(DSI) is a procedure for increasing the efficiency of transmission channels. The procedure dates back to the time before the liberalisation of the telecoms market and is therefore well before the time of flat rates
, which makes this procedure obsolete. However, it is still listed for the sake of completeness. The Digital Speech Interpolation method works with speech pause detection (VAD). During the pauses in speech in a telephone call, the DSI procedure transmits further speech data. With this procedure the speech capacity of a transmission line could be doubled. Digital Speech Interpolation is used in Enhanced Time Division Multiple Access (E-TDMA).