networking pptx

8/6/2019 Networking PPTX

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Mr Sehmbi


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When computers were first developed,

they were mainly intended for a person

to work on their own machine. However,

one day, a bright spark suddenly

thought, "wouldn't it be a good idea to

link two machines together so that can

share files". And so, the first computernetwork was created.


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Why Network?

Sharing hardware peripherals

At home, your computer might be connected to its own printerand scanner. This works well as you are the only person whowill be using them. Much of the time though, they probablyaren't being used and just lie idle. A computer which isn'tconnected to a network is known as a 'stand-alone'

In a school or an office, it would cost a lot of money for everycomputer to have its own printer and for the majority of the time,like your printer at home, it wouldn't be used.

By joining computers together to form a network, they are able

to share one printer. This means that more money can be spentbuying a better quality printer and that the printer is being usedmuch more of the time


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Why Network?

Sharing files

Networks allow you to share files with other users.You might have a folder at school called the 'sharedarea' or something similar. This is often where

teachers might put documents or resources that theywant you to use during the lesson. All students canopen these resources and save them to their ownarea, but they usually can't alter the original copies inthe shared area.

In many organisations, some workers might havepermission to alter the documents in the sharedarea. This means that they can work collaborativelyon a project or document and each person canupdate it as required.


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Why Network?

Log onto any workstation

At home, when you save your work, it usually gets saved ontothe hard disk of the computer that you are actually working on.When you want to access this document again, you can onlyopen it by using the same computer. If you try to use yourbrother's computer in the next room, you usually won't be ableto see the document.

With a network, have you ever thought about how you can logonto any computer, anywhere in the school and still get all ofyour files and folders?

That is because they aren't saved on the computer that you areworking on. Instead, everyone's work is saved on a file server.When you log onto the network, you type in your user name andpassword. Your user name tells the network who you are andthe file server finds your files and makes them available to you.


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Why Network?

Virus checks

Anti-virus software can also be run centrally and cancheck every workstation on the network at the sametime.

Security

If you had to save your documents onto one of thecomputer's hard drives in the school, not only wouldyou be tied to always having to log onto thatcomputer, it would mean that anyone else going ontothat computer could also see all of your work andperhaps alter, delete or copy it.With a network, eachperson can only see their own files and folders, sothis helps to keep your work safe.


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Disadvantages ofnetworking

Viruses

If a virus is introduced to the network, either intentionallyor unintentionally, it will rapidly spread around all of theworkstations and could start to cause havoc to peoples'files or to the efficient working of the network.

Network failure

If the file server fails then no-one on the network canaccess any files or folders. This means that nobody cando any work. For an organisation, this would be extremelycostly and disruptive.

If a cable, hub or switch on the network fails, this wouldmean that any computers connected to that part of thenetwork couldn't be used to access network resources.They could still be used as individual, stand-alonemachines.


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Slow service

As more users log onto the network and request files,send things to be printed and open more softwareapplications, the network can start to slow down. There isonly a limited amount of bandwidth and the more data that

is travelling around the network, the slower thingsbecome.

Cost

Building a network isn't cheap. Every machine has to beconnected to the network either by physical cables or

perhaps by wireless technology. Every workstation needsa network interface card to enable it to be connected tothe network. Other hardware such as hubs, switches androuters are often needed.


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Expert support required

Networks need constant monitoring toensure that the performance is maintained

and that all of the components are workingproperly. This requires specialist staff suchas network managers and technicians whowill spend all of their time ensuring that the

network works efficiently whenever youneed to use it. These staff add a large costto running a network, but without them,things would start to fail.


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Local Area Network (LAN)

When the computers are fairly close to

one another say, in a single office or two

buildings that are separated by a road,

they can be joined together either by

cables or wireless means.

These computers then form a Local

Area Network (LAN).


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Local Area Network (LAN)

Once the computers are connected together into a LAN,many people (users) can share and use the sameresources at the same time. They can share files,software, hard disks and peripherals such as a printer orCD-ROM. Users can also use the LAN to communicate

with each other by e-mail. Data can be transmitted veryquickly between networked computers.

To log onto a LAN, you usually need a user name andpassword. The user name identifies you to the file serverso that it can 'serve' you the correct files. The password

ensures that the user name really does belong to you.

