CIE IGCSE ICT module 4 revision

An ISP is an INTERNET SERVICE PROVIDER. An ISP is a company which provides users with access to the INTERNET. 

A ROUTER is a device which allows computers to be connected in a NETWORK. This means computers can SHARE files and printers. A NETWORK is a group of COMPUTERS LINKED together. 

Connecting computers ointo a network allows files to be shared quickly and easily. 

A MODEM allows computers to connect to the internet. It CHANGES the computer's DIGITAL signal, into an ANALOGUE one which is transmitted down a phone line. The signal is then CONVERTED back to a digital format once it reaches the other computer. 

A WEB BROWSER allows you to find and connect to other websites. 

An EMAIL PROGRAM allows you to send and recieve messages and doccuments over the internet. 

Wi-Fi stands for WIRELESS FIDELITY.

Wi-Fi enabled devices can network with each other. They can send and recieve radio signals over relatively shorty distances. 

BLUETOOTH is a less powerful form of Wi-Fi. It was developed to provide a wireless communication method between devices which are close together. 

For bluetooth to work:

• The range of transmission needs to be SMALL. 
• The size of the data transfered needs to be SMALL. 

Bluetooth can be used for:

• Sending photos
• Using printers
• PDAs in restaurants 

Advantages:

• Allow hardware like printers to be shared
• Easy and quick method of sharing files

Disadvantages:

• Security of data is reduced due to people sharing the system
• Extra hardware is needed

A computer NOT linked to any other computer is called a STAND-ALONE MACHINE.  Most computers in houses will be stand-alone machines.

A LAN (LOCAL AREA NETWORK) is a collection of computers connected togther by either physical cabling or Wi-Fi but occupying one site only. Eg. A school network. 

A WLAN (WIRELESS LOCAL AREA NETWORK) is a LAN which uses RADIO WAVES (Wi-Fi) rather than physical cabling to transmit data from machine to machine. 

Adv: No cabling is required, Computers can connect from anywhere whithin range.

Disadv: Other people can access the network if in range, unless propely protected. 

A WAN (WIDE AREA NETWORK) is a network in which computers are linked togther over a LARGE geographical area (different sites, possibly in different countries.)

Because the computers are linked over such a large space, links cannot be made by cables or by radio like LANs. The use communication media from a THIRD PARTY Eg. BT telephone lines. The INTERNET is a good example of a WAN.

There are a number of methods of communicating over a network like the internet. 

EMAIL (ELECTRONIC MAIL.) A software applicationis used for sending and recieving emails via the internet. 

An INSTANT MESSENGER presents information in real time between two or more users, unlike email which is not a real-time system. 

VIDEO CONFERENCING (See module 2) requires the software, a webcam, a microphone and speakers. It allows interactions via video link from 2 or more locations.

FAX is another method of communciation, however it is not commonly used to today. A FAX MACHINE is a device which can send and recieve printed messages and data over the telephone network.  

There are two types of COMMUNICATION MEDIA that allow signals to be transmitted around a computer network:

• Cables
• Radiowaves

If cable is used, then it will probably be either:

• A twisted-pair cable 
• A fibre-optic cable

TWISTED-PAIR CABLES involve two wires twisted together, down which signals are sent. They are prone to interference from elcectrical machinery so should be placed away from these.

FIBRE-OPTIC CABLES carry light signals. It involves the physics principle of total internal reflection. 

A NIC (NETWORK INTERFACE CARD) allows the computer to use the communication medium to send and recieve messages. For this reason, all computers in a network must have one. 

HUBS & SWITCHES are often found at the centre of a network. They recieve DATA PACKETS from a computer and send them to the other computers on a network.

They look the same, however when they recieve a signal from a computer, they treat it differently. 

For example: In a network there is 8 computers. If computer 1 needs to send a signal to computer 5, the the signal will first be sent to the hub / switch. 

If it is a HUB, it will send the signal to EVERY computer on the network, including computer 1 (which originally sent the signal.)  This creates a lot of needless network traffic. 

A SWITCH on the other hand, will send the signal to ONLY the device which it should be sent to, as it will inspect the adress of each data packet it recieves and sent it to the adressed device.

This reduces network traffic and collisons of data packets, meaning these do not have to be resent and thus increases the performance of the network.

A BRIDGE is used to CONNECT together TWO dissimilar NETWORKS (Eg. A bus network and a Star network.)

Both networks must use the SAME rules for handling the MESSAGES.

A set of rules for successful communication is called a PROTOCOL.

A ROUTER behaves like a bridge as it connects two networks togeteher.

However a router is more 'intelligent' tha  a bridge as it can decide whether data packets should be transmitted between two networks. 

• It can also make the format of messages suitable for a new network.
• It can read information about the messages and decide where and how it should get to its destination. 
• It can provide a connection between a network and the internet because it can join two unlike networks. 

All data traffic (packets) to and from the internet is passsed through the PROXY SERVER. It acts on behalf of all devices whithin the network in requesting and recieving data from the internet. 

It allows all the computers to access the internet by making it look like there is only ONE user. 

Imagine four computers, all wanting to access the internet with the same ISP account. All the data from the computers goes through the proxy serever and the connections from the users ride on a SINGLE connection to the internet. 

The INTERNET is open to ALL. It is a collection of inter-connected computer networks, spread across the world. 

An INTRANET is a private, company-wide network, only accessible to members of that company. 

An intranet is a RESTRICTED DOMAIN which can be accessed and controlled by a limited number of users. 

Advantages:

• The intranet is less susceptible to hacking and viruses because access is limited
• The information will be reliable and useful (no hoax sites)
• Communciation and access to info will be faster as there are fewer users
• You can restrict who can go on the intranet

Disadvantages:

• Possibly not as much information as they are restricted
• Communication can only be made with others allowed on intranet
• Intranets tend to only show one point of view.

When you log on to a network you are asked for a USER ID and PASSWORD.

Each user will have access different areas of the system. The purpose of the USER ID is to identify the user to the operating system so the OS knows which HARDWARE & SOFTWARE that particulr user has access to. 

The PASSWORD is used to prevent UNAUTHORISED access to the network or that user account. 

When someone logs on :

• The OS will look up the USER ID in the table of user IDs.
• It will be given a list of the hardware and software this user has access to. 
• It waits for the input of a PASSWORD.
• If the password matches the password held by the OS for that user, they are given access to things they have prmision to use. 
• If it does not match they will not be allowed in and can try the password again. 

CONFIDENTIALITY OF DATA  is concerened with keeping data private. 

DATA ENCRYPTION is one way of keeping data confidential. 

Encryption is the SCRAMBLING of DATA so that its meaning is HIDDEN. The device used to encrypt a piece of data is called a KEY.

PASSWORDS can also be used to protect data and prevent unortharised acces to certain files. FIREWALLS can also help protect data. 

AUTHENTICATION TECNIQUES are used so you can prove a user is who they say they are. Eg. a bank card is used at an ATM and the PIN are authentication techniques.

Generally TWO items of identification are needed for authentication to gain access to a service / system.