Unit 4Unit 4

ICT A levelICT A level

RevisionRevision

Remember!!Remember!!The focus of A level questions is on you being The focus of A level questions is on you being the designer / advisor to organisations wishing the designer / advisor to organisations wishing to develop their ICT capabilitiesto develop their ICT capabilities

A level questions can contain areas from your A level questions can contain areas from your As knowledgeAs knowledge

You may be asked to apply A level theory to You may be asked to apply A level theory to the applications you studied at As the applications you studied at As

Unit 4Unit 4

NetworksNetworks

Computer Networks

•A computer network is a collection of computers linked together so that they can communicate with each other

•A computer that is not connected to a network is called a stand-alone computer

•There are two different sorts of computer network:

•‘Local Area Network’ or ‘LAN’ - the computers are all in the same building or in different buildings on one site permanently connected to each other with special cables.

•‘Wide Area Network’ or ‘WAN’ - the computers are spread over a large geographical area not permanently connected to each other communicate using telephone lines, radio transmitters or satellite links. Connected by gateways

Factors to consider when Factors to consider when choosing achoosing a networknetwork

1. Cost of the network1. Cost of the networkInitial purchasing of equipmentInitial purchasing of equipmentInstallation and trainingInstallation and trainingMaintenance costsMaintenance costsSize of the available budget will determine Size of the available budget will determine what can be done e.g. fibre optic cable is faster what can be done e.g. fibre optic cable is faster but is also more expensive. Wireless systems but is also more expensive. Wireless systems are flexible but need more maintenance. are flexible but need more maintenance.

2. Size of the organisation2. Size of the organisation

Needs can range from a small LAN Needs can range from a small LAN to a global WAN.to a global WAN.Some communications media are Some communications media are limited to the distance they have to limited to the distance they have to travel.travel.Amount of data processing Amount of data processing required must also be considered.required must also be considered.

3. How the system will be used3. How the system will be used

What type of applications do users require? What type of applications do users require?

Will they need large data storage? Will they need large data storage?

From where will they operate the network e.g. From where will they operate the network e.g. at home in office or remote access from at home in office or remote access from different locationsdifferent locations

4. Existing systems to integrate4. Existing systems to integrate

More often networks are not developed from More often networks are not developed from scratch but need to fit in with existing systems. scratch but need to fit in with existing systems. Sometimes an extension is required e.g. when Sometimes an extension is required e.g. when a new branch office opens. a new branch office opens.

Therefore any new network must fit in with the Therefore any new network must fit in with the operating systems and protocols of the operating systems and protocols of the existing. existing.

It must support any peripherals already in use It must support any peripherals already in use e.g. bar code readers, printers etc.. e.g. bar code readers, printers etc..

5. Performance and speed required5. Performance and speed requiredPerformance in terms of ;Performance in terms of ;

reliability reliability user friendliness user friendliness capacity capacity speed of processing. speed of processing.

Different parts of the organisation may have different Different parts of the organisation may have different performance requirements. E.g. a real-time e- performance requirements. E.g. a real-time e- commerce system may require greater speeds and commerce system may require greater speeds and capacity and security than the in house payroll capacity and security than the in house payroll systemsystem

6. Security issues6. Security issues

Different organisations may have different Different organisations may have different

priorities e.g. priorities e.g.

A large business organisation may be A large business organisation may be primarily concerned with primarily concerned with – Prevention of hacking Prevention of hacking – Avoid viruses Avoid viruses – Secure payment siteSecure payment site

A school may be equally concerned with A school may be equally concerned with blocking the downloading of illicit materialblocking the downloading of illicit material

Clients (Terminals)Thin clients (‘Dumb terminal’)

•Has no built in hard drive, expansion slots and only has enough RAM and processing capacity to run applications and output to a monitor

•Suitable for client server networks.Suitable for client server networks.

Fat clients (‘Intelligent terminal’)

•This is a workstation with full stand alone capacity. It has its own hard drive for storage and a CPU.

•Stations have a processor so can share the Stations have a processor so can share the processing. There are many different ways to do processing. There are many different ways to do this e.g. a station could act as a printer server etc. this e.g. a station could act as a printer server etc. A station could store programs on its disc and A station could store programs on its disc and load them while data files are stored elsewhere load them while data files are stored elsewhere perhaps upon a central fileserver.perhaps upon a central fileserver.•Suitable for peer to peer networksSuitable for peer to peer networks

Both LANs and WANs may be either

Client/Server

or

Peer-to-Peer networks.

