Transcript The World Wide Web - Department of Computer and Information

The Internet is a vast network connecting
computers all over the world
The original plans for the Internet grew out of a
series of memos written by J.C.R. Licklider of the
Massachusetts Institute of Technology (MIT) in
August 1962 discussing his concept of a
“Galactic Network”
Licklider envisioned a global computer network
through which users could access data and
programs from any site on the network
Accessing cross-referenced documents, known as
hypertext linking, is probably the most important
aspect of the Web because it allows you to quickly
open other Web pages
A hypertext link, or hyperlink, contains a
reference to a specific Web page that you can click
to quickly open that Web page
Internet developed in the 1960s by the
Advanced Research Projects Agency
(ARPA) of the U.S. Department of Defense
to connect the main computer systems of
various universities and research institutions
that were funded by ARPA
In 1990 and 1991, Tim Berners-Lee
created what would become the World Wide
Web (WWW), or the Web, at the European
Laboratory for Particle Physics (CERN) in
Geneva, Switzerland, as a way to easily
access cross-referenced documents that
existed on the CERN computer network
A document on the Web is called a Web page,
identified by a unique address called the Uniform
Resource Locator, or URL
URL commonly referred to as a Web address
A URL is a type of Uniform Resource Identifier
(URI), which is a generic term for many types of
names and addresses on the World Wide Web
A Web site refers to the location on the Internet of
the Web pages and related files (such as graphic files)
that belong to a company, organization, or individual
Internet Protocols
TCP/IP
http://
ftp://
telnet:
mailto:
Transfer Control Protocol/Internet Protocol
World Wide Web
File Transfer Protocol
Telnet
E-mail address
When Computers Communicate
• When two or more computers communicate,
they must have a common way in which to
communicate.
• To do this computers use protocols
• A protocol is an agreement by which two or more
computers can communicate.
• Transfer Control Protocol/Internet Protocol is the
underlying protocol for the Internet.
How TCP/IP Works
1) Transfer Control Protocol
(TCP) breaks data into
small pieces of no bigger
than 1500 characters
each. These “pieces” are
called packets.
101010101001
101010101001
101010011010
101010011010
011010210101
011010210101
010101011010
010101011010
111101010111
111101010111
011101110110
011101110110
110000101110
110000101110
110101010101
110101010101
001110101001
001110101001
010111101000
010111101000
How TCP/IP Works
2) Each packet is inserted
into different Internet
Protocol (IP) “envelopes.”
Each contains the
address of the intended
recipient and has the
exact same header as all
other envelopes.
How TCP/IP Works
• A router receives the
packets and then
determines the most
efficient way to send
the packets to the
recipient.
• After traveling along a
series of routers, the
packets arrive at their
destination.
(Router)
101010101
101010101
001101010
001101010
011010011
011010011
How TCP/IP Works
• Upon arrival at their
destination, TCP
checks the data for
corruption against the
header included in
each packet. If TCP
finds a bad packet, it
sends a request that
the packet be retransmitted.
IP Addresses
• Since computers process numbers more
efficiently and quickly than characters, each
machine directly connected to the Internet is
given an IP Address
• An IP address is a 32-bit address comprised of
four 8-bit numbers (28) separated by periods.
Each of the four numbers has a value between 0
and 255
IP Addresses
• Example of an IP Address:
http://134.68.140.1/
The IP Address of the
Computer Science Department’s Web Server
IP Addresses vs. URLs
• While numeric IP addresses work very well for
computers, most humans find it difficult to
remember long patterns of numbers.
• Instead, humans identify computers using
Uniform Resource Locators (URLs), a.k.a. “Web
Addresses”.
IP Addresses vs. URLs
• When a human types a URL into a browser, the
request is sent to a Domain Name Server (DNS),
which then translates the URL to an IP address
understood by computers.
• The DNS acts like a phonebook.
Anatomy of a URL
http://www.cs.iupui.edu/index.html
protocol
sub-sub
domain
machine
name
sub
domain
domain
name
file name
Top Level Domain Names
In the 1980s, seven gTLDs (.com, .edu, .gov, .int, .mil,
.net, and .org) were created. Domain names may be
registered in three of these (.com, .net, and .org)
without restriction; the other four have limited purposes
.com
.net
.org
.edu
.gov
.mil
.int
Commercial Entity
Internet Service Provider
Non-Profit Organization
Educational Institution
Governmental Agency
Military Entity
Internet Assigned Numbers Authority
Assigned Numbers Authority
http://www.icann.org/faq/
Internet Corporation For Assigned Names and Numbers
Country codes
.JP
.IT
.FR
.DK
.AU
.DE
.CN
.ES
Japan
Italy
France
Denmark
Australia
Germany
China
Spain
Top Level Domain Names and Country Codes
http://www.thrall.org/domains.htm