This European Telecommunication Standard (ETS) gives a description of the general baseband operation of full rate speech traffic channels in the transmitter and in the receiver of GSM Mobile Stations (MS)s and Base Station Systems (BSS)s during Discontinuous Transmission (DTX). For clarity, the description is structured according the block diagram s in figures 1 and 4. Except in the case described next, this structur e of distributing the various functions between system entities is not mandatory for implementation, as long as the operation on the air int erface and on the speech decoder output remains the same. In the case of BSSs where the speech transcoder is located remotely in the Base Station Controller (BSC), the implementation of the interfac es between the DTX Handlers and the Radio Subsystem (RSS) as described in this ETS together with all their flags is mandatory, being a part of the A bis interface as described in GSM 08.60. In this case the va rious flags also serve to avoid additional delays. The DTX functions described in this ETS are mandatory for implementati on in all GSM MSs. The receiver requirements are mandatory for impleme ntation in all GSM BSSs, the transmitter requirements only for those w here downlink DTX will be used. DTX shall be in operation in GSM MSs if commanded so by the network, s ee GSM 04.08.