Data Communication Network

1. Data Communication Network 331: STUDY DATA COMMUNICATIONS AND NETWORKS

2. 331: STUDY DATA COMMUNICATIONS AND NETWORKS • 1. Discuss computer networks (5 hrs) • 2. Discuss data communications (15 hrs)

3. 331.2: Discuss Data Communications • PERFORMANCE STANDARD • Given a network system, identify and illustrate the different data communications components clearly • Objectives: • Define elements of a communication system • Define data communications • Discuss various types of transmission media and their characteristics • Discuss encoding of information for transmission • Discuss types of signal & their characteristics • Relate data capacity of a channel and bandwidth • Classify media based on bandwidth • Discuss channel organization

4. SKILL AREA 331.2.3 Discuss encoding of information for transmission

5. Data vs. Information Data • raw facts • no context • just numbers and text Information • data with context • processed data • value-added to data • summarized • organized • analyzed

6. Data in computer • We have all seen computers do seemingly miraculous things with all kinds of sounds, pictures, graphics, numbers, and text. • All of the wonderful multi-media that we see on modern computers is all constructed from simple ON/OFF switches - millions of them - but really nothing much more complicated than a switch. • The trick is to take all of the real-world sound, picture, number etc data that we want in the computer and convert it into the kind of data that can be represented in switches.

7. Data in computer

9. Data Encoding

10. Data Encoding • Data Encoding refers the various techniques of impressing data (0,1) or information on an electrical, electromagnetic or optical signal that would propagate through the physical medium making up the communication link between the two devices.

11. Data Encoding Techniques • Digital Data, Analog Signals [modem] • Digital Data, Digital Signals [wired LAN] • Analog Data, Digital Signals [codec] • Frequency Division Multiplexing (FDM) • Wave Division Multiplexing (WDM) [fiber] • Time Division Multiplexing (TDM) • Pulse Code Modulation (PCM) [T1] • Delta Modulation

12. Data and Signals • Two types of data Analog and Digital • Two types of Signals (transmission techniques) Analog and Digital

13. Advantages of Digital Transmission • The signal is exact • Signals can be checked for errors • Noise/interference are easily filtered out • A variety of services can be offered over one line • Higher bandwidth is possible with data compression

14. Advantages of Analog Transmission • Most mediums support analog transmission - used for wireless communication • The telephone infrastructure provides a relatively cheap “individual point-to-point” transmission

15. Interpreting Signals • Need to know • Timing of bits - when they start and end • Signal levels • Factors affecting successful interpreting of signals • Signal to noise ratio • Data rate • Bandwidth

16. Comparison of Encoding Schemes (1) • Signal Spectrum • Lack of high frequencies reduces required bandwidth • Lack of dc component allows ac coupling via transformer, providing isolation • Concentrate power in the middle of the bandwidth • Clocking • Synchronizing transmitter and receiver • External clock • Sync mechanism based on signal

17. Comparison of Encoding Schemes (2) • Error detection • Can be built in to signal encoding • Signal interference and noise immunity • Some codes are better than others • Cost and complexity • Higher signal rate (& thus data rate) lead to higher costs • Some codes require signal rate greater than data rate

19. Analog Signals Carrying Analog and Digital Data

20. Digital Signals Carrying Analog and Digital Data

22. Digital Data - Digital Signal • It is logical to represent digital data with a digital signal • Digital signal • Discrete, discontinuous voltage pulses • Each pulse is a signal element • Binary data encoded into signal elements • Signal changes value as the data changes value from 0 to 1 and 1 to 0 • Several line encoding schemes are possible. Each has pros and cons

23. Encoding Schemes • There are many encoding schemes. We will focus on: • Nonreturnto Zero-Level (NRZ-L) • Nonreturn to Zero Inverted (NRZI) • Manchester • Differential Manchester

24. Nonreturn to Zero-Level (NRZ-L) • Two different voltages for 0 and 1 bits • Voltage constant during bit interval • no transition I.e. no return to zero voltage • e.g. Absence of voltage for zero, constant positive voltage for one • More often, negative voltage for one value and positive for the other • This is NRZ-L

25. Nonreturn to Zero Inverted • Nonreturn to zero inverted on ones • Constant voltage pulse for duration of bit • Data encoded as presence or absence of signal transition at beginning of bit time • Transition (low to high or high to low) denotes a binary 1 • No transition denotes binary 0 • An example of differential encoding

26. NRZ

27. NRZ pros and cons • Pros • Easy to engineer • Make good use of bandwidth • Cons • dc component • Lack of synchronization capability • Used for magnetic recording • Not often used for signal transmission

28. Manchester Digital Encoding Schemes • Ensures that each bit has some type of signal change • Solves the synchronization problem. • There is always a transition in the middle of the interval. • Manchester code signal: • Changes from high to low in the middle of the interval to transmit a 0, and • Changes from low to high in the middle of the interval.

29. Differential Manchester • Used in most local area networks • No transmission in the beginning interval = 1 • Transmission in the beginning interval = 0 • Receiver can synchronize itself with the incoming bit stream. • Disadvantage: Nearly half of the time there will be two transitions during each bit. Hardware has to work twice as hard of that of NRZ encode signal. • Therefore it can be inefficient.

30. Manchester Encoding

31. Differential Manchester Encoding

32. Digital Data - Digital Signal Examples of four digital encoding schemes

33. Analog Data, Digital Signal • Digitization • Conversion of analog data into digital data • Digital data can then be transmitted using NRZ-L • Digital data can then be transmitted using code other than NRZ-L • Digital data can then be converted to analog signal • Analog to digital conversion done using a codec • Pulse code modulation • Delta modulation

34. Digitizing Analog Data

35. Analog Data, Digital Signal • Digitization • Conversion of analog data into digital data • Digital data can then be transmitted using NRZ-L • Digital data can then be transmitted using code other than NRZ-L • Digital data can then be converted to analog signal • Analog to digital conversion done using a codec • Pulse code modulation • Delta modulation

36. Digitizing Analog Data

37. Pulse Code Modulation(PCM) (1) • If a signal is sampled at regular intervals at a rate higher than twice the highest signal frequency, the samples contain all the information of the original signal. • Voice data limited to below 4000Hz • Require 8000 sample per second • Analog samples (Pulse Amplitude Modulation, PAM) • Each sample assigned digital value

38. Pulse Code Modulation(PCM) (2) • 4 bit system gives 16 levels • Quantized • Quantizing error or noise • Approximations mean it is impossible to recover original exactly • 8 bit sample gives 256 levels • Quality comparable with analog transmission • 8000 samples per second of 8 bits each gives 64kbps

39. Analog Data, Analog Signals • Why modulate analog signals? • Higher frequency can give more efficient transmission • Permits frequency division multiplexing • Types of modulation • Amplitude • Frequency • Phase

40. Analog Modulation

41. QUESTION?