Transmission media


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Transmission media

  1. 1. BY KINISH KUMAR(www
  2. 2. Transmission media Transmission media are located below the physical layer Computers use signals to represent data. Signals are ransmitted in form of electromagnetic energy.
  3. 3. Transmission Media Transmission Media and Physical Layer
  4. 4. Transmission Media  Guided Media (Wired)  Twisted-Pair Cable  Coaxial Cable  Fiber-Optic Cable  Unguided Media (Wireless)  Radio Waves  Microwaves  Infrared
  5. 5. Classes of transmission media
  6. 6. GUIDED MEDIAGuided media, which are those that provide a conduitfrom one device to another, include twisted-pair cable,coaxial cable, and fiber-optic cable.
  7. 7. Overview The transmission media that are used to convey information can be classified as guided or unguided. Guided media provide a physical path along which the signals are propagated; these include twisted pair, coaxial cable, and optical fiber. Unguided media employ an antenna for transmitting through air, vacuum, or water. The characteristics and quality of a data transmission are determined both by the characteristics of the medium and the characteristics of the signal. In the case of guided media, the medium itself is more important in determining the limitations of transmission. For unguided media, the bandwidth of the signal produced by the transmitting antenna is more important than the medium in determining transmission characteristics. One key property of signals transmitted by antenna is directionality. In general, signals at lower frequencies are omnidirectional; that is, the signal propagates in all directions from the antenna. At higher frequencies, it is possible to focus the signal into a directional beam. In considering the design of data transmission systems, key concerns are data rate and distance: the greater the data rate and distance the better.
  8. 8. Data Rate and Bandwidth Any transmission system has a limited band of frequencies This limits the data rate that can be carried
  9. 9. Design Factors Bandwidth  higher bandwidth gives higher data rate Transmission impairments  eg. attenuation Interference Number of receivers in guided media  more receivers introduces more attenuation
  10. 10. Guided Media – Twisted-pair Cable Twisted-pair cable
  11. 11. Twisted Pair
  12. 12. Twisted pair One of the wires carries signal, the other is used only as a ground reference. The receiver uses the difference b/w the two levels. Twisting increases the probability that both wires are effected by the noise in the same manner, thus the difference at the receiver remains same. Therefore, number of twists per unit length determines the quality of the cable.
  13. 13. Twisted Pair - TransmissionCharacteristics analog  needs amplifiers every 5km to 6km digital  can use either analog or digital signals  needs a repeater every 2-3km limited distance limited bandwidth (1MHz) limited data rate (100MHz) susceptible to interference and noise
  14. 14. Unshielded Versus Shielded Twisted-Pair Cable UTP and STP cables
  15. 15. Unshielded Twisted Pair (UTP) Ordinary telephone wire Cheapest Easiest to install Suffers from external EM interference
  16. 16. Shielded Twisted Pair (STP) Metal braid or sheathing that reduces interference More expensive Harder to handle (thick, heavy)
  17. 17. Near End Crosstalk coupling of signal from one pair to another occurs when transmit signal entering the link couples back to receiving pair ie. near transmitted signal is picked up by near receiving pair
  18. 18. Categories of unshielded twisted-pair cables
  19. 19. UTP Categories
  20. 20. Guided Media – UTP UTP Connector
  21. 21. Guided Media - UTP  Applications:  Telephone lines connecting subscribers to the central office  DSL lines  LAN – 10Base-T and 100Base-T
  22. 22. Twisted Pair - Applications Most common medium Telephone network Within buildings For local area networks (LAN)
  23. 23. Twisted Pair - Pros and Cons Cheap Easy to work with Low data rate Short range
  24. 24. Guided Media – Coaxial Cable Coaxial Cable
  25. 25. Coaxial Cable
  26. 26. Coaxial cable Inner conductor is a solid wire outer conductor serves both as a shield against noise and a second conductor
  27. 27. Coaxial Cable Applications Most versatile medium Television distribution Long distance telephone transmission Can carry 10,000 voice calls simultaneously Short distance computer systems links Local area networks
  28. 28. Coaxial Cable - TransmissionCharacteristics superior frequency characteristics to TP performance limited by attenuation & noise analog signals  amplifiers every few km  closer if higher frequency  up to 500MHz digital signals  repeater every 1km  closer for higher data rates
  29. 29. Guided Media – Coaxial Cable Categories of coaxial cables
  30. 30. Guided Media – Coaxial Cable BNC Connectors
  31. 31. BNC connectors BNC = Bayone-Neill- Concelman BNC Connector is used to connect the end of the cable to a device BNC T is used in networks to branch out a cable for connection to a computer or other device BNC Terminator is used at the end of the cable to prevent the reflection of signal.
