Twisted pair

Twisted pair

Twisted pair cabling is a type of wiring in which two conductors (the forward and return conductors of a single circuit) are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs. It was invented by Alexander Graham Bell.

Explanation

In balanced pair operation, the two wires carry equal and opposite signals and the destination detects the difference between the two. This is known as differential mode transmission. Noise sources introduce signals into the wires by coupling of electric or magnetic fields and tend to couple to both wires equally. The noise thus produces a common-mode signal which is cancelled at the receiver when the difference signal is taken. This method starts to fail when the noise source is close to the signal wires; the closer wire will couple with the noise more strongly and the common-mode rejection of the receiver will fail to eliminate it. This problem is especially apparent in telecommunication cables where pairs in the same cable lie next to each other for many miles. One pair can induce crosstalk in another and it is additive along the length of the cable. Twisting the pairs counters this effect as on each half twist the wire nearest to the noise-source is exchanged. Providing the interfering source remains uniform, or nearly so, over the distance of a single twist, the induced noise will remain common-mode. Differential signaling also reduces electromagnetic radiation from the cable, along with the associated attenuation allowing for greater distance between exchanges.

The twist rate (also called pitch of the twist, usually defined in twists per meter) makes up part of the specification for a given type of cable. Where nearby pairs have equal twist rates, the same conductors of the different pairs may repeatedly lie next to each other, partially undoing the benefits of differential mode. For this reason it is commonly specified that, at least for cables containing small numbers of pairs, the twist rates must differ.

In contrast to FTP (foiled twisted pair) and STP (shielded twisted pair) cabling, UTP (unshielded twisted pair) cable is not surrounded by any shielding. It is the primary wire type for telephone usage and is very common for computer networking, especially as patch cables or temporary network connections due to the high flexibility of the cables.

History

Wire transposition on top of pole

The earliest telephones used telegraph lines, or open-wire single-wire earth return circuits. In the 1880s electric trams were installed in many cities, which induced noise into these circuits. Lawsuits being unavailing, the telephone companies converted to balanced circuits, which had the incidental benefit of reducing attenuation, hence increasing range.

As electrical power distribution became more commonplace, this measure proved inadequate. Two wires, strung on either side of cross bars on utility poles, shared the route with electrical power lines. Within a few years the growing use of electricity again brought an increase of interference, so engineers devised a method called wire transposition, to cancel out the interference. In wire transposition, the wires exchange position once every several poles. In this way, the two wires would receive similar EMI from power lines. This represented an early implementation of twisting, with a twist rate of about four twists per kilometre, or six per mile. Such open-wire balanced lines with periodic transpositions still survive today in some rural areas.

Twisted pair cables were invented by Alexander Graham Bell in 1881. By 1900, the entire American telephone line network was either twisted pair or open wire with transposition to guard against interference. Today, most of the millions of kilometres of twisted pairs in the world are outdoor landlines, owned by telephone companies, used for voice service, and only handled or even seen by telephone workers.

Unshielded twisted pair (UTP)

Unshielded twisted pair

UTP cables are found in many Ethernet networks and telephone systems. 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 colors (white/blue, blue/white, white/orange, orange/white) shows up in most UTP cables.

For urban outdoor telephone cables containing hundreds or thousands of pairs, the cable is divided into smaller but identical bundles. Each bundle consists of twisted pairs that have different twist rates. The bundles are in turn twisted together to make up the cable. Pairs having the same twist rate within the cable can still experience some degree of crosstalk. Wire pairs are selected carefully to minimize crosstalk within a large cable.

Unshielded twisted pair cable with different twist rates

UTP cable is also the most common cable used in computer networking. Modern Ethernet, the most common data networking standard, utilizes 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 optical fiber and coaxial cable.

UTP is also finding increasing use in video applications, primarily in security cameras. Many middle to high-end cameras include a UTP output with setscrew terminals. This is made possible by the fact that UTP cable bandwidth has improved to match the baseband of television signals. While the video recorder most likely still has unbalanced BNC connectors for standard coaxial cable, a balun is used to convert from 100-ohm balanced UTP to 75-ohm unbalanced. A balun can also be used at the camera end for ones without a UTP output. Only one pair is necessary for each video signal.

