High-speed digital transmission can be achieved with existing phone lines and HDSL chipsets while retaining plain old telephone service (POTS) with full failsafe capability. Two original ISDN signals [4,5] at a rate of 160 kbps and one POTS channel [10] digitized at 64 kbps are multiplexed by a MIPCS card [6] of a signal provider [1]. The resulting digital signal is transported over a twisted cable pair [2] which has an approximate maximum length of 16 kft based on the current technology. At a receiving end, the signal is demultiplexed and regenerated by a subscriber's MIPCS card [7]. The subscriber's MIPCS card is line-powered via the cable [2] to avoid dependence upon local power. The regenerated signals are transmitted over one POTS line [42] and two ISDN cables [8,9] to remote premises. Both MIPCS cards have bypass relays for the POTS lines to ensure the subscriber's POTS access in the event of a local power outage or electronic failure.