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Black Box Guide to Structured Cabling

Section NameSection Name

Cabling

Balanced Twisted-Pair Cable Specifications

CAT5 CAT5e CAT6 CAT6a CAT7

Frequency 100 MHz 100 MHz 250 MHz 500 MHz 600 MHz

Attenuation (min. at 100 MHz) 22.0 dB 22.0 dB 19.8 dB — 20.8 dB

Characteristic Impedance 100 ohms ± 15% 100 ohms ± 15% 100 ohms ± 15% — 100 ohms ± 15%

NEXT (min. at 100 MHz) 32.3 dB 35.3 dB 44.3 dB 27.9 dB 62.1 dB

PS-NEXT (min. at 100 MHz)

—

32.3 dB 42.3 dB — 59.1 dB

EL-FEXT (min. at 100 MHz) — 23.8 dB 27.8 dB 9.3 dB (not yet specified)

PS-ELFEXT (min. at 100 MHz) — 20.8 dB 24.8 dB — (not yet specified)

PS-ANEXT (min. at 500 MHz) — — — 49.5 dB —

PS-AELFEXT (min. at 500 MHz) 16.0 dB 20.1 dB 20.1 dB 23.0 dB 14.1 dB

Return Loss (min. at 100 MHz) 16.0 dB 20.1 dB 20.1 dB 8.0 dB 14.1 dB

Delay Skew (max. per 100 m) — 45 ns 45 ns — 20 ns

Networks Supported 100BASE-TX 1000BASE-T 1000BASE-T 10GBASE-T (not yet specified)

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 backwards-

compatible 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 mid-

span 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 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.

Copper cable standards

NOTE: The ISO currently has Class F

(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.

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