Ethernet
Ethernet is a family of wired computer networking technologies commonly used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as ECMA-82 and shortly after as IEEE 802.3. It is a good example of an open standard.
Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET.
The original 10BASE5 Ethernet uses a thick coaxial cable as a shared medium. This was largely superseded by 10BASE2, which used a thinner and more flexible cable that was both less expensive and easier to use. More modern Ethernet variants use twisted pair and fiber optic links in conjunction with switches. Over the course of its history, Ethernet data transfer rates have been increased from the original to the latest Terabit Ethernet|, with rates up to under development. The Ethernet standards include several wiring and signaling variants of the OSI physical layer.
Systems communicating over Ethernet divide a stream of data into shorter pieces called frames. Each frame contains source and destination addresses, and error-checking data so that damaged frames can be detected and discarded; most often, higher-layer protocols trigger retransmission of lost frames. Per the OSI model, Ethernet provides services up to and including the data link layer. The 48-bit MAC address was adopted by other IEEE 802 networking standards, including IEEE 802.11, as well as by FDDI. EtherType values are also used in Subnetwork Access Protocol headers.
Ethernet is widely used in homes and industry, and interworks well with wireless Wi-Fi technologies. The Internet Protocol is commonly carried over Ethernet and so it is considered one of the key technologies that make up the Internet.
History
The original forms of Ethernet used a shared communications channel. This concept originated in ALOHAnet, designed in the late 1960s by Norman Abramson. ALOHANet was a 4800 bps radio network used by the University of Hawaii. When a sender detected that its message hadn't been received, it would resend the message after waiting for a randomly selected period of time.In 1972, Robert Metcalfe and David Boggs adapted the ALOHAnet approach to transmission over a shared coaxial cable in the Xerox Palo Alto Research Center. This network connected ALTO computers using a coaxial cable. It first ran on May 22, 1973 with a bit rate of 2.94 Mbps. In a memo written at that time, Metcalfe named the concept "Ethernet." The name was inspired by the former idea that the universe was filled with a "luminiferous aether" that carried electromagnetic waves, and calling it Ethernet emphasized its ability to run over any transmission medium. Ethernet improved the original ALOHANet design because a sender would first listen to the channel to determine if it was already in use. The combination of the new idea of Carrier Sense with Multiple Access and Collision Detection from ALOHANet became Carrier-Sense Multiple Access/Collision Detection, or CSMA/CD.
In 1975, Metcalfe, Boggs and their colleagues Charles Thacker and Butler Lampson filed for a patent on Ethernet, which was granted in 1977. By 1976, 100 ALTOs at Xerox PARC were connected using Ethernet. In July 1976, Metcalfe and Boggs published the seminal paper Ethernet: Distributed Packet Switching for Local Computer Networks in Communications of the ACM. Subsequently between 1976-1978 Ron Crane, Bob Garner, Hal Murray, and Roy Ogus designed a 10Mbps version of Ethernet running over coaxial cable.
There were multiple local area network technologies in the 1970s. These included IBM's token ring, Network Systems Corporation's HYPERchannel and Datapoint's ARCnet. All were proprietary at the time. Metcalfe, Gordon Bell, and David Liddle developed a strategy of standardizing Ethernet rather than keeping it vendor-specific, and convinced Digital Equipment Corporation, Intel, and Xerox to work together on a standard, subsequently known as the DIX standard, based on the 10Mbps version of Ethernet and published in 1980 as the Ethernet Blue Book. Version 2 was published in November 1982.
In June 1981, the Institute of Electronic and Electrical Engineers Project 802 created an 802.3 subcommittee to produce an Ethernet standard based on DIX. In 1983, a standard was published for 10 Mbps Ethernet over a coaxial cable of up to 500 meters. It differed only in some details from the DIX standard. As part of the standardization process, Xerox turned over all its Ethernet patents to the IEEE, and anyone can implement 802.3. IEEE 802.3 is now considered the same as Ethernet. The cooperation of Xerox with Intel and Digital on the Ethernet standard ultimately made it a truly open standard.
In June 1979, Metcalfe left Xerox to found the Computer, Communication, and Compatibility Corporation, better known as 3Com, along with Howard Charney, Ron Crane, Greg Shaw, and Bill Kraus. Metcalfe's vision was to sell Ethernet adapters for all personal computers. Apple quickly agreed, but IBM was committed to their own LAN protocol, the Token Ring. Nonetheless, 3Com developed the EtherLink ISA adapter and started shipping it with DOS driver software, making it usable on IBM PCs.
The EtherLink adapter had several advantages over competitors. It was the first network interface card to use VLSI semiconductor technology. This meant most of the functions, including the transceiver, could be contained on a single chip, so the price for Etherlink was significantly lower than of its competitors. 3Com introduced a new, thinner coaxial cable for the card, called Thin Ethernet, making it more convenient to install and use. Finally, Etherlink was the first Ethernet adapter for the IBM PC.
