Computer Networks

Computer Network ► A computer network is a group of computers that are linked together.

Benefits of Networks ► Computers networks allow users to –  Share information and programs  Communicate electronically. and shared network areas.  Share expensive hardware. Peripherals such as printers & scanners.

Local Area Network (LAN) ► A local area network is used to connect computers within the same room or building. ► Dunoon Grammar School has a LAN has a LAN

LAN Transmission Media ► Computers in a LAN can be connected using network cables ► Cables can either be copper wire (utp) or optical fibre.

LAN Transmission Media ► Computers in a LAN can also be connected using wireless technologies.  Bluetooth. 10 metre range and transfer rates of 1 Mbps.  WiFi used in a LAN. Ranges up to 50 metres and transfer rates of 20 Mbps

Wireless LAN

Wide Area Network ► A wide area network is used to connect computers in different buildings, towns, countries and continents ► Usually called a WAN The Internet is one example of a public WAN. Many companies link their offices worldwide with a private WAN.

WAN Transmission Media ► The most common method of transferring data over long distance is using the copper wire and fibre optic cables of the telephone system. For large distances, submarine cables can be used. ► For very large worldwide distances, microwave, and satellite links are used.

WAN Transmission Media ► Microwaves are used in the public telephone system. Highly directional. ► Satellite links – A single satellite link can carry a very large number of separate transmissions.

Network Security ► Information on a network must be guarded carefully. Security measures include:  Passwords  Encryption  Physical methods

Passwords ► All users must be issued with a secure password. It should:  Be like your toothbrush – don’t let anyone else use it and change it regularly.  Don’t pick words that others could easily guess.  No dictionary words  Between 6 – 10 characters

Encryption ► Putting data into code so it can’t be understood by others. ► Used to protect or files sent over a network. ► Ecommerce and digital banking sites encrypt their communications for security.

Drawbacks of Networks ► Users may accidentally delete or damage important files ► Computers can be infected by computer viruses ► Hackers may be able to access computers

Physical Methods ► Prevents unauthorised users getting access to the system.  Lock rooms  Lock Hard Drives  Lock disks away Biometrics  Fingerprint scanning  Iris Scanning  Voice Print

Transmission media Security ► Optical Fibre prevents tapping because it uses light. ► Electrical signals on copper cable can be tapped anywhere along the line. ► Wireless data can be intercepted. ► No security method is absolute!

Client/Server Networks ► ‘Clients’ are the computers that are connected to the network. ‘Servers’ are more powerful computers that carry out certain tasks. ► A Network Interface Card (NIC) is needed in a client computer to connect to the network. ► Back-up can be done centrally.

Client/Server networks ► File Server – gives users access to centrally stored files. Also, centralised backup can be done. ► Print Server - Allows a user access to a shared printer. ► Server - Stores users’ e:mails in a mailbox until they log in to receive/read . ► Servers may look like a normal desktop computer but will have more RAM, a faster processor and more backing storage.

Networks There is a lot more to think about than simply the computers and the wires: ► Social Issues ► Legal Issues ► Ethical Issues

Social Issues ► Teleworking. This is using Wide Area networks to work from home rather than an office.  You can choose your working hours  Save time, money & pollution – no travelling. Save on child minding costs.

Ethical Issues ► Information rich ► Information poor ► Privacy ► Censorship

Information Rich ► Having access to the wealth of information available on the Internet means people can make informed choices about many important aspects.

Information poor ► Not having access to the information available through the Internet can disadvantage peoples educational and employment prospects.

Privacy ► Should what we do on a network be private? ► There are people who use networks to steal, hack, plant viruses, and many other criminal & terrorist activities. ► Therefore, we need laws that enable our use of networks to be policed effectively.

Censorship ► Can censorship be a good thing? ► Why do we need censorship? ► Who decides what is appropriate?

Censorship ► What is legal in one country may not be legal in another. ► Not all governments encourage free debate ► China heavily censors all Internet material.