Computer networks 2 A Informatica prof.sse ALLEMANI e CARUSO

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Computer networks2 A Informatica prof.sse
ALLEMANI e CARUSO
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Yesterday.

• Central architecture

Before the coming of the PC, the common
architecture was made up of a central computer -
the only one with a processing capability with
some stupid terminals.
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Today

• Several computers linked in a network, with
  indipendent processing capability, which share
  resources and provide services

networks of networks
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What is a network?

• A computer network is a group of computers linked
  together by means of cables or aerials which
  communicate data and share resources through a
  series of protocols and rules.

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Why a network?

• It is possible
• To share expensive peripherals, such as printers,
  scanner, plotter.
• To send data to users without any other support.
  Moreover there are fewer restrictions concerning
  the size of the file which can be transferred
  through a network.
• To centralize fundamental programs. Sometimes
  users must be allowed to access the same program,
  in order to work on it simultaneously.
• To create automatic backup systems of files.

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Network classification

• Typology ( distance among computers )
• Topology (geometric shape used to create the
  network )

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Network Typologies

• LAN (Local Area Network ) (1m 2km)it is a
  network in a restricted area, such as an office
  room, a building or a campus
• MAN (Metropolitan Area Network ) ( 2km - 10Km
  )it is a network made of groups of devices or
  LANs linked by a phone line or other types of
  cables in a large geographical area, such as a
  town.
• WAN (Wide Area Network ) it is a network
  made of the devices which let the connection of
  LANs and MANs over a large geographical area, or
  even around the world ( an example is the
  Internet ).

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Network Topologies
Bus
Ring
Star
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BUS Topology

• Each node is connected one right after the other
  along the same backbone. Information sent from a
  node travels along the backbone until it reaches
  its destination node. All the computers can
  communicate with each other without having to go
  through the server.
• Advantages A computer or device that has gone
  down does not affect the others.
• Disadvantages It cannot connect a large number
  of computers.

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RING Topology

• It connects the computers and other devices one
  to the other in a circle.
• There is no central hub that holds all the data.
• Communication flows in one direction around the
  ring.
• Advantages It requires less cabling and so it is
  less expensive.
• Disadvantages If one node goes down, it takes
  down the whole network.

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STAR Topology

• The computers are connected to a central device
  called hub.
• The hub takes a signal that comes from any node
  and passes it along to all the other nodes in the
  network.
• Advantages
• -It gives close control of data
• -Each PC sees all the data
• -If a computer (not the hub) fails, no other
  computer is affected
• Disadvantages If the hub or its software goes
  down, the whole network is down.

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What is the Internet?

• The Internet is a network of networks, which
  links computers able to share information and
  resources with one another.
• The Internet can be defined as a mean of
  transport for the information and resources
  which are inside the computers.
• The Internet has been compared to a motorway.
• The Internet itself does not contain any
  information it is wrong to say that a document
  has been found in the Internet or on the
  Internet. It would be better to say that it has
  been found through the Internet or using the
  Internet.

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Internet Services

• The computers connected to the Internet can take
  advantage of several services
• E- MAIL It allows you to send and receive
  e-mails and to access to a forum.
• FTP (File Transfer Protocol) It allows you to
  have a quick access to a file in another
  computer, save on your computer and vice versa.
• WWW (World Wide Web) - You must not confuse the
  Internet with WWW this is only a part of the
  Internet.

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What is the World Wide Web?

• The World Wide Web is a global network of
  computers. This means that all the computers
  which belong to this global network ( the web )
  can share data and information.
• The computers must use a common language, in
  order to understand each other.
• The common language used by all the computers in
  the web is ruled by the standard protocol HTTP.

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How does the World Wide Web work?

• The information are stored in documents called
  web pages.
• The web pages are files placed into computers
  called web server.
• The computers which read the pages stored into
  web servers are called web client.
• The web clients show the user the web pages, by
  using a program called web browser.

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How does the browser show the web pages?

• The web pages stored into web servers are written
  in a standard language the HTML.
• The pages written in html contain the
  instructions for the browser in order to be
  correctly shown.