How The Internet Works, Lecture Notes - Computer Science, Study notes of Introduction to Computers

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The InterWebs

and how they work

What is the Internet?

"The Internet is not something that you

just dump something on. It's not a big

truck. It's, it's a series of tubes."

--Former Senator Ted Stevens (R-Alaska)

Too Many Acronyms

 IP

 FTP

 HTTP

 TCP

 DHCP

 UDP

 ASAP

 SMTP

Protocol

a set of rules used to communicate

For example:

 First, I call you.

 Then you answer and say "hello".

 Then I say my name.

 Now I can start talking ...

Example: A Time Server

Howdy.

Say, what

time is it?

Dial astronaut's number

Answer phone

Hang up Hang up

Calling

 What do you need to know in order to place a

call to a server?

 The server computer's "telephone number"--

its IP address.

 For example: 128.2.10.

 These numbers tell the network how to route

your call to the correct computer.

Ask a Name Server (DNS)

Howdy.

Say, what is the

IP address for

www.cmu.edu?

"Dials" Name Server's IP address Answers

Name Server

Question: How do you know the Name Server's IP address?

Answer: Your router tells you when you boot up your computer (DHCP).

Multiple Programs

 A computer can run multiple programs

that access the Internet.

 When your computer receives a "call",

how does it know which program

should answer?

The Web

 What does HTML stand for?

 Hyper Text Markup Language

All Things Cow

Cows: 50% off!

All Things Cow

Cows: 50% off!

HTML

what the browser shows

The Web

 What does HTTP stand for?

 Hypertext Transfer Protocol

 In other words, a protocol for

transfering HTML from a web server to

your web browser (IE, Firefox, etc).

Links

 Suppose a web page contains a link to

www.cows.com.

 The HTML used to generate that page

might contain the following:

Click

here for great cow deals!

Web Search

 Suppose you tell Google to search for

"cows"

 How does Google know what web

pages contain the word "cows"?

Web Search

 Yeah, but how does Google do that so

quickly?

 Google cheats.

 Google's web crawlers run while you're

asleep.

Indexing

Using its web crawlers, Google builds up

an enormous index , where each entry

indicates what web pages contain a

particular word.

cow : en.wikipedia.org/wiki/Cattle, www.cowdance.com,

www.cows.com, ...

coward: dictionary.reference.com/browse/coward,

www.cowardshoe.com, ...