Cable shielding

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Main article: Electromagnetic shielding

ScTP, also known as FTP

STP cable format

S/STP, also known as S/FTP.

S/UTP cable format

S/STP cable format

Twisted pair cables are often shielded in an 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, and is improved by grounding the drain wire along with the shield.

Shielded twisted pair (STP or STP-A) 

150 ohm STP shielded twisted pair cable defined by the IBM Cabling System specifications and used with token ring or FDDI networks. This type of shielding protects cable from external EMI from entering or exiting the cable and also protects neighboring pairs from crosstalk.

Screened twisted pair (ScTP or F/TP) 

ScTP cabling offers an overall sheath shield across all of the pairs within the 100 Ohm twisted pair cable. F/TP uses foil shielding instead of a braided screen. This type of shielding protects EMI from entering or exiting the cable.

Screened shielded twisted pair (S/STP or S/FTP) 

S/STP (Screened Shielded Twisted Pair) or S/FTP (Screened Foiled Twisted Pair) cabling offer shielding between the pair sets and an overall sheath shield within the 100 Ohm twisted pair cable. This type of shielding protects EMI from entering or exiting the cable and also protects neighboring pairs from crosstalk.

S/STP cable 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, and also eliminates alien crosstalk.

Note that different vendors and authors use different terminology (i.e. STP has been used to denote both STP-A, S/STP, and S/UTP). See below for the ISO/IEC attempt to internationally standardise the various designations.

Comparison of some old and new abbreviations, according to ISO/IEC 11801:

Old name

New name

cable screening

pair shielding

UTP

U/UTP

none

none

STP

U/FTP

none

foil

FTP

F/UTP

foil

none

S-STP

S/FTP

braiding

foil

S-FTP

SF/UTP

foil, braiding

none

The code before the slash designates the shielding for the cable itself, while the code after the slash determines the shielding for the individual pairs:

TP = twisted pair

U = unshielded

F = foil shielding

S = braided shielding

Most common cable categories

Category

Type

Frequency Bandwidth

Applications

Notes

Cat1

0.4 MHz

Telephone and modem lines

Not described in EIA/TIA recommmendations. Unsuitable for modern systems.

Cat2

? MHz

Older terminal systems, e.g. IBM 3270

Not described in EIA/TIA recommmendations. Unsuitable for modern systems.

Cat3

UTP

16 MHz

10BASE-T and 100BASE-T4 Ethernet[6]

Described in EIA/TIA-568. Unsuitable for speeds above 16 Mbit/s. Now mainly for telephone cables

Cat4

UTP

20 MHz

16 Mbit/sToken Ring

Not commonly used

Cat5

UTP

100 MHz

100BASE-TX & 1000BASE-T Ethernet

Common in most current LANs

Cat5e

UTP

100 MHz

100BASE-TX & 1000BASE-T Ethernet

Enhanced Cat5. Same construction as Cat5, but with better testing standards.

Cat6

UTP

250 MHz

1000BASE-T Ethernet

Most commonly installed cable in Finland according to the 2002 standard. SFS-EN 50173-1

Cat6e

250 MHz (500 MHz according to some)

Not described in EIA/TIA recommmendations.

Cat6a

500 MHz

10GBASE-T Ethernet

ISO/IEC 11801:2002 Amendment 2.

Cat7

S/FTP

600 MHz

Telephone, CCTV, 1000BASE-TX in the same cable. 10GBASE-T Ethernet.

Four pairs, S/FTP (shielded pairs, braid-screened cable). Development complete - ISO/IEC 11801 2nd Ed.

Cat7a

1000 MHz

Telephone, CATV, 1000BASE-TX in the same cable. 10GBASE-T Ethernet.

Four pairs, S/FTP (shielded pairs, braid-screened cable). Development complete - ISO/IEC 11801 2nd Ed. Am. 2.

Cat8

1200 MHz

Under development, no applications yet.

Four pairs, S/FTP (shielded pairs, braid-screened cable). Standard under development.

Solid core cable vs stranded cable

A solid core cable uses one solid wire per conductor and in a four pair cable there would be a total of eight solid wires. Stranded conductor uses multiple wires wrapped around each other in each conductor and in a four pair with seven strands per conductor cable, there would be a total of 56 wires.