Your school will probably be using a LAN network. Askyour teacher or the network technician.


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Wide Area Network (WAN)

Many modern companies have offices, shops or factories in various locations aroundthe country, and for large corporations, across the world. Even though staff work indifferent places, they often need to be able to access the same information no matterwhere they are.

It would not be possible to connect computers in different buildings together using theLAN cables. Imagine how many roads would need to be dug up to lay cables betweena building in London and one in Birmingham.

Computers on LANs in one building can be connected to computers on LANs inanother building usually through the telephone system, often using a modem. They canalso be connected via fibre optic cables, microwave links or satellite.

By linking LANs together, the network is no longer local to one building, it is now spreadover a wide area. It is known as aWide Area Network (WAN)

Did you know that the largestWAN in existence is the Internet?


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Client-Server Network

A client-server network is the type of network that we have beendiscussing on the previous pages.

A server Is a powerful computer that is dedicated to managing thetraffic around the network, managing disk drives and networkperipherals such as printers and scanners.

There might be different types of server on a network such as a fileserver which is used to store all of the users' files and folders. The fileserver 'serves' files to the users when they log onto the network.

There might be an email server which deals with the internal emailsystem. A web server controls access to the Internet and blocks access

to any unsuitable sites.

The workstations connected to the network are known as 'clients'.Clients rely on servers for resources and access to files and peripheraldevices.


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Client-Server Network

Advantages Disadvantages

All files are stored in a central locationA specialist network operating system

is needed

Network peripherals are controlled

centrallyThe server is expensive to purchase

Backups and network security is

controlled centrally

Specialist staff such as a network

manager is needed

Users can access shared data which

is centrally controlled

If any part of the network fails a lot of

disruption can occur


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Peer-to-Peer Network

This is where two or more computers are connected together withoutneeding a file server to be part of the network.

This type of network can be as simple as two people in the same roomtemporarily connecting their computers via a Universal Serial Bus toenable them to transfer or share files directly with one another. It can

also include a more permanent network where say half-a-dozencomputers in a small office are connected together with copper cables.

This type of network means that every PC, once connected to thenetwork is acting both as a server and a client. There is no need for aspecial network operating system. Access rights to files, folders anddata is controlled by setting the sharing permissions on individualmachines. So for example, if User A wants to access some files from

User B's computer, User B must set their permissions to allow this.Otherwise, User A won't be able to see or access any of User B's work.

Permissions can be set to allow complete access to every file, folderand document stored on your system or just for particular things.


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Peer-to-Peer NetworkAdvantages Disadvantages

No need for a network operating systemBecause each computer might be being accessedby others it can slow down the performance for theuser

Does not need an expensive server becauseindividual workstations are used to access the files

Files and folders cannot be centrally backed up

No need for specialist staff such as networktechnicians because each user sets their ownpermissions as to which files they are willing toshare.

Files and resources are not centrally organised into

a specific 'shared area'. They are stored onindividual computers and might be difficult to locateif the computer's owner doesn't have a logical filingsystem.

Much easier to set up than a client-server network -does not need specialist knowledge

Ensuring that viruses are not introduced to thenetwork is the responsibility of each individual user

If one computer fails it will not disrupt any other partof the network. It just means that those files aren't

available to other users at that time.

There is little or no security besides thepermissions. Users often don't need to log onto

their workstations.


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StandardsandProtocols

Earlier in the syllabus we looked at why

standards are used by all manufacturers of

hardware devices. In order to get a monitor

developed by one manufacturer to workwith a graphics card developed by another

they must both follow the same standards.

In much the same way, computers on a

network must all have a way of being able

to 'talk' or 'communicate' with one another

and they do this by following a protocol.


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StandardsandProtocols

A protocol is a set of rules which define:y How to establish communication between the machines

y The format of any data which is to be exchanged betweenthe machines

y How errors in the data will be detected

y How errors will be corrected

y Methods of compressing the data to transmit it faster andmore efficiently

y How the connection between the machines is to beterminated

The protocol that is used on most LAN

s and theInternet is known as the TCP/IP protocol.

If any computers on the Internet are not using thisstandard then they will not be able to communicatewith others that are.

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