High compression rate codecs in gateways servicing Voice-over-Internet Protocol (VoIP) and Voice Band Data (VBD) calls distort modem/fax Answer Back Tones (e.g., 2100 Hz), which may lead to signal distortion and call hang-ups. To prevent such occurrences, a method or corresponding apparatus forces originating...http://www.google.de/patents/US7646763?utm_source=gb-gplus-sharePatent US7646763 - Method and apparatus for improving voice band data (VBD) connectivity in a communications network
