1.1 TCP/IP and the Internet

In 1969 the Advanced Research Projects Agency (ARPA) funded a research and development project to create an experimental packet-switching network. This network, called the ARPANET , was built to study techniques for providing robust, reliable, vendor-independent data communications. Many techniques of modern data communications were developed in the ARPANET.

The experimental ARPANET was so successful that many of the organizations attached to it began to use it for daily data communications. In 1975 the ARPANET was converted from an experimental network to an operational network, and the responsibility for administering the network was given to the Defense Communications Agency (DCA). [1] However, development of the ARPANET did not stop just because it was being used as an operational network; the basic TCP/IP protocols were developed after the ARPANET was operational.

[1] DCA has since changed its name to Defense Information Systems Agency (DISA).

The TCP/IP protocols were adopted as Military Standards (MIL STD) in 1983, and all hosts connected to the network were required to convert to the new protocols. To ease this conversion, DARPA [2] funded Bolt, Beranek, and Newman (BBN) to implement TCP/IP in Berkeley (BSD) UNIX. Thus began the marriage of UNIX and TCP/IP.

[2] During the 1980s and early 1990s, ARPA, which is part of the U.S. Department of Defense, was named Defense Advanced Research Projects Agency (DARPA). Currently known as ARPA, the agency is again preparing to change its name to DARPA. Whether it is known as ARPA or DARPA, the agency and its mission of funding advanced research has remained the same.

About the time that TCP/IP was adopted as a standard, the term Internet came into common usage. In 1983, the old ARPANET was divided into MILNET, the unclassified part of the Defense Data Network (DDN), and a new, smaller ARPANET. "Internet" was used to refer to the entire network: MILNET plus ARPANET.

In 1985 the National Science Foundation (NSF) created NSFNet and connected it to the then-existing Internet. The original NSFNet linked together the five NSF supercomputer centers. It was smaller than the ARPANET and no faster - 56Kbps. Nonetheless, the creation of the NSFNet was a significant event in the history of the Internet because NSF brought with it a new vision of the use of the Internet. NSF wanted to extend the network to every scientist and engineer in the United States. To accomplish this, in 1987 NSF created a new, faster backbone and a three-tiered network topology that included the backbone, regional networks, and local networks.

In 1990, the ARPANET formally passed out of existence, and the NSFNet ceased its role as a primary Internet backbone network in 1995. Still, today the Internet is larger than ever and encompasses more than 95,000 networks worldwide. This network of networks is linked together in the United States at several major interconnection points:

• The three Network Access Points (NAPs) created by the NSF to ensure continued broad-based access to the Internet.

• The Federal Information Exchanges (FIXs) interconnect U.S. government networks.

• The Commercial Information Exchange (CIX) was the first interconnect specifically for commercial Internet Service Providers (ISPs).

• The Metropolitan Area Exchanges (MAEs) were also created to interconnect commercial ISPs.

The Internet has grown far beyond its original scope. The original networks and agencies that built the Internet no longer play an essential role for the current network. The Internet has evolved from a simple backbone network, through a three-tiered hierarchical structure, to a huge network of interconnected, distributed network hubs. It has grown exponentially since 1983 - doubling in size every year. Through all of this incredible change one thing has remained constant: the Internet is built on the TCP/IP protocol suite.

A sign of the network's success is the confusion that surrounds the term internet . Originally it was used only as the name of the network built upon the Internet Protocol. Now internet is a generic term used to refer to an entire class of networks. An internet (lowercase "i") is any collection of separate physical networks, interconnected by a common protocol, to form a single logical network. The Internet (uppercase "I") is the worldwide collection of interconnected networks, which grew out of the original ARPANET, that uses Internet Protocol (IP) to link the various physical networks into a single logical network. In this book, both "internet" and "Internet" refer to networks that are interconnected by TCP/IP.

Because TCP/IP is required for Internet connection, the growth of the Internet has spurred interest in TCP/IP. As more organizations become familiar with TCP/IP, they see that its power can be applied in other network applications. The Internet protocols are often used for local area networking, even when the local network is not connected to the Internet. TCP/IP is also widely used to build enterprise networks. TCP/IP-based enterprise networks that use Internet techniques and World Wide Web tools to disseminate internal corporate information are called intranets . TCP/IP is the foundation of all of these varied networks.