A cable twisted pairs describes a model of wiring where a Line of transmission is made of two rolled up drivers helical one around the other, this configuration with for goal to precisely maintain the distance between wire and to decrease the Diaphonie.
The maintenance of the distance between wire of pair makes it possible to define a characteristic Impédance pair, in order to remove the reflections of signals to the connections and in end of line. The geometrical constraints (thickness of insulator/diameter of the wire) maintain this impedance around 100 ohm:
- 100 ohm for the networks Ethernet out of star
- 150 or 105 ohm for the networks Token Ring
- 100 or 120 ohm for the networks of telephony
- 90 ohm for the cables USB.
The more important the number of twists is, the more the Diaphonie is reduced. The average number of twists per meter belongs to the specification of the cable, but each pair of a cable is twisted in a slightly different way to avoid the Diaphonie.
The use of the symmetrical differential Signalisation makes it possible to reduce the interferences more.
Types of shieldings
See also: Shielding
The twisted pairs are often armoured in order to limit the interferences. As the shielding is made of metal, this one also constitutes a reference frame of mass. The shielding can be applied individually to the pairs or the unit formed by those. When the shielding is applied to the whole of the pairs, one speaks about écrantage.
There exist five types of twisted pairs:
Not armor-plated twisted pair - Unshielded Twisted pair (UTP) - official designation U/UTP
The not armor-plated twisted pair (or UTP for Unshielded twisted pair ) is not surrounded by a protective shielding. It is the type of cable often used for the Téléphone and some data-processing networks.
Écrantée twisted pair - Foiled Twisted pair (FTP) or Screened Unshielded Twisted pair - official designation (F/UTP)
The twisted pairs have a general shielding ensured by an aluminum foil. The screen is laid out between the external sheath and the 4 twisted pairs. It is used for the Téléphone and the data-processing networks.
Armor-plated twisted pair - Shielded Twisted pair (STP) - news denomination U/FTP
Each armor-plated twisted pair (or STP for even Shielded twisted ) is surrounded by a conducting layer of Blindage, in a way similar to a Coaxial cable. That allows a better protection against the Interférence S. It is commonly used in the networks Token-ring
Écrantée and armor-plated twisted pair - Shielded and Foiled Twisted pair (SFTP) - new denomination SF/UTP
- Cable equipped with a double screen common to the whole of the pairs (sheet metallized and braids)
Armor-plated and general twisted pair armor-plated - Shielded and Shielded Twisted pair (SSTP) - new denomination S/FTP
- Câble ftp equipped in addition to one common screen enters the external sheath and the 4 pairs
Categories of cables
The UTP is standardized in various categories of integrity of the signal. These various categories are ratified regularly by the authorities of standardization ANSI/TIA/EIA. Several of them have European equivalents standardized by the international standard ISO/CEI 11801 and French standard NF/EN 50173-1 defining structured wiring.
Category 1
Category 1 is a type of abandoned wiring. This category of cable was intended for the telephone calls. This standard is not any more topicality.
Category 2
Category 2 is a type of abandoned wiring. This category of cable allowed the data transmission 4 Mbit/s with a band-width of 2 MHz, in particular for the networks of the type Token-ring.
Category 3
Category 3 is a type of Câblage allowing a band-width of 16 M Hz, it is defined in standard ANSI/TIA/EIA-568B. This type of Câble nowadays is not used mainly any more as for telephony on the produce market, as well for the analogical lines as numerical (telephone systems, for example: Norstar, etc). It is also used for the networks Fast Ethernet (100 Mbps). This type of wiring is in the course of abandonment (in 2007) by the operators for the benefit of cables of the category 5th or higher, for the transmission of the Voix like Donnée S.
Category 4
Category 4 is a type of wiring allowing a band-width of 20 MHz. This standard was mainly used for the Token-ring networks in 16 Mbps or the networks 10BaseT. It was quickly replaced by categories 5 and 5th. In current standard ANSI/TIA/EIA-568B, only category 3 is described.
Category 5
Category 5 is a type of wiring allowing a band-width of 100 MHz. This standard allows the use of the 100BASE-TX and the 1000BASE-T, like various applications of telephony or networks (Token-ring, ATM). It was described in old standard ANSI/TIA/EIA-568-A. In the current standard, only the categories 5th and 6 remain described.
Category 5th/class D
The category 5th ( enhanced ) is a type of wiring allowing a band-width of 100 MHz (appeared in standard TIA/EIA-568A-5). The standard is an adaptation of category 5 (resistance < 9.38 ohm/100 m, mutual capacity < 5.6 nF/100 m, capacity with the mass < 330 PF for a frequency ranging between 1 Khz and 1 GHz, impedance of the pair diff adapted to 100 ohm +-15% for a frequency ranging between 1 MHz and 1 GHz, time travel < 5.7 ns/m@10 MHz, the type of shielding and the appairage in length are not specified).
Category 6/class E
Category 6 is a type of wiring allowing a band-width of 250 MHz and more (standard ANSI/TIA/EIA-568-B.2-1 and ISO/CEI 11801 ed.2).
6a Category/class Ea
Currently with the state of draft, the future standard 6a is directed towards an extension of category 6 for a band-width of 500 MHz (standard ANSI/TIA/EIA-568-B.2-10). This standard will permetra transfers to 10 Gbit. Active component are already deliverable.
Category 7/class F
Category 7 has a band-width of 600 MHz.
7a category/class F
The 7a category has a band-width of 1 GHz and is under study.
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