Standards

• UTP cable standards are organized by the Telecommunications Industry Association (TIA). The TIA has created a number of different definitions of UTP cabling. Category 3 was originally favored for Ethernet. This standard was supplanted by Category 5, which has been updated as Category 5e for current use. This is the most widely-implemented standard to date. There is also a Category 6.
  
  

Configuration

• UTP comes in two formats: two-pair and four-pair. Two-pair (four wires) is used for telephones; four-pair (eight wires) is used for data network cabling and it is this configuration that is used for Ethernet. Within the jacket of the cable are four pairs of wires. Each pair is twisted together. This configuration reduces interference from external magnetic sources.
  
  

Pairs

• The UTP standards specify the uses of each pair of wires in the cable configuration. The four pairs of wires are color-coded. Ethernet data-out connections use the orange pair and data-in connections use the green pair. The other two pairs of wires (brown and blue) are not used by Ethernet connections.