This draft European Telecommunication Standard (ETS) defines a frame substitution and muting procedure which shall be used by the Receive (RX) Discontinuous Transmission (DTX) handler when one or more lost speech or Silence Descriptor (SID) frames are received from the Radio Sub System (RSS). The requirements of this ETS are mandatory for implementation in all GSM Base Station Systems (BSS)s and Mobile Stations (MS)s capable of supporting the enhanced full-rate speech traffic channel. It is not mandatory to follow the bit exact implementation outlined in this specification and the corresponding C-source code.