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Physical media

  1. 1. Data Communications Transmission Media By: Faiza Tariq
  2. 2. Classes of transmission media  Conducted or guided media – use a conductor such as a wire or a fiber optic cable to move the signal from sender to receiver  Wireless or unguided media – use radio waves of different frequencies and do not need a wire or cable conductor to transmit signals
  3. 3. Design Factors for Transmission Media     Bandwidth: All other factors remaining constant, the greater the band-width of a signal, the higher the data rate that can be achieved. Transmission impairments. Limit the distance a signal can travel. Interference: Competing signals in overlapping frequency bands can distort or wipe out a signal. Number of receivers: Each attachment introduces some attenuation and distortion, limiting distance and/or data rate.
  4. 4. Guided Media (Physical Media) UTP STP Coaxial Fiber Optics
  5. 5. Guided Transmission Media  Transmission capacity depends on the distance and on whether the medium is point-to-point or multipoint  Examples – – – twisted pair wires coaxial cables optical fiber
  6. 6.
  7. 7. Twisted Pair Wire Two or more pairs of single conductor wires that have been twisted around each other. Twisted pair wire is classified by category. Twisted pair wire is currently Category 1 through Category 5e. Twisting the wires helps to eliminate electromagnetic interference between the two wires. Shielding can further help to eliminate interference.
  8. 8. Twisted Pair Wires      Consists of two insulated with insulating material (like plastic) copper wires arranged in a regular spiral pattern If you wrap one good conductor around another one they make a field that protects the conducting wires from RF noise. i.e. one approach taken by the twisted pair cable. The simple twist change the properties of the wire and help make it suitable for network They limit the electromagnetic energy the wire emits or to minimize the electromagnetic interference between adjacent pairs Twists also prevent help in preventing signals on other wires from interfering with the pair
  9. 9.    UTP Often used at customer facilities and also over distances to carry voice as well as data communications. Low frequency transmission medium UTP (unshielded twisted pair) – UTP has four pairs of wire – each wire is insulated with plastic wrap, but the pair is encased in an outer covering – It is used in Ether Networks (10 BaseT and 100 BaseT) Advantages  Easy to install  Least expensive of all media  Small diameter of cable  Proper termination procedures insures reliable connection
  10. 10. Shielded Twisted Pair (STP) STP has two pairs of wires – the pair is wrapped with metallic shield or foil to insulate the pair from electromagnetic interference (extra conducting layer) – It is commonly used in Token Ring network  Foil shields provide greater protection against EMI & RFI.  Increased cost of cable 
  11. 11. UTP and STP    This does not necessarily imply that STP is always better protected from RF noise than UTP, but only that the two cable types take different approaches Theory with UTP is that the two wires wrapped around each other individually conduct noise but cancel out each other’s noise. The theory with STP is that the conductors are best protected with a layer of conducting wires rather than the two conductors being wrapped around each other.
  12. 12.  Ratings of Twisted Pair Category 3 UTP – data rates of up to 10mbps are achievable with atleast three twists per foot.  Category 5 UTP – data rates of up to 100mbps are achievable – Operates at a maximum frequency of 100 MHz, but to support speeds of 100 Mbp a frequency of only 62.5 MHz is required. That is why? – How fast cable could transmit the data under ideal conditions – more tightly twisted than Category 3 cables – more expensive, but better performance  STP – More expensive, harder to work with
  13. 13. Table 7.1 Categories of unshielded twisted-pair cables
  14. 14. Figure 7.5 UTP connector
  15. 15. Twisted Pair Advantages    Inexpensive and readily available Flexible and light weight Easy to work with and install
  16. 16. Coaxial Cable
  17. 17. Advantages  Longer cable runs than UTP & STP (up to 500m)  Cheaper than using fiber for your backbone  Technology is well known (Cable TV)  Better at reducing EMI than UTP or STP
