Cabling
Copper cable
Some of the most obvious advantages copper offers is that it’s less expensive than fiber cable and much easier to terminate in the field. Because copper is the most commonly installed cable, there is a vast selection of connecting hardware and networking devices, which are also less expensive than fiber equipment.
Unshielded twisted pair (UTP).
UTP. This is the most widely used cable. Known as balanced twisted pair, UTP consists of twisted pairs
(usually four) in a PVC or plenum jacket. When installing UTP cable, make sure you use trained technicians. Field terminations, bend radius, pulling tension, and cinching can all loosen pair twists and degrade performance. Also take note of any sources of EMI. Choose UTP for electrically quiet environments.
Shielded twisted pair (STP, F/UTP,
S/FTP, ScTP, S/STP).
Use shielded cable to extend distances and to minimize EMI. Sources of EMI, commonly referred to as noise, include elevator motors, fluorescent lights, generators, air conditioners, and printers, etc. In
10-GbE, shielded cable can also reduce ANEXT.
Shielded cable can be less balanced than UTP cable because of the shield. The metal sheaths in the cable need to be grounded to cancel the effect of EMI on the conductors. Shielded cable is also more expensive, less flexible, and can be more difficult to install than UTP cable. Most shielded cable is thicker than UTP, so it fills conduits quicker. Keep that in mind as you plan your cable pathways.
STP. This is twisted pair cabling with a shield. There are two common shields: foil sheaths and copper braids. Foil gives a 100% shield while a copper braid provides 85% to 95% coverage because of the holes in the braid. But, a braided shield offers better overall protection because it’s denser than foil and absorbs more EMI. A braided shield also performs better at lower frequencies. Foil, being thinner, rejects less interference, but provides better protection over a wider range of frequencies. For these reasons, combination foil and braid shields are sometimes used for the best protection. Shields can surround all the twisted pairs and/or the individual twisted pairs.
Foiled/Unshielded Twisted Pair (F/UTP). Foil is the most basic cable shield. Cables with an overall foil shield surrounding all the pairs are called F/UTP.
These may also be called FTP cables.
Shielded Foiled Twisted Pair (S/FTP). This cable features individual foil-shielded pairs and an outer shield, which can be braided or foil. It offers the best protection from external noise and ANEXT. This cable was traditionally called Screened Twisted Pair (ScTP).
You may also see it listed as S/STP.
Solid vs. stranded conductors.
Copper cable conductors can be solid or stranded, whether the cable is shielded or unshielded.
Solid-conductor. This cable is designed for both backbone and horizontal cable runs. Use it for runs between equipment rooms or from the telecommunications room to the wallplate. Solid cable shouldn’t be bent, flexed, or twisted. Its attenuation is lower than that of stranded-conductor cable.
Stranded-conductor. This cable is used primarily as a patch cable between the outlet and desktop and between patching equipment. Stranded-conductor cable is more flexible than solid-core cable. However, attenuation is higher, so the total length of a stranded cable in your channel should be kept to
10 meters or less to reduce signal degradation.
PVC vs. plenum.
PVC cable features an outer polyvinyl chloride jacket that gives off toxic fumes when it burns. It’s most commonly used between the wallplate and workstation. It can be used for horizontal and vertical runs, but only if the building features a contained ventilation system.
Plenum cable has a special coating, such as Teflon ®
FEP, which doesn’t emit toxic fumes when it burns.
A plenum is a space within the building designed for the movement of environmental air. In most office buildings, the space above the ceiling is used for the
HVAC air return. If cable goes through that space, it must be “plenum-rated.” LS0H (Low Smoke, Zero
Halogen) is a type of plenum cable with a thermoplastic compound that reduces the amount of toxic and corrosive gases emitted during combustion.
Unshielded twisted-pair cable (UTP)
Foil
Foiled/unshielded twisted-pair cable (F/UTP)
Foil Braid
Shielded/foiled twisted-pair cable (S/FTP)
Solid conductor
Stranded conductor
TECH TIP
AWG — American
Wire Gauge (AWG) is a classification system for the diameter of the conducting wire. The more a wire is drawn or sized, the smaller the diameter. For example, a
24-gauge wire is smaller than an 18-gauge wire.
724-746-5500 • blackbox.com
9
Copper cable standards
As the need for increased bandwidth grows and applications continually get more complex, so does copper twisted-pair cable.
Below are brief explanations of specifications for twisted-pair cabling and the applications for which each is best suited.
