| 摘要 |
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 and terminating gateways to stay in a low complexity non-voice compression codec (e.g., ITU G.711) after prenegotiating a high complexity, voice compression codec (e.g., G.729 or G.726) during a short beginning period of a voice call. The low complexity codec avoids distorted answer back tone leakage associated with previous solutions that use a notch filter to block the leakage, thereby significantly improving the success rate of a VBD call by completely eliminating modem answer back tone distortion caused by high complexity codecs that use voice compression and by completely eliminating use of the notch filter.
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