Transcript Unit 2 c. The Internet

The Internet
Networks
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What is the Internet?
The Internet is a network of networks that connects
governments, people and companies all over the world.
10 Downing Street,
London, England
Koji Araki,
Japan
Sydney Opera
House, Australia
The Internet
Patel’s Fine Silks,
India
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Jim’s
Skateboards
USA,
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The Internet began in the 1980s to allow US universities
to share computer resources, and grew so that in the
1990s it became possible for people to use the Internet
from home.
The World Wide Web (WWW) was developed to make
browsing (viewing) easier though HTTP (HyperText
Transfer Protocol).
HTTP is a set of standards that allow web browsers and
servers to communicate.
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Uses of the Internet
People use the Internet for many reasons: for business,
for research and for pleasure. People can communicate
in different ways with people all over the world.
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How does it work?
When you connect to the Internet you connect your
computer to an Internet Service Provider (ISP). This is
done through telephone or cable services.
Computer signals are digital and normal telephone lines
are analogue, so you need an analogue to digital
converter if you are using an analogue telephone line.
This is called a modem (modulator/demodulator).
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Broadband connections connect through an ADSL
modem. ADSL – Asymmetric Digital Subscriber Line – is a
way of transmitting data at high speeds through existing
telephone lines. Broadband allows the user fast
download speeds and the ability to stay connected to the
service without having to dial up.
ISDN lines are digital and they transmit data faster than
analogue lines. ISDN – Integrated Services Digital
Network – is a set of communications standards allowing
a single wire or optical fibre to carry voice, digital network
services and video. ISDN is intended to eventually
replace the telephone system. To connect to an ISDN line
you need an ISDN router.
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Using the Internet to access a web site follows the same
procedure as shown on slide 7.
Try and remember what’s involved next time you are
tapping your foot impatiently waiting for a web page to
load!
The actual connections may be made using microwaves
and satellite links, in the same way that telephone calls are
connected.
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IP address
But how does your computer know where to send the data?
Every computer that is connected to the Internet has to
have its own address, just as you need an address to
have post delivered to you.
An Internet address is called an IP (Internet Protocol)
address, and it is a series of numbers separated by
dots like this:
217.27.240.45
Can you imagine how difficult it would be if you had to
remember the IP address of all the sites you wanted to
visit? It’s much easer to remember a web address in
words, like:
http://www.theboardworks.co.uk.
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URLs
The domain name system links the IP address
(217.27.240.45) with the text name
(http://www.theboardworks.co.uk) automatically, which
makes it much easier to use.
The text name is what we usually call the web address,
but its proper name is a URL or Uniform Resource
Locator.
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URLs are usually made up of these parts:
www, standing for World Wide Web
an organization name (.theboardworks)
a top level domain (.co)
a country (.uk)
There are many top level domains, for instance .com,
.org (organization), .sch (school), .ac (university).
When you are deciding whether the information from a web
site is reliable, take a look at the URL, as it will give you
some idea of where the information is coming from.
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Speaking the same language
To allow different types of computers in different parts of
the world to interact, there has to be some agreement
about how they communicate.
These standards are called
protocols.
http is the first part of many web
addresses – it stands for HyperText
Transfer Protocol, and states the
protocol that the site will use to
communicate.
HTML stands for HyperText Markup Language, and it is the standard
language that web pages are
written in.
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Software needed
In order to connect to the Internet, you will probably need
software from your ISP that sets up your connection.
Web pages are loaded using a web browser, usually
either Microsoft Internet Explorer or Netscape Navigator.
A web browser displays the web pages and does other
things too:
it allows you to move back and forward through web
pages
it can allow you to bookmark sites you use regularly or
add them to your favourites list
you can set the page your browser first loads up (the
home page)
it can store the sites you have recently visited, as
history.
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Web pages
A web page is a file that is loaded by a web browser. It is
written in HTML code, and contains hyperlinks.
When you click on to a hyperlink, it takes you to another
web page, either on the same site or a different one. Most
web sites are several pages linked together which you
navigate through using the hyperlinks.
Screenshot courtesy of http://www.nrich.maths.org.uk/
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Web pages can contain pictures, videos, animated
graphics and sounds as well as text. File sizes for
multimedia can be very large and this can slow down the
loading of the web page.
Reproduced with permission of Yahoo! Inc © 2003 by Yahoo! Inc.
YAHOO! and the Yahooligans! logo are trademarks of Yahoo! inc.
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Summary
The Internet is a network of networks that connects
governments, people and companies all over the world.
The World Wide Web (WWW) was developed to make
browsing (viewing) easier using HTTP (HyperText
Transfer Protocol).
HTTP is a set of standards (protocols) that allow web
browsers and servers to communicate.
You need an Internet Service Provider (ISP) to
connect to the Internet.
Each computer has an IP address (numbers) and each
web site has a URL (name) which are linked together.
A web page is a file that is loaded by a web browser. It
is written in HTML code, and contains hyperlinks.
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