1 Computers, part of your - hselspark

Computers,

part of your

life

Grade 11

1

Local area

networks

2 Module 2.1

A computer network is a group of computing devices (e.g. computers, printers,

scanners, etc.)

that are connected to each other by means of some

communication medium (cable or wireless)

in order to communicate with each other.

3 Computer network –

definition

Types of networks

PAN – organised around an individual

HAN – network in a home environment

LAN – small area, generally in one building

Internet – worldwide computer network

Intranet – organisation’s private network

4

Classified according to the area that they cover

Computers and peripherals

Client

desktop laptop tablet smartphone

Basic components of a

network – Hardware5

Computers and peripherals

Server

file server

email server

internet / proxy server

web server

print server

database server

6Basic components of a

network – Hardware

How do you

know you are

connected

to a network?

Presence of extra

(logical) drives such

as U:, V: and T:

Presence of other

computers in

Network

Access to devices (e.g. printers) not

directly attached to

the computer

Indicator showing

network activity in

the notification area

7

8

Network Interface Controller

NIC – to connect device to

network via cable

Wireless adapter

and NIC –both built

into device

Switch

To connect computers in a

network – so communication

can occur


network – Hardware

9

Basic components of

a network

LAN (Local area network) a network that covers a small

area such as a classroom,

school, office building or

campus.

In a LAN the infrastructure

needed to connect the

computers in a network, is the

private property of the

institution – no service provider

(e.g. Telkom) is needed to

establish the network.

10 LAN – definition

WLAN (Wireless local area

network) a LAN connected via a wireless

communication medium.

11 WLAN – definition

Image:

http://www.telenor.com/wp-content/uploads/2010/12/WLAN-SIM-no-

text.jpg

PAN (Personal area network) devices such as tablets

and smart phones are

connected to each other

over a small area

(±10 m radius).

Usually via Bluetooth.

12 PAN – definition

Image:

http://www.brunel.ac.uk/__data/assets/image/0007/197134/PA

N.gif

HAN (Home area network) devices connected in a

small area such as a house,

usually by means of

radio waves (WiFi).

13 HAN – definitions

Image:

http://www.att.com/Common/DSL/center/images/connected_ho

use.gif

14

WLAN advantages compared to LAN

Easier to install

Easier and more practical between

buildings

Easy to add or move computers

Adds mobility – users with mobile devices

Avoids clutter


network –

Communication methods

Communication

Sharing devices e.g. printers and scanners

Sharing data

Share software

Better security

Easier backup

15 Advantages of a LAN/WLAN

Files stored on central computer – users access from

any computer in network

Files transferred without use of

devices

Software shared by users

Hardware shared by users

Security in network controlled

Single internet connection

shared by users

Easier to keep software up to

date

Software can be

demonstrated or broadcast

to other computers

Internet access monitored

and controlled

16 Advantages of a LAN

Cost – it can be expensive to set up and maintain a LAN.

If the LAN is not well planned, it can become even more expensive.

Viruses – a computer virus can spread very easily in a network if security measures are not in place.

Data security can be a problem, because many users have access to data in a network.

17 Disadvantages of a LAN

Network administrator – sometimes an administrator is needed to manage a network. Thus the cost of keeping the network up to date increase.

Signal weakening – the length of cables restrict the size of a LAN. If the cables are too long (more than 100m), the signal strength decrease.

The communication speed is determined by the communication medium.

If the server fails, the whole network is out of order.

18 Disadvantages of a LAN

Can be expensive to install

and maintain

Network administrator

often needed to manage

Network security must be

maintained

If file server faulty, no one can access their files

Security can be compromised – easier

for unauthorised persons to gain access

Performance can decrease as number of computers connected increases

Signal loss or interference due to

electrical interference

19

Additional potential disadvantages

if wireless (WLAN)

Disadvantages of a LAN

20

Communication methods

Cables

UTP (Unshielded Twisted Pair)

Fibre optic cable

Wireless

Wireless access points

Wireless enabled /

wireless adaptor


network

21

UTP cable

• Only spans certain

distance – signal loss

• Can be ‘eavesdropped’

on

• Affected by electrical

sources

• Uses electrical signals to

transmit data

Fibre cable

• Spans much longer

distances

• Immune to

‘eavesdropping’

• Not affected by electrical

sources

• Uses light signals to

transmit data

• Faster data transmission

than UTP cable


network

Maximum speed depends on cabling

and devices (switches and NICs)

802.11 specification – wireless adapter(802.11g and 802.11n – different speeds)

WLAN is slower than a cabled LAN

22 Basic components of a

network

Data transmission speed

Rate at which data is transferred

over the media used

E.g. 100 Mbps / 1000 Mbps

Workstations (clients)

The computers used by the users of

the network and are connected to

the server. They usually use the

recourses and services provided by

the server.

