Twisted Pair Cabling Systems


American National Standards Institute/Electronic Industries Association) Standard 568 is one of several standards that specify "categories" (the singular is commonly referred to as "CAT") of twisted pair cabling systems (wires, junctions, and connectors) in terms of the data rates that they can sustain effectively. The specifications describe the cable material as well as the types of connectors and junction blocks to be used in order to conform to a category. These categories are:

Category Maximum data rate Usual application
CAT 1 Up to 1 Mbps (1 MHz) analog voice (POTS)
Integrated Services Digital Network Basic Rate Interface in ISDN
Doorbell wiring
CAT 2 4 Mbps Mainly used in the IBM Cabling System for Token Ring networks
CAT 3 16 Mbps Voice and data on 10BASE-T Ethernet
CAT 4 20 Mbps Used in 16 Mbps Token Ring
Otherwise not used much
CAT 5 100 Mbps
1000 Mbps (4 pair)
100 Mbps TPDDI
155 Mbps ATM
No longer supported; replaced by 5E
CAT 5E 1000 Mbps
(10000 Mbps prototype)
100 Mbps TPDDI
155 Mbps ATM
Gigabit Ethernet
Offers better near-end crosstalk than CAT 5
CAT 6 Up to 400 MHz Super-fast broadband applications
Most popular cabling for new installs
CAT 6E Up to 625 MHz
(field-tested to 500 MHz)
Support for 10 Gigabit Ethernet (10GBASE-T)
CAT 7 (ISO Class F) 600-700 MHz
1.2 GHz in pairs with Siemon connector
Full-motion video
Government and manufacturing environments
Shielded system

While longer connections for Gigabit Ethernet use optical fiber, the goal is to leverage the CAT 5 and CAT 5E twisted-pair wiring most organizations already have in place for connections out to the desktop. (Four pairs of twisted pair are used.)

The two most widely-installed categories are CAT 3 and CAT 5. While the two cables may look identical, CAT 3 is tested to a lower set of specifications and can cause transmission errors if pushed to faster speeds. CAT 3 cabling is near-end crosstalk-certified for only a 16 MHz signal, while CAT 5 cable must pass a 100 MHz test. CAT 5E has recently replaced CAT 5 as the prevalent standard.

The CAT 6 specification is now completed and for some time products have been offered that conform to this specification which improves on CAT 5E in terms of near-end crosstalk and other ways. According to IEEE, 70% of new installs in 2004 were CAT 6.

A CAT 7 specification exists but is not yet official.


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