Peer to peer networkPeer to peer network

All stations are joined together in the network have All stations are joined together in the network have equal status. equal status. EEach station can communicate directly with every other workstation on the network without going through a server.They are both client and server sharing resources.They are both client and server sharing resources. Are often a form of distributive processing sharing Are often a form of distributive processing sharing the processing between intelligent terminals. the processing between intelligent terminals. Hardware and data files can be access from several Hardware and data files can be access from several computers.computers. Applications may be stored on different computers Applications may be stored on different computers and accessed by all as longer as the owner gives and accessed by all as longer as the owner gives permission. permission. Work is backed up on individual user PCsWork is backed up on individual user PCs ..

Client Server NetworkClient Server Network

The term Client/Server is used to describe networks that have computers or terminals (clients) that are connected to a more powerful computer called the NETWORK SERVER.

A central file serverA central file server store the data and programs store the data and programs Access is determined by user access privileges controlled Access is determined by user access privileges controlled by their logon names and passwordsby their logon names and passwords

A print serverA print server would spool data ready fro despoiling to a would spool data ready fro despoiling to a printer when the printer is readyprinter when the printer is ready

A communication servers e.g. web server; email serverA communication servers e.g. web server; email server may control all email and internet access.may control all email and internet access.

Peer to PeerPeer to Peer Client serverClient server

CheaperCheaper: initial start up costs and : initial start up costs and network operating system less network operating system less complicatedcomplicated

More expensive as software system more More expensive as software system more complex and need to but servers.complex and need to but servers.

Less vulnerable to central server Less vulnerable to central server crashescrashes

If server crashes or cable fails no user If server crashes or cable fails no user can continue workcan continue work

Simpler to set up and maintainSimpler to set up and maintain Require specialist personnel to manage Require specialist personnel to manage systemsystem

Slower processing of tasksSlower processing of tasks Faster processing of tasksFaster processing of tasks

Only works well on small networks <15Only works well on small networks <15 Can manage large networksCan manage large networks

Security and backup are not centralised Security and backup are not centralised and difficult to manageand difficult to manage

Centralised control with servers often Centralised control with servers often doing many management functions doing many management functions themselves e.g. regular backups, themselves e.g. regular backups, auditingauditing

Access to data depends upon the Access to data depends upon the owner’s permission.owner’s permission.

Offers easy access to centralised dataOffers easy access to centralised data

Network Topology

Network topology refers to the layout used to connect the computers together. There are three common topologies:

• Bus

• Ring

• Star

Any of these topologies can be used regardless of whether a network is local or wide area, server based or peer-to-peer.

BUS

2.This is the cheapest network topology as the smallest amount of cabling is required

•Workstations are connected to the main central cable/bus •Data can travel in both directions •Two nodes could attempt to transmit at the same time and a collision will occur. To avoid this, a node waits until no traffic on the bus and pauses slightly before transmitting. If a collision occurs both nodes wait and try again at a random time interval. •The main bus standard is known as Ethernet the communications uses a broadcast channel so all attached workstations can hear every transmission.

AdvantagesAdvantagesLess cable need than a ring. Relatively cheaper and Less cable need than a ring. Relatively cheaper and easier to install and maintain.easier to install and maintain.Easy to add new nodes by removing terminatorEasy to add new nodes by removing terminatorIf a workstation/terminal goes down the others will If a workstation/terminal goes down the others will continuecontinueDisadvantagesDisadvantagesHeavy traffic can cause network failure and delaysHeavy traffic can cause network failure and delaysHeavily dependent upon the cable backbone and Heavily dependent upon the cable backbone and cable damage can cause network failure.cable damage can cause network failure.

Terminal

Fileserver

PLOTTER

PRINTER

Terminal

Terminator

RING NETWORKRING NETWORKThe Cambridge ring The Cambridge ring has has no central host no central host computercomputer and none of and none of the nodes need to the nodes need to have overall control of have overall control of access to the network. access to the network. Messages in the ring Messages in the ring flow in one direction flow in one direction from node to node. from node to node. The ring consists of a The ring consists of a series of repeaters series of repeaters which are joined by which are joined by cables. cables.

