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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. Learning Objectives. Explain the concepts of bit rate, baud rate, frequency, and bandwidth

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business data communications fourth edition

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.

learning objectives
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

learning objectives1
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

introduction
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

signal representation
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

signal representation1
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

slide7

Figure 2-1. Frequency spectrum.

Chapter 2: Fundamentals of Data Communications 7

signal representation2
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

signal representation3
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

signal representation4
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

signal representation5
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

digital signals versus analog signals
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

digital signals versus analog signals1
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

digital signals versus analog signals2
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

digital signals versus analog signals3
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

digital signals versus analog signals4
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

data codes
Data Codes
  • General Description
    • Data codes represent characters
    • Rules for converting bits to characters
    • ASCII, EBCDIC, Unicode

Chapter 2: Fundamentals of Data Communications 22

data codes1
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

data codes2
Data Codes
  • Extended Binary-Coded Decimal Interchange Code (EBCDIC)
    • 8-bit code

Chapter 2: Fundamentals of Data Communications 26

data codes3
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

telecommunications voice communications
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

telecommunications voice communications1
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

telecommunications voice communications2
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

telecommunications voice communications3
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

telecommunications voice communications4
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

summary
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

summary1
Summary
  • Telephone network
  • Quality of telephone lines
  • Telephone numbering system

Chapter 2: Fundamentals of Data Communications 39

communications trailblazer
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

spotlight on
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