| 摘要 |
An improved telecommunication system is capable of supporting an enhanced audio transmission mode and a conventional PCM waveform encoding mode. The enhanced audio transmission mode is governed by an audio coding protocol, while the PCM mode is governed by a PCM protocol such as mu-law encoding. The telecommunication system performs an in-band signaling routine during a first communication session in accordance with the PCM protocol. The in-band signaling routine employs a form of robbed bit signaling to transmit information between the calling codec and the called codec. The signaling information is utilized to determine whether the called codec is compatible with the enhanced audio coding mode and, as necessary, to initiate the transition between the PCM mode and the audio coding mode. The audio coding mode transmits signals using a wider bandwidth than that used during the PCM mode. The use of a wider bandwidth results in a higher quality sound that better resembles person-to-person speech.
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