Twisted pair Ethernet

Ethernet over twisted pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network.

Early Ethernet had used various grades of coaxial cable, but in 1984, StarLAN showed the potential of simple unshielded twisted pair. This led to the development of 10BASE-T and its successors 100BASE-TX and 1000BASE-T, supporting speeds of 10, 100 and 1,000 Mbit/s respectively.

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. Higher speed standards, 2.5GBASE-T up to 40GBASE-T running at 2.5 to 40 Gbit/s, consequently define only full-duplex point-to-point links which are generally connected by network switches, and don't support the traditional shared-medium CSMA/CD operation.

All these standards use 8P8C connectors, and the cables from Cat3 to Cat8 have four pairs of wires; though 10BASE-T and 100BASE-TX only use two of the pairs.

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.

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