• Focused beam
• Requires line of sight
• Used for mobile phones, satellite networks
• Higher frequencies give higher data rates

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Line of Sight Propagation
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Satellite Microwave

• Satellite is a relay station
• It receives on one frequency (uplink), amplifies
  or repeats signal and transmits on another
  frequency (downlink)
• Requires geo-stationary orbit
• Height of 35,863 km
• Applications
• Television live cast
• Long distance telephone
• Private business networks

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Satellite Point to Point Link
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Satellite Broadcast Link
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Primary Mission Four-year tour to study
Saturn, its rings, moons and magnetosphere
Launch 15 October 1997 from Cape Canaveral Air
Force Station, Florida Arrival at Saturn 1 July
2004 Distance Travelled 3.5 billion km

• NASA.GOV 2004

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Infrared

• Line of sight (or reflection)
• Shirt-range communications
• Blocked by walls
• e.g. TV remote control, infrared port on
  printers, laptops, mobile phones, PDAs etc.

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Summary

• Guide Media
• Twisted pair, Coaxial cable, Optical fibre
• Unguided or wireless media
• Uses antenna as transmitter and receiver
  (transceiver)
• Terrestrial microwave, satellite microwave,
  Broadcast radio, Infrared
• Characteristics and quality determined by medium
  and signal
• For guided transmission, the medium is more
  important
• For unguided, the bandwidth produced by the
  antenna is more important