1. The Saigon CTT Semester 1 CHAPTER 4 Le Chi Trung

2. The Saigon CTT  Content Electricity The digital multimeter - LAB Signals and noise The encoding of networking signals

3. The Saigon CTT  Schedule

4. The Saigon CTT ELECTRICITY

5.  Periodic table

6. The Saigon CTT  Conductors Materials that allow electrons to flow through them with great ease. These electrons can easily be freed from the atom when voltage is applied. Examples : –Metals : Gold, Silver, Copper... –Water. –Humans!!

7. The Saigon CTT  Insulators Materials that allow electrons to flow through them with great difficulty, or not at all. Electron orbits are very close to the nucleus. Examples : –Plastic, glass, wood … –Air and other gases.

8. The Saigon CTT  Semi-conductors Materials where the amount of electricity they conduct can be controlled. Because silicon is widely available (sand), it is the material we use for computer chips. Examples : –Carbon. –Germanium. –Silicon.

9. The Saigon CTT  Parts of an atom

10. The Saigon CTT  Forces within an atom

11. The Saigon CTT  Stable atom Why don't the electrons fly in towards the protons? –Velocity of electrons keep them in orbit around nucleus. Why don't the protons fly away from each other? –Nuclear force keep the protons don't fly away from each other.

12. The Saigon CTT  Static electricity Electrons have been loosened from the atom and stay in one place, without moving. Electrostatic discharge (ESD). –ESD, though usually harmless to people, can create serious problems for sensitive electronic equipment. –How to handle the printed circuit boards ?

13. The Saigon CTT  Measuring electricity: Voltage Force or pressure caused by the separation of electrons and protons. Symbol: U. Volt (V).

14. The Saigon CTT  Measuring electricity: Current The flow of charges that is created when electrons move. Symbol: I. Ampere (A).

15. The Saigon CTT  Measuring electricity: Resistance Property of a material that opposes, and can control the electrical flow. Symbol: R. Ohm (Ω).

16. The Saigon CTT  Simple circuit I = U / R

17. The Saigon CTT  Electrical definitions: AC and DC Alternating Current (AC): –Electrical current flows in both directions; positive and negative terminals continuously trade places (polarity). Direct Current (DC): –Electrical current flows in one direction; negative to positive.

18. The Saigon CTT  Oscilloscope

19. The Saigon CTT  Electrical definitions: Impedance Total opposition to the flow of electrons. Equivalent to resistance but for AC and pulsed circuits. Symbol: Z. Ohm (Ω).

20. The Saigon CTT  Electrical definitions: Ground Ground can refer to the place on the earth. Ground can also mean the reference point, or the 0 volts level, when making electrical measurements.

21. The Saigon CTT  Safety ground wire (SGW) SGW prevents electrons from energizing metal parts of the equipments.

22. The Saigon CTT  Review Conductor, insulator, semi-conductors. Measuring electricity. Definitions. Grounding.

23. The Saigon CTT THE DIGITAL MULTIMETER

24. The Saigon CTT  Multimeter Voltage measurement. Current measurement. Resistance measurement. Continuity measurement.

25. The Saigon CTT  Preparation for LAB 4.2.1: Use of multimeter. 4.2.2: Resistance measurement. 4.2.3: Voltage measurements. Lab companion: –4.2.1. –4.2.2. –4.2.3.

26. The Saigon CTT  Review Using digital multimeter.

27. The Saigon CTT SIGNALS AND NOISE

28. The Saigon CTT  Signals Signal refers to a form to carry information. Example: –A desired electrical voltage. –A light pattern. –A modulated electromagnetic wave.

29. The Saigon CTT  Analog signals

30. The Saigon CTT  Digital signals

31. The Saigon CTT  Fourier synthesis

32. The Saigon CTT  One bit on physical media Voltage level Light intensity Burst of waves Bits must arrive at the destination undistorted in order to be properly interpreted.

33. The Saigon CTT  Bits on travel Propagation Attenuation Reflection Timing Problems Collisions Noise

34. The Saigon CTT  Propagation A bit takes at least a small amount of time to travel (propagate) down the wire.

35. The Saigon CTT  Propagation (cont.) If the receiving device cannot handle the speed of the arriving bits, data will be lost. To avoid data loss, the device either... –Buffers the arriving bits into memory for later processing, or. –Sends a message to the source to slow down the speed of propagation.

