1 / 74

4123702 Data Communications System

4123702 Data Communications System. By Ajarn Preecha Pangsuban. Chapter 7 – Transmission Media. Relation to Internet Model. Actually located below the physical layer Directly controlled by the physical layer. Introduction.

tarala
Télécharger la présentation

4123702 Data Communications System

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 4123702Data Communications System By Ajarn Preecha Pangsuban

  2. Chapter 7 – Transmission Media

  3. Relation to Internet Model • Actually located below the physical layer • Directly controlled by the physical layer 4123702 Data Communications System @YRU

  4. Introduction • Data must be converted into electromagnetic signals to be transmitted from device to device • Signals can travel through a vacuum, air, or other media • May be in the form of power, voice, radio waves, infrared light, and X, gamma, and cosmic rays • Each of these forms constitutes a portion of the electromagnetic spectrum 4123702 Data Communications System @YRU

  5. Electromagnetic Spectrum 4123702 Data Communications System @YRU

  6. Categories of Media • Guided Media • Twisted pair, coaxial, and fiber-optic • Unguided Media • Radio waves, infrared light, visible light, and X, gamma, and cosmic rays • Sent by microwave, satellite, and cellular transmission 4123702 Data Communications System @YRU

  7. Guided Media • Twisted-pair and coaxial use copper conductors to accept and transport signals in form of electrical current • Optical fiber is glass or plastic cable that accepts and transports signals in form of light 4123702 Data Communications System @YRU

  8. Twisted-Pair Cable • Two conductors surrounded by insulating material • One wire used to carry signals; other used as a ground reference • Twisting wires reduces the effect of noise interference or crosstalk since both wires will likely be equally affected • More twists = better quality 4123702 Data Communications System @YRU

  9. Effect of noise on parallel line 16 Effect of noise on parallel line 4123702 Data Communications System @YRU

  10. Effect of noise on twisted-pair lines 4123702 Data Communications System @YRU

  11. Unshielded Twisted Pair (UTP) • Most common type; suitable for both voice and data transmission • Frequency range is from 100 Hz to 5 MHz • Categories are determined by cable quality • Cat 3 commonly used for telephone systems (up to 10 Mbps) • Cat 5e usually used for data networks (up to 100 Mbps) • Performance is measured by attenuation versus frequency and distance 4123702 Data Communications System @YRU

  12. UTP example 4123702 Data Communications System @YRU

  13. UTP (cont) • Adv: cheaper, flexible, easy to install • UTP connectors attach to wire; most commonly used is RJ45, which have 8 conductors, one for each of four twisted pairs 4123702 Data Communications System @YRU

  14. Shielded Twisted Pair (STP) • By IBM • A metal foil or braided-mesh covering encases each pair of insulated conductors to prevent electromagnetic noise called crosstalk • Uses same connectors • More expensive but less susceptible to noise 4123702 Data Communications System @YRU

  15. STP example 4123702 Data Communications System @YRU

  16. Categories of unshielded twisted-pair cables Category Max Speed Digital/Analog Use 1 < 100 kbps Analog Telephone 2 2 Mbps Analog/digital T-1 lines 3 10 Mbps Digital LANs 4 16 Mbps Digital LANs 5e 1 Gbps Digital LANs 6 1 Gbps Digital LANs 7 (Draft) 10 Gbps Digital LANs 4123702 Data Communications System @YRU

  17. Pair # Primary color Secondary color (stripe) 1 Blue White 2 Orange White 3 Green White 4 Brown White Color code for 4cable pairs 4123702 Data Communications System @YRU

  18. UTP connector 4123702 Data Communications System @YRU

  19. The T568A and T568B wiring patterns T568A Jack T568B Jack W/G G W/O B W/B O W/Br Br W/O O W/G B W/B G W/Br Br 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 Pair 3 Pair2 Pair 3 Pair 1 Pair 1 Pair 2 Pair 4 Pair 4 8-pin modular jack (front view) 8-pin modular jack (front view) 4123702 Data Communications System @YRU

  20. UTP performance 4123702 Data Communications System @YRU

  21. Coaxial Cable • Has a central core conductor enclosed in an insulating sheath, encased in an outer conductor of metal foil • Frequency range is between 100 KHz and 500 MHz • RG numbers denote physical specs such as • wire gauge • thickness and type of insulator • construction of shield • size/type of outer casing 4123702 Data Communications System @YRU

  22. RG numbers • RG-8, RG-9, and RG-11 used in thick Ethernet (50) • RG-58 used in thin Ethernet (50) • RG-59 used for TV (75) 4123702 Data Communications System @YRU

  23. Coaxial Cable example 4123702 Data Communications System @YRU

  24. Coaxial Cable Connectors • Most common is barrel connector (BNC) • T-connectors are used to branch off to secondary cables • Terminators are required for bus topologies to prevent echoing of signals 4123702 Data Communications System @YRU

