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Ethernet over twisted pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. Early Ethernet cabling had generally been based on various grades of coaxial cable, but in 1984, StarLAN showed the potential of simple ''unshielded'' twisted pair by using Cat3 cable—the same simple cable used for telephone systems. This led to the development of 10BASE-T and its successors 100BASE-TX and 1000BASE-T, supporting speeds of 10, 100 and 1000 Mbit/s respectively. Often the higher-speed implementations support the lower-speed standards making it possible to mix different generations of equipment; with the inclusive capability designated 10/100 or 10/100/1000 for connections that support such combinations. All these three standards define both full-duplex and half-duplex communication. However, half-duplex operation for gigabit speed isn't supported by any existing hardware. The higher speed 10GBASE-T running at 10 Gbit/s, consequently defines only full duplex point-to-point links which are generally connected by network switches, and doesn't support the traditional shared-medium CSMA/CD operation. All these standards use 8P8C connectors,〔The 8P8C modular connector is often called ''RJ45'' after a telephone industry standard.〕 and the cables from Cat3 to Cat7 have four pairs of wires; though 10BASE-T and 100BASE-TX only require two of the pairs. A 40GBASE-T standard, transporting 40 Gbit/s over up to 30 m Cat.8 cable is being defined as P802.3bq.〔(【引用サイトリンク】url=http://www.ieee802.org/3/bq/ )〕 ==History== The Institute of Electrical and Electronics Engineers (IEEE) standards association ratified several versions of the technology. The first two early designs were StarLAN, standardized in 1986, at one megabit per second,〔 and LattisNet, developed in January 1987, at 10 megabit per second.〔〔 Both were developed before the 10BASE-T standard (published in 1990 as IEEE 802.3i) and used different signalling, so they were not directly compatible with it.〔 In 1988 AT&T released StarLAN 10, named for working at 10 Mbit/s. The StarLAN 10 signalling was used as the basis of 10BASE-T, with the addition of "link beat" to quickly indicate connection status. (A number of network interface cards at the time could work with either StarLAN 10 or 10BASE-T, by switching link beat on or off.) Using twisted pair cabling, in a star topology, for Ethernet addressed several weaknesses of the previous standards: * Twisted pair cables could be used more generally and were already present in many office buildings, lowering overall cost. * The centralized star topology was a more common approach to cabling than the bus in earlier standards and easier to manage. * Using point-to-point links instead of a shared bus greatly simplified troubleshooting and was less prone to failure. * Exchanging cheap repeater hubs for more advanced switching hubs provided a viable upgrade path. * Mixing different speeds in a single network became possible with the arrival of Fast Ethernet. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ethernet over twisted pair」の詳細全文を読む スポンサード リンク
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