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. 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 | Less than 1 Mbps | 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
Gigabit Ethernet |
| CAT 5E | 100 Mbps | 100 Mbps TPDDI
155 Mbps ATM |
| CAT 6 | 200-250 MHz | Super-fast broadband applications |
While longer connections for Gigabit Ethernet use optical fiber, the goal is to leverage the CAT 5 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 popular specifications 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.
The CAT 6 specification was not yet formally approved by the EIA as of March, 2001, although products are being offered that conform to a proposed specification. A CAT 7 specification is reportedly being considered.
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