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  Internet  


  What is the Internet?  


The Internet is network of networks that, together, create one large world-wide network.

  Internet History  


1960's
In 1969 an experimental network called ARPANET was created. It connected four universities and enabled scientists to share information across long distances.

1970's
In the 1970's, ARPANET helped support the development of rules, or protocols, for transferring data between different types of computer networks. These "Internet" (from "internetworking") protocols made it possible to develop the worldwide Internet we have today.

1980's
In 1983 the TCP/IP suite of networking protocols, or rules, becomes the only set of protocols used on the ARPANET. This decision sets a standard for other networks, and generates the use of the term "Internet" as the network of networks which use the TCP/IP protocols.

1990's
The Internet is always growing, new networks are being added and new computers are being added to existing networks daily. It is estimated that number of Internet users will grow to 1.5 billion by 2001.

   The TCP/IP Connection  


The Internet is the largest network on the planet, with all kinds of different computers connected to it. The computers talk to each other using protocols, which are rules or agreements on how to communicate. Think of protocols as a kind of rules for networking. For two different types of computers to communicate with each other, they have to be using the same protocol. TCP/IP, which stands for Transmission Control Protocol/Internet Protocol, is the standard protocol of the Internet. It lets all the different computers connected to the Internet to communicate with each other. Any computer that wants to communicate with any other computer on the Internet must speak TCP/IP.

   How Information Moves accross the Internet  


The Internet is a communications and data movement medium primarily based on the TCP/IP packed-switching networking scheme. A packet-switching network breaks data into small chunks; each chunk is sent across the network in a packet that contains source and destination information. Because each packet has its addressing information built in, it can travel independently. This information allows an enormous number of packets to flow through the network using different routes, yet each reaches its appropriate destination in one piece. The packets may arrive out of order, but because each packet also contains sequence information, the receiving computer can reconstruct the original data. Because it uses this process of transmitting data, the Internet is referred to as a packet-switched network.

  Internet Addressing  


Every computer directly connected to the Internet has its own address, much like a postal address. Knowing the Internet address is as important as knowing postal address for sending letters. Two main types of addresses work together on the Internet - IP addresses and Domain names - to make up an Internet address.

IP addressing
Each computer that uses TCP/IP protocol is distinguished from other computers on the Internet by a unique IP address. An IP address is composed of four numbers, separated by periods, which are hierarchical, from left to right; for example, "194.168.1.17". An IP address identifies a host on the Internet, it is its "identity". The set of the first two (or three) of these numbers is called a "subnet", usually representing a major computer network. Originally, computers connected on the Internet were identified only by their IP numeric addresses.

Domain Names
IP numeric addresses can be difficult to remember, so a text system was developed called Domain Name System (DNS). The general idea is to use ordinary names instead of numbers and a transparent to user procedure should find out what name is registered at what IP address, looking at the databases with names and IP numbers. Like the IP addressing scheme, we have dots but they now separate words instead of numbers, as in "info.forthnet.gr" and there is no four-digits limit. Domain names are organized in a hierarchical fashion, as are IP addresses, except in reverse order: the most specific (computer name) at the left and the most general top-level domain at the right. Two of the most important features of this system are:
a) The name of a host can remain the same, even if it is moved from the network that it is connected to, therefor changing IP address. What needs changing is just the reference at the names database.
b) a name does not represent a geographical location. It does represent however a company, an organization, a school etc.

In the beginning, there were only six top-level domains referring to U.S. sites:
Later, each country got its own top-level domain. Some examples are:
  Routing  


Internet is a "packet switching" network. Each of these "packets" has its own addressing information embedded in it. What is needed is "something" that will actually read this addressing information and will forward the packets towards its destination. This is called routing and the systems that handle the routing, routers.

  Internet Tools  


The Internet is often called the Information Superhighway. When you drive down the Highway, you are not really "using" the road in sense that you are not physically "doing" anything with the road. Instead you are using your car. This analogy illustrates that you don't really use the Internet (Highway); instead you use tools (cars/ trucks/ buses) that use the Internet.
The most commonly used tools are:
1. Electronic Mail - E-mail is used for sending and receiving of electronic messages between people on the Internet.
2. FTP (File Transfer Protocol) - It allows users to transfer files from one computer to another computer.
3. Telnet - It is a program that allows users to work on remote computer.
4. UseNet (Network News) - It is a massive, distributed conferencing system with many ongoing conferences (called news groups) being conducted, 24 hours a day, 365 days a year. These News Groups allow users to correspond with other Internet users with similar interests.
5. WWW (World-Wide-Web) - It is a system, based on hypertext1 links and HTTP2, for providing, organizing, and accessing a wide variety of resources (text, images, sound) that are available via the Internet.






1 Hypertext is text that is specially coded so links are created. These links can be textual or graphical, and when clicked on, can "link" the user to another resources such as documents, text files, graphics, animation and sound.
2 HTTP is short for Hypertext Transfer Protocol. It is set of rules, or protocol, that governs the transfer of hypertext between two or more computers.