Overview of Data Communications Systems: Transmission Media and Internet Models

1. 4112323Data Communications System By Ajarn Preecha Pangsuban

2. Chapter 3 – 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, Step-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