10 things you may not know about Ethernet

Ethernet's value to networking and IT is well established over the past 40 years. But did you know that "Ethernet" refers to two slightly different ways of sending information between endpoints on a LAN? That and some other perhaps lesser known facts about this 40-year-old technology are reviewed here (also read "What's next for Ethernet?":

" Ethernet was inspired by ALOHAnet, which was developed at the University of Hawaii to use low-cost commercial radio equipment to connect Oahu and the other Hawaiian islands with a central time-sharing computer on the main Oahu campus. ALOHAnet used a hub/star configuration over shared media, in which each client randomly sent data and an acknowledgment/retransmission scheme was used to deal with collisions. Robert Metcalfe had studied ALOHAnet as part of his PhD dissertation and the technique was the basis for early Ethernet development.

" Ethernet was named after luminiferous ether, a 19th century theory on a substance believed to act as the medium for transmission of electromagnetic waves. The theory was eventually disproven by, among other studies, Einstein's theory of relativity. Einstein's theory assumed that the speed of light, or any electromagnetic wave, is a universal constant.

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" Early in its development, Ethernet was referred to as the "DIX" standard, for "Digital/Intel/Xerox." These companies, which worked on Ethernet in its early stages in Xerox PARC in California, in 1980 proposed a 10Mbps data transmission standard with 48-bit destination and source addresses and a global 16-bit Ethertype field to identify the frame as belonging to a particular protocol family.

" Ethernet, Token Ring and Token Bus were vying to become a single IEEE LAN standard in 1980. But the IEEE split the 802 LAN standard group into three subgroups and each proposal proceeded on a separate standards track after a consensus could not be reached. The slow pace of the standards process threatened to delay the introduction of Ethernet products. So Ethernet proponents enlisted German telecom giant Siemens to standardize Ethernet internationally as an office communications technique. Siemens took Ethernet beyond the IEEE establishing the "Local Networks" Task Group within the ECMA TC24 European standards body. ECMA TC24 and its corporate members reached agreement on a standard for CSMA/CD based on the IEEE 802 draft in early 1982. The IEEE 802.3 CSMA/CD standard, based on the "DIX" proposal, was then approved in late 1982. IEEE then published the 802.3 standard as a draft in 1983 and as a standard in 1985.

" Ethernet rendered Token Ring and Token Bus virtually obsolete due to its ability to adapt to market fluctuations and support inexpensive and ubiquitous twisted pair wiring. Less expensive Ethernet products soon inundated the market and Ethernet became the dominant LAN technology in the late 1980s.

" Digital Equipment Corp. built a 10,000-node corporate network based on its Unibus to Ethernet adapter in 1986. At the time, it was one of the largest computer networks in the world. 3Com shipped its first 10Mbps Ethernet transceiver in 1981, and an Ethernet adapter card for the IBM PC was released in 1982. By 1985, 3Com had sold 100,000 Ethernet adapters.

" Ethernet on unshielded twisted-pair cables began in the mid-1980s at 1Mbps with StarLAN. AT&T developed StarLAN, which uses a star topology instead of a bus used by shared media Ethernet, to reuse existing telephony on-premises wiring and maintain compatibility with analog telephone signals in the same cable bundle. StarLAN and Synoptics' 10Mbps star-wired LattisNet provided the basis for the 10Base-T Ethernet over unshielded twisted pair standard.

" Radia Perlman, inventor of Ethernet's Spanning Tree protocol, penned a poem about her work shortly after completion:


       I think that I shall never see       a graph more lovely than a tree.       A tree whose crucial property       is loop-free connectivity.       A tree that must be sure to span       so packet can reach every LAN.       First, the root must be selected.       By ID, it is elected.       Least-cost paths from root are traced.       In the tree, these paths are placed.       A mesh is made by folks like me,       then bridges find a spanning tree.

                        Radia Perlman

" "DIX" Ethernet and the IEEE 802.3 definition of Ethernet are slightly different standards. They have different terminology and data formats for their frames, but are otherwise almost identical. The IEEE 802.3 group standardized the operation of a CSMA/CD network that was functionally equivalent to the DIX Ethernet. The message format in the DIX version of Ethernet is the most commonly used today, as it is the one supported by the Internet. When you hear the term Ethernet, it usually refers generically to both the "DIX" Ethernet and the IEEE 802.3 standard.

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