Ethernet

Ethernet is a large and diverse family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. more...

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It defines a number of wiring and signaling standards for the physical layer, two means of network access at the Media Access Control (MAC)/Data Link Layer, and a common addressing format.

Ethernet has been standardized as IEEE 802.3. Its star-topology, twisted pair wiring form became the most widespread LAN technology in use from the 1990s to the present, largely replacing competing LAN standards such as coaxial cable Ethernet, token ring, FDDI, and ARCNET. In recent years, WiFi, the wireless LAN standardized by IEEE 802.11, has been used in addition to or instead of Ethernet in many installations.

History

Ethernet was originally developed as one of the many pioneering projects at Xerox PARC. A common story states that Ethernet was invented in 1973, when Robert Metcalfe wrote a memo to his bosses at PARC about Ethernet's potential. But Metcalfe claims Ethernet was actually invented over a period of several years. In 1976, Metcalfe and his assistant David Boggs published a paper titled Ethernet: Distributed Packet-Switching For Local Computer Networks.

The experimental Ethernet described in that paper ran at 3 Mbit/s, and had 8-bit destination and source address fields, so Ethernet addresses weren't the global addresses they are today. By software convention, the 16 bits after the destination and source address fields were a packet type field, but, as the paper says, "different protocols use disjoint sets of packet types", so those were packet types within a given protocol, rather than the packet type in current Ethernet, which specifies the protocol being used.

Metcalfe left Xerox in 1979 to promote the use of personal computers and local area networks (LANs), forming 3Com. He convinced DEC, Intel, and Xerox to work together to promote Ethernet as a standard, the so-called "DIX" standard, for "Digital/Intel/Xerox"; it standardized the 10 megabits/second Ethernet, with 48-bit destination and source addresses and a global 16-bit type field. The standard was first published on September 30, 1980. It competed with two largely proprietary systems, token ring and ARCNET, but those soon found themselves buried under a tidal wave of Ethernet products. In the process, 3Com became a major company.

Metcalfe sometimes jokingly credits Jerome H. Saltzer for 3Com's success. Saltzer cowrote an influential paper suggesting that token-ring architectures were theoretically superior to Ethernet-style technologies. This result, the story goes, left enough doubt in the minds of computer manufacturers that they decided not to make Ethernet a standard feature, which allowed 3Com to build a business around selling add-in Ethernet network cards. This also led to the saying "Ethernet works better in practice than in theory," which, though a joke, actually makes a valid technical point: the characteristics of typical traffic on actual networks differ from what had been expected before LANs became common in ways that favor the simple design of Ethernet. Add to this the real speed/cost advantage Ethernet products have continually enjoyed over other (token, FDDI, ATM, etc.) LAN implementations and we see why today's result is that "connect the PC to the network" means connect it via Ethernet. Even when the PC is connected by Wi-Fi, nearly all Wi-Fi gear uses Ethernet for connecting to the rest of the network.

Read more at Wikipedia.org