  18. 18. Coaxial Cable    A single wire surrounded by the braided metal shield is very good at blocking electromagnetic signals from entering the cable and producing noise. Base band co-axial – Uses digital signalling in which cable carries only one channel of digital signals Broadband co-axial – Transmits analog signals & is capable of supporting multiple channels of data simultaneously – If each channel occupies a bandwidth of approximately 6 MHz. When 50 channels are transmitted together, the cable is supporting a composite signal = 50 X 6 MHz = 300 MHz
  19. 19. COAXIAL CABLE
  20. 20. Coaxial Cable (or Coax)     Used for cable television, LANs, telephony Has an inner conductor surrounded by a a heavier metal shield. The heavy metal shield in a coaxial cable forms a flexible cylinder around the inner wire and provides a barrier to electromagnetic radiation. This barrier isolates the inner wire in two ways – It protects the wire from incoming electromagnetic energy that could cause interference – Keeps signal on the inner wire from radiating electromagnetic energy that could affect other wires.  Both conductors share a common center axial, hence the term “co-axial”
  21. 21. Coax Layers outer jacket (polyethylene) shield (braided wire) insulating material copper or aluminum conductor
  22. 22. Coaxial Cables  Can transmit signal perfectly up to 185 metre, then you need a repeater  PC’s can be connected directly without hub Outer Insulation Mesh Shielding Insulation Conductor
  23. 23. Figure 7.8 BNC connectors Category Impedance Use RG-59 75 Ω Cable TV RG-58 50 Ω Thin Ethernet RG-11 50 Ω Thick Ethernet
  24. 24. Coax Disadvantages  High attenuation rate makes it expensive over long distance  Bulky  Thick Coaxial Cable – Approximately 6 – 10 mm in diameter – Used as broadband  Thin Coaxial Cable – Approximately 4 mm in diameter – Carries base band signals
  25. 25. Bending of light ray
  26. 26. Figure 7.12 Propagation modes
  27. 27. Figure 7.13 Modes
  28. 28. Table 7.3 Fiber types Type Core Cladding Mode 50/125 50 125 Multimode, graded-index 62.5/125 62.5 125 Multimode, graded-index 100/125 100 125 Multimode, graded-index 7 125 Single-mode 7/125
  29. 29. Figure 7.14 Fiber construction
  30. 30. Figure 7.15 Fiber-optic cable connectors
  31. 31. Fiber Optics Advantages  Longer runs than any other cable (2km)  Higher data rates than any other cable (>100Mbps)  NO EMI!!
  32. 32. Fiber Optic Cable      Relatively new transmission medium used by telephone companies in place of long-distance trunk lines Also used by private companies in implementing local data communications networks This medium uses light to transport data A transmitter at one end of a fiber (light source) uses a light emitting diode (LED) or laser (Injection Laser Diode – ILD) to send pulses of light down the fiber. A receiver at the other end (detector) is a photodiode which uses a light sensitive transistor to detect the pulses and generates electrical pulse when light fall on.
  33. 33. Fiber Optics Disadvantages  Very expensive!!  Difficult to install Therefore, fiber is used only for backbone installations.
  34. 34. Fiber Optic Layers  Data Transmission is unidirectional.  consists of three concentric sections plastic jacket glass or plastic fiber core cladding
  35. 35. Fiber Optic Cable      Fibre Optic can transmit data at 1000 Mbp for 1000 km Powerful lasers can drive a fiber 100 km long without repeaters, although at much lower speed. Fibre optic cable may have more than one fibre in it meaning multiple pathway exist Like different motorway’s lanes One method used to send data through the optic fibre cables is simply turning light on and off. When light is on a 1 is transmitted and when light is off a 0 is transmitted
  36. 36. Plastic Covering Fibre Glass Optics Glass Conductor (Core) Cladding Side View Of A Fibre Optic Cable Plastic Covering 0.009 inches diameter Glass Cladding 0.0049126 inches diameter Glass Core 0.001965 inches diameter Cross Section Of A Fibre Optic Cable
  37. 37. Fiber Optic Cable  There are two types of fiber optic cable  Single-mode – It sends transmission along a single path – The beam of light is very intense, so it can carry more data for longer distance (interbuilding) – Suitable either for applications that are very traffic-intensive or need to travel for long distance.