PRINTER SERVER

HARDDISK

FILESERVER

T2

T1T8

COMMUNICATIONSSERVER

T7

SCANNER

T6

T5 T4T3

RINGCABLE

The choice of cable The choice of cable depends upon the distance depends upon the distance to be travelled and to be travelled and required speeds. Fibre required speeds. Fibre optic cabling is the best but optic cabling is the best but the most expensive. Fibre the most expensive. Fibre optic cabling would allow a optic cabling would allow a ring of about 100 ring of about 100 kilometres.kilometres.

Token passing techniqueToken passing techniqueAn imaginary token is continuously passed around the RING. A An imaginary token is continuously passed around the RING. A token is a small packet that contains bits of data which passes token is a small packet that contains bits of data which passes around the ring (Always the same way around)around the ring (Always the same way around)The token is recognised as a unique character sequence. The token is recognised as a unique character sequence. If a device is waiting to transmit it catches a token and with it the If a device is waiting to transmit it catches a token and with it the authority to send data. It attaches its data. The packet will contain authority to send data. It attaches its data. The packet will contain the destination address.the destination address.As long as one device has a token no other device can send data. As long as one device has a token no other device can send data. A receiving device acknowledges it has received the message by A receiving device acknowledges it has received the message by inverting a 1 bit field.inverting a 1 bit field.Once the sending workstation has received acknowledgement that Once the sending workstation has received acknowledgement that the message has been received the token is free for use by another the message has been received the token is free for use by another device.device.

Advantages of a Ring networkAdvantages of a Ring networkThere is no dependence upon a central host as data transmission is There is no dependence upon a central host as data transmission is supported by all devices on the ring. Each node has sufficient supported by all devices on the ring. Each node has sufficient intelligence to control the transmission of data from and to its own intelligence to control the transmission of data from and to its own node.node.Works effectively when processing is distributed across a site.Works effectively when processing is distributed across a site.Very high transmission speeds are possible.Very high transmission speeds are possible.It is deterministic i.e. different performance levels can be determined It is deterministic i.e. different performance levels can be determined for different traffic levels.for different traffic levels.Routing between devices is simple because messages normally travel Routing between devices is simple because messages normally travel in one direction.in one direction.As data is in one direction it can transmit large volumes of data As data is in one direction it can transmit large volumes of data

DisadvantagesDisadvantages - - Systems depends upon the reliability of the ring repeater although it Systems depends upon the reliability of the ring repeater although it can be designed to bypass faulty repeaters. If one node malfunctions can be designed to bypass faulty repeaters. If one node malfunctions this can affect the operation of the network.this can affect the operation of the network.Cabling costs Cabling costs Difficult to extend the ring.Difficult to extend the ring.

STAR NETWORKSTAR NETWORKEach node is connected to a CPU at the Each node is connected to a CPU at the centre. Popular topology for a centre. Popular topology for a WAN.WAN.

Messages pass through host which Messages pass through host which interconnects different devices on the network. interconnects different devices on the network. The central host The central host switchesswitches messages point to messages point to point.point.

FILESERVER

Scanner

PRINTER

T1 T2 T3

T4

HARDDISC

T5

T6T7

T8

COMMUNICATIONSSERVER

Advantages of a Star networkAdvantages of a Star networkSuitable for WANs where large organisations rely on a central Suitable for WANs where large organisations rely on a central computer for the bulk of data processing taskscomputer for the bulk of data processing tasksCentral control of message switching allow a high degree of securityCentral control of message switching allow a high degree of securityEach spoke is dependent upon the rest. If one spoke breaks down the Each spoke is dependent upon the rest. If one spoke breaks down the others can continue and the central CPU can identify any faultsothers can continue and the central CPU can identify any faultsData transmission speeds can vary from spoke to spoke so one can Data transmission speeds can vary from spoke to spoke so one can use a high-speed device and another a low speed e.g.. disc drive.use a high-speed device and another a low speed e.g.. disc drive.Saves cabling.Saves cabling.

