Twisted pair
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Twisted pair cabling is a common form of wiring in which two conductors are wound around each other for the purposes of canceling out electromagnetic interference known as crosstalk. The number of twists per meter make up part of the specification for a given type of cable. The greater the number of twists, the more crosstalk is reduced. Twisting wires decreases interference because:
- The loop area between the wires (which determines the magnetic coupling into the signal) is reduced as much as physically possible.
- The directions of current generated by a uniform coupled magnetic field is reversed for every twist, canceling each other out.
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Cable types
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Shielded Twisted Pair (STP)
This cable has a conductive braided or foil casing for each pair and theoretically offers very good protection from interference and crosstalk. It was commonly used for token ring networks. Shielded Twisted Pair is rarely used due to the fact that the potential performance increase over UTP is not worth the much greater cost of STP.
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Screened Shielded Twisted Pair (S/STP)
S/STP is like STP, but with an extra outer braided or foil shield similar to coaxial cable, which offers still improved protection from interference from external sources.
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Unshielded Twisted Pair (UTP)
UTP cable is not surrounded by any shielding. It is the primary wire type for telephone usage and is very common for computer networking, especially in patch cables or temporary network connections due to the high flexibility of the cables.
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Foiled Twisted Pair (FTP)
FTP cable is basically a UTP cable surrounded by an outer foil shield increasing protection from external interference.
Screened Unshielded Twisted Pair (S/UTP)
The same as FTP but with a braided shield instead of foil.
Screened Foiled Twisted Pair (S/FTP)
This is a combination of S/UTP and FTP i.e. with a combined braided and foil shielding.
Twisted pair cabling is standardized into various categories by number, which indicate signal integrity attributes. Category 5 cable is commonly used for Ethernet with 10BASE-T or 100BASE-TX.
In telephone applications, UTP is often grouped into sets of 25 pairs according to a standard 25-pair color code originally developed by AT&T. A typical subset of these colors (white/blue, blue/white, white/orange, orange/white) shows up in most UTP cables.
See also
es:Cable de par trenzado fr:Paire torsadée he:זוג שזור nl:Twisted pair ja:ツイストペアケーブル pl:Skrętka pt:Cabo de par entrançado ru:Витая пара fi:Parikaapeli sv:Twisted Pair-kabel zh:双绞线