Solid core cable is supposed to be used for permanently installed runs. It is less flexible than stranded cable and is more prone to failure if repeatedly flexed. Stranded cable is used for fly leads at patch panel and for connections from wall-ports to end devices, as it resists cracking of the conductors. Stranded core is generally more expensive than solid core.

Connectors need to be designed differently for solid core than for stranded. Use of a connector with the wrong cable type is likely to lead to unreliable cabling. Plugs designed for solid and stranded core are readily available, and some vendors even offer plugs designed for use with both types. The punch-down blocks on patch-panel and wall port jacks are designed for use with solid core cable.

Advantages

·         It is a thin, flexible cable that is easy to string between walls.

·         More lines can be run through the same wiring ducts.

·         UTP costs less per meter/foot than any other type of LAN cable.

·         Electrical noise going into or coming from the cable can be prevented.

·         Cross-talk is minimized.

Disadvantages

·         Twisted pair’s susceptibility to electromagnetic interference greatly depends on the pair twisting schemes (usually patented by the manufacturers) staying intact during the installation. As a result, twisted pair cables usually have stringent requirements for maximum pulling tension as well as minimum bend radius. This relative fragility of twisted pair cables makes the installation practices an important part of ensuring the cable’s performance.

·         In video applications that send information across multiple parallel signal wires, twisted pair cabling can introduce signaling delays known as skew which results in subtle color defects and ghosting due to the image components not aligning correctly when recombined in the display device. The skew occurs because twisted pairs within the same cable often use a different number of twists per meter so as to prevent common-mode crosstalk between pairs with identical numbers of twists. The skew can be compensated by varying the length of pairs in the termination box, so as to introduce delay lines that take up the slack between shorter and longer pairs, though the precise lengths required are difficult to calculate and vary depending on the overall cable length.

Minor twisted pair variants

·         Loaded twisted pair: A twisted pair that has intentionally added inductance, common practice on telecommunication lines, except those carrying higher than voiceband frequencies. The added inductors are known as load coils and reduce distortion.

·         Unloaded twisted pair: A twisted pair that has no added load coils.

·         Bonded twisted pair: A twisted pair variant in which the pairs are individually bonded to increase robustness of the cable. Pioneered by Belden, it means the electrical specifications of the cable are maintained despite rough handling.

·         Twisted ribbon cable: A variant of standard ribbon cable in which adjacent pairs of conductors are bonded and twisted together. The twisted pairs are then lightly bonded to each other in a ribbon format. Periodically along the ribbon there are short sections with no twisting to enable connectors and pcb headers to be terminated using the usual ribbon cable IDC techniques.

Category 1 cable

Category 1 cable (Cat 1) a.k.a. voice-grade copper is a misnomer, probably adopted by those who assumed that TIA set up "Categories" for all types of cables originally defined by Anixter International, the distributor, under the grades called "Levels." Cat 1 cable is used in earlier times. It is used for typically voice networks that carry only voice traffic example telephones. TIA/EIA-568 only recognized cables of Category 3 ratings or above. Anixter "Level 1" was a grade of unshielded twisted pair cabling designed for telephone communications, and was the most common on-premises wiring.

Category 2 cable

Category 2 cable, or simply Cat 2, is a misnomer, probably adopted by those who assumed that the Telecommunications Industry Association set up "Categories" for all types of cables originally defined by Anixter, the distributor, under the grades called Levels. TIA-568 only recognized cables of Category 3 ratings or above. Anixter Level 2 was a grade of UTP cable capable of transmitting data at up to 4 Mbit/s. It is the first cable which can transmit voice and data up to 4mbps. Anixter Level 2 cable was frequently used on ARCnet and 4 Mbit/s token ring networks, it is also used in telephone networks but it is no longer commonly used.

Category 3 cable

Category 3 cable, commonly known as Cat 3 or station wire, is an unshielded twisted pair (UTP) cable designed to reliably carry data up to 10 Mbit/s, with a possible bandwidth of 16 MHz. It is part of a family of copper cabling standards defined jointly by the Electronic Industries Alliance and the Telecommunications Industry Association.

Category 3 was a popular cabling format among computer network administrators in the early 1990s, but fell out of popularity in favor of the very similar, but higher performing, Category 5 cable standard. Since the early 2000s most new structured cable installations are built with Cat 5e or Cat 6 cable.

