Categories of twisted pair cabling systems

ANSI/EIA (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:

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.

Source:searchNetworking.com