Communications & Networks

National 4 & 5 Computing Science

• We will learn :

–What is a Network

–Local Area Networks

–Wide Area Networks

–Connecting Networks

Lesson Objectives

What is a Network?

• A series of computers linked together so they can send and receive data.

• We use them for sending e-mails, downloading files, shopping, etc

• They are divided into two types:– Local Area Network

(LAN)– Wide Area Network

(WAN)

Local Area Network (LAN)• Cover a small area such as one room or

building.– The school has a LAN

• Each computer on a LAN is called a station

• One station is called the file server. – The file server is where

all the data & files are kept

Advantages of a LAN

• Share data• Share peripherals (resource sharing)• E-mail• Passwords keep data secure• Different levels of access

– stop unauthorised access• Flexible access

– Use any station connected to the LAN• Many users can use same document at the

same time (workgroup computing)

Connecting a LAN• Stations can be connected by cables or

wireless technology• Cables:

• Uses electrical signals to transmit data• Cheap but can get interference

–Optical fibre • Uses light beams to transmit data• Expensive but doesn't get interference

Connecting a LAN

• Wireless– Infrared communication

• Like the TV controls

– Bluetooth• Range of about 10 metres

– WIFI (Wireless Fidelity Alliance)

• Range of about 12-50 metres – popular for home use and public places

Bluetooth & WIFI use radio waves

Wide Area Networks (WAN)• Connect computers across large distances • Spread across countries & cities worldwide

using telecommunications links• Similar advantages to LAN but on a bigger

scale.

Connecting a WAN

• Telecommunications links– The communication of information over a

distance using:• Microwave transmission• Satellite links

Network Security• Security methods include:

– Passwords & user IDs– Encryption– Firewalls– Physical methods – eg locks

• We will learn about:

–Network Interface Cards

–Social, Legal & Ethical Issues

Lesson Objectives

Recap - LAN

• Area: Room, building or group of buildings

• Stations & File Server

• Connecting LAN:– Copper cable (Cat 5)– Fibre optics– wireless

• Advantages of LANs– Share data– Resource sharing– Different levels of

access – Flexible access– workgroup

computing

Recap - WAN

• Area: town, city,world

• Transmission Medium:– Telecommunications

Links• Satellites• Microwave

transmission

• Network Security:– Passwords & user

IDs– Encryption– Physical methods

Network Interface Card

• Allows the computer system to communicate with the network

• Every device that is connected to the LAN will need a NIC, for example, computer, printer and scanner.• It take the data sent by your

computer– stores it in its own memory

locations, – then adapts it ensuring it

follows the communication rules

Social Issues

• Teleworking– Process of using a WAN to work from home

• WANs can improve communications for people in remote areas

• Some people can’t afford the cost so a gap could form between the “Information Rich” and the “Information Poor”

• Some people believe that computers cause social isolation

Legal & Ethical Issues

• Legal:– Computer Misuse Act– Copyright, Designs & Patents Act– Data Protection Act

• Ethical:– Invasion of personal privacy– Censorship & freedom of speech

Communications & Networks

Electronic Communications

Lesson Objectives

•Electronic Communication•Text/Instant Messaging•E-Mail

•Advantages & Disadvantages•File Attachments

•Netiquette

Electronic Communication

• The process of sending and receiving electronic messages.

• Electronic messages include:– Electronic mail– Text messaging– File transfer (attachments)

Text Messaging

• Types:–Short text message.– Instant messaging.

• Language used:–Casual/Informal–Abbreviations–Acronyms

E-mail• Advantages:

– Fast compared to post– Cheap – ISP connection only– Web mail – access anywhere– Send multiple copies (CC)– Organise folders

• Disadvantages:– Spam– Viruses– Lack of Netiquette

• File Transfer– Files can be attached– Size limit– Attached viruses

Netiquette

• DON’T WRITE IN CAPS!• Don’t leave the Subject Field blank• Don’t over use Formatting• Don’t give out personal details• Don’t start Flame Wars (Trolling)• Use proper English in e-mails.• Don’t send dumb jokes, chain mail, etc

