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The Internet and World Wide Web |
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Some of this material can be found in Chapters 7
and 8 in Computing Essentials 2000-2001 (O’Leary and O’Leary) |
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A network is a collection of computers connected
together so that they can share information |
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A network is called a local area network (or
LAN) if the constituent computers are all located in the same vicinity |
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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 |
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In the client/server arrangement, a more
powerful computer (the server) manages the resources shared by the rest of
network (the clients) |
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The client requests to use the server’s
resources |
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A client crashes (bad news); the server crashes (disaster) |
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When two or more networks are connected, they
form an internet (small i) |
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The Internet (capital I) is the global
collection of connected networks |
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“The biggest WAN of them all” |
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An early ancestor of the Internet was called
ARPANET (Advanced Research Project Agency Network) |
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It was built in the late 60’s by a collaboration
of universities and the military |
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One desired feature was a network that would
still function if part of it was “knocked out” |
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The whole point of being “connected” is that
information can be passed back and forth |
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information (signals) can be sent through the
air (as in radio or non-cable television), but computers are typically
“wired” |
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twisted pair wire looks like the wire to your
telephone |
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coaxial cable looks like the wire to your cable
tv |
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fiber optic cable sends light beams |
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each successive wire has more bandwidth; bandwidth
is related to the rate of information that can be send |
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(bandwidth ¹ wire thickness) |
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Voiceband |
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Refers to the transmission rate of the phone
lines |
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Modems are one way to connect computers to the
internet; the connection is via the phone line |
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Their speed measured in bits per second (bps) |
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Medium band (faster) |
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Broadband (even faster) |
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Broadband has high enough information rate to
carry several “channels” at once |
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The information is broken into pieces, called packets,
which are sent individually over the wire |
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The packets must also contain the information
that allows the computer to reassemble them |
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more like sending letters than talking on the
phone |
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packets are to letters as routers are to sorters
in the post office |
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A router is the intelligent part of the
connection that directs the information to the right place |
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The analog of one’s address is and zip code is
the Internet protocol (IP) address |
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DEMO (of sorts) |
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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) |
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A firewall restricts the flow of information
both in and out |
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an attempt to have the best of both worlds:
connectivity and access to information on one hand, privacy and security on
the other |
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In the mail analogy, it is as though your mail
is being censored |
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The World Wide Web is only part of the Internet |
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The Internet also includes |
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e-mail (electronic mail): to send messages to and receive messages
from on the same or other networks |
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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) |
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The Internet also incudes: |
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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) |
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gopher:
to find files on the internet; gopher is a precursor to a “search
engine” |
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usenet: to promote discussions on various topics
among discussion or news groups |
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The Web is a hyperlinked multimedia database |
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HUH? |
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It is a vast collection of information stored in
files (hence a database) |
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Above we are using the term database is a loose
sense; some only use “database” to mean a highly-structured collection of
information |
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It appears as documents with text, as well as
graphics, audio, animation, and video (hence multimedia) |
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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 |
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Moving about in this fashion is generally
referred to as “surfing” |
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Gopher is older than the Web and also allows one
to access files |
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It has a “hierarchical” or tree structure |
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The branches are analogous to folders and files |
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One could not jump from branch to another; one
had to climb back down the tree |
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The Web, if less structured, is more highly
connected |
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the fancy term for a web site address is a uniform
resource location (URL) |
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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 |
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http - “hypertext transfer protocol” (others:
ftp, gopher, telnet, news) |
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http://www.lasalle.edu/lsu-site/it/notes.htm#attach |
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domain: denotes the computer that holds the web
page (stands in for the IP address) |
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often starts with www (World Wide Web) |
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ends with the type of organization operating the
site or the country |
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edu (education), gov (government), mil (military),
org (organization), net (networks), uk (United Kingdom), ch (Switzerland) |
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http://www.lasalle.edu/lsu-site/it/notes.htm#attach |
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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 |
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the file or document (often an html file) |
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http://www.lasalle.edu/lsu-site/it/notes.htm#attach |
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anchor or fragment, indicates a specific part of
a document |
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target:
takes you from one part of a web page to another |
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relative:
takes your from one web page to another, but the web pages are on
the same web site |
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absolute: takes you to another web page on
another web site |
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“We’d like you to know a little bit about our
four files.” |
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Hypertext markup language (HTML) text with
hyperlinks |
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Extensible Markup language (XML) is trying to
overcome some limitations of HTML |
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Graphics Interchange Format (GIF) graphics,
especially computer drawn pictures |
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Joint Photographic Experts Group (JPEG),
graphics, esp. photos |
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Portable document format (PDF), mix of text and
graphics |
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Higher quality but requires reader (special
software) |
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browser: software used to navigate (move around)
the web |
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e.g. Netscape Navigator or Microsoft Internet
Explorer |
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search engine: software used to locate
information on the Web |
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e.g. Yahoo, Alta Vista, InfoSeek, Lycos, HotBot |
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Notes