Data communication networks : open systems interconnection (OSI) protocol specifications, conformance testing: recommendations X.220 - X.290 /International Telecommunication Union
Data communication networks : interworking between networks, mobile data transmission systems, internetwork management: recommendations X.300 - X.370 /International Telecommunication Union
Data communication networks : directory: recommendations X.500 - X.521/International Telecommunication Union
Functional specification and description language (SDL) : criteria for using formal description techniques (FDTs): recommendation Z.100 and annexes A, B, C and E, recommendation Z.110 / International Telecommunications Union