This Technical Report presents the results of an investigation into the feasibility and advisability of bi-directional high-bit-rate digital subscriber lines (HDSL) that operate over twisted wire pairs in the outside loop plant with a payload capacity substantially greater than ISDN Basic Access DSLs. The Report describes an HDSL system that could provide an alternative to T1 repeatered lines to transport DS1-based services with a nominal rate of 1.544 Mb/s. The Report discusses HDSL system support of the ANSI T1.403-1988 and ANSI T1.408-1990 interface standards.