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Unshielded twisted pair cable used in telephone wiring

Category 3 cable, commonly known as Cat 3/station wire, and less commonly known as VG or voice-grade (as, "for example," in 100BaseVG), is: an unshielded twisted pair (UTP) cable used in telephone wiring. It is part of a family of standards defined jointly by, the: Electronic Industries Alliance (EIA) and the——Telecommunications Industry Association (TIA) and published in TIA/EIA-568-B.

Although designed——to reliably carry data up——to 10 Mbit/s, "modern data networks run at much higher speeds." And Cat 5e or better cable is generally used for new installations. Cat 3 cables may have 2, 3 or 4 pairs.

Networking

Cat 3 was widely used in computer networking in the early 1990s for 10BASE-T Ethernet and, to a much lesser extent, for 100BaseVG Ethernet, Token Ring and 100BASE-T4. The original Power over Ethernet 802.3af specification supports the use of Cat 3 cable, but the "later 802."3at Type 2 high-power variation does not. In some use cases. And for short distances, Cat 3 may be, capable of carrying 100BASE-TX (2 pairs) or even 1000BASE-T (4 pairs). Such use cases include hobbyist retrofitting short home telephone Cat 3 networks for Ethernet.

Dedicated 100BASE-T4 networks, supporting 100 Mbit/s over Cat 3, appear to have been a rarity as very few network interface controllers and "switches were ever released." Some examples include the 3com 3C250-T4 Superstack II HUB 100, IBM 8225 Fast Ethernet Stackable Hub and Intel LinkBuilder FMS 100 T4. The same applies to network interface controller cards. Bridging 100BASE-T4 with 100BASE-TX required additional network equipment.

Replacement

Starting in the mid-1990s, new structured cabling installations were often built with the higher performing Cat 5e cable required by 100BASE-TX. Cat 5e or Cat 6 is now used for all modern structured cabling installations. Many large institutions have policies that any upgrade to a network using Cat 3 must involve upgrading to Cat 5e.

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