The specification for category 5 cable was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95. These documents specified performance characteristics and test requirements for frequencies of up to 100 MHz.
Category 5 cable includes four twisted pairs in a single cable jacket. This use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and other pairs (this latter form of interference is called crosstalk). It is most commonly used for 100 Mbit/s networks, such as 100BASE-TX Ethernet, although IEEE 802.3ab defines standards for 1000BASE-T - Gigabit Ethernet over category 5 cable. Cat 5 cable typically has three twists per inch of each twisted pair of 24 gauge copper wires within the cable.
Cat 5 e cable is an enhanced version of Cat 5 that adds specifications for far end crosstalk. It was formally defined in 2001 as the TIA/EIA-568-B standard, which no longer recognizes the original Cat 5 specification. Although 1000BASE-T was designed for use with Cat 5 cable, the tighter specifications associated with Cat 5e cable and connectors make it an excellent choice for use with 1000BASE-T. Despite the stricter performance specifications, Cat 5e cable does not enable longer cable distances for Ethernet networks: cables are still limited to a maximum of 100 m (328 ft) in length (normal practice is to limit fixed ("horizontal") cables to 90 m to allow for up to 5 m of patch cable at each end). Cat 5e cable performance characteristics and test methods are defined in TIA/EIA-568-B.2-2001.
Category 6 cable, commonly referred to as Cat-6, is a cable standard for Gigabit Ethernet and other network protocols that is backward compatible with the Category 5/5e and Category 3 cable standards. Cat-6 features more stringent specifications for crosstalk and system noise. The cable standard provides performance of up to 250 MHz and is suitable for 10BASE-T / 100BASE-TX and 1000BASE-T (Gigabit Ethernet). It is expected to suit the 10GBASE-T (10Gigabit Ethernet) standard, although with limitations on length if unshielded Cat 6 cable is used. Category 6 cable can be identified by the printing on the side of the cable sheath.
The cable contains four twisted copper wire pairs, just like earlier copper cable standards. Although Cat-6 is sometimes made with 23 gauge wire, this is not a requirement; the ANSI/TIA-568-B.2-1 specification states the cable may be made with 22 to 24 AWG gauge wire, so long as the cable meets the specified testing standards. When used as a patch cable, Cat-6 is normally terminated in 8P8C modular connectors, often incorrectly referred to as "RJ-45" electrical connectors. Cat-6 connectors are made to higher standards that help reduce noise caused by crosstalk and system noise. Attenuation, NEXT (Near End Crosstalk), and PSNEXT (Power Sum NEXT) are all significantly lower when compared to Cat-5/5e.
Category 7 cable (CAT7), (ISO/IEC 11801:2002 category 7/class F), is a cable standard for Ethernet and other interconnect technologies that can be made to be backwards compatible with traditional CAT5 and CAT6 Ethernet cable. CAT7 features even more strict specifications for crosstalk and system noise than CAT6. To achieve this, shielding has been added for individual wire pairs and the cable as a whole.
The CAT7 cable standard has been created to allow 10 gigabit Ethernet over 100 m of copper cabling (also, 10-Gbit/s Ethernet now is typically run on Cat6A). The cable contains four twisted copper wire pairs, just like the earlier standards. CAT7 can be terminated either with RJ-45 compatible GG45 electrical connectors which incorporate the RJ-45 standard or with TERA connectors. When combined with GG-45 or TERA connectors, CAT7 cable is rated for transmission frequencies of up to 600 MHz.
Researchers in November 2007 proved that it is "definitely possible" to transport 100 gigabits per second over 70 meters of CAT7 cable and they are now working on extending it to 100 m. This technology may be available in early 2013.