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Sorry to ask you this, but...

The syllabus says that you should be able to:

a. describe a router and its purpose;b. describe the use of WIFI and Bluetooth in networks;c. describe how to set up a small network involving

access to the Internet, understanding the need to setup the use of a browser, email and an ISP;

d. identify the advantages and disadvantages of usingcommon network environments such as the Internet;

e. describe what is meant by the terms user id andpassword, stating their purpose and use;

f. identify a variety of methods of communicationsuch as:

fax,e-mail,bulletin boards,tele/video conferencing;

g. define the terms:Local Area Network (LAN)Wireless Local Area Network (WLAN)Wide Area Network (WAN)

h. describe the difference between LANs and WANs,identifying their main characteristics;

i. describe the characteristics and purpose of commonnetwork environments, such as intranets and theInternet;

j. describe other common network devices (includinghubs, bridges, switches and proxy servers);

k. discuss the problems of confidentiality and securityof data, including problems surrounding commonnetwork environments;

l. identify the need for encryption, authenticationtechniques, including the use of user identification andpasswords, when using common networkenvironments such as the Internet.

Notes covering this section:

What is a Network?Why Use Networks?Why Not Use Networks?Computers in a NetworkTypes of NetworkLAN Topologies (dropped by CIE)Networking HardwareThe InternetIntranetsSetting Up a Small NetworkNetwork & Data Security

Help with this section:

Ask questions and get help on this section of thesyllabus in the help forum .

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What is a Network? | IGCSE ICT



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A network is two or more computers, or other electronic devices,connected together so that they can exchange data.

For example a network allows computers to share files, users tomessage each other, a whole room of computers to share a singleprinter, etc.

Network connections between computers are typically created usingcables (wires). However, connections can be created using radiosignals (wireless / wi-fi), telephone lines (and modems) or even, forvery long distances, via satellite links.

A computer that is not connectedto a network is known as astandalone computer.

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Using a computer connected to a network allows us to…

Easily share files and dataShare resources such as printers and Internet connectionsCommunicate with other network users (e-mail, instantmessaging, video-conferencing, etc.)Store data centrally (using a file server) for ease of access andback-upKeep all of our settings centrally so we can use any workstation

In particular, if we use a computer connected to The Internet, we can…

Make use of on-line services such as shopping (e-commerce)or bankingGet access to a huge range of information for researchAccess different forms of entertainment (games, video, etc.)Join on-line communities (e.g. MySpace, Facebook, etc.)

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Using a computer connected to a network means that…

The computer is vulnerable to hackersIf the network breaks, many tasks become very difficultYour computer can more easily be attacked by a virus

In particular, if we use a computer connected to The Internet…

We have to be careful about revealing personal informationWe have to be careful to avoid suspect websites that mightcontain malwareWe have to be aware that information found on The Internet isnot always accurate or reliable

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Computers in a Network | IGCSE ICT



Computers connected together to create a network fall into twocategories: servers and clients (workstations).

Clients

Client computers, or workstations, are the normal computers thatpeople sit at to get their work done.

When you use your Web browser,you are in fact using a Web client.When you type in the URL of a webpage, you are actually providing theaddress of a Web server. e.g. www.bbc.co.uk is the addressof the BBC’s web server. Your Web browser/client asks thisserver for the web page you want,and the server ‘serves’ the pageback to the browser/client for you tosee.

Servers

Servers are special, powerful computers that provide ‘services’ to theclient computers on the network.

These services might include:

Providing a central, common file storage areaSharing hardware such as printersControlling who can or can’t have access the networkSharing Internet connections

Servers are built to be very reliable. This means that they are muchmore expensive that normal computers.

In a small network one server might provide all of these services. In alarger network there might be many servers sharing the work.

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Local Area Network (LAN)

A Local Area Network is a network confined toone building or site. Often a LAN is a private network belonging toan organisation or business.

Because LANs are geographically small, theyusually use cables or low-power radio(wireless) for the connections.

Wireless Local Area Network (WLAN)

A wireless LAN (WLAN) is a LAN that usesradio signals (WiFi) to connect computersinstead of cables.

At the centre of the WLAN is a wireless switchor router - a small box with one or two antennassticking out the back - used for sending andreceiving data to the computers. (Most laptopshave a wireless antenna built into the case.)

It is much more convenient to use wirelessconnections instead of running long wires allover a building.

However, WLANs are more difficult to make secure since otherpeople can also try to connect to the wireless network. So, it is veryimportant to have a good, hard-to-guess password for the WLANconnections.

Typically, the range of a wirelessconnection is about 50m, but itdepends how many walls, etc. arein the way.

