Internet

Concept of protocols

INTERNET

Internet Service Provider (ISP) has connected to the Internet

INTERNET

You need a telephone line and a modem to connect to your ISP and then through ISP to Internet modem

Telephone line

Connection to ISP

Information provided by ISP for connection through modem

• modem dial-up number

• user name

• password

• ISP’s computer name

Why do you need a modem ?

Modem

• At the sender side, it change computer signal (digital) to telephone signal(analog)

• Signal is then transmitted through the telephone line

• At the receiver side, it can change back telephone signal (analog) to computer signal(digital)

INTERNET

Two computers are connected through the

Internet by use of modems

How do 2 computers communicate when they are

connected through the Internet?

They have their protocols to communicate

Hi !

How are you ?

I am Computer X

Computer X

Hi !

How are you ?

I am Computer YComputer Y

Computer Y !

How can I send messages to you ?

Computer X

Computer X !

You can send messages to me by using protocols called TCP/IP

.

Computer Y

Computer Y !

TCP/IP can divide messages into packets and arrive to you safely

What is your IP address?

Computer X

Computer X!

My IP address is

250.143.035.001

But humans call me compy.com.hk

because a group of numbers is difficult to remember for human being.

What is your IP address?

Computer Y

Computer Y!

My IP address is

250.143.075.255

But human calls me compx.com.hk

Can I send messages to you now?

Computer X

Computer X!

Now, you can send your messages according to my IP address

Computer Y

Computer Y!

Since your IP address is unique,

I can send messages to you now

Are you ready?

Computer X

Computer X!

Now, I am readyComputer Y

Computer Y!

I am sending now ... Computer X

Protocol

• A standard rule governing the communication between 2 computers

• For example– TCP (Transmission Control Protocol)– IP (Internet Protocol)– HTTP (Hypertext Transfer Protocol)

Domain Name

• Every Internet server has IP address

• It consists of 4 octets, which is very precise (e.g. 250.143. 35.1)

• But humans have trouble with remembering numbers and they prefer to use meaningful text address

(e.g. compy.com.hk)

I want to access the internet resources. What should I need in order to connect the Internet?

You need

• ISP

• telephone line and a modem

• a browser

• URL

Terms• Internet Service Provider (ISP)

– a company that gives you access to the Internet for a feE

• Uniform Resource Locator(URL)– an address that identifies a server, a directory or a specific

file such as HTTP URLs orWeb addresses

• Browser– a program that lets you view and explore information on t

he Web such as Internet Explorer or Netscape Communicator