High-bit-rate Digital Subscriber Line (HDSL) technology is a transparent replacement for a T-1 repeatered line. It allows DS-1 signals to be transported over distances of up to 12,000 feet (3700 meters) on unconditioned copper cable, which are cables without line repeaters.
HDSL is easier to maintain and provision than conventional T-carrier span designs because HDSL requires a repeater only at both ends of the line, not every 1800 meters (6000 feet), as required by conventional T1 lines.
HDSL was designed as an alternative to T-carrier services (such as T1 and E1 lines). HDSL essentially operates in the same way as ADSL except that it is always symmetrical, which means the data speeds are the same both up and downstream. HDSL can carry both voice and data over a single communication link.