  38. 38. Multimode     Allow multiple modes to pass through the cable at once. Suitable for within the building use. Multiple channels, each on a different color of light can be used to increase capacity. This is called WDM (Wave Division Multiplexing) and it allows many separate channels of data each carried by different color of light in an optic fibre cable Two kinds of multimode A mode is a ray of light entering a fibre at a particular angle
  39. 39. Fiber Optic Types  multimode step-index fiber – The light beam bounce around inside the cable in zigzag pattern – the reflective walls of the fiber move the light pulses to the receiver  multimode graded-index fiber – Rounded pattern of the light movement like a sine wave – acts to refract the light toward the center of the fiber by variations in the density  single mode fiber – the light is guided down the center of an extremely
  40. 40. Optical Fiber Transmission Modes
  41. 41. Fiber Optic Signals fiber optic multimode step-index fiber optic multimode graded-index fiber optic single mode
  42. 42. Fiber Optic Advantages  Greater capacity (bandwidth of up to 2 Gbps)  smaller size and lighter weight  lower attenuation  As light is used which neither cause electrical interference in other cables nor are they susceptible to electrical interference  i.e. immunity to environmental interference  highly secure due to tap difficulty and lack of signal radiation  Pairs of wires not required  Greater Repeater Spacing
  43. 43. Fiber Optic Disadvantages  Installing fiber requires special equipment that polishes the ends to allow light to pass through  If fiber breaks inside the plastic jacket (e.g. being bent at a right angle).  Repairing is difficult as special equipment is needed to join two fiber so that light can pass through the joint.  expensive over short distance  requires highly skilled installers  adding additional nodes is difficult
  44. 44.  It very common to mix fiber with twisted pair in LANs.
  45. 45. Connectors
  46. 46. Thick Ethernet 10 Base 5
  47. 47. 10 Base 2 (Thin Ethernet)
  48. 48. 7-2 UNGUIDED MEDIA: WIRELESS Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Topics discussed in this section: Radio Waves Microwaves Infrared
  49. 49. Wireless or Unguided Media    Within buildings the LAN may use copper wire or fibre optic but connecting buildings may require digging up the streets to lay a cable, which may be an expensive task (it may also be illegal, if it is a public road) On the other hand putting a laser or infrared transmitter and receiver on the roof of each building is inexpensive, easy to do and nearly always legal Wireless communication does not require direct physical connection between computers.
  50. 50. Wireless Media Radio, satellite transmissions, and infrared light are all different forms of electromagnetic waves that are used to transmit data. Note in the following figure how each source occupies a different set of frequencies.
  51. 51. Wireless Examples  Microwave  Infrared  Laser  Broadcast Radio
  52. 52. Wireless Communication    Radio waves are used for multicast communications, such as radio and television, and paging systems Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Infrared signals can be used for shortrange communication in a closed area using line-of-sight propagation.
  53. 53. Propagation methods Radio waves are used for multicast communications, such as radio and television, and paging systems. Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.
  54. 54. Table 7.4 Bands
  55. 55. Wireless (Unguided Media) Transmission  Transmission and reception are achieved by means of an antenna (TX and RX)  Directional (Line-of-Sight Transmission) – Transmitting antenna puts out focused beam – Transmitter and receiver must be aligned  Omni directional – – – Signal spreads out in all directions Can be received by many antennas Higher frequency required
  56. 56. Omnidirectional antennas
  57. 57. Unidirectional antennas
  58. 58. Broadcast Radio Radio Waves Earth
  59. 59. Microwave Radio Transmission:       Electromagnetic radiation beyond the frequency used for radio and television can also be used to transport information i.e. higher frequency version of radio waves. Many telephone companies use microwave transmissions to carry telephone conversations. Unlike radio broadcast in all directions, a microwave can be aimed in a single direction, preventing others from intercepting the signal. Microwave transmission can carry more information than lower frequency RF transmission Microwave can not penetrate metal structures. Suitable for long distance communication, widely used in network as an alternative of cables.
  60. 60. Microwave Radio Transmission  The higher the tower, the greater the range.  With a 100 – meter distance of 100 km between towers are feasible. Therefore much cheaper rather than digging 100 km  No need of expensive repeaters  It may be affected by thunderstorms.  Microwave occur at frequencies between 2 and 40 GHz and these frequencies have been divided into bands for common carrier, government military and other users.
