Transcript 1-Structure - Lehigh University

Internet Research
Structure of the Internet
Understanding the
• Even long-time computer users do not
understand the fundamental structure and
concepts underlying the Internet and World
Wide Web.
• But Internet research is enhanced with even
a basic understanding of an apparent
alphabet soup, such as http, URL, IP, .com,
www and others.
The Internet is a network
• The Internet is a
network of thousands
of connected computer
networks around the
world.
Networks, clients & servers
• Computer networks are built
upon client-server
relationships.
• Simply, the client requests
information or a file. The
server stores information and
responds to requests for
information.
A Client Request
• Your personal computer software is
a client.
• For example, when you linked to a
class web site: Your client software
made a request of the university
server that stored and sent you the
web site.
• You don’t go to the web site. The
server sends the web site to you.
Client software: The browser
• The client software used to make
requests of servers, and then
display the response to those
requests, is called a browser.
• The most common Web browsers
are Netscape Communicator
(previously Navigator) and
Microsoft Internet Explorer.
• Others include Opera and Lynx.
IP
• How do browsers find the file you
want? Like the mailman, they go to
a specific address.
• Every computer connected to the
Internet has been assigned an
Internet Protocol number. A
Protocol is the rules by which
different computers can
communicate and transfer files.
URL: an address
• Usually this long string of numbers is in four
parts, separated by dots: 323.556.123.8
• But who can remember such numbers? The
computer and its number thus are also given a
name (an alias) that can serve as an address.
• Clients and servers request, identify and send files
on the Web using these names in the Uniform (or
Universal) Resource Locator: URL.
http://www.lehigh.edu
• The URL tells you where the
information can be found
and how to access the
information.
• For example, the URL for
Lehigh University is:
http://www.lehigh.edu
http: the protocol
• Most Web addresses begin with http://. This
is the protocol, the rules by which different
computers can communicate on the Web.
• Most information on the Web uses the
Hypertext Transfer Protocol: http.
• The protocol comes first in a Web address
so the computers know what kind of
“language they should speak together.”
www.host
• After the protocol comes three
separation marks ://
• Then comes the name of the “host”
computer. Often the host is the
server computer linked directly to
the World Wide Web from which
you are requesting information.
www.old
• www was used in the early days of
the Internet to tell people that the
site was on the Web.
• Now with most information on the
Web, the www is mostly a tradition.
Many web sites can be reached
without even typing the www.
Master of your domain
• To help further identify information, the
URL follows the host with a “domain”
name.
• Domains further organize information,
according to the type of organization or the
name of a country.
.com
•
•
•
•
•
•
.com is a commercial or business site
.org is a non-profit organization
.gov is a government site
.mil is a military site
.ca is a site in Canada
.jp is a site in Japan
Home page
• If you only specify a name and
domain, you will likely receive
the host site’s home page from
the server.
• If you want to access other
information on that computer,
you will use the usual “path” and
“file name” format used by
computers.
Slash
• ///////
• You will reach information on the
computer by typing a slash, then
giving a directory or folder name,
and perhaps another slash, with
another folder’s name.
• For example,
http://www.wired.com/news/today
Finding the file
• It’s good to remember exactly what
you are doing.
• From your computer, you are
finding, requesting, receiving and
opening a file that was saved on
someone else’s computer perhaps
halfway around the world.
• That is Internet research.