HDSL2 (ADC/ADTRAN) is held to the same standards as a repeatered T1 facility by ILEC's. HDSL2 modulates a 4-wire DS1 payload onto a boradband/analog carrier between 2 digital transceiver units(HDSL Line Unit/HDSL Remote Unit)over 1 2-wire cable pair. HDSL2 does not work as well as a repeatered T1 facility on marginal OSP facilities due to it using only a single conductor for its simplex power loop between the HLU & HRU. Light ground-faults and high-resistance opens and shorts that may not typically cause troule or go unnoticed on a T-1 facility can play havoc on HDSL2/4. As long as it is carried over healthy OSP facilities between the telco and customer, HDSL is just as reliable as any other DS1 transport technology.