  61. 61. Microwave  parabolic dish transmitter, mounted high  used by common carriers as well as private networks  requires unobstructed line of sight between source and receiver  curvature of the earth requires stations (repeaters) ~30 miles apart
  62. 62. Microwave Relay Station
  63. 63. Microwave Transmission Disadvantages  Line of sight requirement  Expensive towers and repeaters  Subject to interference such as passing airplanes and rain
  64. 64. Advantages/Disadvantages of Microwave  Advantages – Fast – Cost-effective – Easy implementation  Disadvantages – Interference from other radio waves – Limited by "line of sight" distance (30 miles apart) – Insecure (easily intercepted) – Affected by environmental factors (such as high humidity)
  65. 65. Infrared       The wireless remote controls used electrical appliances like television, stereo and air conditioner communicate with infrared transmission. Infrared is limited to a small area (e.g. a single room), and usually requires that transmitter be pointed toward receiver. Infrared is inexpensive as compared to other wireless means and do not require antenna. Computer networks can use infrared technology for data transmission Notebook computers offer wireless communication with network It is fully digital communication and is immune of tapping or jamming as it is highly directional.
  66. 66. Infrared Transmission
  67. 67. Infrared  Uses transmitters/receivers (transceivers) that modulate infrared light.  Transceivers must be within line of sight of each other (directly or via reflection ).  Unlike microwaves, infrared does not penetrate walls.
  68. 68. Laser      A beam of light can be used to carry data through air (especially between buildings). A laser communication system, like microwave consists of two sites that each have transmitter and receiver. The equipment is mounted in a fixed position often on a tower and aligned so the transmitter at one location sends its beam of light directly to the receiver. Unfortunately laser beam can not penetrate weather conditions like fog, rain and snow, therefore laser transmission has limited use. It is fully digital communication and is immune of tapping or jamming as it is highly directional.
  69. 69. Satellites       RF Technology can be combined with satellites to provide communication along the longer distances. The satellite contains transponder that consists of a radio receiver and transmitter. The transponder accepts an incoming radio transmission, amplifies it and transmits amplified signal to ground station at some different angle. A single satellite uses multiple transponders (as it is expensive to place satellite in orbit) to work independently Each transponder uses different frequency (Channel) Satellite transmission can be heard by any one with a dish & tuning to a right frequency causing potential security risk.
  70. 70. Satellite Microwave Similar to terrestrial microwave except the signal travels from a ground station on earth to a satellite and back to another ground station. Satellites can be classified by how far out into orbit each one is (LEO, MEO, GEO, and HEO).
  71. 71. Satellite Microwave LEO - Low Earth Orbit - 100 miles to 1000 miles. Used for pagers, wireless e-mail, special mobile telephones, spying, videoconferencing. MEO - Middle Earth Orbit - 1000 to 22,300 miles. Used for GPS and government. GEO - Geosynchronous Orbit - 22,300 miles. Used for weather, television, and government operations.
  72. 72. Satellite Microwave HEO – Highly Elliptical Orbit A fourth type of orbit used by the military for spying and by scientific organizations for photographing celestial bodies. When satellite is far out into space, it takes photos. When satellite is close to earth, it transmits data.
