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  2. 2. 2 oA Transmission Media  is a material substance that can     propagate energy waves.
  3. 3.  GUIDED MEDIA uses a "cabling" system that guides the data signals along a specific path.  The data signals are bound by the "cabling" system. Guided Media is also known as Bound Media.  There are basic four types of Guided Media:  1. Open Wire 2. Twisted Pair 3. Coaxial Cable 4. Fibre Optical 3
  4. 4.  Open Wire is traditionally used to describe the electrical wire  joined along power poles.   There is a single wire joined between poles. No shielding or  protection from noise interference is used.   The definition of Open Wire is any data signal path without  shielding or protection from noise interference.   This media is susceptible to a large degree of noise and  interference and consequently not acceptable for data  transmission except for short distances under 20 ft.    4
  5. 5.  One of the oldest and still most common transmission media  is twisted pair.   A  twisted  pair  consists  of  two  insulated  copper  wires,  typically about 1 mm thick. The wires are twisted together in  a helical form, just like a DNA molecule. Twisting is done  because  two  parallel  wires  constitute  a  fine  antenna.  When  the wires are twisted, the waves from different twists cancel  out, so the wire radiates less effectively. 5
  6. 6. 6  Each pair would consist of a wire used for the +ve data signal  and  a  wire  used  for  the  -ve  data  signal.  Any  noise  that  appears on 1 wire of the pair would occur on the other wire.  Because  the  wires  are  opposite  polarities,  they  are  180  degrees out of phase. When the noise appears on both wires,  it cancels or nulls itself out at the receiving end.  Twisted Pair cables are most effectively used in systems that  use a balanced line method of transmission: polar line coding  (Manchester  Encoding)  as  opposed  to  unipolar  line  coding  (TTL logic).
  7. 7.  The degree of reduction in noise interference is determined specifically by the number of turns per foot. Increasing the number of turns per foot reduces the noise interference. To further improve noise rejection, a foil or wire braid shield is woven around the twisted pairs. This "shield" can be woven around individual pairs or around a multi-pair conductor .  STP :Cables with a shield are called Shielded Twisted Pair.  STP or Shielded Twisted Pair is used with the traditional Token Ring cabling or ICS - IBM Cabling System. It requires a custom connector. IBM STP (Shielded Twisted Pair) has a characteristic impedance of 150 ohms. 7 STPUTP
  8. 8. 8  UTP :Cables without a shield are called Unshielded Twisted Pair.  Twisting the wires together results in a characteristic impedance for the cable. A typical impedance for UTP is 100 ohm for Ethernet 10BaseT cable.  UTP or Unshielded Twisted Pair cable is used on Ethernet 10BaseT and can also be used with Token Ring. It uses the RJ line of connectors (RJ45, RJ11, etc..)   STPUTP
  9. 9.  Coaxial Cable consists of 2 conductors. The inner conductor is held inside an insulator with the other conductor woven around it providing a shield. An insulating protective coating called a jacket covers the outer conductor.  The outer shield protects the inner conductor from outside electrical signals.  The distance between the outer conductor (shield) and inner conductor plus the type of material used for insulating the inner conductor determine the cable properties or impedance. 9
  10. 10.  Typical impedances for coaxial cables are 75 ohms for Cable TV, 50 ohms for Ethernet Thinnet and Thicknet.  The excellent control of the impedance characteristics of the cable allow higher data rates to be transferred than Twisted Pair cable.
  11. 11.  Optical Fibre consists of thin glass fibres that can carry information at frequencies in the visible light spectrum and beyond.  The typical optical fibre consists of a very narrow chain(string)of glass called the Core. Around the Core is a concentric layer of glass called the Cladding. A typical Core diameter is 62.5 microns (1 micron = 10-6 meters). Typically Cladding has a diameter of 125 microns., however. 11
  12. 12. 12  Coating the cladding is a protective coating consisting of plastic, it is called the Jacket.  it provides good combination of high bandwidth and excellent noise immunity. The bandwidth possible depends on the cable quality, length, and signal-to-noise ratio of the data signal. Modern cables have a bandwidth of close to 1 GHz. Coaxial cables used to be widely used within the telephone system for long-distance lines but have now largely been replaced by fiber optics on long-haul routes. Coax is still widely used for cable television and metropolitan area networks, however.
  13. 13.  UNGUIDED MEDIA transports electromagnetic waves without using physical conductor. It is also known as wireless communication.  The data signals are not bound to a cabling media and as such are often called Unbound Media.  Signals are broadcast to air and thus are available to anyone who has a device capable of receiving them. 13
  14. 14. 14  There are basic four types of Unguided Media 1. Radio wave transmission(freq between 3kzh and 1ghz) 2.Microwave transmission(1ghz to 300ghz) 3.Infrared transmission (300ghz to 400 thz)
  15. 15.  Radio waves are easy to generate, can travel long distances, and can penetrate buildings easily, so they are widely used for communication, both indoors and outdoors.  Radio waves also are omni directional, meaning that they travel in all directions from the source, so the transmitter and receiver do not have to be carefully aligned physically.  There are 3 types of RF (Radio Frequency) Propagation: 1.Ground Wave 2. Ionospheric 3. Line of Sight (LOS) Propagation. 15
  16. 16. 16  Ground Wave Propagation follows the curvature of the Earth. Ground Waves have carrier frequencies up to 2 MHz. AM radio is an example of Ground Wave Propagation.  Ionospheric Propagation: It bounces off of the Earths Ionospheric Layer in the upper atmosphere. It operates in the frequency range of 30 - 85 MHz. Because it depends on the Earth's ionosphere, it changes with weather and time of day. The signal bounces off of the ionosphere and back to earth. Ham radios operate in this range.
  17. 17. 17 oLine of Sight Propagation: transmits exactly in the line of sight. The receive station must be in the view of the transmit station. It is sometimes called Space Waves or Tropospheric Propagation. It is limited by the curvature of the Earth for ground based stations (100 km: horizon to horizon). Reflected waves can cause problems. Examples of Line of Sight Propagation are: Microwave and Satellite.
  18. 18.  Microwave communication is so widely used for long- distance telephone communication, mobile phones, television distribution,etc.  It has several significant advantages over fibre. The main one is that by buying a small plot of ground every 50 km and putting a microwave tower on it, one can bypass the telephone system and communicate directly. Microwave is also relatively inexpensive. 18
  19. 19. 19  Microwave transmission is line of sight transmission. The Transmit station must be in visible contact with the receive station. This sets a limit on the distance between stations depending on the local geography.  Microwaves carry large quantities of data due to the large bandwidth.
  20. 20.  Signals with frequencies from 300ghz to 400thz.  Prevents interference between one system and other.  Short range communication system .in one room cannot be affected by another system in other room.  Band is almost excellent for data transmission . It can be used to transmit digital data with very high data rate. 20
  21. 21. 21  By using these signal for communication between devices such as keyboard,mic,pc and printers.  These signals transmits through Line Of Sight.  Used for short range in a close area using Line Of Sight propogation.
  22. 22.