TIA/EIA-568B specifies several “categories” for both the components and the cable. The ISO/IEC specifies “categories” for the components and “classes” for the cabling.
Cable categories.
Category 3 (CAT3) cable is rated for networks operating up to
16 Mbps. It is suitable for voice transmissions (not VoIP). ISO/IEC refers to the end-to-end channel as Class C.
Category 4 cable is rated for transmission of 16 Mbps up to
100 meters. It is considered obsolete.
Category 5 (CAT5) cable was common for 100-Mbps LANs.
It was ratified in 1991 and is now considered obsolete.
Enhanced Category 5 (CAT5e/Class D) cable, ratified in 1999, was designed to enable twisted-pair cabling to support full-duplex,
100-MHz applications such as 100BASE-TX and 1000BASE-T. CAT5e introduces stricter performance parameters such as Power-Sum
Near-End Crosstalk (PS-NEXT), Equal-Level Far-End Crosstalk
(EL-FEXT), and Power-Sum Equal-Level Far-End Crosstalk (PS-ELFEXT).
It also introduces channel and component testing.
Category 6 (CAT6/Class E) cable easily handles Gigabit Ethernet
(1000BASE-T) applications. It’s a 100-ohm cable with a frequency of 250 MHz. CAT6 has far more stringent performance parameters than CAT5e, and is characterized by channel, link, and component testing. In addition, CAT6 components must be backwardscompatible with lower-level components. It’s important to note with
CAT6, as with all categories, that all the components in a channel must be of the same level. If not, the channel will perform at the lowest level.
The TIA TSB-155: Characterizing Existing Category 6 Cabling to Support 10-Gb Ethernet, ISO/IEC 24750, and IEEE 802.3an all address 10GBASE-T over UTP cabling. They also address installation practices to mitigate Alien Crosstalk (ANEXT) though it is not a specified CAT6 measurement. CAT6 is also recommended for midspan PoE applications. At the time of this publication (mid 2007),
CAT6 cabling is the system of choice for new installations because of the increased headroom.
Augmented Category 6 (CAT6a/Class E
A
), a relatively new standard, is designed to meet or exceed the requirements of
10-Gigabit Ethernet over copper at 100 meters. It extends the frequency range of CAT6 from 250 MHz to 500 MHz. Like CAT6, it includes an integrated set of channel, permanent link, and component requirements. It introduces an Alien Crosstalk
(ANEXT) measurement for closely bundled “six around one” cable configurations. (For information on ANEXT, see pages 28–29.) Both
UTP and F/UTP cables can be used in CAT6a deployments. The F/UTP cable, though, virtually eliminates the problem of ANEXT.
Frequency
Attenuation (min. at 100 MHz)
Characteristic Impedance
NEXT (min. at 100 MHz)
PS-NEXT (min. at 100 MHz)
EL-FEXT (min. at 100 MHz)
PS-ELFEXT (min. at 100 MHz)
PS-ANEXT (min. at 500 MHz)
PS-AELFEXT (min. at 500 MHz)
Return Loss (min. at 100 MHz)
Delay Skew (max. per 100 m)
Networks Supported
Balanced Twisted-Pair Cable Specifications
CAT5
100 MHz
22.0 dB
100 ohms ± 15%
32.3 dB
—
—
—
—
16.0 dB
16.0 dB
—
100BASE-TX
CAT5e
100 MHz
CAT6
250 MHz
22.0 dB 19.8 dB
100 ohms ± 15% 100 ohms ± 15%
35.3 dB
32.3 dB
23.8 dB
20.8 dB
44.3 dB
42.3 dB
27.8 dB
24.8 dB
—
20.1 dB
20.1 dB
45 ns
1000BASE-T
—
20.1 dB
20.1 dB
45 ns
1000BASE-T
CAT6a
500 MHz
—
—
27.9 dB
—
9.3 dB
—
49.5 dB
23.0 dB
8.0 dB
—
10GBASE-T
CAT7
600 MHz
20.8 dB
100 ohms ± 15%
62.1 dB
59.1 dB
(not yet specified)
(not yet specified)
—
14.1 dB
14.1 dB
20 ns
(not yet specified)
NOTE: The ISO currently has Class F
A
(Category 7a) requirements under development. They are based on Class F requirements and the
Category 7 non-RJ style plug. They specify a bandwidth of 600 to 1000 MHz.
10 Black Box Guide to Structured Cabling