DisadvantagesDisadvantagesNetwork is vulnerable to central hub failures.Network is vulnerable to central hub failures.As a distributed system, some processing is still possible at the nodes As a distributed system, some processing is still possible at the nodes but internode connection is lost.but internode connection is lost.If servicing a WAN a mini or mainframe system is needed for control of If servicing a WAN a mini or mainframe system is needed for control of messaging. So hardware and software is expensive.messaging. So hardware and software is expensive.

A Wide Area Network (WAN)

Workstation

Workstation

Workstation

Printer

Print Server File Server

Remote PC Modem

Gateway

network cables

telephone lines

Modem

Remote PC

LANs and WANsLANs and WANs

Internet, Intranet and ExtranetInternet, Intranet and ExtranetThe InternetThe Internet is a is a Wide Area NetworkWide Area Network - actually it is a huge - actually it is a huge collection of networks collection of networks

connectedconnected together by what are called together by what are called gatewaysgateways - these make the system act as - these make the system act as if it was one huge network.if it was one huge network.

Many networks in industry, business, higher education and government institutions Many networks in industry, business, higher education and government institutions are all connected to the Internet although anybody can now get connected to the are all connected to the Internet although anybody can now get connected to the system with the appropriate hardware and software and access to an system with the appropriate hardware and software and access to an ISPISP ( (Internet Internet Service ProviderService Provider )...e.g. Freeserve, AOL, Demon and hundreds of others. )...e.g. Freeserve, AOL, Demon and hundreds of others.A user can get information on just about everything. There are A user can get information on just about everything. There are search toolssearch tools which which allow you to search the World Wide Web for any topic, and each page has allow you to search the World Wide Web for any topic, and each page has linkslinks to to another and so on....another and so on....- it is also possible to - it is also possible to downloaddownload software and files (e.g. NASA graphics) software and files (e.g. NASA graphics)- - bulletin boardsbulletin boards (forums) or (forums) or newsgroupsnewsgroups are also set up where you can leave are also set up where you can leave messages, or communicate directly with other users.messages, or communicate directly with other users.Businesses set up Businesses set up websiteswebsites on the Internet because... on the Internet because.....they can advertise. It enables people to find out what they do and what they sell. ..they can advertise. It enables people to find out what they do and what they sell. ..people can email them with enquiries; orders; requests; ..people can email them with enquiries; orders; requests; ..they can reach an international audience. ..they can reach an international audience.

IntranetsIntranetsAn An intranetintranet is set up entirely within a LAN. Web pages can be is set up entirely within a LAN. Web pages can be stored and accessed from anywhere on the network and email stored and accessed from anywhere on the network and email can be sent internally within the LAN.can be sent internally within the LAN.A company can set up an intranet and allow its workers to send A company can set up an intranet and allow its workers to send messages to each other and use a browser to access company messages to each other and use a browser to access company information saved as web pages. It can also be used for staff information saved as web pages. It can also be used for staff training.training.

ExtranetsExtranetsIf a company allows some access from outside to its intranet, If a company allows some access from outside to its intranet, then it becomes an then it becomes an extranetextranet. Access would normally be through . Access would normally be through a a firewallfirewall (software which only allows permitted users to access (software which only allows permitted users to access the data).the data).

Wireless Media

Infra-red

Radio waves

Bluetooth

Broadband

Microwaves

Mobile phones use microwaves. Ideal for linking computers in two separate buildings fairly near to each other. Satellite systems also make use of microwaves.

Infra red light.Infra red light.InfraredInfrared refers to light waves of a lower frequency refers to light waves of a lower frequency than human eyes can receive and interpret. Infrared than human eyes can receive and interpret. Infrared is used in most television remote control systems, is used in most television remote control systems, and with a standard called IrDA (Infrared Data and with a standard called IrDA (Infrared Data Association) it's used to connect some computers Association) it's used to connect some computers with peripheral devices. For most of these computer with peripheral devices. For most of these computer and entertainment purposes, infrared is used in a and entertainment purposes, infrared is used in a digital mode -- the signal is pulsed on and off very digital mode -- the signal is pulsed on and off very quickly to send data from one point to another. quickly to send data from one point to another.

AdvantagesAdvantages Infrared communications are fairly Infrared communications are fairly reliable and don't cost very much to build into a reliable and don't cost very much to build into a device.device.Disadvantages Disadvantages It can only travel short distancesIt can only travel short distances..