Cat 3 is currently still in use in two-line telephone systems. It may be used for 10BASE-T Ethernet, token ring, or ATM25 networks. The seldom used 100BASE-T4 standard, which achieves speeds of 100 Mbit/s by using all 4 pairs of wires, allowed older Cat 3 based infrastructures to achieve a much higher bandwidth.

Cat 3 is compatible with the original Power over Ethernet specification though it does not support the new 802.1at Type 2 high-power variation.[1]

Note that unlike Cat 1, 2, 4, and 5 cables, Cat 3 is still recognized by TIA/EIA-568-B, its defining standard.

Category 4 cable

Category 4 is a description of a cable that consists of four unshielded twisted-pair (UTP) wires with a data rate of 16 Mbit/s and performance of up to 20 MHz. It was used in token ring networks, 10BASE-T, 100BASE-T4, and is no longer common or used in new installations. It is used in telephone networks which can transmit voice and data from 12 Mbit/s to 16 Mbit/s. It was quickly superseded by Category 5/5e cable, both of which have 100±15 ohm impedance.

Category 4 is not recognized by the TIA/EIA-568 data cabling standards

Category 5 cable

Category 5 patch cable in T568B wiring

Category 5 cable (Cat 5) is a twisted pair cable for carrying signals. This type of cable is used in structured cabling for computer networks such as Ethernet. It is also used to carry other signals such as telephony and video. The cable is commonly connected using punch down blocks and modular connectors. Most Category 5 cables are unshielded, relying on the twisted pair design and differential signaling for noise rejection. Category 5 has been superseded by the Category 5e specification.

TIA/EIA-568-A.1-2001 T568A Wiring

Pin

Pair

Wire

Color

1

3

1

white/green

2

3

2

green

3

2

1

white/orange

4

1

2

blue

5

1

1

white/blue

6

2

2

orange

7

4

1

white/brown

8

4

2

brown

TIA/EIA-568-B.1-2001 T568B Wiring

Pin

Pair

Wire

Color

1

2

1

white/orange

2

2

2

orange

3

3

1

white/green

4

1

2

blue

5

1

1

white/blue

6

3

2

green

7

4

1

white/brown

8

4

2

brown

USOC/RJ61 Wiring

Pin

Pair

Wire

Color

1

4

tip

white/brown

2

3

tip

white/green

3

2

tip

white/orange

4

1

ring

blue

5

1

tip

white/blue

6

2

ring

orange

7

3

ring

green

8

4

ring

brown

Partially stripped cable showing the twisted pairs.

A Cat 5e Wall outlet showing the two wiring schemes: A for T568A, B for T568B.

Cable standard

The specification for Category 5 cable was defined by the Telecommunications Industry Association in ANSI/TIA/EIA-568-A, with clarification in TSB-95.[citation needed] These documents specified performance characteristics and test requirements for frequencies of up to 100 MHz. Cable types, connector types and cabling topologies are defined by TIA/EIA-568-B. The cable is terminated in either the T568A scheme or the T568B scheme. The two schemes work equally well and may be mixed in an installation so long as the same scheme is used on both ends of each cable. Nearly always, 8P8C modular connectors, often referred to as RJ45, are used for connecting category 5 cable. The USOC/RJ-61 standard is used in multi-line telephone connections.

Each of the four pairs in a Cat 5 cable has differing precise number of twists per metre to minimize crosstalk between the pairs. Although cable assemblies containing 4 pairs are common, Category 5 is not limited to 4 pairs. Backbone applications involve using up to 100 pairs. This use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and crosstalk from other pairs. Category 5 cabling is most commonly used for faster Ethernet networks, such as 100BASE-TX and 1000BASE-T.

The cable is available in both stranded and solid conductor forms. The stranded form is more flexible and withstands more bending without breaking and is suited for reliable connections with insulation piercing connectors, but makes unreliable connections in insulation-displacement connectors (IDCs).[clarification needed] The solid form is less expensive[citation needed] and makes reliable connections into insulation displacement connectors, but makes unreliable connections in insulation piercing connectors.[clarification needed] Taking these things into account, building wiring (for example, the wiring inside the wall that connects a wall socket to a central patch panel) is solid core, while patch cables (for example, the movable cable that plugs into the wall socket on one end and a computer on the other) are stranded. Outer insulation is typically PVC or LSOH. The specific category of cable in use can be identified by the printing on the side of the cable.[2]

Conductors required

10BASE-T and 100BASE-TX Ethernet connections require two cable pairs. 1000BASE-T Ethernet connections require four cable pairs.

