Transcript Computer Networks

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Compiled by Mr. Benjamin Muganzi
Computer Networks
IGCSE ICT Section 4
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Compiled by Mr. Benjamin Muganzi
Introduction
Objective:
To be acquainted with:
• The definitions of networking
• Network topology
• Network peripherals, hardware and software
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Network Definition
• A network can be defined as two or more computers connected
together in such a way that they can share resources.
• The purpose of a network is to share resources.
• A resource may be:
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A file
A folder
A printer
A disk drive Or
just about anything else that exists on a computer.
• A network is simply a collection of computers or other hardware
devices that are connected together, either physically or logically,
using special hardware and software, to allow them to exchange
information and cooperate.
• Networking is the term that describes the processes involved in
designing, implementing, upgrading, managing and otherwise
working with networks and network technologies.
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Advantages of Networking
• Computers can communicate and share data and
files.
• Storage facilities, and other hardware peripherals
such as printers can be shared.
• Data from all the computers can easily be backed
up centrally.
• Communication with other network users (email, instant messaging, video-conferencing, etc.)
is possible.
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Disadvantages of networking
• A computer on a network is vulnerable
to hackers
• If the network breaks, many tasks become very
difficult
• Your computer can more easily be attacked by
a virus
• Installing a network is expensive as it involves
purchasing of networking hardware such as Hubs,
cables, network cards, bridges, routers etc.
• Large networks require specialist to maintain
them, which again involves time and money.
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Computers on a network
• Computers connected together to create a
network fall into two categories:
• servers and clients (workstations).
• Client computers are the normal computers
that people sit at and get their work done.
• Servers are special, powerful computers that provide
‘services’ to the client computers on the network.
These services might include:
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Providing a central, common file storage area
Sharing hardware such as printers
Controlling who can or can’t have access the network
Sharing Internet connections
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Servers
There are different types of servers, e.g.
 File servers, which allow users to save and load
data/files
 Application servers, which allow distribution of
application software to each computer
 Printer server, which ensures that printing on a
network is done in a queue.
 Proxy server, which is used as a buffer between
WAN and LAN.
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Types of Networks
Local Area Network
 A local area network (LAN) is a computer network
covering a small geographical area, like a home,
office, or small group of buildings, such as a school, or
an airport.
 Often a LAN is a private network belonging to an
organization or business.
 Because LANs are geographically small, they usually
use cables or low-power radio (wireless) for the connections.
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Types of Network
Wireless Local Area Network (WLAN)
• A wireless LAN (WLAN) is a LAN that uses radio
signals (WiFi) to connect computers instead of cables.
 It is much more convenient to use wireless connections instead
of running long wires all over a building.
 However, WLANs are more difficult to make secure since other
people can also try to connect to the wireless network. So, it is
very important to have a good, hard-to-guess password for the
WLAN connections.
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Types of networks
Wide Area Network (WAN)
• A Wide Area Network is a network that
extends over a large area.
• A WAN is often created by joining several
LANs together, such as when a business that
has offices in different countries links the
office LANs together.
• The largest and most well known WAN is the
Internet.
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LAN, WAN and WLAN
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Sample Questions
1. What is the difference between a LAN and a WAN ?
1. Give
(a) one example of a LAN and
(b) one example of a WAN.
3. Describe two advantages that a network has over a
set of stand-alone computer systems.
4. What is the purpose of
(a) a file server and
(b) a printer server.
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NETWORK HARDWARE
• In order for a computer to operate on a
network, there are a range of different
hardware components that are required.
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Network Hardware
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1. Network Interface Card (NIC)
• Any computer that is to be connected to a network,
needs to have a network interface card (NIC).
• Modern computers have inbuilt NICs. However you
can also add an expansion NIC card.
• Most laptops have two inbuilt NICs; one for the
wireless network, and another for the wired
network.
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Network Hardware
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2. Network cables
• They are used to connect different devices
together.
• Cables are still used in most networks, rather
than using only wireless, because
• they can carry much more data per second,
• They are more secure (less open to hacking).
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Network Hardware
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3. Hubs
• A hub is a hardware device that connects multiple computers
together in a network and allows them to share data packets.
• Each computer will be connected to a single 'port' on the hub.
• The typical use of a hub is at the centre of a star network
• A hub is a ‘dumb’ device: if it receives a message, it sends it to
every computer on the network.
• This means that hub-based networks are not very secure everyone can listen in to communications.
These days hubs are not
common. They have
been replaced by
switches.
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Network Hardware
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4. Switches
• A switch is a more advanced form of a hub.
• It is a more ‘intelligent’ device than a hub
 If it receives a message, it checks which computer
it is addressed to, and only sends it to that specific
computer.
• Because of this, networks that use switches are more
secure than those that use hubs,
• Switches are a little more expensive.
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Network Hardware
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5. Routers
• A router is a network device that connects
together two or more networks.
• It transfers data from between the networks
in an intelligent way; i.e. it forwards data
packets to their destination using the most
efficient route.
A common use of a router
is to join a LAN to the
Internet (WAN).
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Network Hardware
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6. Bridges
• A bridge is a network device that links
together two different parts of a LAN.
• It allows a large network to be segmented into
two LANs to reduce traffic being passed
around the network.
• The linked LANs act as if it is one LAN.
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Network Hardware
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7. Proxy servers
• A proxy server is a computer setup to share a resource,
usually an Internet connection.
• It keeps a copy of often-used web pages in its local 'cache'.
• If a client computer requests for a web site then the proxy
server checks to see if it has a copy - if it does, then that local
page is sent to the client and there is no need to use up
bandwidth calling for it over the internet
A proxy server can also act as a
data filter, only allowing data
packets that conform to
company policy. E.g. blocking
certain websites at certain
times.
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Network Hardwares
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8. Firewalls
• A firewall is a device, or a piece of software that is placed
between a computer/LAN and the rest of the network to
block unauthorized connections being made to your
computer/LAN.
 Normal data is allowed through the firewall (e.g. e-mails or web pages)
but other suspicious data is blocked.
• If you wish to protect your LAN from hackers out on the
Internet, you would place a firewall between the LAN and the
Internet connection.