1998ETSI PRETS 300 726-1998 Digital Cellular Telecommunications System )Phase 2+); Enhanced Full Rate (EFR) Speech Transcoding GSM 06.60; Version 5.2.0
1996ETSI PRETS 300 726-1996 Digital Cellular Telecommunications System; Enhanced Full Rate (EFR) Speech Transcoding GSM 06.60; Version 5.0.0