Bending radius

Most Category 5 cables can be bent at any radius exceeding approximately four times the diameter of the cable.

Maximum cable segment length

According to the ANSI/TIA/EIA standard for category 5e cable (TIA/EIA 568-5-A), the maximum length for a cable segment is 100 meters (328 feet). If longer runs are required, the use of active hardware such as a repeater, or a switch, is necessary. The specifications for 10BASE-T networking specify a 100 metre length between active devices. This allows for 90 metres of fixed cabling, two connectors and two patch leads of 5 metres, one at each end.

Characteristics

Electrical characteristics for Cat 5e UTP

Property

Nominal Value

Tolerance

Unit

ref

Characteristic impedance @ 100 MHz

100

± 15

Ω

[8]

Nominal characteristic impedance @ 100 MHz

100

± 5

Ω

[8]

DC-Loop resistance

≤ 0.188

Ω/m

[8]

Propagation speed

0.64

c

[8]

Propagation delay

4.80-5.30

ns/m

[8]

Delay skew < 100 MHz

< 0.20

ns/m

[8]

Capacitance at 800 Hz

52

pF/m

[8]

Inductance

525

nH/m

[9]

Corner frequency

≤ 57

kHz

[9]

Max tensile load, during installation

100

N

[8]

Wire size

AWG-24 (0.205 mm² )

[8][10]

Insulation thickness

0.245

mm

[8]

Maximum current per conductor

0.577

A

[10]

Temperature operating

-55 to +60

°C

[8]

Dielectric

Example materials used as dielectric in the cable[11]

Acronym

Material

PVC

Polyvinyl Chloride

PE

Polyethylene

FP

Foamed polyethylene

FEP

Teflon/fluorinated ethylene propylene

FFEP

Foamed Teflon/fluorinated ethylene propylene

AD/PE

Air dielectric/polyethylene

Individual twist lengths

By altering the length of each twist, crosstalk is reduced, without affecting the characteristic impedance. The distance per twist is commonly referred to as pitch.

  

Pair color

[cm] per turn

Turns per [m]

Green

1.53

65.2

Blue

1.54

64.8

Orange

1.78

56.2

Brown

1.94

51.7

Environmental ratings

US & Canada fire certifications[12][13]

Class

Phrase

Standards

CMP

Communications Plenum

CSA FT7 or NFPA 262[ (UL 910)

CMR

Communications Riser

UL 1666

CMG

Communications General purpose

CSA FT4

CM

Communications

UL 1685 (UL 1581, Sec. 1160) Vertical-Tray

CMX

Communications Residential

UL 1581, Sec. 1080 (VW-1)

CMH

CSA FT1

CMR (Communications Riser), insulated with high-density polyolefin and jacketed with low-smoke polyvinyl chloride (PVC) can be replaced by a CMP (Communications Plenum), insulated with fluorinated ethylene propylene (FEP) and polyethylene (PE) and jacketed with low-smoke polyvinyl chloride (PVC), due to better flame test ratings. CM (Communications) is insulated with high-density polyolefin, but not jacketed with PVC and therefore is the lowest of the three in flame resistance.

Some cables are "UV-rated" or "UV-stable" meaning they can be exposed to outdoor UV radiation without significant destruction. The materials used for the mantle are usually PVC.

Any cable that contains air spaces can breathe in moisture, especially if the cable runs between indoor and outdoor spaces. Warm moist air can cause condensation inside the colder parts of the cable outdoors. It may be necessary to take precautions such as sealing the ends of the cables. Some cables are suitable for "direct burial", but this usually requires that the cable be gel filled in order to hinder moisture migration into the cable.

When using a cable for a tower, attention must be given to vertical cable runs that may channel water into sensitive indoor equipment.[16] This can often be solved by adding a drip-loop at the bottom of the run of cable.

