ITU-T-X-SERIES

ITU-T X-series data networks ~400 specs.

Definition

ITU-T X-series organisation: X.1-X.199 (Public Data Networks PDN), X.200-X.299 (Open Systems Interconnection OSI), X.300-X.399 (Interworking between networks), X.400-X.499 (Message Handling Systems MHS), X.500-X.599 (Directory Services), X.600-X.699 (OSI networking and system aspects), X.700-X.799 (OSI management), X.800-X.849 (Security), X.850-X.899 (OSI applications), X.1000+ (Information and network security). Key recommendation: X.509 (Public Key Infrastructure certificates, used by TLS/SSL globally). Key recommendation: X.690 (DER ASN.1 encoding rules).

Origin

ITU-T (formerly CCITT) founded 1865 ; X-series introduced 1970s ; X.25 published 1976 ; X.500 published 1988 ; X.509 published 1988 (multiple revisions, current 9th edition 2019).

Example in context

All HTTPS connections on Internet use X.509 certificates issued by CAs (Lets Encrypt, DigiCert, Sectigo) ; DER ASN.1 format compliant with X.690 encoding rules.

Related terms

• ITU-T Q-series — other standards family.