ETSI ETS 300 723-1997 Digital Cellular Telecommunications System; Enhanced Full Rate (EFR) Speech Processing Functions; General Description GSM 06.51; Version 5.1.2
2000ETSI ETS 300 723-2000 Digital Cellular Telecommunications System; Enhanced Full Rate (EFR) Speech Processing Functions; General Description (GSM 06.51; Version 5.2.1; Second Edition)
1997ETSI ETS 300 723-1997 Digital Cellular Telecommunications System; Enhanced Full Rate (EFR) Speech Processing Functions; General Description GSM 06.51; Version 5.1.2