Infrared is a "line of sight" technology. Infrared is a "line of sight" technology. Infrared is almost always a "one to one" technology. Infrared is almost always a "one to one" technology.

Wireless networking- cable less Wireless networking- cable less connectivityconnectivity

Radio TransmissionRadio Transmission

Devices have radio transmission facilities and radio Devices have radio transmission facilities and radio receivers. These radio receivers constantly scan the receivers. These radio receivers constantly scan the airways for incoming signals. When it detects the airways for incoming signals. When it detects the signal it recognises it captures it and converts it to signal it recognises it captures it and converts it to digital form. The digital signal can be transmitted to digital form. The digital signal can be transmitted to the CPU by wireless routers the CPU by wireless routers

ExamplesExamplesPeople now need to be mobile and still access their People now need to be mobile and still access their networks, email accounts e.g. at wireless nodes in networks, email accounts e.g. at wireless nodes in an airportan airportPart of a WAN or Virtual Private Network e.g. a Part of a WAN or Virtual Private Network e.g. a delivery driver using a hand held device to confirm delivery driver using a hand held device to confirm deliveries with a central databasedeliveries with a central database

More examples….More examples….

Landscape gardeners use a laptop with wireless Landscape gardeners use a laptop with wireless connectivity to access a library of garden designs connectivity to access a library of garden designs back at HQback at HQ

Doctors at the scene of an accident can accessing Doctors at the scene of an accident can accessing patient records.patient records.

Wireless networks may be used as part of a LAN Wireless networks may be used as part of a LAN e.g. a mobile bar code reader in a warehouse e.g. a mobile bar code reader in a warehouse transmitting data to a shop or HQtransmitting data to a shop or HQ

Hand held chip and pin data entry in restaurants for Hand held chip and pin data entry in restaurants for entering details of cars payments.entering details of cars payments.

Wireless devices such as Printers/ keyboards/mobile Wireless devices such as Printers/ keyboards/mobile phones and description of use.phones and description of use.

Bluetooth technologyBluetooth technology

The Bluetooth PDA Adapter Card, The Bluetooth PDA Adapter Card, PC Card, and USB Adapter plug PC Card, and USB Adapter plug

into into your PDA, PC, or notebook your PDA, PC, or notebook computer, enable the user to computer, enable the user to effortlessly transfer data to other effortlessly transfer data to other Bluetooth devices such as desktop Bluetooth devices such as desktop

or or notebook computers, input devices, notebook computers, input devices, PDAs, scanners, printers, and even PDAs, scanners, printers, and even mobile phones. Connect with up to mobile phones. Connect with up to seven other Bluetooth devices at a seven other Bluetooth devices at a time.time.

Broadband and Broadband and wireless networkingwireless networking

The broadband connection gives faster The broadband connection gives faster access speeds to the Internet and wireless access speeds to the Internet and wireless routers give wireless connection to the routers give wireless connection to the wireless adaptor in your PC. Average home wireless adaptor in your PC. Average home speeds of about 54 Mps are possible.speeds of about 54 Mps are possible.

Wireless technology means no cablesWireless technology means no cables

Allows remote use in wireless zones such as Allows remote use in wireless zones such as airports and hotels.airports and hotels.

Advantages of BroadbandAdvantages of BroadbandFaster connection when you want to be onlineFaster connection when you want to be onlineSavings on telephone billsSavings on telephone billsFaster downloading of programs, email, attachments Faster downloading of programs, email, attachments songs, graphics-rich sites, animations and video clipssongs, graphics-rich sites, animations and video clipsPlay interactive games at top speed against gamers Play interactive games at top speed against gamers around the globearound the globeUse telephone and be on the InternetUse telephone and be on the InternetRealtime services such as web cams, radio better Realtime services such as web cams, radio better qualityqualityWork from home with high speed access to corporate Work from home with high speed access to corporate networksnetworks

DisadvantagesDisadvantages

Higher subscription costsHigher subscription costs

Local exchanges may not be capable of very Local exchanges may not be capable of very high speed digital transmissionhigh speed digital transmission

Software components of a networkSoftware components of a network

User accounts and logsUser accounts and logsEach user must have an account with a user name Each user must have an account with a user name and password. and password. The account will have permissions i.e. access rights The account will have permissions i.e. access rights to files and data such as read only, right only, read to files and data such as read only, right only, read and write, and there will be restrictions of programs and write, and there will be restrictions of programs or data they can access. e.g. a member of the or data they can access. e.g. a member of the Personnel Department may be able to write, add and Personnel Department may be able to write, add and delete files of workers but a worker may only be able delete files of workers but a worker may only be able to read their personnel file.to read their personnel file.The resources; disk space, printers they can use etc The resources; disk space, printers they can use etc will be allocated to their account.will be allocated to their account.

