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Topic 4 : I/O Devices & Networks

Topic 4 : I/O Devices & Networks. Computer Networks Reference : G & L pp 172-179. Connecting Devices and Computers. Computers and other devices can be connected using either serial or parallel communications. Serial and Parallel Communications. Parallel communications. Dest. Source.

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Topic 4 : I/O Devices & Networks

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  1. Topic 4 : I/O Devices & Networks Computer Networks Reference : G & L pp 172-179.

  2. Connecting Devices and Computers • Computers and other devices can be connected using either serial or parallel communications.

  3. Serial and Parallel Communications • Parallel communications. Dest. Source

  4. Serial and Parallel Communications • Parallel communications. 1 Dest. Source 0 1 0 1 0 0 0

  5. Serial and Parallel Communications • Parallel communications. 1 Dest. Source 0 1 0 1 0 0 0

  6. Serial and Parallel Communications • Parallel communications. 1 Dest. Source 0 1 0 1 0 0 0

  7. Serial and Parallel Communications • Parallel communications. 1 Dest. Source 0 1 0 1 0 0 0

  8. Serial and Parallel Communications • Serial communications Dest. Source 1010110

  9. Serial and Parallel Communications • Serial communications 1010110 Dest. Source

  10. Serial and Parallel Communications • Serial communications 1010110 Dest. Source

  11. Serial and Parallel Communications • Serial communications 1010110 Dest. Source

  12. Serial and Parallel Communications • Serial communications 1010110 Dest. Source

  13. Serial and Parallel Communications • Serial communications Dest. Source 1010110

  14. Serial and Parallel Communications • Computers and other devices can be connected using either serial or parallel communications. • Parallel communications only used over short distance because the bits get skewed across the lines.

  15. Computer Networks • Networking computers allows:- • enhanced communication • sharing of data • sharing of resources • Communications needed between other computers and i/o devices.

  16. Networking Hardware: The Connection • Computers can be connected using different communications medium:- • Fibre optic cable • Copper cable • Infrared • Radio

  17. Basic Properties of Communications Medium • Fiber optic • fast: upto 2.6 Gbps, cheap, uses patterns of light. • Copper cable • slower: upto 1 Gbps, cheap, uses changing signals on the line. • Infrared • slower still: upto 4 Mbs, only works indoors. • Radio • real slow outdoors: upto 19.2 Kps, uses changes in amplitude or frequency of radio signal.

  18. The Network Interface • This is the connection between the computer and the physical network. • Interface defines, for example, the signals and voltage levels applied to the network. • In the case of high-speed networks a dedicated card is used. • For networks requiring analogue signals we use a modem.

  19. Agreeing Communications • Imagine if we want to communicate with other people - what do we need to agree ?

  20. The Physical Layer • How do we send a signal ?

  21. Frequency Modulation • Change frequency to represent changes in data. 1

  22. Frequency Modulation • Change frequency to represent changes in data. 1 0

  23. Frequency Modulation • Change frequency to represent changes in data. 1 0 1 1

  24. Amplitude Modulation • Change the volume of the signal to represent changes in data,.

  25. Amplitude Modulation • Change the volume of the signal to represent changes in data,.

  26. The Link Layer • How do we check/correct errors ?

  27. The Link Layer • How do we check/correct errors ? OR

  28. The Network Layer • How do we know who the message is for and how to deliver it ?

  29. The IP Protocol • The infamous IP protocol. • Basis for ‘the net’. • All machines addressed in the form of: 148.88.152.26 • domain, net, subnet, host

  30. The Transport layer • How do we keep things in the correct order ? • Example protocols: TCP and UDP.

  31. The Session Layer • How do we start and stop a conversation ?

  32. The Presentation Layer • How do we interpret the contents of the message ? &

  33. The Presentation Layer • How do we interpret the contents of the message ? A &

  34. The Application Layer • Are there application level conventions ? email destination email source message type message data

  35. Networks and Protocols • A protocol specifies how the system copes with all the considerations we have discussed. • Therefore, a networked computer system comprises hardware to physically interconnect the machines and hardware/software which implements a particular protocol.

  36. The Internet • A collection of heterogeneous machines and networks linked by a common set of protocols, i.e. IP + TCP or UDP. • Growing at an unbelievable rate - much of the world now covered. • Most campus machines are connected so you can send/receive email etc.

  37. Summary • Looked at applications of computer networks. • Characteristics of different communications medium. • Serial and parallel communications. • Modulation techniques. • Different issues in computer network and protocol design.

  38. Coming Next Week • Performance. Computer Architecture Design and Performance, Barry Wilkinson

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