100Base-T4 Hear it!

100Base-T4 Telecom Definition
A 100Base-T extension that specifies Cat 3 or better unshielded twisted pair (UTP), operating in either half-duplex (HDX) or full duplex (FDX) over distances up to 100 meters. See also 100Base-T, Cat 3, FDX, HDX, and UTP.