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.
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