  25. Coaxial Performance • Higher bandwidth than twisted-pair • However, attenuation is higher and requires frequent use of repeaters 4123702 Data Communications System @YRU

  26. Coaxial Applications • Analog telephone networks , • single coaxial network could carry 10,000 voice signals • Digital telephone networks , • single coaxial network could carry digital data up to 600 Mbps • Cable TV networks • Traditional Ethernet LANs 4123702 Data Communications System @YRU

  27. Coaxial cable performance 4123702 Data Communications System @YRU

  28. Fiber-Optic Cable • Made of glass or plastic; • signals are transmitted as light pulses from an LED or laser • Speed depends on density of medium it is traveling through; • fastest when in a vacuum, 186,000 miles/second 4123702 Data Communications System @YRU

  29. Refraction 4123702 Data Communications System @YRU

  30. Critical Angle 4123702 Data Communications System @YRU

  31. Reflection 4123702 Data Communications System @YRU

  32. Fiber Construction (1) 4123702 Data Communications System @YRU

  33. Fiber Construction (2) 4123702 Data Communications System @YRU

  34. Propagation Modes • Method for transmitting optical signals: • Multimode • Multimode step-index fiber • Multimode graded-index fiber • Single Mode 4123702 Data Communications System @YRU

  35. Propagation Modes (cont) 4123702 Data Communications System @YRU

  36. Multimode • Multiple beams from light source move through core at different paths • Multimode step-index fiber • Index refers to the index of refraction • Density remains constant from center to edges • Light moves in a straight line until it reaches the cladding • Some beams penetrate the cladding and are lost, while others are reflected down the channel to the destination 4123702 Data Communications System @YRU

  37. Multimode (cont) • As a result, beams reach the destination at different times and the signal may not be the same as that which was transmitted • Multimode graded-index fiber • May be used to decrease this problem and to allow for more precise transmissions • Graded-index refers to varying densities of the fiber; highest at center and decreases at edge 4123702 Data Communications System @YRU

  38. Multimode (cont) • Since the core density decreases with distance from the center, the light beams refract into a curve • Eliminates problem with some of the signals penetrating the cladding and being lost 4123702 Data Communications System @YRU

  39. Single Mode • Only one beam from a light source is transmitted using a smaller range of angles • Smaller diameter • Makes propagation of beams almost horizontal; • delays are negligible • All beams arrive together and can be recombined without signal distortion 4123702 Data Communications System @YRU

  40. Light Sources • Light source is light-emitting diode (LED) or a laser • LEDs are cheaper but not as precise (unfocused); limited to short-distance use • Lasers can have a narrow range, better control over angle • Receiving device needs a photosensitive cell (photodiode) capable of receiving the signal 4123702 Data Communications System @YRU

  41. Size 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 7 125 Single-mode Fiber types 4123702 Data Communications System @YRU

  42. Single mode 7/125 Multimode 62.5/125 Multimode 100/125 Multimode 50/125 Fiber Sizes 4123702 Data Communications System @YRU

  43. Packing methods for fiber cable 4123702 Data Communications System @YRU

  44. Fiber-Optic cable connectors (1) • Subscriber Channel (SC) Connection • It uses Push/pull locking system mechanism • Used in cable TV • Straight-tip (ST) Connection • It uses a bayonet locking system • Used for connecting cable to networking devices • More reliable than SC • MT-RJ • New connector with the same as RJ45 4123702 Data Communications System @YRU

  45. Fiber-Optic cable connectors (2) 4123702 Data Communications System @YRU

  46. Optical fiber performance 4123702 Data Communications System @YRU

  47. Applications of Fiber Optics • Backbone networks due to wide bandwidth and cost effectiveness • Up to 1600 Gbps with WDM (Synchronous Optical Network : SONET) • Cable TV • LANS • 100Base-FX (Fast Ethernet) • 1000Base-X 4123702 Data Communications System @YRU

  48. Advantages of Fiber Optics • Higher bandwidth than twisted-pair and coaxial cable; not limited by medium, but by equipment used to generate and receive signals • Noise resistance • Less signal attenuation • Immunity to EMI • More resistant to corrosive materials • Lightweight • Greater security (More immune to tapping) 4123702 Data Communications System @YRU

  49. Disadvantages of Fiber Optics • Installation/maintenance • Relatively new technology • need expertise • Unidirectional, bidirectional communication two fibers are needed • Cost • Cable and interface are relatively more expensive • Bandwidth is not high, often the use of fiber cannot justified 4123702 Data Communications System @YRU

  50. Unguided Media: Wireless • Wireless communication; transporting electromagnetic waves without a physical conductor 4123702 Data Communications System @YRU

More Related