Data communication basics


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  • Easy to add extra computers . If computer goes down it doesn’t affect rest of network
  • Data communication basics

    1. 1. <ul>Communications Systems </ul>
    2. 2. <ul>5 Basic Components </ul><ul>Communications Systems </ul><ul>Every communication system has 5 basic requirements </ul><ul><li>Data Source (where the data originates)
    3. 3. Transmitter (device used to transmit data)
    4. 4. Transmission Medium (cables or non cable)
    5. 5. Receiver (device used to receive data)
    6. 6. Destination (where the data will be placed) </li></ul>
    7. 9. <ul>Data is transmitted, on a single channel, one bit at a time one after another - Much faster than parallel because of way bits processed (e.g. USB and SATA drives) </ul><ul>Serial Transmission </ul><ul>Sender transmitted </ul><ul>Receiver received </ul><ul>1 </ul><ul>0 </ul><ul>1 </ul><ul>0 </ul><ul>0 </ul><ul>1 </ul><ul>1 </ul><ul>0 </ul>
    8. 10. <ul>Receiver received </ul><ul><li>each bit has it’s own piece of wire along which it travels </li></ul><ul>- often used to send data to a printer </ul><ul>Parallel Transmission </ul><ul>Sender transmitted </ul><ul>All bits are sent simultaneously </ul><ul>1 </ul><ul>0 </ul><ul>0 </ul><ul>1 </ul><ul>1 </ul><ul>0 </ul><ul>0 </ul><ul>1 </ul>
    9. 11. <ul>Why Not use Parallel Instead of serial? </ul><ul><li>Due to inconsistencies on channels data arrives at different times
    10. 12. Because of the way it is transmitted packet switching cannot be used
    11. 13. The above two points makes parallel slower than serial and requires higher bandwidth.
    12. 14. Parallel transmissions are rarely used anymore </li></ul>
    13. 15. <ul>Synchronous Transmission all data sent at once and no packet switching Asynchronous Transmission </ul><ul><li>Uses stop/ start bits
    14. 16. most common type of serial data transfer
    15. 17. Allows packet switching
    16. 18. Allows sharing of bandwidth (i.e. talk on phone while another person is using internet) </li></ul><ul>Synchronous Vs Asynchronous Transmissions </ul>
    17. 19. <ul>Start and Stop Bits </ul><ul><li>In the asynchronous method, each character is placed between start and stop bits ( framing ) </li></ul><ul>Framing ASCII ‘A’ (41H) </ul><ul>LSB </ul><ul>MSB </ul>
    18. 20. <ul>Data Transfer Rate </ul><ul><li>Rate of data transfer: bps (bits per second)
    19. 21. Another widely used terminology for bps is baud rate
    20. 22. For Asynchronous serial data communication, the baud rate is generally limited to 100,000bps </li></ul>
    21. 23. <ul>- simplex: One direction only </ul><ul>Transmission Direction </ul>
    22. 24. <ul>Half Duplex Transmission </ul><ul>half duplex: Both directions but only one direction at a time </ul>
    23. 25. <ul>Full Duplex Transmission </ul><ul>full duplex: send and receive both directions at once </ul>
    24. 26. Computer Networks and Topologies
    25. 27. <ul><li>A network is a number of computers and
    26. 28. peripheral devices connected together so as to
    27. 29. be able to communicate (i.e. transfer data)
    28. 30. Each device in a network is called a node.
    29. 31. Terminals are data entry points which can also
    30. 32. display. </li></ul><ul>What is a Network? </ul>
    31. 33. <ul>Advantages </ul><ul>- Easy to set up and maintain failure of one node does not affect network </ul><ul>Disadvantages </ul><ul><li>Higher rate of data collision than with a bus network
    32. 34. fails if there is any damage to the bus </li></ul><ul>A bus is a form of Ethernet. Nodes linked by a cable known as the bus. Bus transmits in both directions and uses CSMA/CD protocol </ul><ul>BUS TOPOLOGY </ul>
    33. 36. Ethernet <ul><li>Developed at Xerox in 1976.
    34. 37. First protocol approved as an industry standard protocol 1983
    35. 38. LAN protocol used on bus and star
    36. 39. Most popular LAN protocol
    37. 40. Inexpensive </li></ul>
    38. 41. <ul>Uses an empty data packet called a token and a special protocol called “token ring”. Packets travel around the ring in a clockwise direction. Clients require an empty token to transmit data. </ul><ul>Advantages </ul><ul>- no collisions because all data travels in same direction. </ul><ul>Disadvantages </ul><ul>- fails if an individual node in the network fails </ul><ul>Ring Topology </ul>
    39. 42. <ul>All data is sent from one client to another through the server. </ul><ul>Advantages </ul><ul>- If one client fails no other clients are affected. </ul><ul>Disadvantages </ul><ul>- If central file server fails the network fails. </ul><ul>Star Topology </ul>