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 aswhen a business that has offices in different countries links the officeLANs together.

Because WANs are often geographically spread over large areas andlinks between computers are over long distances, they often use



quite exotic connections technologies: optical fibre (glass) cables,satellite radio links, microwave radio links, etc.

The Internet is an example of aglobal WAN .In fact it is the world’slargest WAN. Computers on the InternationalSpace Station are linked to theInternet, so the you could say thethe Internet is now the first off-planet WAN!

Bluetooth (Personal Area Network)

Bluetooth is a wireless networking technologydesigned for very short-range connections(typically just a few metres).

The idea of Bluetooth is to get rid of the need forall of those cables (e.g. USB cables) thatconnect our computer to peripheral devices suchas printers, mice, keyboards, etc.

Bluetooth devices contain small, low-powerradio transmitters and receivers. When devicesare in range of other Bluetooth devices, theydetect each other and can be 'paired'(connected)

Typical uses of Bluetooth:

Connecting a wireless keyboard to a computerConnecting a wireless mouse to a computerUsing a wireless headset with a mobile phonePrinting wirelessly from a computer or PDATransferring data / music from a computer to an MP3 playerTransferring photos from a phone / camera to another deviceSynchronising calendars on a PDA and a computer

Because Bluetooth networking onlyworks over very short distances,and with devices belonging to oneuser, this type of network issometimes called a 'Personal AreaNetwork'

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LAN Topologies | IGCSE ICT

The word topology means ‘arrangement’, so when we talk about thetopology of a network, we mean how the different parts are arrangedand connected together.

There are three common network topologies...

Bus Network

In this type of network, a long, central cable, the ‘bus’ is used toconnect all of the computers together. Each computer has a shortcable linking it to the ‘bus’.

A bus network…

Is cheap to install (just one long cable)Can be quite slow since all computersshare the same cable whencommunicatingWill stop working if there is a break in thecentral bus cable.

Ring Network

In this type of network each computer is connected to a loop ofcable, the ‘ring’. (If you took a bus network and connected theends of the bus cable together, you would have a ring network.)

A ring network…

Can cope with a break in the ring cable since allcomputers are still joined together (it is now a busnetwork)

Star Network

In this type of network every computer is connected to a centraldevice. The device passes messages between computers.

At the centre of a star network you might use a hub (cheap, butslower) or a switch (more expensive, but faster).

A star network…





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Is quite expensive to install (you have to buy lots ofcable and the central device)Is very fast since each computer has its own cable whichit doesn’t need to shareCan cope with a broken cable (only one computer will beaffected)Will stop working if the central device breaksIs the most common network topology

Hybrid Network

A hybrid network is simply one that combines two or more ofthe above basic topologies.

E.g. A network that has several star networks linked togetheris a hybrid network

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Networking Hardware | IGCSE ICT

Network Interface Card (NIC)

Any computer that is to be connected to a network, needs to have anetwork interface card (NIC).

Most modern computers have these devices built into the motherboard,but in some computers you have to add an extra expansion card (smallcircuitboard)

Some computers, such as laptops,have two NICs: one for wiredconnections, and one for wirelessconnections (which uses radiosignals instead of wires)

In a laptop, the wireless radioantenna is usually built in to theside of the screen, so you don'tneed to have a long bit of plasticsticking out the side of yourcomputer!

Network Cable

To connect together different devices to make up a network, you needcables.

Cables are still used in most networks, rather than using only wireless,because they can carry much more data per second, and are moresecure (less open to hacking).

The most common type of networkcable cable in use today looks likethe one shown above, with plasticplugs on the ends that snap intosockets on the network devices. Inside the cable are several copperwires (some used for sending datain one direction, and some for theother direction).



Hub

A hub is a device that connects a number of computers together tomake a LAN.

The typical use of a hub is at the centre of a star network (or as partof a hybrid network) - the hub has cables plugged into it from eachcomputer.

A hub is a ‘dumb’ device: if it receives a message, it sends it to everycomputer on the network. This means that hub-based networks arenot very secure - everyone can listen in to communications.

Hubs are pretty much obsolete now(you can't buy them any more),having been superseded by cheapswitches.

Switch

A switch, like a hub, is a device that connects a number of computerstogether to make a LAN.

The typical use of a switch is at the centre of a star network (or aspart of a hybrid network) - the switch has cables plugged into it fromeach computer.

A switch is a more ‘intelligent’ device than a hub: if it receives amessage, it checks who it is addressed to, and only sends it to thatspecific computer. Because of this, networks that use switches aremore secure than those that use hubs, but also a little moreexpensive.

