Computer NetworksComputer Networks

Computer NetworkComputer Network► A computer network is a group of A computer network is a group of

computers that are linked together.computers that are linked together.

Benefits of NetworksBenefits of Networks► Computers networks allow users to –Computers networks allow users to –

Share information and programsShare information and programs Communicate electronically. Email and Communicate electronically. Email and

shared network areas.shared network areas. Share expensive hardware. Peripherals Share expensive hardware. Peripherals

such as printers & scanners.such as printers & scanners.

Local Area Network (LAN)Local Area Network (LAN)► A local area network is used to connect A local area network is used to connect

computers within the same room or computers within the same room or building.building.

► Dunoon Grammar SchoolDunoon Grammar School has a LANhas a LAN

LAN Transmission MediaLAN Transmission Media► Computers in a LAN can be connected using Computers in a LAN can be connected using

network cablesnetwork cables

► Cables can either be copper wire (utp) or Cables can either be copper wire (utp) or optical fibre. optical fibre.

LAN Transmission MediaLAN Transmission Media►Computers in a LAN can also be Computers in a LAN can also be

connected using connected using wirelesswireless technologies. technologies.

Bluetooth.Bluetooth. 10 metre range and 10 metre range and transfer rates of 1 Mbps.transfer rates of 1 Mbps.

WiFiWiFi used in a LAN. Ranges used in a LAN. Ranges up to 50 metres and transfer up to 50 metres and transfer rates of 20 Mbpsrates of 20 Mbps

Wireless LANWireless LAN

Wide Area NetworkWide Area Network► A wide area A wide area

network is used to network is used to connect computers connect computers in different in different buildings, towns, buildings, towns, countries and countries and continentscontinents

► Usually called a Usually called a WANWAN

The Internet is one example of a public WAN. Many companies link their offices worldwide with a private WAN.

WAN Transmission MediaWAN Transmission Media► The most common method of transferring data The most common method of transferring data

over long distance is using the copper wire and over long distance is using the copper wire and fibre optic cables of the fibre optic cables of the telephone systemtelephone system.. For For large distances, submarine cables can be used.large distances, submarine cables can be used.

► For very large worldwide distances, For very large worldwide distances, microwave, and satellite microwave, and satellite links are used.links are used.

WAN Transmission MediaWAN Transmission Media►MicrowavesMicrowaves are used in the public are used in the public

telephone system. Highly directional.telephone system. Highly directional.

►Satellite linksSatellite links – A single satellite – A single satellite link can carry a very large link can carry a very large number of separate number of separate transmissions.transmissions.

Network SecurityNetwork Security► Information on a network must be Information on a network must be

guarded carefully. Security measures guarded carefully. Security measures include:include:

PasswordsPasswords EncryptionEncryption Physical methodsPhysical methods

PasswordsPasswords► All users must be issued with a secure All users must be issued with a secure

password. It should:password. It should: Be like your toothbrush – don’t let anyone else Be like your toothbrush – don’t let anyone else

use it and change it regularly.use it and change it regularly. Don’t pick words that others could easily guess.Don’t pick words that others could easily guess. No dictionary wordsNo dictionary words Between 6 – 10 charactersBetween 6 – 10 characters

EncryptionEncryption► Putting data into code so it can’t be Putting data into code so it can’t be

understood by others.understood by others.► Used to protect email or files sent over a Used to protect email or files sent over a

network.network.► EcommerceEcommerce and and digital bankingdigital banking sites sites

encrypt their communications for security.encrypt their communications for security.

Drawbacks of NetworksDrawbacks of Networks► Users may accidentally delete or Users may accidentally delete or

damage important filesdamage important files

► Computers can be Computers can be infected by computer virusesinfected by computer viruses

► Hackers may be able to access Hackers may be able to access computerscomputers

Physical MethodsPhysical Methods► Prevents unauthorised usersPrevents unauthorised users

getting access to the system.getting access to the system. Lock roomsLock rooms Lock Hard DrivesLock Hard Drives Lock disks awayLock disks away

BiometricsBiometrics Fingerprint scanningFingerprint scanning Iris ScanningIris Scanning Voice PrintVoice Print

Transmission media SecurityTransmission media Security►Optical Fibre prevents tapping Optical Fibre prevents tapping

because it uses light.because it uses light.►Electrical signals on copper cable can Electrical signals on copper cable can

be tapped anywhere along the line.be tapped anywhere along the line.►Wireless data can be intercepted.Wireless data can be intercepted.►No security method is absolute!No security method is absolute!

Client/Server NetworksClient/Server Networks► ‘‘Clients’ are the computers that are Clients’ are the computers that are

connected to the network. ‘Servers’ connected to the network. ‘Servers’ are more powerful computers that are more powerful computers that carry out certain tasks.carry out certain tasks.

►A Network Interface Card (NIC) is A Network Interface Card (NIC) is needed in a client computer to needed in a client computer to connect to the network.connect to the network.

►Back-up can be done centrally.Back-up can be done centrally.

Client/Server networksClient/Server networks►File Server – File Server – gives users access to gives users access to

centrally stored files. Also, centralised centrally stored files. Also, centralised backup can be done.backup can be done.

►Print Server - Print Server - Allows a user access to a Allows a user access to a shared printer.shared printer.

►Email Server - Email Server - Stores users’ e:mails in Stores users’ e:mails in a mailbox until they log in to receive/read a mailbox until they log in to receive/read email.email.

► Servers may look like a normal desktop Servers may look like a normal desktop computer but will have more RAM, a faster computer but will have more RAM, a faster processor and more backing storage.processor and more backing storage.

NetworksNetworksThere is a lot more to think about than There is a lot more to think about than simply the computers and the wires:simply the computers and the wires:

►Social IssuesSocial Issues►Legal IssuesLegal Issues►Ethical IssuesEthical Issues

Social IssuesSocial Issues►Teleworking.Teleworking.

This is using Wide Area networks to This is using Wide Area networks to work from home rather than an office.work from home rather than an office. You can choose your working hoursYou can choose your working hours Save time, money & pollution – no Save time, money & pollution – no

travelling. Save on child minding costs.travelling. Save on child minding costs.

Ethical IssuesEthical Issues► Information richInformation rich

► Information poorInformation poor

►PrivacyPrivacy

►CensorshipCensorship

Information RichInformation Rich►Having access to the wealth of Having access to the wealth of

information available on the Internet information available on the Internet means people can make informed means people can make informed choices about many important choices about many important aspects.aspects.

Information poorInformation poor► Not having access Not having access

to the information to the information available through available through the Internet can the Internet can disadvantage disadvantage peoples educational peoples educational and employment and employment prospects.prospects.

PrivacyPrivacy►Should what we do on a network be Should what we do on a network be

private?private?►There are people who use networks to There are people who use networks to

steal, hack, plant viruses, and many steal, hack, plant viruses, and many other criminal & terrorist activities.other criminal & terrorist activities.

►Therefore, we need laws that enable Therefore, we need laws that enable our use of networks to be policed our use of networks to be policed effectively.effectively.

CensorshipCensorship► Can censorship be aCan censorship be a

good thing?good thing?► Why do we needWhy do we need

censorship?censorship?► Who decides what isWho decides what is

appropriate?appropriate?

CensorshipCensorship►What is legal in one country may not What is legal in one country may not

be legal in another.be legal in another.►Not all governments encourage free Not all governments encourage free

debatedebate►China heavily censors all Internet China heavily censors all Internet

material.material.