This Recommendation covers Physical Layer characteristics for transporting Asynchronous Transfer Mode (ATM) cells at a nominal bit rate of 51 840 kbit/s over Category 3 Unshielded Twisted Pair (UTP) cabling at the S, reference point of the B-ISDN User Network Interface (UNI). The maximum distance is approximately 100 m. This specification may be used to take advantage of existing building wiring.