Fundamentals of Data Communications

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Chapter 2

• Fundamentals of Data Communications

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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
• Define the data codes used in data communications

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Learning Objectives

• Describe the structure of the telephone network
• Describe the difference between a switched and
  dedicated circuit

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Introduction

• Data is transmitted from one point to another
• Data must be in acceptable format
• Errors must be detected and corrected
• Telephone system examined

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Signal Representation

• Bit rate
• Bit - smallest unit of information
• Binary notation
• Data codes
• Byte
• Bit rate
• Bits per second

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Signal Representation

• Baud Rate
• Baud
• Current
• Alternating current (AC)
• Direct current (DC)
• Dibit
• Tribit

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Signal Representation

• Frequency
• Number of times current goes through a cycle
• Hertz (Hz)
• Kilohertz (KHz)
• Megahertz (MHz)
• Gigahertz (GHz)
• Audio frequencies

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Signal Representation

• Bandwidth
• Range of frequencies
• BW High frequency - Low frequency
• Guardbands

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Digital Signals Versus Analog Signals

• Digital data
• Analog data
• Frequency modulation
• Process control

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Digital Signals Versus Analog Signals

• Modems
• MOdulator/DEModulator
• Internal vs. external

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Digital Signals Versus Analog Signals

• Modems
• MOdulator/DEModulator
• Internal vs. external
• PC cards
• Modem speeds
• PC to server connection

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Digital Signals Versus Analog Signals

• Modems
• MOdulator/DEModulator
• Internal vs. external
• PC cards
• Modem speeds
• PC to server connection
• Internet Service Providers
• On-line services

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Digital Signals Versus Analog Signals

• Modems
• Modem eliminator (null modems)
• Short-haul modem
• Fax modem

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Data Codes

• General Description
• Data codes represent characters
• Rules for converting bits to characters

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Data Codes

• American Standard Code for Information
  Interchange (ASCII)
• Standard ASCII - 7 bit code

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Data Codes

• American Standard Code for Information
  Interchange (ASCII)
• Standard ASCII - 7 bit code
• Extended ASCII - 8 bit code

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Data Codes

• American Standard Code for Information
  Interchange (ASCII)
• Standard ASCII - 7 bit code
• Extended ASCII - 8 bit code
• Special ASCII characters

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Data Codes

• American Standard Code for Information
  Interchange (ASCII)
• Standard ASCII - 7 bit code
• Extended ASCII - 8 bit code
• Special ASCII characters
• Extended Binary-Coded Decimal Interchange Code
  (EBCDIC)
• 8-bit code

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UNICODE

• 16-bit code
• Support 65,536 characters
• Used for languages with many characters
• Not all operating systems support UNICODE

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Telecommunications - Voice Communications

• Introduction
• Good quality transmission medium
• Telephone network components
• The Telephone
• Converts human voice to electrical signal
• Converters

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Telecommunications - Voice Communications

• Introduction
• Good quality transmission medium
• Telephone network components
• The Telephone
• Converts human voice to electrical signal
• Converters
• Transmitter and Receiver

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Telecommunications - Voice Communications

• Introduction
• Good quality transmission medium
• Telephone network components
• The Telephone
• Converts human voice to electrical signal
• Converters
• Transmitter and Receiver
• Touch-Tone/Rotary phones

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Telecommunications - Voice Communications

• The Telephone Network
• End office

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Telecommunications - Voice Communications

• The Telephone Network
• End office
• Local loop
• Circuits
• Telephone calls
• Tandem office

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Telecommunications - Voice Communications

• The Telephone Network
• End office
• Local loop
• Circuits
• Telephone calls
• Tandem office
• Long-distance calls
• Toll offices

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Telecommunications - Voice Communications

• The Telephone Network
• Telephone lines
• Voice-grade circuits
• Multiplexing
• Telephone signals

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Telecommunications - Voice Communications

• Telephone Numbering Systems
• Direct distance dialing (DDD)
• Area codes
• Exchange codes
• Country codes
• 800 service
• 900 service

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Summary

• Signals transmit information
• Data codes convert information
• Transmission speed
• Transmission capacity
• Digital versus analog data
• ASCII code, EBCDIC code

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Summary

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

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EndChapter 2