Twisted pair

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It has been suggested that Unshielded twisted pair be merged into this article or section. (Discuss)
25-pair color code Chart
25-pair color code Chart
10BASE-T Cable
10BASE-T Cable

Twisted pair cabling is a form of wiring in which two conductors are wound together for the purposes of canceling out electromagnetic interference (EMI) from external sources and crosstalk from neighboring wires.

Twisting wires decreases interference because the loop area between the wires (which determines the magnetic coupling into the signal) is reduced. In balanced pair operation, the two wires typically carry equal and opposite signals (differential mode) which are combined by subtraction at the destination. The noise from the two wires cancel each other in this subtraction because the two wires have been exposed to similar EMI.

The twist rate (usually defined in twists per meter) makes up part of the specification for a given type of cable. The greater the number of twists, the greater the attenuation of crosstalk. Where pairs are not twisted, as in most residential interior telephone wiring, one member of the pair may be closer to the source than the other, and thus exposed to slightly different induced EMF.


Contents

[edit] Uses

Twisted pair cabling headed with a registered jack
Twisted pair cabling headed with a registered jack

[edit] UTP Cables

Twisted pair cables were first used in telephone systems by Bell in 1881 and by 1900 the entire American network was twisted pair, or else open wire with similar arrangements to guard against interference. Most of the billions of conductor feet (millions of Kilometers) of twisted pairs in the world are outdoors, owned by telephone companies, used for voice service, and only handled or even seen by telephone workers. The majority of data or Internet connections use those wires.

For indoor 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 AD1L colors (white/blue, blue/white, white/orange, orange/white) shows up in most UTP cables.

Twisted pair cabling is often used in data networks for short and medium length connections because of its relatively lower costs compared to fiber and coaxial cabling.

[edit] Cable Shielding

Main article please see Electromagnetic shielding.

Twisted pair cables are often shielded in attempt to prevent electromagnetic interference. Because the shielding is made of metal, it may also serve as a ground. However, usually a shielded or a screened twisted pair cable has a special grounding wire added called a drain wire. This shielding can be applied to individual pairs, or to the collection of pairs. When shielding is applied to the collection of pairs, this is referred to as screening. The shielding must be grounded for the shielding to work.

[edit] Unshielded Twisted Pair (UTP)

Unshielded Twisted Pair
Unshielded Twisted Pair
UTP cables are not shielded. This lack of shielding results in a high degree of flexibility as well as rugged durability. UTP cables are found in many ethernet networks and telephone systems.

[edit] Shielded Twisted Pair (STP)

Shielded Twisted Pair
Shielded Twisted Pair
STP cabling includes metal shielding over each individual pair of copper wires. This type of shielding protects cable from external EMI (electromagnetic interferences). e.g. the 150 ohm shielded twisted pair cables defined by the IBM Cabling System specifications and used with token ring networks.

[edit] Screened Shielded Twisted Pair (S/STP)

S/STP cabling, also known as Screened Fully shielded Twisted Pair (S/FTP)[1], is both individually shielded (like STP cabling) and also has an outer metal shielding covering the entire group of shielded copper pairs (like S/UTP). This type of cabling offers the best protection from interference from external sources.
Screened Shielded Twisted Pair
Screened Shielded Twisted Pair

[edit] Screened Unshielded Twisted Pair (S/UTP)

S/UTP, also known as Fully shielded (or Foiled) Twisted Pair (FTP), is a screened UTP cable.
A Dissected S/UTP cable
A Dissected S/UTP cable
Screened Unshielded Twisted Pair, Foiled Twisted Pair, Screened Foiled Twisted Pair
Screened Unshielded Twisted Pair, Foiled Twisted Pair, Screened Foiled Twisted Pair


[edit] Minor Twisted Pair variants

  • Nonloaded twisted pair: A twisted pair that has no intentionally added inductance. Wires that go more than a mile (1.6 Km) usually have load coils to increase their inductance, unless they are to carry higher than voiceband frequencies.

[edit] See also

[edit] External links

  • Cat 1: Currently unrecognized by TIA/EIA. Previously used for POTS telephone communications, ISDN and doorbell wiring.
  • Cat 2: Currently unrecognized by TIA/EIA. Previously was frequently used on 4 Mbit/s token ring networks.
  • Cat 3: Currently defined in TIA/EIA-568-B, used for data networks using frequencies up to 16 MHz. Historically popular for 10 Mbit/s Ethernet networks.
  • Cat 4: Currently unrecognized by TIA/EIA. Provided performance of up to 20 MHz, and was frequently used on 16 Mbit/s token ring networks.
  • Cat 5: Currently unrecognized by TIA/EIA. Provided performance of up to 100 MHz, and was frequently used on 100 Mbit/s ethernet networks. May be unsuitable for 1000BASE-T gigabit ethernet.
  • Cat 5e: Currently defined in TIA/EIA-568-B. Provides performance of up to 100 MHz, and is frequently used for both 100 Mbit/s and gigabit ethernet networks.
  • Cat 6: Currently defined in TIA/EIA-568-B. It provides performance of up to 250 MHz, more than double category 5 and 5e.
  • Cat 6a: Future specification for 10 Gbit/s applications.
  • Cat 7: An informal name applied to ISO/IEC 11801 Class F cabling. This standard specifies four individually-shielded pairs (STP) inside an overall shield. Designed for transmission at frequencies up to 600 MHz.
See also: TIA/EIA-568-B • Ethernet • 8P8C • Ethernet crossover cable • Twisted pair

[edit] Historical

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