The document discusses how the Internet works. It explains that the Internet is a worldwide network of computer networks that use common TCP/IP protocols to exchange data. When a user requests information from a website, the request is broken into packets that travel across multiple networks and host computers before being reassembled at their destination server. The top layers of the client-server model, including applications, are only implemented on end hosts like personal computers and servers, while lower network layers are implemented everywhere on the network.

1. HOW INTERNET
WORKS ?
BY ANURAG KUMAR
12D173

2. 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.

3. 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.

4. How the Internet Works
• TCP/IP
• Routing Traffic Across the Internet
• Network Layers on Client & Server end

5. 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.

6. 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.

8. How the Internet Works -
Network Layers on Client & Server end
Internet
Also known as a “host”…

9. Clients and Servers
• Client program
• Running on end host
• Requests service
• E.g., Web browser
GET /index.html

10. 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”

11. 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

12. 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

13. 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

14. Physical Communication
• Communication goes down to physical network
• Then from network peer to peer
• Then up to relevant layer
Transport
Network
Datalink
Physical
Transport
Network
Datalink
Physical
Network
Datalink
Physical
Application Application
Host A Host BRouter