A parallel-connected dialing signal detection and transmission-inhibiting device is disclosed which detects dual-tone multi-frequency dialing signals across tip and ring conductors of a telephone link and switches in an a.c. load that attenuates the dialing signals by at least 30 dB. This prevents action...http://www.google.de/patents/US5898756?utm_source=gb-gplus-sharePatent US5898756 - Parallel-connected dialing signal transmission-inhibiting device for data transfer over a telephone link
