Transcoder and Rate Adaptation Unit, or TRAU, performs transcoding function for speech channels and RA (Rate Adaptation) for data channels in the GSM network.

Transcoding, i.e. the compression of speech data from 64 kbit/s to 13/12.2/5.6 kbit/s in case FR/EFR/HR speech coding.

• Full Rate
• Half Rate
• Enhanced Full Rate
• Adaptive Multi-Rate

TRAU was also the term used for the frame format used in transport of the compressed bits from these speech coders.shariq