06.013GPPFull Rate Speech Processing FunctionsTS
In the receiver, frames may be lost due to transmission errors or frame stealing. GSM 06.11  describes the actions to be taken in these cases, both for lost speech frames and for lost SID‑frames in DTX operation.
In order to mask the effect of an isolated lost frame, a scheme is used, where the lost speech frame is substituted by a predicted frame based on previous frames. Insertion of silence frames is not allowed. For several lost frames in a row, some muting technique must be used to indicate to the customer that transmission is interrupted.