Business Data Communications, Fourth Edition

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 Communications 2

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 Communications 3

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 Communications 4

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 Communications 5

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 Communications 6

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

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 Communications 8

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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 Communications 10

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 Communications 11

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 Communications 12

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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 Communications 14

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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 Communications 16

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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 Communications 18

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 Communications 19

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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 Communications 21

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

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 Communications 23

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

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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 Communications 28

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 Communications 29

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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 Communications 32

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 Communications 33

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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 Communications 36

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 Communications 37

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 Communications 38

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

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 Communications 40

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 Communications 41

42. Chapter 2 Complete