  32. 32. Coaxial cable performance
  33. 33. Guided Media – Coaxial Cable  Applications:  Analog telephone networks  Cable TV networks  Traditional Ethernet LAN – 10Base2, 10Base5
  34. 34. Guided Media – Fiber-Optic CableFiber-optic cable transmit signals in the form of light. Bending of light ray
  35. 35. Bending of light ray Angle of Incidence (I): the angle the ray makes with the line perpendicular to the interface between the two substances Critical Angle: the angle of incidence which provides an angle of refraction of 90-degrees.
  36. 36. Guided Media – Fiber-Optic Cable Optic Fiber
  37. 37. Optical fiber Uses reflection to guide light through a channel Core is of glass or plastic surrounded by Cladding Cladding is of less dense glass or plastic
  38. 38. Optical Fiber
  39. 39. Optical Fiber - Benefits greater capacity  data rates of hundreds of Gbps smaller size & weight lower attenuation electromagnetic isolation greater repeater spacing  10s of km at least
  40. 40. Optical Fiber - Benefits The following characteristics distinguish optical fiber from twisted pair or coaxial cable: Greater capacity: The potential bandwidth, and hence data rate, of optical fiber is immense; data rates of hundreds of Gbps over tens of kilometers have been demonstrated. Compare this to the practical maximum of hundreds of Mbps over about 1 km for coaxial cable and just a few Mbps over 1 km or up to 100 Mbps to 10 Gbps over a few tens of meters for twisted pair. Smaller size and lighter weight: Optical fibers are considerably thinner than coaxial cable or bundled twisted-pair cable. For cramped conduits in buildings and underground along public rights-of-way, the advantage of small size is considerable. The corresponding reduction in weight reduces structural support requirements. Lower attenuation: Attenuation is significantly lower for optical fiber than for coaxial cable or twisted pair, and is constant over a wide range. Electromagnetic isolation: Optical fiber systems are not affected by external electromagnetic fields. Thus the system is not vulnerable to interference, impulse noise, or crosstalk. By the same token, fibers do not radiate energy, so there is little interference with other equipment and there is a high degree of security from eavesdropping. In addition, fiber is inherently difficult to tap. Greater repeater spacing: Fewer repeaters mean lower cost and fewer sources of error. The performance of optical fiber systems from this point of view has been steadily improving. Repeater spacing in the tens of kilometers for optical fiber is common, and repeater spacings of hundreds of kilometers have been demonstrated.