Plenum-rated cables are slower to burn and produce less smoke than cables using a mantle of materials like PVC. This also affects legal requirements for a fire sprinkler system. That is if a plenum-rated cable is used, sprinkler requirement may be eliminated.[17]

Shielded cables (FTP/STP) are useful for environments where proximity to RF equipment, may introduce electromagnetic interference, and can also be used where eavesdropping likelihood should be minimized.

Category 6 cable

Category 6 cable, commonly referred to as Cat 6, is a cable standard for Gigabit Ethernet and other network physical layers that is backward compatible with the Category 5/5e and Category 3 cable standards. Compared with Cat 5 and Cat 5e, Cat 6 features more stringent specifications for crosstalk and system noise. The cable standard provides performance of up to 250 MHz and is suitable for 10BASE-T, 100BASE-TX (Fast Ethernet), 1000BASE-T/1000BASE-TX (Gigabit Ethernet) and 10GBASE-T (10-Gigabit Ethernet).

Whereas Category 6 cable has a reduced maximum length when used for 10GBASE-T; Category 6a cable, or Augmented Category 6, is characterized to 500 MHz and has improved alien crosstalk characteristics, allowing 10GBASE-T to be run for the same distance as previous protocols.

Category 6

Like most earlier cables, Category 6 cable contains four twisted wire pairs. Although it is sometimes made with 23 AWG wire, the increase in performance with Cat 6 comes mainly from better insulation; 22 to 24 AWG copper is allowed if the ANSI/TIA-568-B.2-1 performance specifications are met. Cat 6 patch cables are normally terminated in 8P8C modular connectors. Attenuation, near end crosstalk (NEXT), and PSNEXT (power sum NEXT) in Cat 6 cable and connectors are all significantly lower than Cat 5 or Cat 5e, which also uses 24 AWG wire.

The heavier insulation in some Cat 6 cables makes them too thick to attach to 8P8C connectors without a special modular piece, resulting in a technically out-of-compliance assembly.

Connectors use either T568A or T568B pin assignments; the choice is arbitrary provided both ends of a cable are the same.

. If Cat 6 rated patch cables, jacks, and connectors are not used with Cat 6 wiring, overall performance is degraded to that of the cable or connector.

Because the conductor sizes are generally the same, Cat 6 jacks may also be used with Cat 5e cable.

Pins on 8P8C plug face

8P8C Wiring (T568A termination)

Pin

Pair

Wire

Color

1

3

1

white/green

2

3

2

green

3

2

1

white/orange

4

1

2

blue

5

1

1

white/blue

6

2

2

orange

7

4

1

white/brown

8

4

2

brown

8P8C Wiring (T568B termination)

Pin

Pair

Wire

Color

1

2

1

white/orange

2

2

2

orange

3

3

1

white/green

4

1

2

blue

5

1

1

white/blue

6

3

2

green

7

4

1

white/brown

8

4

2

brown

USOC/RJ61 Wiring

Pin

Pair

Wire

Color

1

4

1

white/brown

2

3

1

white/green

3

2

1

white/orange

4

1

2

blue

5

1

1

white/blue

6

2

2

orange

7

3

2

green

8

4

2

brown

Note: This is from left to right, with the (plastic) tab faced away from you.

Category 6 cable can be identified by the printing on the side of the cable sheath.[1]

Category 6a

The latest standard from the TIA for enhanced performance standards for twisted pair cable systems was defined in February 2008 in ANSI/TIA/EIA-568-B.2-10. Category 6a (or Augmented Category 6) is defined at frequencies up to 500 MHz—twice that of Cat. 6.

Category 6a performs at improved specifications, in particular in the area of alien crosstalk as compared to Cat 6 UTP, which exhibited high alien noise in high frequencies.

The global cabling standard ISO/IEC 11801 has been extended by the addition of amendment 2. This amendment defines new specifications for Cat. 6A components and Class EA permanent links. These new global Cat. 6A/Class EA specifications require a new generation of connecting hardware offering far superior performance compared to the existing products that are based on the American TIA standard.[2]

The most important point is a performance difference between ISO/IEC and EIA/TIA component specifications for the NEXT transmission parameter. At a frequency of 500 MHz, an ISO/IEC Cat., 6A connector performs 3 dB better than a Cat. 6A connector that conforms with the EIA/TIA specification. 3 dB equals 100% increase of near-end crosstalk noise reduction when measured in absolute magnitudes; see 3dB-point.