Router

A router is a network device that connects together two or morenetworks.

A common use of a router is to join a home or business network (LAN)to the Internet (WAN).

Routers are the devices that jointogether the various differentnetworks that together make up theInternet. These routers are much morecomplex than the one you mighthave in your home



The router will typically have the Internet cable plugged into it, as wellas a cable, or cables to computers on the LAN.

Alternatively, the LAN connection might be wireless (WiFi), making thedevice a wireless router. (A wireless router is actually a router andwireless switch combined)

Proxy Server

A proxy server is a computer setup toshare a resource, usually anInternet connection.

Other computers can request a webpage via the proxy server. The proxyserver will then get the page using itsInternet connection, and pass it backto the computer who asked for it.

Proxy servers are often used insteadof router since additional softwarecan be easily installed on thecomputer such as anti-virus, webfiltering etc.

Bridge

A bridge is a network device that typically links together two differentparts of a LAN.



Whereas a router is usually used to link a LAN to a WAN (such as theInternet), a bridge links independent parts of a LAN so that they act asa single LAN.

Firewall

A firewall is a device, or a piece of software that is placed betweenyour computer and the rest of the network (where the hackers are!)

If you wish to protect your whole LAN from hackers out on theInternet, you would place a firewall between the LAN and the Internetconnection.

A firewall blocks unauthorised connections being made to yourcomputer or LAN. Normal data is allowed through the firewall (e.g. e-mails or web pages) but all other data is blocked. In addition to physical devices,

firewalls can also be software. In fact most computer operatingsystems have a software firewallbuilt in (e.g. Windows, Linux andMac OS)



Modem

Before the days of broadband Internet connections, most computersconnected to the Internet via telephone lines (dial-up connections).

The problem with using telephone lines is that they are designed tocarry voices, which are analogue signals. They are not designed fordigital data.

The solution was to use a special device to join the digital computerto the analogue telephone line. This device is known as a modem.

A modem contains a DAC and an ADC .

The DAC in the modem is required so that the digital computer cansend data down the analogue telephone line (it converts digital datainto noises which is exactly what the telephone line is designed tocarry.)

The ADC in the modem is required so that the analogue signals(noises) that arrive via the telephone line can be converted back intodigital data.

The reason telephone lines wereused is that almost every buildingin the world is already joined toevery other via the telephonesystem. Using the telephone system forconnecting computers meant thatpeople didn’t have to install newwires to their houses and officesjust for computer use. In the last few years however, thisis exactly what people have done.Special cables have been installedjust for Internet access. These special cables are designedto carry digital data, so no modemis required.

The word modem is anabbreviation of MOdulatorDEModulator. A modulator acts as a DAC, and ademodulator acts as an ADC.

So, simply put, a modem is required because computers are digital devices and the telephone system isanalogue. The modem converts from digital to analogue and from analogue to digital.

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If you have ever used a dial-upconnection, you have probablyheard the noises sent by themodem down the telephone line. They sound like a horriblescreeching beeping sound.

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The Internet | IGCSE ICT



The Internet is a world-wide network that has grown and evolvedfrom an experimental network (ARPANet) created by the US militaryback in the 1960s. Over the years, as more and more computers andnetworks have connected to this network, it has grown into the Internetthat we know today.

The Internet connects millions of people, and thousands of businesses,governments, schools, universities and other organisations.

What Can We Use the Internet For?

The Internet provides the network connections that links computerstogether. There are many ways that we can use these connections:

View web pages on the WWW (World-Wide Web)Sending and receiving e-mail messagesSharing filesCommunicating using voice (VOIP) and video (video-conferencing)Playing multi-player gamesListening to streamed music or watching streamed video

The small, hand-drawn map aboveshow the plan for the firstconnections between fourcomputers on the ARPANet. It wasdrawn by one of the engineers whocreated the network back in 1969. From these tiny beginnings, theInternet has grown to a size thatwould be hard to believe forty yearsago. Statistics published at the start of2008 show that 1.3 billion peoplenow have access to the Internet(20% of world population).

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An intranet is the name given to a private network that providessimilar services to The Internet: e-mail, messaging, web pages, etc.

However, these services are only for the users of the intranet – theyare private, not public (unlike Internet services which are generallypublic).

Businesses and other organisations often have intranets for use bytheir employees.

Typical uses of an intranet would be:

Viewing internal web pages (e.g. company calendars, etc.)Internal e-mail and instant-messaging between workersSharing of internal documents

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If you were asked to build a small, Internet-connected network fromscratch, what would you need to do?

