communications & networks national 4 & 5 computing science
TRANSCRIPT
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