computer networks
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Computer Networks. IGCSE ICT Section 4. Introduction. Objective: To be acquainted with: The definitions of networking Network topology Network peripherals, hardware and software. Network Definition. - PowerPoint PPT PresentationTRANSCRIPT
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Computer Networks
IGCSE ICT Section 4
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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:
• 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 (e-mail, 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 computersthat 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:• 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
LAN
WLAN
WAN
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Sample Questions1. What is the difference between a LAN and a WAN ?
2. 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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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.
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).
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.
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.
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).
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.
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.
Network Hardware
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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.
Network Hardwares