Confusion therefore arises because of the different naming conventions and performance benchmarks laid down by the International ISO/IEC and American TIA/EIA standards, which in turn are different from the regional European standard, EN 50173-1. In broad terms, the ISO standard for Cat6A is the highest, followed by the European standard and then the American.[3][4]

Maximum length

When used for 10/100/1000BASE-T, the maximum allowed length of a Cat 6 cable is 100 meters (330 ft)This consists of 90 meters (300 ft) of solid "horizontal" cabling between the patch panel and the wall jack, plus 10 meters (33 ft) of stranded patch cable between each jack and the attached device. Since stranded cable has higher attenuation than solid cable, exceeding 10 metres of patch cabling will reduce the permissible length of horizontal cable.

When used for 10GBASE-T, Cat 6 cable's maximum length is 55 meters (180 ft) in a favourable alien crosstalk environment, but only 37 meters (121 ft) in a hostile alien crosstalk environment such as when many cables are bundled together. However, because the effects of alien crosstalk environments on cables are difficult to determine prior to installation, it is highly recommended that all Cat6 cables being used for 10GBASE-T are electrically tested once installed. Because of the high labor cost to test every cable in the field and the risk of having an installed cable not work, it is generally recommended to use Cat6A cable in all 10GBASE-T applications. Cat6A does not need to be tested after installation.

Installation caveats

Category 6 and 6a cable must be properly installed and terminated to meet specifications. Incorrect installation practices include kinking or bending the cable too tightly. The cable bend radius should be no less than 4 times the outer diameter of the cable. Incorrect termination practices include untwisting the wire pairs or stripping the outer jacket back more than 1/2 inch.

All shielded cables must be grounded for safety and effectiveness. A continuous shield connection maintained from end to end. Ground loops develop when there is more than one ground connection and the difference in common mode voltage potential at these ground connections introduces noise into the cabling.

Class F Cable

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Class F cable

Class F cable, (ISO/IEC 11801:2002 Class F), is a cable standard for Ethernet and other interconnect technologies that can be made to be backward compatible with Class D and Class E. Class F features even more strict specifications for crosstalk and system noise than Class E. To achieve this, shielding has been added for individual wire pairs and the cable as a whole. Besides the foil shield, the twisting of the pairs and number of turns per inch causes RF shielding and protects from crosstalk. Class F is recognized for all the country organizations members of ISO.

The Class F cable standard has been created to allow 10 Gigabit Ethernet over 100 m of copper cabling (also, 10 Gbit/s Ethernet now is typically run on Cat 6a). The cable contains four twisted copper wire pairs, just like the earlier standards. Class F can be terminated either with 8P8C compatible GG45 electrical connectors which incorporate the 8P8C standard or with TERA connectors. When combined with GG45 or TERA connectors, Class F cable is rated for transmission frequencies of up to 600 MHz.[citation needed]

As of November 2010[update], all manufacturers of active equipment have chosen to support the 8P8C for their 10 Gigabit Ethernet products on copper, and not the GG45 or TERA in order to function on Cat 6a. Class F is not currently recognized by the TIA/EIA.

Class Fa

Class Fa (or Augmented Class F) is defined at frequencies up to 1000 MHz, suitable for multiple applications including CATV (862 MHz).[citation needed] Each pair offers 1.2Ghz of bandwidth.[citation needed] Simulation results have shown that 40 Gigabit Ethernet may be possible at 50 meters and 100 Gigabit Ethernet at 15 meters.[citation needed] In 2007, researchers at Pennsylvania State University predicted that either 32 nm or 22 nm circuits would allow for 100 Gigabit Ethernet at 100 meters.[1][2]

However, similar studies in the past have shown that Cat5e could support 10 Gbit/s, so these should be read with caution. Furthermore, the IEEE did not include Class Fa for 40 Gbit/s or 100 Gbit/s in the 802.3ba standard ratified in June 2010. It may in the future, but there is absolutely no guarantee that such applications will ever exist.

Class F is currently in ISO standards for channel performance in Amendment 1, recently component performance has been ratified in Amendment 2. The formal names are ISO 11801 Amendment 1 (2008) and ISO 11801 Amendment 2 (2010). Class Fa is not recognized in TIA/EIA-568.