Download Note

How Does the Internet Work?
Protocols
• Protocols are rules that describe how computers
communicate and exchange data.
• The Internet has a series of these protocols:
– TCP/IP – Rules which tell data how to move between
computers on the Internet.
– HTTP (Hypertext Transfer Protocol) – rules to get
and send information on web pages on the World
Wide Web.
– SMTP (Simple Mail Transfer Protocol) – rules for
sending and receiving e-mail.
– FTP (File Transfer Protocol) – rules for transferring
files from one computer to another.
IP address
• An IP address is a unique address assigned to
each computer connected to the Internet.
• It is used by TCP/IP to identify computers when
sending packets of information from one
computer to another.
• Because computers use numbers to
communicate, an IP address consist of four sets
of numbers ranging from 0 to 255 separated by
a period (for example 249.7.13.53)
Uniform Resource Locator (URL)
• Unlike computers, people have a hard time
remembering and working with numbers.
• The Internet (including the WWW) would be very
difficult for us to use if it was completely based
on numbers.
• Fortunately, the Domain Name System (DNS)
was created. This system assigns an English
name to every web site. This name is called the
Uniform Resource Locator (URL).
• Examples of URL’s are www.hctoday.ca and
www.nhl.com
• URL’s are much easier for us to remember and
use.
Domain Name System (DNS) Servers
• A DNS server stores the URL and the IP address
of each web site.
• When you type the URL, this information is sent
to a DNS server.
• The DNS server matches the URL with the
correct IP address and tells your computer which
computer to look for the web site
• It works like a telephone book. People have a
tough time remembering phone numbers but
easily remember names. By looking up the
name in the phone book, the matching phone
number is quickly found.
Parts of a Typical URL
http://www.amazon.com/books/children.html
• "http“
– Transfer protocol
• "www"
– Signifies the site is part of the WWW
• “amazon"
– Second-level domain name. The second level domain is
often the name of the company or organization
• “com"
– Top-level domain name
• "books"
– Directory name on the computer where the site is stored
• “children"
– File name of the web page
• "html"
– File type – all web pages have this extension
Common Top Level Domains
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.com – commercial/company site
.edu - educational
.gov – government site
.org – non-profit organization
.mil – military sites
.net – network providers
.ca – sites originating in Canada
.uk – sites originating United Kingdom
• .us – sites originating United States
How Data Moves Between Computers on the Internet
• Remember that the Internet is a massive collection of
computer networks which are connected together.
• A router is a piece of hardware which has the job of
transferring information between two networks.
• Data sent from one computer to another on the
Internet gets broken up into a number of small
sections called data packets. Each data packet is
assigned the address of the destination computer.
• The packets travel from one router to another. Each
router reads the IP address of the packet and decides
which path on the Internet will be the fastest.
• Since the amount and destination of data sent
on the Internet is always changing, these data
packets will travel separate routes and arrive at
the destination computer at different times.
• The destination computer reassembles the
packets once they all arrive.
• Amazingly, this complicated process happens in
a matter of milliseconds.
• This process is called packet switching and is
the most important part of TCP/IP.
An Illustration of Packet Switching
Your computer
Your network’s router
Routers
Routers
Destination network’s router
Destination computer
http://www.youtube.com/watch?v=PBWhzz
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