Transcript Get the Net! - La Salle University

Get the Net!
The Internet and World Wide Web
Some of this material can be found in
Chapters 7 and 8 in Computing Essentials
2000-2001 (O’Leary and O’Leary)
Networks


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

Metropolitan area networks (MANs) are
spread throughout a city or county. For
example, a cellular phone network

Wide area networks (WANs) are spread
over an even wider area, a telephone
company, for instance
Client/Server



In the client/server arrangement, a more
powerful computer (the server)
manages the resources shared by the
rest of network (the clients)
The client requests to use the server’s
resources
A client crashes (bad news); the server
crashes (disaster)
Internet



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



An early ancestor of the Internet was called
ARPANET (Advanced Research Project
Agency Network)
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


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





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)
Bandwidths

Voiceband
– Refers to the transmission rate of the phone lines
– Modems are one way to connect computers to the
internet; the connection is via the phone line
– Their speed measured in bits per second (bps)


Medium band (faster)
Broadband (even faster)
– Broadband has high enough information rate to
carry several “channels” at once
Packets



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




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

inter: between or among

intra: within or inside of

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



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


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 (we’ll use this to post
our web pages later in the semester)
The Net > The Web

The Internet also incudes:
– telnet: to log onto a computer that one is
not physically in front of (we’ll use this to
post our web pages later in the semester)
– 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



The Web is a hyperlinked multimedia
database
HUH?
It is a vast collection of information stored in
files (hence a database)
– Above we are using the term database is a loose
sense; some only use “database” to mean a
highly-structured collection of information

It appears as documents with text, as well as
graphics, audio, animation, and video (hence
multimedia)
The Web


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


Gopher is older than the Web and also allows
one to access files
It has a “hierarchical” or tree structure
– The branches are analogous to folders and files


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)

the fancy term for a web site address is
a uniform resource location (URL)
A URL consists of several parts, e.g.

http://www.lasalle.edu/lsu-site/it/notes.htm#attach

– protocol: a set of standards allowing
computers to exchange information
– http - “hypertext transfer protocol” (others:
ftp, gopher, telnet, news)
URL’s (cont.)

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.)

http://www.lasalle.edu/lsu-site/it/notes.htm#attach
– the folder (or directory) containing the file,
also known as the path

http://www.lasalle.edu/lsu-site/it/notes.htm#attach
– the file or document (often an html file)

http://www.lasalle.edu/lsu-site/it/notes.htm#attach
– anchor or fragment, indicates a specific
part of a document
Hyperlinks



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

“We’d like you to know a little bit about our
four files.”
– Hypertext markup language (HTML) text with
hyperlinks
• Extensible Markup language (XML) is trying to overcome
some limitations of HTML
– 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
• Higher quality but requires reader (special software)
Browsers and Search Engines




browser: software used to navigate
(move around) 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, Lycos,
HotBot