Media for Internet

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Media for Internet



Transmission Media
  • The transmission medium is the physical path by which a message travels from sender to receiver.


Classes of transmission media




Guided Media
Guided media, which are those that provide a conduit/ medium from one device to another.

There are three categories of guided media:
    1. Twisted-pair cable
    2. Coaxial cable
    3. Fiber-optic cable
Twisted-pair cable
  • Twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together.
  • The twisting helps to reduce the interference (noise) and crosstalk



  • Twisted-pair cable comes in two forms: unshielded (UTP) and shielded (STP)



Coaxial cable carries signals of higher frequency ranges than twisted-pair cable.



  • Metal cables transmit signals in the form of electric current. Optical fiber is made of glass and transmits signals in the form of light.
  • Optical fibers use reflection to guide light through a channel.
  • A glass or core is surrounded by a cladding(shield) of less dense glass or plastic.
  • Information is encoded onto a beam of light as a series of on-off flashes that represent 1 and 0 bits.



  • Unguided media, or wireless communication, transport electromagnetic waves without using a physical conductor. Instead the signals are broadcast though air or water.
  • Unguided signals can travel in three ways: ground propagation, sky propagation, and line-of-sight propagation:



  • Ground propagation These low-frequency signals originate in all directions from the transmitting antenna and follow the curvature of the planet. The distance depends on the power in the signal.
  • In Sky propagation, higher-frequency radio waves radiate upward into the ionosphere where they are reflected back to earth. This type of transmission allows for greater distances with lower power output.
  • In Line-of-Sight Propagation, very high frequency signals are transmitted in straight lines directly from antenna to antenna.
  • Figure 7.19 Wireless transmission waves




Figure 7.17 Electromagnetic spectrum for wireless communication




  • Radio waves are used for multicast communications, such as radio and television, and paging systems.
  • Use omni directional antennas.
  • Can penetrate buildings easily, so that are widely use for communication both indoors outdoors.
  • Microwaves are used for unicast communication such as cellular telephones, satellite networks,
    and wireless LANs.
  • Use directional antennas - point to point line of sight communications.
  • Higher frequency ranges cannot penetrate walls.
Microwave Applications
  • Television distribution
  • Long-distance telephone transmission
  • Private business networks
  • Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.
  • Cannot pass through solid objects, like walls and be easily contained in a room.
  • They are cheap, easy to build and do not require any government license to use them.


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