HOW INTERNET WORKS ?

BY ANURAG KUMAR

12D173

Internet• The Internet is a worldwide collection of computer

networks, cooperating with each other to exchange data using a common software standard.

• The Internet was created by the Advanced Research Projects Agency (ARPA) and the U.S. Department of Defense for scientific and military communications.

Internet• Internet allows users to:

• connect easily through ordinary personal computers and local phone numbers;

• exchange electronic mail (E-mail) with friends and colleagues with accounts on the Internet;

• post information for others to access, and update it frequently;

• access multimedia information that includes sound, photographic images and even video; and

• access diverse perspectives from around the world.

How the Internet Works

• TCP/IP

• Routing Traffic Across the Internet

• Network Layers on Client & Server end

How the Internet Works - TCP/IP

• Every computer and network on the Internet uses the same protocols (rules and procedures) to control timing and data format

• The protocol used by the Internet is the Transmission Control Protocol/Internet Protocol, or TCP/IP.

• No matter what type of computer system you connect to the Internet, if it uses TCP/IP, it can exchange data with any other type of computer.

How the Internet Works - Routing Traffic Across the Internet

• Most computers don't connect directly to the Internet. Instead, they connect to a smaller network that is connected to the Internet backbone.

• The Internet includes thousands of host computers (servers), which provide data and services as requested by client systems.

• When you use the Internet, your PC (a client) requests data from a host system. The request and data are broken into packets and travel across multiple networks before being reassembled at their destination.

How the Internet Works - Network Layers on Client & Server end

Internet

Also known as a “host”…

Clients and Servers

• Client program• Running on end host

• Requests service

• E.g., Web browser

GET /index.html

Clients and Servers

• Client program• Running on end host

• Requests service

• E.g., Web browser

• Server program• Running on end host

• Provides service

• E.g., Web server

GET /index.html

“Site under construction”

Client-Server Communication

• Client “sometimes on”• Initiates a request to the

server when interested

• E.g., Web browser on your laptop or cell phone

• Doesn’t communicate directly with other clients

• Needs to know the server’s address

• Server is “always on”• Services requests from many

client hosts

• E.g., Web server for the www.cnn.com Web site

• Doesn’t initiate contact with the clients

• Needs a fixed, well-known address

Data traveling process• Five layers

• Lower three layers implemented everywhere

• Top two layers implemented only at hosts

Transport

Network

Datalink

Physical

Transport

Network

Datalink

Physical

Network

Datalink

Physical

Application Application

Host A Host BRouter

Logical Communication

• Layers interacts with peer’s corresponding layer

Transport

Network

Datalink

Physical

Transport

Network

Datalink

Physical

Network

Datalink

Physical

Application Application

Host A Host BRouter

Physical Communication• Communication goes down to physical

network

• Then from network peer to peer

• Then up to relevant layerTransport

Network

Datalink

Physical

Transport

Network

Datalink

Physical

Network

Datalink

Physical

Application Application

Host A Host BRouter