100BaseT4 defines the Fast Ethernet physical layer specification defined in the IEEE 802.3u document that uses Category 3 UTP cable with a maximum segment length of 100 meters. 100BaseT4 uses all four pairs of wires in the Cat 3 cable. Other implementations of Ethernet UTP specifications, such as 100BaseTX and 10BaseT, use only two pairs. Because the majority of UTP cable installed today is at least Category 5, 100BaseT4 is seldom used.