• Compression:
    • data encoded using algorithms
    • encoding data using fewer bits
    • makes it move faster
    • reduces resource usage —> bandwidth wise
    • however requires hardware/software
    • less bits per second —> have to get rid of information because not enough storage
  • Characteristics of data
    • importance of data / sensitivity — safety (encryption)
    • speed
    • cost
    • transmission reliability
    • hardware:
      • ethernet cable / wireless
      • device with NIC (Network Interface Controller)
      • modem
      • router
  • Decompression Software
    • evaluate different types of decompression software
  • Lossless
    • data compressed without loosing any data
    • decompression — every bit remembered
    • identifies and eliminates redundancy
    • When used?
      • for important data —> like spreadsheets about money, sound, etc.
  • Lossy
    • gets rid of unnecessary information
    • part of data lost — used when this loss not prominent
    • When used?
      • for data not as important, or where difference not needed
        • e.g. YouTube videos
  • Real World Situations
    • (team speak)
    • allowed fast transferring of data via the internet, thus news shared immediately —> able to interfere with “history"
    • however, now everybody uploading —> clogs internet with useless stuff
    • makes information move more rapidly
      • more comfortable
  • .raw — plain data
    • dataloss depends on file format
    • seeing it depends on raw file
    • gif can only take 265 colours —> gif compression reduces amount of colours
    • jpeg —> at lowest quality —> pixelated —> takes 8x8 pixel squares and takes average colour —> stores difference between average and real
  • audio
    • mp3 — filters out frequency that doesn’t interfere with perception of sound
      • if bits per second reduced, then sound like robot
  • 3.1.8 Explain why the speed of data transmission across a network can vary.
    • many users transmitting at the same time — bandwidth reduced
    • interference from outside causing corruption of packets —retransmission needed
  • 3 3.1.9 Explain why compression of data is often necessary when transmitting across a network. 3 S/E, INT Compression has enabled information to be disseminated more rapidly.
    • compression —> faster transmitting
    • however, also more data transmitted now thus need compression to get all things across
  • EXAMPLES
    • gif
      • only stores 256 colours
      • has a zip compression in it (checks for redundancy)
      • diffusion —foggy/unclear
      • pattern — patterned —> usually nicer
    • jpeg
      • almost similar but only about 10% file size of original
      • takes 8 by 8 pixels calculates average and stores average and then difference between original and average
    • digital cameras
      • file format big


Created By: Lucie Magister
Last update: 19/03/2015

Sources:
  • Classnotes.