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How the Internet Works:
What happens when information is sent from your computer?
You should know
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what a protocol is.
how TCP/IP works.
how IP addresses work.
what domain names are.
the different protocols available on the
Internet.
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.
TCP/IP
Three Important Concepts:
TCP/IP
Internet Addresses
the Domain Name System
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
101010011010
011010110101
010101011010
111101010111
011101110110
110000101110
110101010101
001110101001
010111101000
101010101
001101010
011010011
101010101
001101010
011010011
101010101
001101010
011010011
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.
101010101
001101010
011010011
131.194.83.47
101010101
001101010
011010011
101010101
001101010
011010011
131.194.83.47
131.194.83.47
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.
• There may be more than one route
available. When a message is sent, the
packets may take different routes or
may arrive in the wrong order.
How TCP/IP Works
• Upon arrival at the 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.
• You can see examples of packets
traveling the Internet by using the
tracert command. In Windows, the
tracert command can be accessed from
the command line (DOS prompt).
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Using Tracert
Start your connection to the Internet
Choose Run for the Start menu
At the Open prompt, key cmd and click OK. A
command prompt will open.
• At the prompt, key in tracert and the website (e.g.,
tracert www.trinity.edu)
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://131.194.83.47/
CLS 344 Instructor Station
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 (what machines know) vs. URLs
(what humans type in)
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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.
A master database keeps track of what name servers are the
authority for each and every domain name. For example, if you
register your own domain, part of the registration process requires
that you indicate what domain name servers (DNS) will know
where to look for your web site.
Every time you use a domain name, you use the Internet's domain
name servers (DNS) to translate the human-readable domain name
into the machine-readable IP address.
Anatomy of a URL
http://www.cs.iupui.edu/index.html
protocol
file name
domain
name
Top Level Domain Names
.edu
.gov
.mil
.com
.net
.org
Educational Institution
Governmental Agency
Military Entity
Commercial Entity
Internet Service Provider
Non-Profit Organization
. . .and some new ones!
Internet Protocols
http://
mailto:
ftp://
telnet:
World Wide Web
E-mail address
File Transfer Protocol
Telnet
Terms you should know
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Backbone
Computer network
Domain Name Server
Internet
Internet Protocol (IP)
IP address
Local Area Network (LAN)
Packet-switched network
Protocol
Router
Transmission Control Protocol (TCP)