Transmission Media

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Transmission Media
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Introduction

• All communication relies on moving energy
• Air voices and music
• Electricity telephone
• Electro-magnetic T.V. and radio
• Light reading
• Computers can use each of these

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Wires

• Use to transmit electricity
• Often made of copper and often called copper
• Antennas are simply wires, as are transmitters
• Ergo, all wires will act as antenna and
  transmitters

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Wires Continued

• Adjacent wires will transmit to each other,
  causing interference (cross talk)
• Interference and real signal cannot be
  distinquished
• Amount of interference based on strength of
  signal and direction
• Right angles reduce interference

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Wires Continued

• Unfortunately, wires often parallel to each other
• Inside and outside computers
• Can also be near other sources of interference
• Appliances, etc., etc.
• To minimize use twisted pair or co-axial

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Twisted

• Pairs of wires twisted together
• Reduces interference
• Typically carry opposite signals
• Types
• Category (cat) 3 phone cable
• Cat 5 computer
• Tighter twists, thicker wire, sheath
• 10 Base T

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Twisted Picture
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Co-ax

• Used in T.V. antennas and cable
• Provides much more protection
• Inner wire, insulation, outer shield
• 10 Base 5 and 10 Base 2

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Co-ax Picture
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Fiber Is Good For You

• Flexible glass fiber
• Very transparent
• Flexible
• Very high bandwidth
• Transmission via Light Emitting Diode or LASER
• Reception via photo detector

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Advantages

• No interference
• Light can travel long distances before needing
  amplification
• Much more information
• Need only a single fiber
• Lightweight
• Doesnt corrode

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Disadvantages

• Difficult to join fibers
• Installation expensive with special equipment
  needed
• Hard to locate breaks

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Radio

• Radio, cordless phones, cell phones, T.V., etc.,
  etc.
• Wireless LAN 802.11b

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Satellites

• Long range radio
• Ground station sends to satellite
• Satellite receives, amplifies, resends
• Other ground stations receive
• T.V.
• DishPC

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Satellites Contined

• Two types
• Geo-synchronous and low-earth-orbit (LEO)

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GEOs

• At 20,000 miles where they appear to stand still
  at equator
• Called high earth orbit
• Must be separated, limits number
• Expensive to put in order, then free
• Delay of .25 second each direction

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LEOs

• 200 400 miles
• Must orbit quickly, every 1.5 hours
• In the atmosphere
• Wear and orbit degrades
• Less expensive to launch
• Ground stations must change satellites
  continuously

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LEOs Continued

• Several attempts made to have full earth coverage
• Iridium
• Have not been commercially successful

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Microwave

• High frequency radio
• Used in the phone system
• MCI
• Directional and affect by water
• Need line of sight
• Used to connect buildings

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Infrared

• Most remote controls
• Just below the visible
• Wont go through walls
• Good for slower connections
• IrDA (Infrared Data Association)

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LASER

• Use with fiber
• Can also be used unguided through air
• Line of sight
• Used to connect buildings