Ethernet over twisted pair
Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers.
Early Ethernet 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, 1000BASE-T, 10GBASE-T and 40GBASE-T, supporting speeds of 10 and 100 megabit per second, then 1, 10 and 40 gigabit per second respectively.[a]
Two new variants of 10 megabit per second Ethernet over a single twisted pair, known as 10BASE-T1S and 10BASE-T1L, were standardized in IEEE Std 802.3cg-2019.[2] 10BASE-T1S has its origins in the automotive industry and may be useful in other short-distance applications where substantial electrical noise is present.[3] 10BASE-T1L is a long-distance Ethernet, supporting connections up to 1 km in length. Both of these standards are finding applications implementing the Internet of things. 10BASE-T1S is a direct competitor of CAN XL in the automotive space and includes a PHY-Level Collision Avoidance scheme (PLCA).[4]
The earlier standards use 8P8C modular connectors,[b] and supported cable standards range from Category 3 to Category 8. These cables typically have four pairs of wires for each connection, although early Ethernet used only two of the pairs. Unlike the earlier -T standards, the -T1 interfaces were designed to operate over a single pair of conductors and introduce the use of two new connectors referred to as IEC 63171-1[5] and IEC 63171-6.[6]
Autonegotiation and duplex[edit]
Ethernet over twisted-pair standards up through Gigabit Ethernet define both full-duplex and half-duplex communication. However, half-duplex operation for gigabit speed is not supported by any existing hardware.[29][30] Higher speed standards, 2.5GBASE-T up to 40GBASE-T[31] 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 do not support the traditional shared-medium CSMA/CD operation.[32]
Many different modes of operations (10BASE-T half-duplex, 10BASE-T full-duplex, 100BASE-TX half-duplex, etc.) exist for Ethernet over twisted pair, and most network adapters are capable of different modes of operation. Autonegotiation is required in order to make a working 1000BASE-T connection.
When two linked interfaces are set to different duplex modes, the effect of this duplex mismatch is a network that functions much more slowly than its nominal speed. Duplex mismatch may be inadvertently caused when an administrator configures an interface to a fixed mode (e.g. 100 Mbit/s full-duplex) and fails to configure the remote interface, leaving it set to autonegotiate. Then, when the auto-negotiation process fails, half-duplex is assumed by the autonegotiating side of the link.
The first two early designs of twisted-pair networking were StarLAN, standardized by the IEEE Standards Association as IEEE 802.3e in 1986, at one megabit per second,[7] and LattisNet, developed in January 1987, at 10 megabit per second.[8][9] Both were developed before the 10BASE-T standard (published in 1990 as IEEE 802.3i) and used different signaling, so they were not directly compatible with it.[10]
In 1988, AT&T released StarLAN 10, named for working at 10 Mbit/s.[11] The StarLAN 10 signaling was used as the basis of 10BASE-T, with the addition of link beat to quickly indicate connection status.[c]
Using twisted-pair cabling in a star topology addressed several weaknesses of the previous Ethernet standards:
Although 10BASE-T is rarely used as a normal-operation signaling rate today, it is still in wide use with network interface controllers in wake-on-LAN power-down mode and for special, low-power, low-bandwidth applications. 10BASE-T is still supported on most twisted-pair Ethernet ports with up to Gigabit Ethernet speed.
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