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, such as wires, junctions, and connectors.

Cabling systems are categorized 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. For ISO/IEC standards, the category refers to the cable and class refers to the connector. ISO are international standards and can be followed anywhere in the world. A standard is different than a code in that standards are voluntary and provide a guideline so that all manufacturers have a minimum set of parameters to work with. A code, on the other hand, is law and is enforced through an AHJ (Authority having Jurisdiction).

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.) In old split pair configurations, PoE MidSpan can not be used. PoE is supported on 5e or better; however the higher performing cable provides better heat performance with shielded systems better than UTP.

The two most widely-installed categories are CAT 3 (voice) and CAT 5e, traditionally, however with new installations, category 5e for voice and one high speed to support 10GBASE-T for long term usage are the most common. According to a BSRIA study, 78% of all new installations are shielded. 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 replaced CAT 5 in both standards groups.

The CAT 6 specification, published in 2002 (the same time as ISO Category 7/class F), improves on CAT 5E in terms of near-end crosstalk, balance, and bandwidth. According to IEEE, 70% of new installs in 2004 were CAT 6.

Category 7/Class F (ISO/IEC), published in 2002, is a fully shielded system. The shielding provides superior noise immunity and performance. Until February 2008, it was the only published standard to support 10GBASE-T to a full 100m.

CAT 7A/Class FA and Category 6A/Class EA specifications were published in February 2008.

The standards categories

Category Maximum data rate Usual application
CAT 1 (de facto name, never a standard) Up to 1 Mbps (1 MHz) analog voice (POTS)
Basic Rate Interface in ISDN
Doorbell wiring
CAT 2(de facto name, never a standard) 4 Mbps Mainly used in the IBM cabling system for Token Ring networks
CAT 3 16 Mbps Voice (analog most popular implementation)
10BASE-T Ethernet
CAT 4 20 Mbps Used in 16 Mbps Token Ring, otherwise not used much. Was only a standard briefly and never widely installed.
CAT 5 100 MHz 100 Mbps TPDDI
155 Mbps ATM
No longer supported; replaced by 5E.
4/16MBps Token Ring
Analog Voice
CAT 5E 100 MHz 100 Mbps TPDDI
155 Mbps ATM
gigabit Ethernet
Offers better near-end crosstalk than CAT 5
CAT 6 Up to 250 MHz Minimum cabling for data centers in TIA-942.
Quickly replacing category 5e.
(field-tested to 500 MHz)
Support for 10 Gigabit Ethernet (10GBASE-T)
May be either shielded (STP, ScTP, S/FTP) or unshielded (UTP)
This standard published in Feb. 2008.
Minimum for Data Centers in ISO data center standard.
(ISO Class F)
600 MHz
1.2 Ghz in pairs with Siemon connector
Full-motion video
Government and manufacturing environments
Fully Shielded (S/FTP) system using non-RJ45 connectors but backwards compatible with hybrid cords.
Until February 2008, the only standard (published in 2002) to support 10GBASE-T for a full 100m.
This was last updated in March 2010

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