– Internet originated in 1969 as a scientific-academic network of four computers financed by the U.S. defense establishment. It is now a public, self-sustaining facility accessible to tens of millions of people worldwide. Physically, the Internet uses a subset of the total resources of all of the currently existing public telecommunication networks. Technically, what distinguishes the Internet as a cooperative public network is its use of a set of protocols called TCP/IP (Transmission Control Protocol/Internet Protocol). Although e-mail is the most widely used application on the Internet, the World Wide Web is the most compelling, with its powerful concept of linking the world’s information as hypertext.
– Intranet is a network within an enterprise. It may consist of many interlinked local area networks and also use leased-lines in the wide-area network. The main purpose of an intranet is usually to share company information and computing resources among employees. Larger enterprises usually allow connection outside of the intranet to the Internet through firewall servers that have the ability to screen messages in both directions so that company security is maintained.
– Extranet is a collaborative network that uses Internet technology to link businesses with their suppliers, customers, or other businesses that share common goals. An extranet can be viewed either as part of a company’s intranet that is made accessible to other companies or as a collaborative Internet connection with other companies. The shared information can be accessible only to the collaborating parties or can be publicly accessible.
– Firewall is either the program or the computer it runs on, usually an Internet gateway server, that protects the resources of one network from users from other networks. Typically, an enterprise with an intranet that allows its workers access to the wider Internet uses a firewall to prevent outsiders from accessing its own private data resources.
