Transcript Get the Net! - La Salle University

Get the Net!
The Internet and World Wide Web
Networks
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A network is a collection of computers
connected together so that they can
share information
A network is called a local area network
(or LAN) if the constituent computers
are all located in the same vicinity
Other networks
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Metropolitan area networks (MANs) are
spread throughout a city or county. For
example, a cellular phone network
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Wide area networks (WANs) are spread
over an even wider area, a telephone
company, for instance
Internet
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When two or more networks are
connected, they form an internet
(small i)
The Internet (capital I) is the global
collection of connected networks
“The biggest WAN of them all”
A Little History
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An early ancestor of the Internet was
called ARPANET (Advanced Research
Project Agency)
It was built in the late 60’s by a
collaboration of universities and the
military
One desired feature was a network that
would still function if part of it was
“knocked out”
Connections
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The whole point of being “connected” is
that information can be passed back
and forth
information (signals) can be sent
through the air (as in radio or non-cable
television), but computers are typically
“wired”
Wire
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twisted pair wire looks like the wire to
your telephone
coaxial cable looks like the wire to your
cable tv
fiber optic cable sends light beams
each successive wire has more
bandwidth; bandwidth is related to the
rate of information that can be send
(bandwidth  wire thickness)
Packets
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The information is broken into pieces,
called packets, which are sent
individually over the wire
The packets must also contain the
information that allows the computer to
reassemble them
more like sending letters than talking on
the phone
Routers
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packets are to letters as routers are to
sorters in the post office
A router is the intelligent part of the
connection that directs the information
to the right place
The analog of one’s address is and zip
code is the Internet protocol (IP)
address
DEMO (of sorts)
Inter Vs. Intra
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inter: between or among
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intra: within or inside of
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intranet: a set-up like the Internet
(having browsers, email, etc.) but not
connected to the outside world (often
used by companies wanting to maintain
some privacy)
Firewalls
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A firewall restricts the flow of information
both in and out
an attempt to have the best of both
worlds: connectivity and access to
information on one hand, privacy and
security on the other
In the mail analogy, it is as though your
mail is being censored
The Web  The Net
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The World Wide Web is only part of the
Internet
The Internet also includes
– e-mail (electronic mail): to send messages
to and receive messages from on the same
or other networks
– ftp (file transfer protocol): to put or get files
from other computers
The Net > The Web
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The Internet also incudes:
– telnet: to log onto a computer that one is
not physically in front of
– gopher: to find files on the internet; gopher
is a precursor to a “search engine”
– usenet: to promote discussions on various
topics among discussion or news groups
The World Wide Web
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The Web is a hyperlinked multimedia
database
HUH?
It is a vast collection of information
stored in files (hence a database)
It appears as documents with text, as
well as graphics, audio, animation, and
video (hence multimedia)
The Web
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Finally, the documents (web pages) are
connected to one another via
hyperlinks, a reference to another web
page which if clicked takes one to that
page
Moving about in this fashion is generally
referred to as “surfing”
Web Vs. Tree
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Gopher is older than the Web and also
allows one to access files
It has a “hierarchical” or tree structure
One could not jump from branch to
another; one had to climb back down
the tree
The Web, if less structured, is more
highly connected
Tree (like
Windows
Explorer)
Web
Getting Around (URL’s)
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the fancy term for a web site address is
a uniform resource location (URL)
A URL consists of several parts, e.g.
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http://www.lasalle.edu/lsu-site/it/notes.htm#attach
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– protocol: a set of standards allowing
computers to exchange information
– http - “hypertext transfer protocol” (others:
ftp, gopher, telnet, news)
URL’s (cont.)
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http://www.lasalle.edu/lsu-site/it/notes.htm#attach
– domain: denotes the computer that holds
the web page (stands in for the IP address)
– often starts with www (World Wide Web)
– ends with the type of organization
operating the site or the country
• edu (education), gov (government), mil
(military), org (organization), net (networks), uk
(United Kingdom), ch (Switzerland)
URL’s (cont.)
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http://www.lasalle.edu/lsu-site/it/notes.htm#attach
– the folder (or directory) containing the file,
also known as the path
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http://www.lasalle.edu/lsu-site/it/notes.htm#attach
– the file or document (often an html file)
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http://www.lasalle.edu/lsu-site/it/notes.htm#attach
– anchor or fragment, indicates a specific
part of a document
Hyperlinks
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target: takes you from one part of a
web page to another
relative: takes your from one web page
to another, but the web pages are on
the same web site
absolute: takes you to another web
page on another web site
Web File Types
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“We’d like you to know a little bit about our
four files.”
Hypertext markup language (HTML) text with
hyperlinks
Graphics Interchange Format (GIF) graphics,
especially computer drawn pictures
Joint Photographic Experts Group (JPEG),
graphics, esp. photos
Portable document format (PDF), mix of text
and graphics
Browsers and Search Engines
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browser: software used to navigate the
web
e.g. Netscape Navigator or Microsoft
Internet Explorer
search engine: software used to locate
information on the Web
e.g. Yahoo, Alta Vista, InfoSeek