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Transcript
Communications & Networks
Standard Grade Revision:
Networks
What is a Network?
• A series of computers linked together so
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)
Transmission media for LAN
• Stations can be connected by cables or
wireless technology
• Cables:
–Unshielded Twisted Pair of copper
wire (UTP)
• Uses electrical signals to transmit data
• Cheaper but can get interference
–Optical fibre
• Uses light beams to transmit data
• Expensive but doesn't get interference
Transmission media for LAN
• Wireless
– Infrared communication
• Like the TV controls
– Bluetooth
• Range of about 10 metres
– WIFI (Wireless Fidelity Alliance)
• Range of about 12-50
metres
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.
Transmission Media for WANs
• Telecommunications links
– The communication of information over a
distance using:
• Microwave transmission
• Satellite links
Network Security
• Security methods include:
– Passwords & user IDs
– Encryption
– Physical methods
Lesson Objectives
• We will learn about:
– Client Server Networks
– Network Interface Cards
– Multi-Access Computers
– Social, Legal & Ethical Issues
Recap - LAN
• Area: Room, building or •
group of buildings
• Stations & File Server
• Transmission Medium:
– Copper cable
– Fibre optics
– wireless
Advantages of LANs
– Share data
– Resource sharing
– Different levels of
access
– Flexible access
– workgroup computing
Recap - WAN
• Area: town, city,world
• Network Security:
• Transmission Medium:
– Telecommunications
Links
• Satellites
• Microwave transmission
– Passwords & user IDs
– Encryption
– Physical methods
Client & Server Networks
• A method of network organisation
• Each workstation is called a client
• Each workstation is connected to a central
system called a server
• The server can be used for:
– Holding all the data files and application
software
– Organising printing on the network
– Organising the clients’ access to the internet
Client / Server Network
Client
Client
Client
Printer
Client
Server
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
Multi-Access Computers
• Enable many users to:
– Access the system at the same time
– Share the proccessing power of the system
– Share the available memory
– Share the data on backing storage
• The terminals attached to these computers
useually have no processing power of their
own.
• The terminals would be made up of just a
monitor and keyboard
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
• Code of conduct used in e-communications
•
•
•
•
•
•
•
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
Communications & Networks
The Internet
Lesson
Objectives
• Internet Services
• Accessing the
Internet
• The World Wide
Web
• Search Engines
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
• Modem
– The telephone line doesn’t understand binary
– A modem is needed to translate for the computer
• 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
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
• Hyper Text Mark-up Language
• The language used to write web pages
<"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>
Search Engine
• Special web site to help you find
information
• A big database!
• Some of the main search engines:
Lesson
Objectives
• Software on the
internet
• Video conferencing
• Streaming media
• Internet services
• Mobile Internet
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 (Blog)
– 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