ITU-T G.711 Pulse code modulation (PCM) of voice frequencies, 1998
ITU-T X.509 Information technology - Open Systems Interconnection - The directory: Public-key and attribute certificate frameworks, 2000
Note: ITU-T Recommendation X.509 is similar to ISO/IEC 9594-8 1990. However, the ITU-T recommendation is the more familiar form, and was revised in 1993 and 2000, with two sets of corrections in 2001. ITU-T was formerly known as CCITT.