TCP/IP OVERVIEW

The TCP/IP protocols were adopted as Military Standards in 1983, and all hosts connected to the network were required to convert to the new protocols. To ease this conversion, funded Bolt, Beranek, and Newman (BBN) to implement TCP/IP in Berkeley (BSD) Unix. Thus began the marriage of Unix and TCP/IP. 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. Still, 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 in 1995 the NSFNet ceased its role as a primary Internet backbone network. Today the Internet is larger than ever and encompasses hundreds of thousands of networks worldwide. It is no longer dependent on a core (or backbone) network or on governmental support. Today's Internet is built by commercial providers. National network providers, called tier-one providers, and regional network providers create the infrastructure. Internet Service Providers (ISPs) provide local access and user services. This network of networks is linked together in the United States at several major interconnection points called Network Access Points (NAPs). 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 IP. 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 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.