1993ETSI ETS 300 232-1993 Transmission and Multiplexing (TM); Optical Interfaces for Equipments and Systems Relating to the Synchronous Digital Hierarchy (ITU-T Recommendation G.957 (1993) Modified)
1992ETSI PRETS 300 232-1992 Transmission and Multiplexing (TM); Optical Parameter for Interfaces for the Synchronous Digital Hierarchy (SDH)