The adaptive conversational speech transmission technique is based on the observation that a speaker engaged in an interactive conversation can be considered to be in one of three modes: talk, listen or double-talk. Double-talk constitutes only about 5 percent of total conversation time and is the only mode in which a symmetrically duplex channel is required. The authors show that by dynamically allocating the capacity of a bi-directional channel allocated to an interactive conversation, it is possible to support simultaneous voice and data transmission. The results also show that it is possible to smooth the resulting pulsed data service by careful least significant bit-dropping within the encoded speech signal and still obtain acceptable quality of speech. The resulting logical data channel has a performance approaching that of a dedicated 16 kb/s channel. This technique therefore provides a flexible method of increasing the efficiency of access to an ISDN.
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