What is Internet?
Global communication is easy now thanks to an intricately linked worldwide computer network that we call the Internet. The Internet's growth has become explosive and it seems impossible to escape the bombardment of www.com's seen constantly on television, heard on radio, and seen in magazines. In less than 20 years, the Internet has expanded to link up around 210 different nations. Even some of the world's poorest developing nations are now connected. Because the Internet has become such a large part of our lives, a good understanding is needed to use this new tool most effectively.
Lots of people use the word "Internet" to mean going online. Actually, the "Internet" is nothing more than the basic computer network. Think of it like the telephone network or the network of highways that criss-cross the world. Telephones and highways are networks, just like the Internet. The things you say on the telephone and the traffic that travels down roads run on "top" of the basic network. In much the same way, things like the World Wide Web, instant messaging chat programs, MP3 music downloading, and file sharing are all things that run on top of the basic computer network that we call the Internet.
The Internet is a collection of standalone computers all loosely linked together, mostly using the telephone network. The connections between the computers are a mixture of old-fashioned copper cables, fiber-optic cables, wireless radio connections, and satellite links.
How does the Internet work?
The Internet do very simple job to move computerized information (data) from one place to another. That's it! The machines that make up the Internet treat all the information they handle in exactly the same way. In this respect, the Internet works a bit like the postal service. Letters are simply passed from one place to another, no matter who they are from or what messages they contain. The job of the mail service is to move letters from place to place.
Because the Internet is a global network of computers each computer connected to the Internet must have a unique address. Internet addresses are in the form oct.oct.oct.oct where oct must be a number from 0 - 255. This address is known as an IP address.
So your computer is connected to the Internet and has a unique address. Let's say your IP address is 184.108.40.206 and you want to send a message to the computer 220.127.116.11. The message you want to send is "Hello computer 18.104.22.168". Obviously, the message must be transmitted over whatever kind of wire connects your computer to the Internet. Let's say you've dialed into your ISP from home and the message must be transmitted over the phone line. Therefore the message must be translated from alphabetic text into electronic signals, transmitted over the Internet, then translated back into alphabetic text. Through the use of a protocol stack. Every computer needs one to communicate on the Internet and it is usually built into the computer's operating system. The protocol stack used on the Internet is referred to as the TCP/IP protocol stack.
The Internet backbone is made up of many large networks which interconnect with each other. These large networks are known as Network Service Providers or NSPs. Some of the large NSPs are UUNet, CerfNet, IBM, BBN Planet, SprintNet, PSINet, as well as others. These networks peer with each other to exchange packet traffic. Each NSP is required to connect to three Network Access Points or NAPs. At the NAPs, packet traffic may jump from one NSP's backbone to another NSP's backbone. NSPs also interconnect at Metropolitan Area Exchanges or MAEs. MAEs serve the same purpose as the NAPs but are privately owned. NAPs were the original Internet interconnect points. Both NAPs and MAEs are referred to as Internet Exchange Points or IXs. NSPs also sell bandwidth to smaller networks, such as ISPs and smaller bandwidth providers.
A computer that gets information from a server is called a client. One of the most commonly used services on the Internet for client server communiation is the World Wide Web (WWW). The application protocol that makes the web work is Hypertext Transfer Protocol or HTTP. HTTP is the protocol that web browsers and web servers use to communicate with each other over the Internet. It is an application level protocol because it sits on top of the TCP layer in the protocol stack and is used by specific applications to talk to one another. In this case the applications are web browsers and web servers. HTTP is a connectionless text based protocol. Clients send requests to web servers for web elements such as web pages and images. After the request is serviced by a server, the connection between client and server across the Internet is disconnected. A new connection must be made for each request. Most protocols are connection oriented. This means that the two computers communicating with each other keep the connection open over the Internet. HTTP does not however. Before an HTTP request can be made by a client, a new connection must be made to the server.
Another commonly used Internet service is electronic mail. E-mail uses an application level protocol called Simple Mail Transfer Protocol or SMTP. SMTP is also a text based protocol, but unlike HTTP, SMTP is connection oriented. SMTP is also more complicated than HTTP. There are many more commands and considerations in SMTP than there are in HTTP.
The other part of communication over internet is peer to peer. When two computers on the Internet swap information back and forth on a more-or-less equal basis, they are known as peers. If you use torrent or an instant messaging program to chat to a friend, and you start swapping party photos back and forth, you're taking part in what's called peer-to-peer(P2P) communication. In P2P, the machines involved sometimes act as clients and sometimes as servers.
Apart from clients and servers, the Internet is also made up of intermediate computers called routers, whose job is really just to make connections between different systems. If you have several computers at home or school, you probably have a single router that connects them all to the Internet.