Abstract: 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.

Abstract: A system in a Voice Over Internet Protocol (VOIP) network eliminates false voice detection in voice band data service (e.g., modem or facsimile transmission) by sequentially enabling silence detection then voice detection. In Voice Band Data (VBD) mode, the system initially enables silence detection and disables voice detection. If silence is detected in a VOIP signal associated with a VOIP call, the system enables voice detection. If voice is detected, the system switches from VBD mode to voice mode and enables processing (e.g., echo cancellation and/or data compression) that improves voice communications.

Abstract: A method, or corresponding apparatus, assumes a call is a Voice Band Data (VBD) call. The method disables a local echo canceller and transmits a tone that disables distal echo canceller(s) along a communications path across which the call is communicated. After disabling the echo cancellers, the echo cancellers are allowed to operate in a typical manner, such as according to ITU standards, after the call is established, including remaining disabled if the call is a Voice Band Data call and being automatically enabled if the call is or becomes a voice call. The method or apparatus is particularly useful in networks having Point of Service (POS) devices that have modems that do not send out a 2100 Hz tone to disable echo cancelling in the communications path. In one embodiment, the method or corresponding apparatus is deployed in a gateway.

Abstract: A testing and performance analysis methodology applies a series of test vector pairs to the input ports of an echo canceller under test. The test vector signal pair may represent a particular speech activity state transition, e.g., a Brady Model transition. A scoring compression function such as a sigmoid squashing function is used to evaluate quantized performance parameters. The sub-scores may be weighted and averaged to provide an overall performance score.