You would need to buy some hardware:

One or more switches / hubs - to link devices togetherNetwork cables to connect devices to the switch, etc.A separate wireless access point (or this could be part of theswitch) - to allow wireless devices (e.g. laptops or smart-phones)to join the networkA router to connect your LAN to the Internet (WAN)A firewall to protect your network from hackersPossibly a bridge if you already have a section of network andyou want your new network to connect to itServer(s) to manage network functions such as networksecurity, network file storage, shared resources (such asprinters)

You would need to organise some other things:

Set up an account with an Internet Service Provider (ISP)Get an Internet connection installed from the ISP to yourlocationConfigure various bits of hardware and software so thateverything worked with the network

For any network that is morecomplex than a small homenetwork, there is a lot to do. It's not just a case of buying theparts and connecting themtogether...

Routers and switches have tobe configured (settingschanged)Network devices need to begiven network addressesSoftware needs to beconfigured to use the networkEtc...

Networks are pretty complex thingto set-up. The people who do thisare called Network Engineers. It'sa very interesting technical job, ifyou like that sort of thing!

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Network & Data Security | IGCSE ICT

As soon as your computer is connected to a network, you have to startthinking about security – security of your files, information, etc.

A network allows a person who does to have physical access to yourcomputer (they are not sitting in front of it) to gain access all the same.If your computer is connected to a network, other people can connectto your computer.

A person who gains unauthorised access to a computer system is oftencalled a hacker.

Preventing Unauthorised Access

There are a number of security measures that you can take to preventhackers accessing your computer and all of the data stored on it:

Physical Security

The first thing to make sure of is that no unauthorised people canphysically access (sit down in front of) any of the computers on yournetwork.

For example, by keeping office doors locked.

Use a Username and Have a Good Password

The most common way to protect your computer’s data is to setupuser accounts with usernames and passwords. Anyone not having ausername, or not knowing the correct password will be denied access.

For this to be effective passwords must be chosen that are not easy toguess. Passwords should be a random combination of lowercaseletters, uppercase letters and numbers (and symbols if this is allowed):

‘Weak’ passwords: password, 123456, david, 27dec1992‘Strong’ passwords: s63gRdd1, G66ew$dQ, gdr298783X

Some computer systems replace the typing of usernames andpasswords with other forms of user identification such as ID cards,fingerprint readers, voice-print recognition, etc.

Strong passwords are often hard toremember. Here is a good methodfor creating a password that is verystrong, but also easy to remember: Think of a phrase that you willnever forget…

“My favourite food is chocolate icecream”

Take the first letter of each word…

mfficic

Change some letters to similarnumbers: I to 1, o to 0, s to 5, etc.and make some letters (e.g. thefirst and last) uppercase…

Mff1c1C

A random-looking mixture of lettersand numbers. As long as you likechocolate ice cream you will neverforget your password!



Always Install and Use a Firewall

A firewall is a device, or a piece of software that is placed betweenyour computer / LAN and the rest of the network / WAN (where thehackers are!)

You can read about firewalls in the Networking Hardware section.

Securing Your Data

Often we have data that is private or confidential. This data needs tobe protected from being viewed by unauthorised people. This isespecially true if the data is to be sent via a public network such asThe Internet.

The best way to protect data is to encrypt it...

Data Encryption

Encryption is the process of converting information into a formthat is meaningless to anyone except holders of a ‘key’.

For example, if Alice wants to send important, personal messages toBob, she must go through the following steps...

Encryption has been used forcenturies to protect secrets. Military leaders as far back asroman times have used encryptionto protect important messages sentto their armies, messages that mustbe kept secret from the enemy. If the messenger was caught by theenemy, the message, beingencrypted, remained secretbecause they didn’t know the codeto decrypt it.

First Alice needs to generate asecret ‘key’.

The key is usually a very long,random number.

The encryption scheme shown hereis called Symmetric Key, or SingleKey encryption. There are many better schemes,such as Public Key Encryption, butthe one shown here is the easiestto understand!

Alice must then give a copy of thiskey to Bob. She must make surethat nobody else can get to the key

(So maybe Alice will visit Bob andgive him a copy of the key on amemory stick or floppy disc).

Now that Bob has a copy of the key,each time Alice needs to send him amessage she starts by encrypting itusing special encryption softwareand the secret key.






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The encrypted message now lookslike a jumble of random letters andnumbers.

Alice then sends the encryptedmessage to Bob.

She can use a public network likethe Internet, since, even if it getsstolen, the encrypted messagecannot be read or understoodwithout the key.

When Bob receives the message, heuses special decryption softwareand his copy of the secret key todecrypt the message.

Bob can now read the originalmessage from Alice.

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