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2011-05-26 17:59:37
Computing fundamentals

data transmission
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  1. Local Area Network (LAN)
    • machines are close together
    • connected together using cables or wireless
    • data is more secure
    • high data transfer rates
    • e.g. in schools, at home
    • hardware: fibre optics, network interface card, server
    • software: network operation system
  2. Wide Area Network (WAN)
    • spread more remotely
    • uses communication system
    • long distance communication technologies
    • e.g. the internet
    • hardware: modem, router
    • software: browser, firewall
  3. Data transmission: serial
    send the byte, one bit at a time, through a single wire
  4. Data transmission: parallel
    uses a number of wires, one for each of the bits in the byte
  5. Data transmission: simplex
    one way data communication
  6. Data transmission: half-duplex
    data can only be sent in one direction at a given time
  7. Data transmission: duplex
    bidirectional data communication
  8. Time sensitivity
    • more wires connecting devices, the more data that can be transmitted in a given period of time
    • bit rate- number of bits that can be transmitted within a timeframe, measured in baud
  9. Echoing back
    • send data back to the sending device
    • compares the data to what was sent
    • if they match it is OK
    • if different, the data is sent again
  10. Check sums
    • data sent is made up of binary numbers
    • original bytes added together and answer sent with data
    • when reached destination checksum is worked out
    • if numbers are differnet the data is resent
  11. Parity check
    • data sent is in fixed bytes
    • eighth bit as parity bit
    • number of 1's have to be the same after as before
  12. Packet switching
    • transmission across a network
    • groups data
    • packets sent any route
    • packets have to be rearranged
  13. Circuit switching
    • uses a dedicated route
    • very fast rates
    • packets sent along in order
  14. Protocol
    • a set of rules that govern the transmission of data
    • Handshake Signal: Sent from one device and acknowledged by the other. This states that both are now ready for communication. Unless both device follow the same rules, there can be no connection
    • Logical: Baud Rate (Compression type), Error correcting technique (file type), Routing (packet size), Flow Control, Synchronisation, Rules governing data
    • Physical: wired, and data can be transferred by either serial or parallel transmission. The data transmission will have different frequencies depending on whether it is wireless or wired.

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