  73. 73. Satellite Microwave Satellite microwave can also be classified by its configuration: Bulk carrier configuration Multiplexed configuration Single-user earth station configuration (e.g. VSAT)
  74. 74.      Satellites Satellite transmissions are subject to subject to noise and long delay. Since every transmission must go from the ground to the satellite and then from satellite to ground, each transmission approximately takes a 45,000 miles trip. Transmission occurs at almost speed of light, so trip takes a quarter of a second. Sending a message and receiving a response means at least half second delay for the round trip In this situation computer could transmit 4800 bits during that time. long delays in satellite transmission can cause “tunnel effects.” where annoying echoes are heard during long distance calls. Although echoes can be removed by echo cancellers
  75. 75. Satellite Radio Earth
  76. 76. Satellite Microwave Transmission  A satellite can act as a big microwave repeater in the sky.  a microwave relay station in space  can relay signals over long distances  geostationary satellites – remain above the equator at a height of 22,300 miles or 36,000 Km (geosynchronous orbit) – When viewed from the ground, the satellite appears to remain at exactly the same point in the sky at all times. – travel around the earth in exactly the time the earth takes to rotate, the satellite period is 24 Hours
  77. 77. Satellites  There is limited space available in geosynchronous orbit above the equator, because communication satellites using a given frequency must be separated to avoid interference.  The minimum separation depends on the power of transmitters, generally angular separation of 4 and 8 degrees. Bearing this fact in mind, how many satellites can be accommodated in the orbit?  Entire 3600 circle above the equator can hold 45 – 90 satellites
  78. 78. Satellite Transmission Links  Earth stations communicate by sending signals to the satellite on an uplink  the satellite then repeats those signals on a downlink  the broadcast nature of the downlink makes it attractive for services such as the distribution of television programming
  79. 79. Communication Satellites  It contains one or more transponders, each of which listens to incoming signals, amplifies it and then re-broadcasts it at another frequency to avoid interference with the incoming signal.  The downward beams can be broad covering the substantial surface of the earth or narrow covering hundreds of kilometres.
  80. 80. Satellite Transmission Process satellite transponder dish dish 22,300 miles uplink station downlink station
  81. 81. Satellite Transmission Applications  Television distribution – A network provides programming from a central location – Direct broadcast satellite (DBS)  Long-distance telephone transmission – High-usage international trunks  Private business networks
  82. 82. Principal Satellite Transmission Bands C – – band: 4(downlink) - 6(uplink) GHz the first to be designated Reserved for telcos  Ku band: 12(downlink) -14(uplink) GHz – rain interference is the major problem, as water is excellent absorber of short microwave – Several downlink stations can overcome this problem  Ka band: 19(downlink) - 29(uplink) GHz – equipment needed to use the band is still very expensive
  83. 83. Electromagnetic Spectrum
  84. 84. Fiber vs Satellite
  85. 85. Radio  Radio is omni directional and microwave is directional  Radio is a general term often used to encompass frequencies in the range 3 KHz to 300 GHz.  Mobile telephony occupies several frequency bands just under 1 GHz.
  86. 86. Frequency Spectrum Classification Frequency (Hz) 1016 1015 1014 1013 1012 1011 1010 109 108 107 106 105 104 103 102 101 Wave Length X-Rays Gamma rays Ultraviolet rays Visible Light Infrared Light Microwaves UHF television VHF television VHF TV (high band) FM radio VHF TV (low band) Shortwave radio AM radio } Very Low frequency
  87. 87. Media Selection Guided Media Media Network Type Cost Transmission Distance Error Security Rates Speed Twisted Pair Coaxial Cable Fiber Optics LAN LAN any Short Short Mod.-long Good Low Good Low V. Good V.Low Low-high Low-high High-V.High Low Mod. High Radiated Media Media Network Type Cost Transmission Distance Security Error Rates Speed Radio Infrared Microwave Satellite LAN Low LAN, BN Low WAN Mod WAN Mod Short Short Long Long Mod Mod Low-Mod Low-Mod Low Low Mod Mod Poor Poor Poor Poor
  88. 88. Private Line Media - Transmission 300, 1200, Speed 9600, 19200, 38400, 2400, 4800, 56000, 64000, 80000 Switched Lines 300, 1200, 2400, 4800, 9600, 19200, 38400 Leased Lines 2400, 4800, 9600, 19200, 56000, 64000 UTP 1M, 10M, 16M, 100M STP 1M, 10M, 16M, 100M Coaxial Cable 1M, 2M, 10M, 50M, 100M Fibre Optics over 2Gbps Microwave up to 45M Broadcast Radio 9600 Infrared Light 1M, 4M Satellite up to 50M
  89. 89. Media Selection Criteria Important factors to consider when choosing a transmission medium • Cost • Speed (or Capacity) • Availability • Expandability • Error Rates • Security • Distance • Environment • Application • Maintenance
  90. 90. Further Reading  Data Communication and Networking Behrouz Forouzan By – Chapter 7 page 187 – 211  Satellites from Tanenbaum’s Text Book

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