ICSA 411 Data Communication

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ICSA 411Data Communication Networking

• Elizabeth Lane Lawley, Instructor

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Nuts Bolts

• Introductions
• Review of syllabus
• Discussion of projects
• Discussion of FirstClass

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Data Information

• What is data?
• Elements that can be represented by a finite set
  of symbols, such as digits or alphabets
• What is information?
• a tangible, measurable thing
• a subjective construction

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What Is Communication?

• Symbolic
• Representational
• The map is not the territory, the thing is not
  the thing named.
• Communication is only as good as the
  representation
• Examples
• spoken language, gestures, actions, icons

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Human Communication v. Data Communication

• Human communication is richer, less predictable
• Words vary in meaning with context
• Many factors influence meaning and perception of
  message
• Data communication is more precise
• Exact replication of information
• Computers do not interpret, they simply relay
• Simple model SMCR

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The IT Perspective

• In CS/EE, only the successful transmission of
  data is important
• In IT, the conversion of data into information is
  also important

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Communication Limitations

• Time
• Distance
• Senses

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Telecommunication

• Uses electricity to transmit messages
• Speed of electricity dramatically extends reach
• Sound waves 670 mph
• Electricity 186,000 (speed of light)
• Bandwidth information-carrying capacity of a
  channel

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Data Communication

• Adding storage overcomes time constraints
• Store-and-forward communication
• E-mail, voice mail, facsimile, file transfer, WWW

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Analog Data

• Continuous signal
• Expressed as an oscillation (sine wave format) of
  frequency
• Example Analog electrical signal generated by a
  microphone in response to continous changes in
  air pressure that make up sounds

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Basic Analog Terms

• Wave frequency Number of times a cycle occurs in
  given time period
• Wave amplitude Height of a wave cycle
• Hertz The number of times a wave cycle occurs in
  one second (commonly used measure of frequency)

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Analog Signaling

• represented by sine waves

phase difference
1 cycle
amplitude (volts)
time
(sec)
frequency (hertz)
cycles per second
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Digital Data

• Represented as a sequence of discrete symbols
  from a finite alphabet of text and/or digits
• Rate and capacity of a digital channel measured
  in bits per second (bps)
• Digital data is binary uses 1s and 0s to
  represent everything
• Binary digits can be represented as voltage pulses

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Basic Digital Terms

• Bit digit in a binary number
• 1 is a 1-bit number (1 in base 10)
• 10 is a 2-bit number (2 in base 10)
• 10011001 is an 8-bit number (153 in base 10)
• Byte eight bits

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VIViD Communication

• Voice
• Image
• Video
• Data

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Converting Voice

• What makes sound? Vibration of air
• How can we record that vibration?
• How can we convert that to an electrical signal?

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Analog Voice Communication

• Primarily used for transmission of human voice
  (telephony)
• Microphone captures voice vibrations, converts
  them to waves than can be expressed through
  variations of voltage
• Examples
• Telephone (3000Hz)
• Hi-Fi Sound (15,000Hz approximate range of human
  ear)
• Compact Disc (20,000Hz for each of two channels)

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Digital Voice Communication

• For good representation, must sample amplitude at
  a rate of at least twice the maximum frequency
• Measured in samples per second, or smp/sec
• Telephone quality 8000smp/sec, each sample using
  8 bits
• 8 bits 8000smp/sec 64kbps to transmit
• CD audio quality 44000smp/sec, each sample using
  16 bits
• 16 bits 44000smp/sec 1.41mbps to transmit
  clearly

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Converting Images

• Break image up into small units
• More units means more detail
• Units called pixels
• Use photocell to read each unit, assign value
• How can we represent those units electrically?
• PACMAN example

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Image Quality Issues

• More pixelsbetter quality
• More compressionreduced quality
• Lossy gives from 101 to 201 compression
• Lossless gives less than 51
• Less compressionreduced speed of transfer
• Choices in imaging technology, conversion, and
  communication all affect end-users satisfaction

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Video Communication

• Sequences of images over time
• Same concept as image, but with the dimension of
  time added
• Significantly higher bandwidth requirements in
  order to send images (frames) quickly enough
• Similarity of adjacent frames allows for high
  compression rates

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Data Communication

• In this context, we mean data stored on computers
• Already digital, so no conversion necessary
• Bandwidth usually affects speed, but not quality
• Examples?

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Bandwidth Requirements

• Review chart on page 27
• What happens when bandwidth is insufficient?
• Poor quality or slow transmission
• How long does it take to become impatient?
• Is data communication ever fast enough?