Computer network

Computer network

"Computer networks" redirects here. For the periodical, see Computer Networks (journal).

"Datacom" redirects here. For other uses, see Datacom (disambiguation).

A computer network is a telecommunications network that allows computers to exchange data. The physical connection between networked computing devices is established using either cable media or wireless media. The best-known computer network is the Internet.

Network devices that originate, route and terminate the data are called network nodes.^[1] Nodes can include hosts such as servers and personal computers, as well as networking hardware. Two devices are said to be networked when a process in one device is able to exchange information with a process in another device.

Computer networks support applications such as access to the World Wide Web, shared use of application and storage servers, printers, and fax machines, and use of email and instant messaging applications. The remainder of this article discusses local area network technologies and classifies them according to the following characteristics: the physical media used to transmit signals, the communications protocols used to organize network traffic, along with the network's size, its topology and its organizational intent.

Before the advent of computer networks, communication between calculation machines and early computers was performed by human users by carrying instructions between them. Today, in spite of the wide use of email and other networking applications, people do continue to transfer information to another person's computer by hand-carrying removable storage media (such as flash drives) — a method jokingly known as "sneakernet".

• In September 1940, George Stibitz used a teletype to send instructions for a problem set from his Model at Dartmouth College to his Complex Number Calculator in New York and received results back by the same means.
• In the late 1950s, early networks of communicating computers included the military radar system Semi-Automatic Ground Environment (SAGE).
• In 1960, the commercial airline reservation system semi-automatic business research environment (SABRE) went online with two connected mainframes.
• In 1962, J.C.R. Licklider developed a working group he called the "Intergalactic Computer Network", a precursor to the ARPANET, at the Advanced Research Projects Agency (ARPA).
• In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing System for distributed users of large computer systems. The same year, at Massachusetts Institute of Technology, a research group supported by General Electric and Bell Labs used a computer to route and manage telephone connections.
• Throughout the 1960s, Leonard Kleinrock, Paul Baran and Donald Davies independently conceptualized and developed network systems which used packets to transfer information between computers over a network.
• In 1965, Thomas Marill and Lawrence G. Roberts created the first wide area network (WAN). This was an immediate precursor to the ARPANET, of which Roberts became program manager.
• Also in 1965, the first widely used telephone switch that implemented true computer control was introduced by Western Electric.
• In 1969, the University of California at Los Angeles, the Stanford Research Institute, the University of California at Santa Barbara, and the University of Utah were connected as the beginning of the ARPANET network using 50 kbit/s circuits.^[2]
• In 1972, commercial services using X.25 were deployed, and later used as an underlying infrastructure for expanding TCP/IP networks.
• In 1973, Robert Metcalfe wrote a formal memo at Xeroc PARC describing Ethernet, a networking system that was based on the Aloha network, developed in the 1960s by Norman Abramson and colleagues at the University of Hawaii. In July 1976, Robert Metcalfe and David Boggs published their paper "Ethernet: Distributed Packet Switching for Local Computer Networks"^[3] and collaborated on several patents received in 1977 and 1978. In 1979, Robert Metcalfe pursued making Ethernet an open standard.^[4]
• In 1976, John Murphy of Datapoint Corporation created ARCNET, a token-passing network first used to share storage devices.
• In 1995, the transmission speed capacity for Ethernet was increased from 10 Mbit/s to 100 Mbit/s. By 1998, Ethernet supported transmission speeds of a Gigabit. The ability of Ethernet to scale easily (such as quickly adapting to support new fiber optic cable speeds) is a contributing factor to its continued use today.^[4]

Today, computer networks are the core of modern communication. All modern aspects of the public switched telephone network (PSTN) are computer-controlled. Telephony increasingly runs over the Internet Protocol, although not necessarily the public Internet. The scope of communication has increased significantly in the past decade. This boom in communications would not have been possible without the progressively advancing computer network. Computer networks, and the technologies that make communication between networked computers possible, continue to drive computer hardware, software, and peripherals industries. The expansion of related industries is mirrored by growth in the numbers and types of people using networks, from the researcher to the home user.