• Code of conduct used in e-communications

Communications & Networks

The Internet

• Internet Services• Accessing the

Internet • The World Wide

Web• Search Engines

Lesson Objective

s

The Internet

• Enables computers and networks worldwide to connect with each other

• The network of networks

Internet Services

• World Wide Web (www or just web)– Used for browsing or searching

• E-mail– Communication & exchange of information

• File transfer– Sending & receiving large

amounts of information

Accessing the Internet

• Internet ready computer• Internet Service Provider (ISP)

– A company that provides access to the internet

• Browser– Software used to view web pages

• Email client– Program for sending and receiving email

Accessing the Internet

• Dial-Up– Uses a modem and an ordinary

phone line to dial up the number of your ISP that connects you to the internet.

• Broadband– Uses either a digital subscriber line

(DSL) or a cable modem

• Modem– The telephone line doesn’t understand binary– A modem is needed to translate for the computer

World Wide Web

• Information is stored in web pages on web sites

• These pages can be viewed in a browser• They are found by an address such as:

– www.google.co.uk – www.msn.com

• Hyperlinks are used to ‘travel’ around the web

The Web - HTML

<"http://www.w3.org/TR/html4/loose.dtd"><html><head> <meta name="Description" content="Your description"> <meta name="Keywords" content="first, second, third"> <title>Title of the document</title> <base href="http://www.yourdomainname.com/images/"></head> <body> The body of the document</body></html>

• Hyper Text Mark-up Language• The language used to write web pages

Search Engine

• Special web site to help you find information

• A big database!• Some of the main search engines:

• Software on the internet

• Video conferencing• Streaming media• Internet services• Mobile Internet

Lesson Objective

s

Software on the Internet

• Freeware– Free software but the author still holds the

copyright– You are not allowed to change it

• Shareware– 30-Day trial period– After that either pay for it or delete it

Software on the Internet

• Commercial– Pay full price up front– Limited to one backup copy– Licence agreements are very detailed

Video Conferencing

• Using networks to send audio and visual data.

• Enables people to have face-to-face meetings

• Saves time and money• No need to travel long distances for

business

Video\Audio Streaming

• The internet is used to send data one way• Online radio stations do this• Uses large amount of network bandwidth

Other Internet Services

• Chat & instant messaging– Text based communication– Communication is in real time (instant)

• Weblogging (Blogs)– A type of online diary– Used for both business & personal

• Bulletin boards– Electronic notice board

Mobile Internet

• Using the internet while on the move– Walk ‘N’ Surf

• Devices include– Mobile phones, Laptops, palmtops, pdas

Client/Server and Peer to Peer

National 4/5 Computing Science

Lesson aims

By the end of this lesson you will be able to:

Describe what a peer to peer network is

Describe what a client server network is

Discuss the differences between them

Client and Server Networks

You are working on a client and server networkYour machine is a CLIENTYour documents are stored and internet

access is managed through the schools SERVER

You connect to a server to use its resourcesThis can vary depending on the serverMight just be to store files…

A sample Client Server network

Client Client

E-mail Server

File Server

Web Server

What can a server do?

• Servers can perform multiple roles – some are– They can run email servers– They can store files and control access

rights to files– Control Internet Access– Host Web Sites– Control printing for multiple computers

Peer to Peer Networks

You can run a peer to peer networkA peer to peer network is where each

computer shares the functions/files of a network.

Peer to peer networks have advantages: Each computer has its own backing storage

so does not rely on an expensive server. No expensive server hardware or software to

purchaseNo complex server software to setup

Uses of Peer to Peer Networks

• Distributed downloading– Where instead of downloading from one

central location you download pieces of a file from multiple machines

• Can be used for legal AND illegal purposes– The technology is legal!– The files being shared may not be!

Comparison

• Cheap to set up• Each user has to take

own backups• Poor Security• Software has to be

installed on every machine

• Doesn’t require a network manager

• Expensive to set up• Centralised backup • High security (Usernames

and passwords)• Software can be installed

centrally• Requires a network

manager

Peer to Peer Client Server