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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.

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computer networks

Computer Networks

IGCSE ICT Section 4



To be acquainted with:

  • The definitions of networking
  • Network topology
  • Network peripherals, hardware and software
network definition
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.
advantages of networking
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.
disadvantages of networking
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.
computers on a network
Computers on a network
  • Computers connected together to create a network fall into two categories:
      • servers andclients (workstations).
  • Client computers are thenormal computersthat people sit at and get theirworkdone.
  • Servers are special, powerful computers that provide ‘services’ to the clientcomputers 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

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.
types of networks
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 cablesor low-power radio (wireless) for the connections.
types of network
Types of Network

Wireless Local Area Network (WLAN)

  • A wireless LAN (WLAN) is a LAN that usesradio 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.
types of networks1
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.
sample questions
Sample Questions
  • What is the difference between a LAN and a WAN ?
  • Give(a) one example of a LAN and

(b) one example of a WAN.

  • Describe two advantages that a network has over a set of stand-alone computer systems.
  • What is the purpose of (a) a file server and (b) a printer server.
network hardware
  • In order for a computer to operate on a network, there are a range of different hardware components that are required.
1 network interface card nic

Network Hardware

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.
2 network cables

Network Hardware

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).
3 hubs

Network Hardware

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.

4 switches

Network Hardware

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.
5 routers

Network Hardware

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).

6 bridges

Network Hardware

6. Bridges
  • A bridge is a network device that linkstogether 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.
7 proxy servers

Network Hardware

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.

8 firewalls

Network Hardwares

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 unauthorizedconnections 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.