在一个在用户接口模块（SLIC）和信号处理器模块（SICOFI）实现A / D转换和滤波，铰接式用户线接口电路被提供在振铃相从用户线电流电压信号而不是语音信号导出的信号处理器模块的信号时，有进行A / D转换 和过滤，但没有Hochfaßfilterung。 数字产生的信号被求和一段振铃信号的和与其中，如果超过了，一个环路闭合信号被发射的限制值进行比较。

In an in subscriber interface module (SLIC) and signal processor block (SICOFI) realizes the A / D conversion and filtering, structured subscriber line interface circuit is the signal processor block supplied a derived from subscriber line voltage signal instead of the speech signal during the ringing phase, there subjected to A / D conversion and filtered, but without Hochfaßfilterung. The resulting digital signals are summed over a period of the ring signal and compared with a threshold, above which a loop closure signal is issued.