1. Business Data Communications, Fourth Edition Chapter 2: Fundamentals of Data Communications Here, you’ll insert a graphic from the cover. This will come much closer to the BBD.

2. Learning Objectives Explain the concepts of bit rate, baud rate, frequency, and bandwidth Distinguish between digital and analog signals Describe the purpose of a modem and define three types of modems Define the data codes used in data communications Chapter 2: Fundamentals of Data Communications2

3. Learning Objectives Describe how a telephone works Describe the structure of the telephone network Describe the telephone numbering system in the United States Chapter 2: Fundamentals of Data Communications3

4. Introduction Data is transmitted from one point to another in data communications Data must be in an acceptable format Various forms of signals are used to transmit the data Telephone system is examined in this chapter Chapter 2: Fundamentals of Data Communications4

5. Signal Representation Signal – electrical charges or pulses of light Bit rate –Bit – smallest unit of information –Binary notation (1 or 0) or (on or off) –Data codes (ways to represent characters) Chapter 2: Fundamentals of Data Communications5

6. Signal Representation Bit rate –Byte (a character) –Bit rate (speed at which data is transmitted) –Bits per second (used to describe bit rate) Chapter 2: Fundamentals of Data Communications6

7. Chapter 2: Fundamentals of Data Communications7 Figure 2-1. Frequency spectrum.

8. Signal Representation Baud Rate –Baud (change in signal) –Baud rate (number of changes per second) –Voltage (+ and – charges) –Current (flow of electric charge) Chapter 2: Fundamentals of Data Communications8

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10. Signal Representation Baud Rate –Alternating current (AC) (electrical outlets) –Direct current (DC) (batteries) –Signals made up of more than 1 bit Dibit (signal made up of 2 bits) Tribit (signal made up of 3 bits) Used for transmission of large files Chapter 2: Fundamentals of Data Communications10

11. Signal Representation Frequency –Number of times the current goes through a cycle –Hertz (Hz) (measure of frequency) –Kilohertz (kHz) (1,000) –Megahertz (MHz) (1,000,000) –Gigahertz (GHz) (1,000,000,000) –Audio frequencies (lowest frequencies) –See Table 2-1 for list of frequencies Chapter 2: Fundamentals of Data Communications11

12. Signal Representation Bandwidth –Range of frequencies –BW = High frequency - Low frequency –Example: 2,500 Hz – 200 Hz = 2,300 Hz BW –Guardbands (prevents frequencies from interfering with each other) –Wider bandwidth means more data can be transmitted Chapter 2: Fundamentals of Data Communications12

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14. Digital Signals Versus Analog Signals Digital data –Discrete items (text, integers) Analog data –Continuous data (light, voice) Frequency modulation –Signal is changed based on the number of waves Process control computers –Process continuous (analog) data Chapter 2: Fundamentals of Data Communications14

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16. Digital Signals Versus Analog Signals Modems –Convert digital to analog and analog to digital –MOdulator/DEModulator –Internal Called a “card”, PC cards for laptops –External Sits on the desk next to the computer Connected by a cable Chapter 2: Fundamentals of Data Communications16

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18. Digital Signals Versus Analog Signals Modems –Modem speeds 9600 to 56,000 bps Table 2-2 shows modem costs –Data compression Transmits fewer characters, resulting in faster transmission speeds Example: V.42bis (32 chars. to 11 chars.) Maximum transmission rate is called the throughput Chapter 2: Fundamentals of Data Communications18

19. Digital Signals Versus Analog Signals Modems –Always used in pairs –Internet Service Providers Provide connection to users Has a permanent Internet connection –On-line services America OnLine, Microsoft Network, Yahoo Connection to Internet & other services Chapter 2: Fundamentals of Data Communications19

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21. Digital Signals Versus Analog Signals Modems –Bulletin Board System – for leaving messages –Cable Modem Maximum speeds of 40 Mbps (compare to 56Kbps) Higher speeds but at a higher cost than ISP –Modem eliminator (null modem) 50 feet or less 1,200 to 38,400 bps –Short-haul modem Up to 20 miles 1,200 to 9,600 bps depending on distance –Fax modem Sends fax through a computer Chapter 2: Fundamentals of Data Communications21

22. Data Codes General Description –Data codes represent characters –Rules for converting bits to characters –ASCII, EBCDIC, Unicode Chapter 2: Fundamentals of Data Communications22

23. Data Codes American Standard Code for Information Interchange (ASCII) –Standard ASCII – 7 bit code –Extended ASCII – 8 bit code –Special ASCII characters for data communications – Table 2-4 Chapter 2: Fundamentals of Data Communications23

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26. Data Codes Extended Binary-Coded Decimal Interchange Code (EBCDIC) –8-bit code Chapter 2: Fundamentals of Data Communications26

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28. Data Codes UNICODE –16-bit code –Supports up to 65,536 characters –Used for languages such as Chinese, Japanese, Korean –Includes mathematical, geometric and other symbols –Only used with OS that can display the codes Chapter 2: Fundamentals of Data Communications28

29. Telecommunications – Voice Communications Introduction –Good quality transmission medium –Telephone network components The Telephone –Converts human voice to electrical signal –Converters (does the conversion) –Transmitter and Receiver (both are converters) –Diaphragm vibrates to convert sound to electricity Telephone network supports many features Chapter 2: Fundamentals of Data Communications29

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32. Telecommunications – Voice Communications The Telephone Network –End office (aka central office, exchange office) –Local loop (connects home to end office) –Local exchange carrier (provides dial tone) –T-Carrier Circuits (1.5Mbps rate) Chapter 2: Fundamentals of Data Communications32

33. Telecommunications – Voice Communications Telephone calls –Local call (made within local end offices) Intraoffice call (same prefix) Interoffice call (different prefix) –Tandem office (handles calls within an area code, unit calls) –Toll offices (handles calls to a different area code) Chapter 2: Fundamentals of Data Communications33

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36. Telecommunications – Voice Communications The Telephone Network –Telephone lines Voice-grade circuits Multiplexing used to combine many calls on a single line (uses guardbands to separate calls) –Used by cable TV as well –Telephone signals Dial tone, ringing, busy, etc. Table 2-5 shows types of signals Chapter 2: Fundamentals of Data Communications36

37. Telecommunications – Voice Communications Telephone Numbering Systems –Direct distance dialing (DDD) –Area codes (expansion in 1995) –Exchange codes (prefix in phone number) –Country codes (identifies other country) –800 service (WATS, toll free) 888, 877, 866 are now also toll free –900 service (caller charged) –Dial around services (10-10-xxx numbers) Chapter 2: Fundamentals of Data Communications37

38. Summary Signals transmit information Data codes convert information Transmission speed Transmission capacity Digital versus analog data ASCII code, EBCDIC code, UNICODE Chapter 2: Fundamentals of Data Communications38

39. Summary Telephone network Quality of telephone lines Telephone numbering system Chapter 2: Fundamentals of Data Communications39

40. Communications Trailblazer John T. Chambers, Cisco Systems –Cisco sells routers & switches –Cisco is successful even when the economy is on a downturn –Chambers has received many awards –Previously at Wang labs and IBM –Has open communication with employees –Promotes tremendous loyalty among employees Chapter 2: Fundamentals of Data Communications40

41. Spotlight On Wireless Technology in Schools –Wireless technology now in grade and high schools as well as universities –Uses In classroom to do research Accessing courses on the Web PDAs to access e-mail, Internet, other users, to take notes –Higher Ed – Classroom on a cart Chapter 2: Fundamentals of Data Communications41

42. Chapter 2 Complete