Origins of the Internet
The Internet was started as a research project sponsored
by the Advanced Research Projects Agency (ARPA)
within the U.S. Dept. of Defense in the late 1960s.
Called ARPAnet, this distributed network was conceived
to support university and military research.
In the 1980s the National Science Foundation (NSF) used
this same technology to create the NSFnet, which was
intended to support education and research.
In the mid 1980s the Internet was commercialized as dot
coms were created. Much traffic on the Internet is now
Web-based and commercial in nature.
What is the Internet?
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The Internet is a constellation of
communicating devices supported by a
common communications protocol (TCP/IP),
offering the following capabilities:
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SMTP – Simple Mail Transport Protocol (aka “Email”)
telnet -- the ability to connect to a remote host and interact as if one
where onsite
FTP – File Transfer Protocol, the ability to connect to a remote host and
upload/download a file
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On the Internet, packets of data
are routed from place to place:
Data may include:
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Email
Web pages
Graphics and multimedia
Chats, conferences
Video and voice
Other types of files and data
Some characteristics of the Internet
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The Internet is agnostic about the data it carries
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Today, the Internet is being used for all kinds of
things not envisioned by its founders, from
telephone calls to e-commerce.
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In Q301, we will learn about many of the uses of
the Internet, and become prepared to use,
develop and shape many of the forms of
communication taking place.
Hostnames and the
Domain Name Server (DNS)
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Every host (aka system or computer) on the
Internet requires a unique identification number,
a numeric address
The Internet requires this number to get data
from a source to a destination address
The number is built up of 4 numbers, each
between 0 and 255 (aka, 4 bytes total)
For every hostname, such as
sislt.missouri.edu, there is a numeric
equivalent (128.206.171.229).
Domain Name Server (DNS)
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The Domain Name Server (DNS) system and
associated sub-systems on the Internet are used
to
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Find out which server handles addressing for a
particular domain (like .com or .unc.edu
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Contact that server
Do a DNS lookup to find out the numeric address
associated with the hostname
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The Internet routing structure then worries
about how to get the data from one location to
the other, using a series of "routes" (which are
maintained by routers and other networking
equipment)
DNS (cont’d):
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Theoretically, data can take different routes
between a source and a destination. In practice,
there is usually only one route that's most likely
between two hosts.
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Top-level domains include .com, .gov, .edu
and .net, which are mostly used for US-based
organizations. .us, .ca, .jp and others are used for
specific countries. New top-level domains include
.biz, .coop and .info.
Internet Protocols:TCP and IP
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Protocols are rules for communication. By
agreeing on such rules, the Internet works.
Many protocols are used for the Internet, to
make sure data get from one place to another.
For example, the HyperText Transport
Protocol (HTTP) governs how Web clients
(browsers) talk with Web servers.
The defining protocol for the Internet is the
Internet Protocol, the IP.
IP : the Internet Protocol
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The Internet is the network of IP networks.
(This is the minimal definition of the Internet).
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IP is a protocol that manages getting data from
one place to the other on the Internet. The IP
doesn't do any quality control or error handling,
other than to make sure the payload arrives
intact.
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TCP does quality control, packet reassembly, and
other things to make sure the data are usable.
Hostnames and the DNS
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For the most part, the DNS operates behind the
scenes. We don't need to know an IP address for
a particular hostname, and don't need to worry
about how the data get from one place to another.
For experts, though, it's good to be able to get
behind the scenes to diagnose problems or errors.
Some utilities available include ping, traceroute,
nslookup and whois. These are available for
Unix/Linux and Windows machines, among
others.
Usage (samples are using Unix, but pine and
nslookup are available in the DOS/Command-line
interface with Windows)
1. whois missouri.edu gets basic information about
the DNS servers for missouri.edu
2. whois -h whois.networksolutions.com
missouri.edu gets more detailed information uncluding the
administrative, technical, billing and zone contact. There are other
registrars than networksolutions.com, but they were one of the
first -- whois can help you to find out where to go to find out about
the human organization on the other side of a hostname.
3. ping www.yahoo.com sends a ICMP packet over the
IP to check whether a host is alive, and how quickly a response is
received. On Sun systems (including the SILS server), use
Usage (cont’d):
4. nslookup www.state.gov gets the IP address(es)
associated with the hostname www.state.gov. Some sites
have more than one IP address for redundancy or loadhandling (try www.whitehouse.gov or
www.yahoo.com).
5. traceroute www.google.com (^C to cancel) traces
the route your packets take to get to www.google.com. This
can be thrown off by firewalls or other systems that block
some types of packets.
The World Wide Web is
A software application, most often
running on the Internet (but not required
to be) using a client – server protocol for
communications.
 When run on the Internet, these apps are
supported by SMTP, telnet, and FTP
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What makes the Web Unique?
Hyperlinks !!!
Hyperlinks (the ability to move from one
source to another in a webbed environment)
are the primary reason why the Web is so
popular (and navigable).
 Hyperlinks are often combinations of the
telnet and FTP functions within TCP/IP
(the so-called “Internet protocol”)
 Hyperlinks are examples of “associative
trails” (Vannevar Bush 1945)
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So what is “client-server”?
Client-server itself is a software
application that supports connectivity
and functionality between users (running
“client software applications”) and hosts,
or servers running server-side software.
 Sometimes we call this design philosophy
an “Open Systems” design, since it
supports multiple H/S platforms.
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The Web (or “WWW”) enables these
functions:
 Text
and graphic presentation to the
end user
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 Hyperlinks
to related materials
created by a web page author
What is HTML?
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The authoring language of the Web is
currently HTML, which stands for
HyperText Markup Language.
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Future versions of the Web are likely to
be based on XML, and eXtensible
Markup Language
HTML does not support such things as:
 Sound,
motion, video
 User interactions
 Counters and market information
But these applications can be accomplished
through external programming tools that
run “under” HTML.