Abstract: A line interfacing apparatus has terminating units connected to lines, a spare terminating unit, a line selector for connecting one of the lines to the spare terminating unit, and a termination controller. The termination controller has switches for switching connections between the terminating units and a switching unit of a higher apparatus. If any one of the terminating units fails, the line selector is controlled to switch the line connected to the failed terminating unit to the spare terminating unit. At the same time, the switches of the termination controller are controlled to supply signals from the spare terminating unit, instead of signals from the failed terminating unit, to the switching unit of the higher apparatus.

Abstract: An HDB3 code violation detector includes a converting part for receiving positive polarity data and negative polarity data from a PCM line and for converting an HDB3 code received via the PCM line into an NRZ signal, and a first judging part receiving the positive polarity data, the negative polarity data and the NRZ signal, for judging whether or not a pattern of the NRZ signal received from the converting part is possible when the NRZ signal is NRZ "1" and for outputting a judgement result. In addition, the detector includes a second judging part receiving the positive polarity data, the negative polarity data and the NRZ signal, for judging whether or not a pattern of the NRZ signal received from the converting part is possible when the NRZ signal has a maximum of three consecutive NRZ "0"s and for outputting a judgement result.