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Transmission Media Keng Siau University of Nebraska-Lincoln Transmission: The Basic Encode data as energy and transmit energy Decode energy at destination back into data Energy can be electrical, light, radio, sound

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transmission media

Transmission Media

Keng Siau

University of Nebraska-Lincoln

transmission the basic
Transmission: The Basic
  • Encode data as energy and transmit energy
  • Decode energy at destination back into data
  • Energy can be electrical, light, radio, sound
  • Each form of energy has different properties and requirements for transmission
transmission media3
Transmission Media
  • Transmitted energy is carried through some sort of medium
  • Transmitter encodes data as energy and transmits energy through medium
  • Requires special hardware for data encoding
  • Media can be copper, glass, air, ...
copper wires
Copper Wires
  • Twisted pair uses two wires
  • Coaxial cable includes shield for improved performance
glass fibers
Glass Fibers
  • Thin glass fiber carries light with encoded data
  • Plastic jacket allows fiber to bend (some!) without breaking
  • Fiber is very clear and designed to reflect light internally for efficient transmission
glass fibers6
Glass Fibers
  • Light emitting diode (LED) or laser injects light into fiber
  • Light sensitive receiver at other end translates light back into data
  • Data transmitted using radio waves
  • Energy travels through the air rather than copper or glass
  • Conceptually similar to radio, TV, cellular phones
  • Can travel through walls and through an entire building
  • Can be long distance or short distance
    • Long distance
      • satellite relay
    • Short distance
      • wireless computer network
  • A communication satellite in orbit around the earth can provide a network connection across an ocean
  • A single satellite usually contains multiple transponders (typically 6-12)
  • Each transponder consists of a radio receiver and transmitter
  • Each transponder uses a different radio frequency (I.e., channel)
    • multiple communications can proceed simultaneously and independently
geosynchronous satellites
Geosynchronous Satellites
  • Place in an orbit that is exactly synchronized with the rotation of the earth
    • Geostationary Earth Orbit (GEO)
  • Distance required for geosynchronous orbit is 36,000 km or 20,000 miles
    • known as high earth orbit
  • The entire 360-degree circle above the equator can only hold 45-90 satellites
    • because satellites need to be separated to avoid interference
low earth orbit satellites
Low Earth Orbit Satellites
  • Orbit a few hundred miles above the earth (200-400 miles)
  • Period of rotation is faster than the rotation of the earth
  • Disadvantages
    • can only be used during the time its orbit passes between two ground stations
    • continuously moving the ground stations so they point directly at the satellites
low earth orbit satellite arrays
Low Earth Orbit Satellite Arrays
  • A set of satellites in low earth orbits
  • Allow continuous communications through satellites in low earth orbit
    • at least one satellite is available at any time
    • around 66 satellites are required to provide service over the entire surface of the earth
  • High frequency radio waves
  • Unidirectional, for point-to-point communication
  • Antennas mounted on towers relay transmitted data
  • Infrared light transmits data through the air
    • similar to technology used in TV remote control
  • Can propagate throughout a room (bouncing off surfaces)
    • but will not penetrate walls
  • Becoming common in personal digital assistants (PDAs) and portable computers
  • Unidirectional, like microwave
  • Higher speed than microwave
  • Uses laser transmitter and photo-sensitive receiver at each end
  • Point-to-point, typically between buildings
choosing a medium
Choosing a Medium
  • Copper wire
    • mature technology
    • rugged and inexpensive;
    • maximum transmission speed is limited
  • Glass fiber
    • higher speed
    • spans longer distances
    • requires only single fiber
    • more expensive; less rugged
choosing a medium18
Choosing a Medium
  • Radio and microwave don't require physical connection
  • Radio and infrared can be used for mobile connections
  • Laser also does not need physical connection and supports
    • higher speeds