Communication and internet technologies

  • Created by: Alexia
  • Created on: 11-12-18 09:55
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  • Communication
    • Data transmission
      • Simplex
        • 1 direction only
      • Half-duplex
        • 2 directions but NOT at the same time
      • Full-duplex
        • 2 directions at the same time
      • Serial
        • data is sent one bit at a time over a single wire
      • Parallel
        • several bits of data are sent down several wires at the same time
      • Universal Serial Bus (USB)
      • Asynchronous
        • data being transmitted is in a pattern - start and stop bit
      • Synchronous
        • continuous stream of data - timing signals generated by an internal clock
    • Error Checking
      • Parity Checks
        • even or odd (number of bits) - PARITY BITS
        • The blocks identify an erroneous (corrupted) bit
        • Cannot identify all errors
          • If the byte hasn't changed but there still is an error
      • Checksum
        • The checksum is sent at the end of the block
        • Based on the number of bytes in the block
        • Data is sent in blocks
        • An error in transmission if the check sums don't match at both ends
      • Echo check
        • Data is returned to the sender
          • Who compares the data sent with the data received
        • If the data is different - transmission error
      • Automatic Repeat Request (ARQ)
        • Uses an acknowledgement to indicate data received correctly
        • A timeout is used - time allowed to elapse before an acknowledgement is received
    • Internet Technologies
      • Internet Service Provider
        • Provides the user with access to the internet - feeed
      • Internet Protocol (IP) address
        • Untitled
      • Media Access Control address (MAC)
        • uniquely identifies a device connected to the internet
      • HTML
        • Structure: part of HTML documents: includes semantics and structural mark-up of documents
        • Presentation: style of the document
      • Hypertext Transfer Protocol (http)
        • rules that must be obeyed when transferring files across the internet

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