GCSE ICT

Networks

Definitions

• What is a network?A series of interconnected computers, linked together either via cabling or wirelessly. Often linked via a central server but can be linked without a central computer.

• What is a stand alone computer?A computer which is not connected to a network (i.e. other machines or a central server). All devices are directly connected to that computer and all data (software and information), is stored on each individual machine.

• They both have advantages and disadvantages and depend upon the situation.

Networks vs. Stand Alone Systems

Review: NetworksAdvantages Disadvantages

•Hardware can be shared.(Printers, scanners, file servers, internet routers). Providing cost savings.

Initial cost of servers, communication devices etc. can be expensive MUST be qualified by the hardware NOT just ‘expensive’

•Shared data. Information can be stored centralised (e.g. a shop database of products).

Reliability and performance. High network traffic , could cause slow down. Central server failure could cause whole network to die.

•Improved communication. E-Mail, Intranets and Collaborative working.

Security. Viruses can potentially affect an ENTIRE network. Hackers could compromise a whole system.

•Shared software. Network licenses for software is often cheaper than individual licenses. Networks: software can be deployed or hosted on an applications server and downloaded on-demand.

Upgrading: Upgrading cabling and machines on a mass scale is expensive.

•Improved, centralised security. Logons, access levels, monitor activity

A network manager may need to be employed – expensive

•Centralised backup. Removing responsibility of individual people.

Review: Stand AlonesAdvantages Disadvantages

•Fewer Hardware requirements. No extra cabling or equipment needed. Just a PC!

•No hardware sharing. You would have to switch to different machines (taking your data with you), to use different hardware (e.g. if a scanner was on another computer).

•Reliability and Performance. Not effected by network traffic. Performance should stay relatively the same.

•Software installed on every machine. Costly and Timely!

•Security. A virus would not effect other machines. Hackers etc would have to be on the actual machine. The machine can be locked away!

• Individual Backups. Each person would be responsible for backing up data on their machine. Imagine the duplication of data in a business!!!

•Little ICT Knowledge Required. No complex understanding of networks etc is required for a stand alone system

• Harder to communicate. No real electronic means to communicate (unless they all had a separate connection to the internet – again, costly!)

Types of Network

Definitions

What is a LAN?Local Area Network. A series of interconnected computers restricted to a close

geographical site. Usually connected with a mix of cables and wireless technologies.

What is a WAN?Wide Area Network. A series of interconnected computers over more than one physical site (area, town, city or even country!)Connected with a range of technologies such as phone lines, satellite links, broadband, physical fibre optic link.

Useful site: www.teach-ict.com/gcse/hardware/networks/miniweb/index.htm

Topologies

• “ The real or logical arrangement of elements on a network”

• OR• “How a network is laid out”

• They can be organised in many different ways. Each have their own advantages and disadvantages.

Quick Review: Star Topology• Each computer connected to a central server.• Everything goes through the central server.• Huge dependence on central server.

+ Central Backup+ Network stays active if one line breaks.+ Easy to expand+ Fewer security problems due to central control.+ High performance. Each client has its own cable.

Quick Review: Ring Topology• All connected to one closed loop.• No main computer• Communication happens by passing data

around the ring.• All data passes through all computers.

– Security problem!

• To add a new client, the whole network must be switched off.• Backup issues• A break in the line causes whole network failure.

+ Very fast transmission rates.+ Not dependant on single server+ Cheap to install (no server, no major cabling).

Quick Review: Bus Topology• Cheap to install. Only one cable needed.• Straightforward and easy to install.• Extra computers can be added easily.• No central server.• Data sent to every machine (security issues).• Backup issues.• Network down if main cable is damaged.

+ Fast transmission.+ Easy to set up and install+ New clients can be added easily.

Ring Topology

Ring Topology(Broken Line)

X

X

X

X

Bus Topology

Bus Topology(Broken Line)

X

X

X

X

Star Topology

Star Topology - (Broken Line)

X

Star Topology - (Broken Server)

X

X

XX

X

XX

GCSE ICTNetwork Hardware

Definitions

• Internet: A series of interconnected computers internationally.

• Intranet: A private internet system that can only be accessed on a LAN (e.g. Tesco Stock Control)

• Extranet: A private internet system that can be accessed externally with a login (e.g. Moodle).

Looking at the hardware

• Let’s look at the hardware needed to make a network.– Switch– Gateway– Bridge– Packet Switching– Router

Switch & Packet Switching

1 2 3

4

If machine 4 wanted to send to machine 1:

A switch figures out where it has to go and sends it to the right place.

It SWITCHES the data from one cable to another:

Definition: A switch analyses each packet of

data and sends it to the computer it was intended for

Data packets travel between source and destination from one router to the next. The process of exchanging data packets is known as Packet

Switching

Bridge

Connects two different LAN’s together.

Useful for joining two sites (e.g. school or company over multiple places)

Site 1: Yarm

Site 2: Middlesbrough

Router• Forwards packets of data along a network• It ‘routes’ information along the best path for forwarding the

data• Generally located at gateways (where 2 networks connect)

GatewayA gateway allows a LAN to connect to other LANs to form a WAN.

E.g. the LAN at Tesco HQ connects to the smaller LANs in all of it’s stores.

This forms a Tesco WAN!