Examples: desktop computers,

laptops, tablets, smart phones.

23 Computer devices (nodes)

Servers

Computers with powerful capabilities:

fast and powerful processor, large

amount of RAM and very big hard

disk space.

All the workstations and other devices

are connected to the server.

The server provides services used by the clients.


Types of servers File server – stores data used by the clients.

No data is supposed to be stored on the client computer.

Print server – provides access to the printers in the network and manage them.

Proxy server – allows safe access to the internet.

e-mail server – used to manage e-mail facilities in the network.

Web server – used to host websites.


Communication media

A communication medium is used to

transfer data from one device to

another.

26 Communication media

Twisted pair (UTP)Used in a LAN in together with a switch.

RJ45 connector is used to connect to the device.

Consists of copper wires.

Signal strength decrease if longer than 100 m.

Is influenced by electromagnetic interference. Can therefore not be used in areas where large electric machinery are used.


Fibre optic cables Transfer data in the form of light signals through very fine glass

strands (fibre glass) or plastic fibre.

Very large amounts of data can be transferred at a very large

transfer speed over very large distances.

Can be used in areas where there are electromagnetic signals.

Expensive and difficult to install.


Wireless (Bluetooth and WiFi) High frequency radio waves are used to transfer data.

Access points are needed to send the radio waves needed for communication. An access point may, however, be a connection to an ADSL telephone line, which is not wireless. It may also be a device making use of cellular services, e.g. GPRS, 3G, HSDPA, EDGE, etc.

Bluetooth – communication between personal devices over a very short area. Used to build a PAN.

WiFi – communication via an access point over a relatively small area (±35 m radius indoors and 100m outdoors).

Signals can travel through solid objects, e.g. walls.


30 Network interface card (NIC)

Needed to connect the network device with the

communication medium.

Used to translate data from the way the device

“understands” it to the way the communication medium can

transfers it, and visa versa.

Can be built into the motherboard of the computer/laptop.

Different types of NIC needed for data transfer over cables

(RJ45-connector needed) and wireless transmission (aerial

needed to send and receive radio signals).

Most portable devices are equipped with a wireless NIC.

Laptops are also equipped with an Ethernet NIC for

connection with UTP cables.

31 Network interface card (NIC)

Device needed to set up a LAN with UTP cables.

Central connection point for all devices in the

network.

32 Switch

The system program needed to set up the

communication between the devices and control

access to the network, e.g. user rights and other

security measurements.

Most operating systems, e.g. Windows 7 and Windows

8, have built-in network facilities.

33 Network software


network –

Network software

34

Software that controls communication and security in a network

Most operating systems have built-innetworking capabilities

For larger networks ‘Server’ editions of the operating system are installed on the servers

Advantages and

disadvantages of a LAN35

36 Basic network security

Rules to ensure the security of a network –

preventing unauthorised access to

information and network misuse

Access to confidential files must be restricted

In a school situation – important that learners do

not have access to tests before they are written

A username and password are used to gain

access to network resources

Choose a password known only to you

Keep your password secret!

At least 8 characters long

Mixture of upper and lowercase letters, numbers

and special characters

Do not use anything that is easy to guess about you

Do not use passwords that follow a pattern on the

keyboard such as ‘asdf’ or ‘1234’

Change password every 2 months or so

Do not use same password for more than one site

37

Example of a good password

Q1w2E3R4t%y

Choosing and managing passwords

Need for acceptable, ethical practices

Acceptable Use Policy (AUP) outlines the

rights and responsibilities of users, especially

in networked environments

AUP lists what users may and may not do on

the network

Designed to protect both the user and the

business / organisation / school when using

ICT facilities

38 Ethical use of networks

Basic netiquette rules

Restrictions on what may be accessed online

Restrictions on amount of data downloaded from internet

Importance of responsible ethical / legal / safe practices

Details on where and when portable storage devices may

be used

Restrictions on installing hardware and software

Procedures for victims of identity theft, malware, cyber-bullying, cyber-stalking

Consequences of violating conditions set out in AUP

39 What should be included in AUP

Written module activity40

1 Computers, part of your - hselspark

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