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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
• Optical Fibre
Network Security
• Security methods include:
– Passwords
– Encryption
– Physical methods
Communications & Networks
Standard Grade Revision:
Electronic Communications
Networks (Recap)
LAN
WAN
Security on Networks
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
• File Transfer
– Files can be attached
– Size limit
– Attached viruses
• Disadvantages:
– Spam
– Viruses
– Lack of Netiquette
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
Standard Grade Revision:
The Internet
E-Communications (Recap)
E-Mail
Text Messaging
Netiquette
The Internet
• A Wide Area Network across the world
• The network of networks
– Lots of smaller networks joined together
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
• 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
• Hyper links 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: