Packet switching soon found favor beyond the confines of ARPANET. Roberts left ARPA in 1972 to become president of one of the first companies to offer networking services to commercial customers. Several European countries had become interested in computer networking, and the U.S. government had other packet-based projects under way. Although ARPANET was presumably destined to remain a well-guarded dominion of computer scientists, some widening of its reach by connecting with other networks seemed both desirable and inevitable. Packet switching soon found favor beyond the confines of ARPANET. Roberts left ARPA in 1972 to become president of one of the first companies to offer networking services to commercial customers. Several European countries had become interested in computer networking, and the U.S. government had other packet-based projects under way. Although ARPANET was presumably destined to remain a well-guarded dominion of computer scientists, some widening of its reach by connecting with other networks seemed both desirable and inevitable. It was clear to Robert Kahn, who had headed the BBN design team, that network-to-network linkages would require an acceptance of diversity, since ARPANET's specifications for packet sizes, delivery rates, and other features of data flow were not a standard. Commonality would instead be imposed in the form of shared rules, or protocols, for communication—some of the rules to apply to the networks themselves, others meant for gateways that would be placed between networks. The job of these gateways, called routers, would be to control traffic, nothing more. What was inside the packets wouldn't matter. To grapple with the various issues, Kahn joined forces with Vinton Cerf, who had been involved in designing the ARPANET protocols for host computers and also had experience with time-sharing systems on the ARPANET. By mid-1974 their recommendations for an overall network-to-network architecture had been accepted. Negotiations to finalize the two sets of rules, jointly known as TCP/IP (transmission control protocol/ internet protocol), took several more years, and ARPANET did not formally incorporate the new system until 1983. By then ARPA—now known as DARPA, the "D" having been added to signal a clearer focus on defense—was looking for release from its network responsibilities. An exit presented itself in mid-decade when another U.S. government entity, the National Science Foundation (NSF), began building five supercomputing centers around the country, along with a connecting backbone of lines that were about 25 times faster than ARPANET's. At that time, research scientists of all kinds were clamoring for network access to allow the kind of easy communication and collaboration that ARPANET users had long enjoyed. NSF answered the need by helping to create a number of regional networks, then joining them together by means of the supercomputer backbone. Many foreign networks were connected. In the late 1980s ARPANET began attaching its sites to the system, and in 1990 the granddaddy of packet-switching networks was decommissioned.
Meanwhile, beyond the world of science, computer networking spread in all directions. Within corporations and institutions, small computers were being hooked together in local area networks, which typically used an extremely fast, short-range packet delivery technique called Ethernet (invented by one-time ARPANET programmer Robert Metcalfe back in 1973) and were easily attached to outside networks. On a nation-spanning scale, a number of companies built high-speed networks that could be used to process point-of-sale transactions, give corporate customers access to specialized databases, and serve various other commercial functions. Huge telecommunications carriers such as AT&T and MCI entered the business. As the 1990s proceeded, the major digital highways, including those of NSF, were linked, and on-ramps known as Internet service providers proliferated, providing customers with e-mail, chat rooms, and a variety of content via telephone lines and modems. The Internet was now a vast international community, highly fragmented and lacking a center but a miracle of connectivity. Meanwhile, beyond the world of science, computer networking spread in all directions. Within corporations and institutions, small computers were being hooked together in local area networks, which typically used an extremely fast, short-range packet delivery technique called Ethernet (invented by one-time ARPANET programmer Robert Metcalfe back in 1973) and were easily attached to outside networks. On a nation-spanning scale, a number of companies built high-speed networks that could be used to process point-of-sale transactions, give corporate customers access to specialized databases, and serve various other commercial functions. Huge telecommunications carriers such as AT&T and MCI entered the business. As the 1990s proceeded, the major digital highways, including those of NSF, were linked, and on-ramps known as Internet service providers proliferated, providing customers with e-mail, chat rooms, and a variety of content via telephone lines and modems. The Internet was now a vast international community, highly fragmented and lacking a center but a miracle of connectivity. What allowed smooth growth was the TCP/IP system of rules originally devised for attaching other networks to ARPANET. Over the years rival network-to-network protocols were espoused by various factions in the computer world, among them big telecommunications carriers and such manufacturers as IBM. But TCP/IP worked well. It was highly flexible, it allowed any number of networks to be hooked together, and it was free. The NSF adopted it, more and more private companies accepted it, and computer scientists overseas came to prefer it. In the end, TCP/IP stood triumphant as the glue for the world's preeminent network of networks.
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