ITU-T X.228-1989 Reliable Transfer: Protocol Specification - Data Communication Networks - Open Systems Interconnection (OSI) Protocol Specifications, Conformance Testing (Study Group VII) 69 pp
that Recommendation X.200 defines the Basic Reference Model of Open Systems Interconnection for CCITT applications
ITU-T X.228-1989 history
1989ITU-T X.228-1989 Reliable Transfer: Protocol Specification - Data Communication Networks - Open Systems Interconnection (OSI) Protocol Specifications, Conformance Testing (Study Group VII) 69 pp