AuditingAuditing

Auditing software keeps a record of who has Auditing software keeps a record of who has logged on, when, how long, what programs logged on, when, how long, what programs and data was used and what was amended. and data was used and what was amended. Therefore any illicit use of the system can be Therefore any illicit use of the system can be tracked and evidenced.tracked and evidenced.

Remote managementRemote managementNetworks can now be managed remotely from Networks can now be managed remotely from other rooms, buildings or across many sites by other rooms, buildings or across many sites by network management companies. e.g.network management companies. e.g.A workstation left unattended can be logged A workstation left unattended can be logged off. off. Network managers can observe what users Network managers can observe what users are doing. are doing. Remote technicians can find and fix software Remote technicians can find and fix software problems with the networkproblems with the network

Security and backup strategySecurity and backup strategy – See Disaster – See Disaster planningplanning

Factors to be considered when Factors to be considered when making configuration choices.making configuration choices.

Applications Software choicesApplications Software choicesWhat applications e.g. an ‘Office type’ suite would What applications e.g. an ‘Office type’ suite would allow easier maintenance and support from IT staff allow easier maintenance and support from IT staff and documents and other data can be shared.and documents and other data can be shared.What appearance on the desktop will be allowed?What appearance on the desktop will be allowed?Restrictions on downloading to prevent harmful Restrictions on downloading to prevent harmful software for personal use.software for personal use.

Operating systems and network management Operating systems and network management softwaresoftware

What operating systems and network is suitable?What operating systems and network is suitable?Windows 2000/ XP network; UNIX ??Windows 2000/ XP network; UNIX ??

HardwareHardwareWhat hardware is on the network? Ideally everyone should What hardware is on the network? Ideally everyone should have identical workstations to make maintenance simpler but have identical workstations to make maintenance simpler but this does not often happen as existing workstation have to be this does not often happen as existing workstation have to be added to a newer network. Replacing all workstations would added to a newer network. Replacing all workstations would be too expensive for most organisations and time for be too expensive for most organisations and time for installation needs to be staggered so the company can installation needs to be staggered so the company can continue functioning. What peripherals should be on the continue functioning. What peripherals should be on the network and who has access to them.network and who has access to them.

Range of User needsRange of User needsSome users will have different skills and requirements. Some Some users will have different skills and requirements. Some may only use 1 package occasionally whilst other uses very may only use 1 package occasionally whilst other uses very technically demanding software constantly. The skills users technically demanding software constantly. The skills users have already and their confidence in using them must be have already and their confidence in using them must be considered and retraining given if required.considered and retraining given if required.

Future proofingFuture proofingMake sure the system has a reasonable life span. Many companies Make sure the system has a reasonable life span. Many companies replace computers every 3 to4 years as they become too slow to replace computers every 3 to4 years as they become too slow to cope with modern software. cope with modern software. The format of the data must be considered. Old archived data must The format of the data must be considered. Old archived data must be able to be processed as well as new data. be able to be processed as well as new data. Storage mediums must be capable of being read in the future. Storage mediums must be capable of being read in the future. Programs must have backward compatibility. Programs must have backward compatibility. Network cabling and network infrastructure such as routers, bridges, Network cabling and network infrastructure such as routers, bridges, switches and servers installed must be capable of taking an switches and servers installed must be capable of taking an expansion in future traffic at reasonable speedexpansion in future traffic at reasonable speedWhen making choices it must be flexible and able to expand. Avoid When making choices it must be flexible and able to expand. Avoid over reliance on one supplier as if they go you may not have the over reliance on one supplier as if they go you may not have the expertise to fix problems.expertise to fix problems.Having an up to date ICT system can inspire confidence in customers Having an up to date ICT system can inspire confidence in customers and give staff better working conditions.and give staff better working conditions.