Ethernet is a family of frame-based computer networking technologies for local area networks (LAN). It defines a number of wiring and signaling standards for the Physical Layer of the standard networking model as well as a common addressing format and a variety of Medium Access Control procedures at the lower part of the Data Link Layer.
Ethernet has been commercially available since around 1980, largely replacing competing wired LAN standards. Most common are Ethernet over twisted pair to connect end systems, and fiber optic versions for site backbones. It is standardized as IEEE 802.3.
History
Ethernet was developed at Xerox PARC between 1973 and 1975. It was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his Ph.D. dissertation. In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker and Butler Lampson as inventors. In 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper.
Metcalfe left Xerox in 1979 to form 3Com. He convinced Digital Equipment Corporation (DEC), Intel, and Xerox to work together to promote Ethernet as a standard. The so-called “DIX” standard, for “Digital/Intel/Xerox” specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and a global 16-bit Ethertype-type field. It was published on September 30, 1980 as “The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications”. Version 2 was published in November, 1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the same time.
Ethernet initially competed with two largely proprietary systems, Token Ring and Token Bus. These proprietary protocols soon found themselves competing in a market inundated by Ethernet products. In the process, 3Com became a major company. 3Com shipped its first 10 Mbit/s Ethernet 3C100 transceiver in March 1981, and that year started selling adapters for PDP-11s and VAXes, as well as Multibus-based Intel and Sun Microsystems computers. This was followed quickly by DEC’s Unibus to Ethernet adapter, which DEC sold and used internally to build its own corporate network, which reached over 10,000 nodes by 1986; one of the largest computer networks in the world at that time.
Through the first half of the 1980s, Ethernet’s 10BASE5, implementation used a coaxial cable 0.375 inches (9.5 mm) in diameter, later called “thick ethernet” or “thicknet”. Its successor, 10BASE2, called “thin ethernet” or “thinnet”, used a cable similar to cable television cable of the era. The emphasis was on making installation of the cable easier and less costly.
Shared cable Ethernet was always hard to install in offices because its bus topology was in conflict with the star topology cable plans designed into buildings for telephony. Modifying Ethernet to conform to twisted pair telephone wiring already installed in commercial buildings provided another opportunity to lower costs, expand the installed base, and leverage building design, and, thus, twisted-pair Ethernet was the next logical development in the mid-1980s, beginning with StarLAN. UTP-based Ethernet became widely deployed with the 10BASE-T standard. This system replaced the coaxial cable systems with a system of full duplex switches linked via UTP.
With the advent of the 10BASE-T standard in 1990, Ethernet switches supplemented the half duplex CSMA/CD scheme with a full duplex system offering higher performance at a lower cost than routers. With the arrival of 100BASE-T, Ethernet switches capable of mixed speed and mixed duplex operation were built.
