For a local area network (LAN), CDDI (Copper Distributed Data Interface) is a standard for data transmission based on FDDI (Fiber Distributed Data Interface) that uses shielded twisted-pair (STP) or unshielded twisted pair (UTP) copper wire instead of fiber optic lines. CDDI supports a dual-ring capacity of 200 Mbps. CDDI's maximum distance is up to 200 meters, which is much shorter than FDDI.
CDDI is defined by the American National Standards Committee X3-T9.5 and conforms to the Open Systems Interconnection (OSI) model of functional layering. CDDI is officially named the Twisted-Pair Physical Medium Dependent (TP-PMD) standard and is also referred to as Twisted Pair Distributed Data Interface (TP-DDI).