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.

http://www.amazon.com/books/children.htmlhttp://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

Parts of a Typical URL

Common Top Level Domains• .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 SwitchingYour computer

Destination computer

RoutersRouters

Your network’s router

Destination network’s router

http://www.youtube.com/watch?v=PBWhzz_Gn10