36. The Saigon CTT  Attenuation The signal degrades or losses amplitude as it travels along the medium.

37. The Saigon CTT  Attenuation (cont.) Loss of amplitude means that the receiving device can no longer distinguish a 1 bit from a 0 bit. Attenuation is prevented by: –Not exceeding a medium’s distance requirement (100 meters for Cat 5 cable). –By using repeaters that regenerate the signal.

38. The Saigon CTT  Reflection Reflection refers to reflected energy.

39. The Saigon CTT  Reflection (cont.) When impedance is mismatched, the digital signal can “bounce back” (reflect) causing it to be distorted as bits run into each other. If enough energy is reflected, the binary, two-state system can become confused by all the extra energy bouncing around.

40. The Saigon CTT  Timing problems Dispersion, Jitter, Latency

41. The Saigon CTT  Timing problems (cont.) Dispersion: similar to attenuation, is the broadening of a signal as it travels down the media. Jitter: caused by unsynchronized clocking signals between source and destination. This means bits will arrive later or earlier than expected. Latency: is the delay of a network signal.

42. The Saigon CTT  Collisions A collision happens when two bit are on a point of media at the same time.

43. The Saigon CTT  Collisions (cont.) Collisions occur in broadcast topologies where devices share access to the network media. A collision happens when two devices attempt to communicate on the shared- medium at the same time. Collisions destroy data requiring the source to retransmit.

44. The Saigon CTT  Noise Noise is unwanted additions to the signal.

45. The Saigon CTT  Noise (cont.)

46. The Saigon CTT  Noise (cont.) Too much noise can corrupt a bit, thus destroying the message. Noise is unavoidable. Kinds of noise: –Thermal Noise. –Near end cross talk. –AC Power/Reference Ground Noise. –Electromagnetic Interference (EMI). –Radio Frequency Interference (RFI).

47. The Saigon CTT  Noise: Thermal Due to the random motion of electrons, thermal noise is unavoidable. Our signaling is usually strong enough to override the effects of thermal noise.

48. The Saigon CTT  Noise: NEXT Near end cross talk (NEXT) : when two wires are near each other, energy from one wire can wind up in an adjacent wire and vice versa. Cross talk is avoided by a network technician using proper installation procedures including: –Strict adherence to RJ-45 termination procedures (chapter 5). –Using high quality twisted pair cabling.

49. The Saigon CTT  Noise: AC Power/Reference ground The signal reference ground is not completely isolated from the electrical ground. AC power line act as an antenna for electrical noise interferes with the digital signals.

50. The Saigon CTT  Noise: EMI/RFI Sources of EMI/RFI include: –Fluorescent lighting (EMI). –Electrical motors (EMI). –Radio systems (RFI). Two ways to prevent EMI/RFI Noise: –Through shielding the wires in the cable with a metal braid or foil. –Through cancellation the wires are twisted together in pairs to provide self-shielding.

51. The Saigon CTT  Cancellation

52. The Saigon CTT  Review Digital signal. By what bits are distorted. Kind of noise.

53. The Saigon CTT BASIC OF ENCODING

54. The Saigon CTT  Encoding Encoding is the process of converting information into a form that can travel on a physical link. Example: –Smoke signals. –Morse mode. –Telephone. –TV/Radio.

55. The Saigon CTT  Signal modulation AM (amplitude modulation): the amplitude, or height, of a carrier sine wave is varied to carry the message. FM (frequency modulation): the frequency, or wiggly-ness, of the carrier wave is varied to carry the message. PM (phase modulation): the phase, or beginning and ending points of a given cycle, of the wave is varied to carry the message.

56. The Saigon CTT  Binary encoding TTL: Transistor-Transistor logic NRZ-L: Non-Return to Zero-Level NRZI: Non-Return to Zero-Inverted NRZ-M: Non-Return to Zero-Mark Manchester Tx (Transmit) MLT3: Multi-Level Threshold-3

57. The Saigon CTT  Binary encoding: TTL

58. The Saigon CTT  Binary encoding: NRZ-L, I

59. The Saigon CTT  Binary encoding: Manchester

60. The Saigon CTT  Binary encoding: MLT3

61. The Saigon CTT  Binary encoding: Used Ethernet: –Manchester Tx+, Tx- Token-ring: –Differential Manchester Fast Ethernet: –MLT-3

62. The Saigon CTT  Review Encoding and Modulation. Binary encoding schemes.