1.		Data communication networks : open systems interconnection (OSI) model and notation, service definition: recommendations X.200 - X.219 /International Telecommunication Union Data Publicação: 1989 Tema: Vária
2.		Data communication networks : open systems interconnection (OSI) protocol specifications, conformance testing: recommendations X.220 - X.290 /International Telecommunication Union Data Publicação: 1989 Tema: Vária
3.		Data communication networks : interworking between networks, mobile data transmission systems, internetwork management: recommendations X.300 - X.370 /International Telecommunication Union Data Publicação: 1989 Tema: Vária
4.		Data communication networks : message handling systems: recommendations X.400 - X.420 /International Telecommunication Union Data Publicação: 1989 Tema: Vária