Dr. Thomas Hicks Computer Science Department Trinity University

1. Data Communication & Networking CSCI 3342 Digital Transmission Dr. Thomas Hicks Computer Science Department Trinity University 4 1

2. Digital To DigitalEncoding

3. Major 4 Encoding Methods Digital-To- Digital Analog-To- Digital Digital-To- Analog Analog-To- Analog Binary Data Must Be Encoded/Converted To A Form That Will Propagate Over A Wire

4. Digital To Digital Encoding • Digital To Digital Encoding – Converting Binary 0’s and 1’s Into A Sequence Of Voltage Pulses That Can Propagate Over A Wire. • Transmit Data From Computer To Printer

5. Signal Encoding Signal Level Data Level

6. Signal Level vs. Data Level

7. Pulse Rate & Bit Rate

8. Pulse Rate = No Pulses Per Second Bit Rate = No Bits Per Second If the pulse carries only one bit, the Bit Rate = Pulse Rate [Not Always The Case]

9. General Case: BitRate = PulseRate x log2 LL = # Data Levels BitRate = PulseRate x log2DataLevels

10. Example 1 A signal has two data levels with a pulse duration of 1 ms. We calculate the pulse rate and bit rate as follows: Pulse Rate = 1/ 10-3= 1000 pulses/s Bit Rate = Pulse Rate x log2 L = 1000 x log2 2 = 1000 bps

11. Example 2 A signal has four data levels with a pulse duration of 1 ms. We calculate the pulse rate and bit rate as follows: Pulse Rate = 1/ 10-3 = 1000 pulses/s Bit Rate = PulseRate x log2 L = 1000 x log2 4 = 2000 bps

12. DC Components

13. We Shall Examine Numerous Coding Schemes Most Coding Schemes Will Have Values Above & Below The Line - Positive & Negative Values. 10110001

14. DC ComponentCoding Schemes Some coding schemes have a residual DC [Direct-Current] that has a zero frequency. The positive and negative voltages do not cancel each other. 10110001 This extra energy on the line is useless and will not pass properly through Transformers! Bad!

15. Synchronization

16. The Receiver's Bit IntervalsMust Match The Sender's Bit IntervalsIf The Signal Is To Be Interpreted Correctly! We Must Have Some Way Of Synchronizing The Signal!

17. Lack Of Synchronization

18. Example 3 In a digital transmission, the receiver clock is 0.1 percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 Kbps? How many if the data rate is 1 Mbps? Solution At 1 Kbps: 1000 bits sent 1001 bits received1 extra bps At 1 Mbps: 1,000,000 bits sent 1,001,000 bits received1000 extra bps

19. Many Line Coding Schemes

20. Only Some Of Major Encoding Methods! Unipolar Polar Bipolar AMI B8ZS HDB3 ETC RZ NRZ NRZ-I Manchester NRZ-L Differential Manchester

21. You May Make A 5"x8" Card To Use On Exam (May Include Titles & Images) NRZ-L

22. Unipolar

23. Unipolar Encodinguses only One Voltage Level.

24. Unipolar Encoding

25. Not Essential Assignment, But Logical! Unipolar Encoding -1 • Unipolar uses either a Positive Or Negative • Unipolar – Very Simple & Very Primitive Encoding Scheme (almost obsolete) • Unipolar – Only one polarity. • Sending Voltage Pulses along a medium link (usually a wire or cable) • Voltage Level = 1’s • Zero Voltage Level = 0’s

26. Unipolar Encoding -2 • Unipolar Requires DC Component • Average Amplitude Is Non-Zero • Not All Mediums Can Handle A DC Component • Unipolar Requires Synchronization • No Way Receiver Can Determine Beginning Or End • Problem With A Long, Uninterrupted Series Of 1’s • Problem With A Long, Uninterrupted Series Of 0’s • Solution To Synchronization Problem – Use A Separate Parallel Line To Carry Clock Pulse • Doubling # Lines Expensive

27. Polar

28. Polar Encoding uses two voltage levels (positive and negative?)

29. Types Of Polar Encoding

30. Polar Encoding • Polar Encoding – Uses Two Voltage Levels–> 0 Positive & 1 Negative – or Visa Versa • Average Amplitude is 0 • DC Component Not Needed • 4+ Types Of Polar Encoding • NRZ • RZ • Manchester • Differential Manchester

31. NRZ-L Encoding (Polar)

32. Polar NRZ-L Encoding In Polar NRZ-L the Level of the Signal is Dependent upon the State of the Bit.

33. Polar Encoding  NRZ-L • NRZ - NonReturn to Zero – Two Most Popular Methods Are NRZ-L and NRZ-I • NRZ-L • Usually 0 Positive & 1 Negative {For Us!} • Biggest Problem With Long Stream Of 1’s or 0’s [Clocks Might Not Be Synchronized]

34. NRZ-L Practice • Sketch The NRZ-L Encoding For The Signal Below.

35. NRZ-I Encoding (Polar)

36. In NRZ-I the signal is InvertedIf a 1 is Encountered.

37. Polar Encoding  NRZ-I • NRZ-I • An Inversion Of The Voltage Represents 1 • If Pos  Neg If Neg  Pos • No Change Represents 0 • Synchronization Occurs With Every 1 Bit • 0’s Can Still Cause Problem – More 1’s Than 0’s • 0 First  Pos • 1 First  Neg • Next Bit Is 1

38. NRZ-I Practice • Sketch The NRZ-I Encoding For The Signal Below.

39. RZ Encoding (Polar)

40. Polar RZ • RZ - Return to Zero – A Signal Change With Every Bit To Assure Synchronization • Several Solutions • RZ • Positive Voltage Means 1 • Negative Voltage Means 0 • Signal Returns To 0 Voltage Half-Through

41. Polar RZ • RZ – 3 Levels Of Amplitude – 3 Voltage Levels

42. Polar RZ Practice • Sketch The RZ Encoding For The Signal Below. Best So Far!

43. A Good Encoded Digital Signal Must Contain a Provision for Synchronization.

44. ManchesterEncoding (Polar)

45. In Manchester Encoding, the Transition at the Middle of the Bitis used for both Synchronization and Bit Representation.

46. Polar Manchester • Manchester • Positive To Negative Transition For 0 • Negative To Positive Transition For 1 • Two Levels Of Amplitude • Inversion At Middle Middle Of Bit Time

47. Polar Manchester (cont) • Manchester • Inversion At Middle Middle Of Bit Time • Synch Signal Change Middle Of Each Bit GreenBlue

48. Polar Manchester Practice • Sketch The Manchester Encoding For The Signal Below. Two Levels Of Amplitude Same Synchronization As RZ

49. I Would Provide KEY Manchester

50. Differential ManchesterEncoding (Polar)