  41. 41. Optical Fiber - TransmissionCharacteristics uses total internal reflection to transmit light  effectively acts as wave guide for 1014 to 1015 Hz can use several different light sources  Light Emitting Diode (LED)  cheaper, wider operating temp range, lasts longer  Injection Laser Diode (ILD)  more efficient, has greater data rate relation of wavelength, type & data rate
  42. 42. Guided Media – Fiber-Optic Cable Propagation Modes
  43. 43. Guided Media – Fiber-Optic Cable Propagation Modes
  44. 44. Optical Fiber Transmission Modes
  45. 45. Guided Media – Fiber-Optic Cable Fiber Construction
  46. 46. Guided Media – Fiber-Optic Cable Fiber-optic Cable Connectors
  47. 47. Guided Media – Optical Fiber Cable Applications:  Backbone networks – SONET  Cable TV – backbone  LAN  100Base-FX network (Fast Ethernet)  100Base-X
  48. 48. Transmission Characteristics of Guided Media Frequency Typical Typical Repeater Range Attenuation Delay SpacingTwisted pair 0 to 3.5 kHz 0.2 dB/km @ 50 µs/km 2 km(with loading) 1 kHzTwisted pairs 0 to 1 MHz 0.7 dB/km @ 5 µs/km 2 km(multi-pair 1 kHzcables)Coaxial cable 0 to 500 MHz 7 dB/km @ 10 4 µs/km 1 to 9 km MHzOptical fiber 186 to 370 0.2 to 0.5 5 µs/km 40 km THz dB/km
  49. 49. Comparison of Physical Media
  50. 50. Electromagnetic Spectrum
  51. 51. Wireless Transmission Frequencies 2GHz to 40GHz  microwave  highly directional  point to point  satellite 30MHz to 1GHz  omnidirectional  broadcast radio 3 x 1011 to 2 x 1014  infrared  local
  52. 52. Unguided Media Propagation Methods
  53. 53. Bands
  54. 54. Unguided Media Wireless transmission waves
  55. 55. Broadcast Radio radio is 3kHz to 300GHz use broadcast radio, 30MHz - 1GHz, for:  FM radio  UHF and VHF television is omnidirectional still need line of sight suffers from multipath interference  reflections from land, water, other objects
  56. 56. Unguided Media – Radio Waves Omnidirectional Antenna  Frequencies between 3 KHz and 1 GHz.  are used for multicasts communications, such as radio and television, and paging system.
  57. 57. Terrestrial Microwave used for long haul telecommunications and short point-to-point links requires fewer repeaters but line of sight use a parabolic dish to focus a narrow beam onto a receiver antenna 1-40GHz frequencies higher frequencies give higher data rates main source of loss is attenuation  distance, rainfall also interference
  58. 58. Unguided Media – Microwaves Frequencies between 1 and 300 GHz. Used for unicast communication such as cellular phones, satellite networks and wireless LANs. Unidirectional Antenna
  59. 59. Satellite Microwave satellite is relay station typically requires geo-stationary orbit  height of 35,784km  spaced at least 3-4° apart typical uses  television  long distance telephone  private business networks  global positioning
  60. 60. Unguided Media – Infrared  Frequencies between 300 GHz to 400 THz.  Can not penetrate walls. Used for short-range communication in a closed area using line-of-sight propagation.
  61. 61. Infrared modulate noncoherent infrared light end line of sight (or reflection) are blocked by walls no licenses required typical uses  TV remote control  IRD port
  62. 62. Antennas electrical conductor used to radiate or collect electromagnetic energy transmission antenna  radio frequency energy from transmitter  converted to electromagnetic energy byy antenna  radiated into surrounding environment reception antenna  electromagnetic energy impinging on antenna  converted to radio frequency electrical energy  fed to receiver same antenna is often used for both purposes
  63. 63. Radiation Pattern power radiated in all directions not same performance in all directions  as seen in a radiation pattern diagram an isotropic antenna is a (theoretical) point in space  radiates in all directions equally  with a spherical radiation pattern
  64. 64. Antenna Gain measure of directionality of antenna power output in particular direction verses that produced by an isotropic antenna measured in decibels (dB) results in loss in power in another direction effective area relates to size and shape  related to gain
  65. 65. Satellite Point to Point Link
  66. 66. Satellite Broadcast Link
  67. 67. Wireless PropagationGround Wave
  68. 68. Wireless PropagationSky Wave
  69. 69. Wireless PropagationLine of Sight
  70. 70. Line of Sight Transmission Free space loss  loss of signal with distance Atmospheric Absorption  from water vapour and oxygen absorption Multipath  multiple interfering signals from reflections Refraction  bending signal away from receiver
  71. 71. Multipath Interference
  72. 72. Comparison of Media Medium Cost Speed Atten Interfere Security UTP Low 1-100M High High Low STP Medium 1-150M High Medium Low Coax Medium 1M–1G Medium Medium Low Fibre High 10M–2G Low Low High Radio Medium 1-10M Varies High Low Microw High 1M–10G Varies High Medium Satellite High 1 M–10G Varies High Medium Cellular High 9.6–19.2K Low Medium Low
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