HDSL
High-bit-rate Digital Subscriber Line
High-bit-rate Digital Subscriber Line is the most mature of the xDSL family of protocols. It allows E1 / T1 rates to be achieved over two pair copper cable. The implementation of HDSL requires equipment both at the exchange and customer premises, but allows standard UTP (Unshielded Twisted Pair) cable to be employed with a maximum distance between the exchange and the customer premises of 12,000 feet.