Because both businesses and home users adopted the IBM PC, its market expanded rapidly, and by 1982, IBM was shipping 200,000 units a month. Since IBM hadn't realized that businesses would want the computers connected by a network, Etherlink sales filled the vacuum and in 1984 3Com was able to file for a public stock offering. The Etherlink approach was standardized by IEEE as 10BASE2 in 1984.
Also in the early 1980s, Novell began selling Network Interface Cards to go with its NetWare operating system. These NE2000 NICs were all Ethernet, and because NetWare became an important application for businesses, this increased the demand for Ethernet adapters. Then in 1989, Novell sold its NIC business and licensed the NE2000 card, creating a highly competitive market and driving the price of Ethernet cards down, while cards for other technologies such as IBM's token ring remained high.
Starting in late 1983, AT&T and NCR promoted a star configuration using unshielded twisted pair cabling, or regular telephone wire. This became StarLAN, running at 1Mbps over cables up to 500 meters, and was standardized as 1BASE5 by IEEE 802.3, but on August 17, 1987, SynOptics introduced LATTISNET with 10Mbps Ethernet also over regular telephone wire. In the fall of 1990, the IEEE issued the 802.3i standard for 10BASE-T, Ethernet over twisted pairs, and the following year, Ethernet sales nearly doubled. By 1992, Ethernet was the de facto standard for LANS.
In the 1990s, the proliferation of PCs combined with their increasing power drove demand for much faster network infrastructure. The Kalpana EtherSwitch EPS-700 helped to meet this demand by increasing the speed of Ethernet dramatically. The switch allowed multiple simultaneous data transmission paths and it used faster cut-through bridging technology in place of store-and-forward. The switch was marketed as a way to improve network performance rather than as a way to connect different LANs, creating a new market category. Then in 1993, Kalpana introduced full-duplex mode for switches, potentially doubling the data transmission rate. In 1997, the IEEE standardized full-duplex flow-control switched in 802.3x.
The 10Mbps rate of Ethernet was still too slow for some networks, though, and most larger networks planned to use FDDI, a very expensive alternative to Ethernet. In August 1991 Howard Charney, David Boggs, Ron Crane, and Larry Birenbaum founded Grand Junction Networks to build and market 100Mbps Ethernet equipment. Their announcement in 1992 triggered a standards war over whether to maintain backward compatibility with the original Ethernet CSMA/CD standard or to adopt a demand-priority protocol pushed by HP and AT&T. Since the competing groups were unable to come to an agreement, IEEE set up a new group, 802.12, for the demand-priority scheme. The supporters of backward compatibility formed the Fast Ethernet Alliance in 1993 to publish an interoperability specification that became the 100BASE-TX standard. At the same time, Grand Junction shipped the first Fast Ethernet hubs and NICs, and more companies announced Fast Ethernet equipment. In 1994, Sun Microsystems followed by 3Com, DEC and others shipped 100BASE-TX compliant products, and the IEEE 802.3u specification for FastEthernet was approved.
Standardization
In February 1980, the Institute of Electrical and Electronics Engineers started project 802 to standardize local area networks. The DIX group with Gary Robinson, Phil Arst, and Bob Printis submitted the so-called Blue Book CSMA/CD specification as a candidate for the LAN specification. In addition to CSMA/CD, Token Ring and Token Bus were also considered as candidates for a LAN standard. Competing proposals and broad interest in the initiative led to strong disagreement over which technology to standardize. In December 1980, the group was split into three subgroups, and standardization proceeded separately for each proposal.The development of the CSMA/CD standard was slowed by conflict over issues such as baseband versus broadband and the lengths of address fields. Some members of the DIX group became impatient with the process and concerned that the ultimate CSMA/CD standard would differ significantly from their "Blue Book" de facto standard. They turned instead to the European Computer Manufacturers Association, where Friedrich Röscheisen of Siemens helped to introduce the Blue Book as a candidate standard to a newly-created "Local Networks" Task Group. Gary Robinson later claimed to have instigated the effort to convince ECMA to standardize CSMA/CD. ECMA approved a standard in June 1982 that was very close to the DIX de facto standard. Because the DIX proposal was the most technically complete and because of the speedy action taken by ECMA, the IEEE group felt compelled to approve the 802.3 CSMA/CD standard in December 1982. It differed only slightly from the DIX standard in terminology and frame format. IEEE published the 802.3 standard as a draft in 1983 and as a standard in 1985.
Approval of Ethernet on the international level was achieved by a similar, cross-partisan action with Ingrid Fromm, Siemens' representative to IEEE 802, as the liaison officer working to integrate with International Electrotechnical Commission Technical Committee 83 and International Organization for Standardization Technical Committee 97 Sub Committee 6. The ISO 8802-3 standard was published on March 23, 1989.
The IEEE has approved changes to its 802.3 standard regularly since 1985. The current standard is available from the IEEE website. With each change to the standard, the IEEE first issues a supplement with a letter designation added to IEEE 802.3. For example, IEEE 802.3u refers to Fast Ethernet. Then when the supplement is formally approved, it is merged with the main standard.
Subsequent standards have provided for ever-faster versions of Ethernet, additional physical media, and network management. For a table of IEEE Ethernet standards, see.