Topic 4 : IO Devices

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Topic 4 I/O Devices Networks

• Computer Networks
• Reference G L pp 172-179.

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Connecting Devices and Computers

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

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Serial and Parallel Communications

• Parallel communications.

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Serial and Parallel Communications

• Parallel communications.

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Serial and Parallel Communications

• Parallel communications.

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Serial and Parallel Communications

• Parallel communications.

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Serial and Parallel Communications

• Parallel communications.

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Serial and Parallel Communications

• Serial communications

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Serial and Parallel Communications

• Serial communications

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Serial and Parallel Communications

• Serial communications

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Serial and Parallel Communications

• Serial communications

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Serial and Parallel Communications

• Serial communications

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Serial and Parallel Communications

• Serial communications

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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.

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Computer Networks

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

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Networking Hardware The Connection

• Computers can be connected using different
  communications medium-
• Fibre optic cable
• Copper cable
• Infrared
• Radio

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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.

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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.

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Agreeing Communications

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

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The Physical Layer

• How do we send a signal ?

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Frequency Modulation

• Change frequency to represent changes in data.

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Frequency Modulation

• Change frequency to represent changes in data.

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Frequency Modulation

• Change frequency to represent changes in data.

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Amplitude Modulation

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

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Amplitude Modulation

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

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The Link Layer

• How do we check/correct errors ?

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The Link Layer

• How do we check/correct errors ?

OR
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The Network Layer

• How do we know who the message is for and how to
  deliver it ?

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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

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The Transport layer

• How do we keep things in the correct order ?
• Example protocols TCP and UDP.

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The Session Layer

• How do we start and stop a conversation ?

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The Presentation Layer

• How do we interpret the contents of the message ?

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The Presentation Layer

• How do we interpret the contents of the message ?

A

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The Application Layer

• Are there application level conventions ?

email destination email source message
type message data
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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.

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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.

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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.

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Coming Next Week

• Performance.
• Computer Architecture Design and Performance,
  Barry Wilkinson