Name     | ISO             | Code (40 chars)    | Description (Full STD Title)
X.400    | ISO/IEC 10021-1 | X.400 (06/1999)    | Message handling system and service overview
X.402    | ISO/IEC 10021-2 | X.402 (06/1999)    | Information technology - Message Handling Systems (MHS): Overall architecture
X.403    | (none)          | X.403 (11/1988)    | Message handling systems: conformance testing
X.407    | ISO/IEC 10021-3 | X.407 (11/1988)    | Message handling systems: Abstract service definition conventions
X.408    | (none)          | X.408 (11/1988)    | Message handling systems: Encoded information type conversion rules
X.411    | ISO/IEC 10021-4 | X.411 (06/1999)    | Information technology – Message Handling Systems (MHS): Message Transfer System: Abstract Service Definition and Procedures
X.413    | ISO/IEC 10021-5 | X.413 (06/1999)    | Information technology - Message Handling Systems (MHS): Message store - Abstract service definition
X.419    | ISO/IEC 10021-6 | X.419 (06/1999)    | Information technology - Message Handling Systems (MHS): Protocol Specifications
X.420    | ISO/IEC 10021-7 | X.420 (06/1999)    | Information technology - Message Handling Systems (MHS): Interpersonal messaging system
X.435    | ISO/IEC 10021-9 | X.435 (06/1999)    | Electronic data interchange messaging system
X.460    | (none)          | X.460 (04/1995)    | Information technology - Message Handling Systems (MHS) Management: Model and architecture
X.462    | (none)          | X.462 (10/1996)    | Information technology - Message Handling Systems (MHS) Management: Logging information
X.467    | (none)          | X.467 (04/1995)    | Management: Message Transfer Agent management
X.500    | ISO/IEC 9594-1  | X.500 (10/2019)    | Information technology - Open Systems Interconnection - The Directory: Overview of concepts, models and services
X.501    | ISO/IEC 9594-2  | X.501 (10/2019)    | Information technology - Open Systems Interconnection - The Directory: Models
X.509    | ISO/IEC 9594-8  | X.509 (10/2019)    | Information technology - Open Systems Interconnection - The Directory: Public-key and attribute certificate frameworks
X.511    | ISO/IEC 9594-3  | X.511 (10/2019)    | Information technology - Open Systems Interconnection - The Directory: Abstract service definition
X.518    | ISO/IEC 9594-4  | X.518 (10/2019)    | Information technology - Open Systems Interconnection - The Directory: Procedures for distributed operation
X.519    | ISO/IEC 9594-5  | X.519 (10/2019)    | Information technology - Open Systems Interconnection - The Directory: Protocol specifications
X.520    | ISO/IEC 9594-6  | X.520 (10/2019)    | Information technology - Open Systems Interconnection - The Directory: Selected attribute types
X.521    | ISO/IEC 9594-7  | X.521 (10/2019)    | Information technology - Open Systems Interconnection - The Directory: Selected object classes
X.525    | (none)          | X.525 (10/2019)    | Information technology - Open Systems Interconnection - The Directory: Replication
X.601    | (none)          | X.601 (10/2010)    | Multi-peer communications framework
X.602    | ISO/IEC 16513   | X.602 (02/2007)    | Group management protocol
X.603    | ISO/IEC 16512-1 | X.603 (02/2007)    | Relayed multicast protocol: Framework
X.603.1  | ISO/IEC 16512-2 | X.603.1 (02/2007)  | Relayed multicast protocol: Specification for simplex group applications
X.603.2  | ISO/IEC 16512-3 | X.603.2 (05/2018)  | Relayed multicast protocol: Specification for N-plex group applications
X.604    | ISO/IEC 24793-1 | X.604 (02/2007)    | Mobile multicast communications: Framework
X.604.1  | ISO/IEC 24793-2 | X.604.1 (02/2007)  | Mobile multicast communications: Protocol over native IP multicast networks
X.604.2  | ISO/IEC 24793-3 | X.604.2 (02/2007)  | Mobile multicast communications: Protocol over overlay multicast networks
X.605    | ISO/IEC 13252   | X.605 (02/2007)    | Enhanced Communications Transport Service (ECTS) definition
X.606    | ISO/IEC 14476-1 | X.606 (02/2007)    | ECTS: Specification of simplex multicast transport
X.606.1  | ISO/IEC 14476-2 | X.606.1 (02/2007)  | ECTS: Specification of QoS management for simplex multicast transport
X.607    | ISO/IEC 14476-3 | X.607 (02/2007)    | ECTS: Specification of duplex multicast transport
X.607.1  | ISO/IEC 14476-4 | X.607.1 (02/2007)  | ECTS: Specification of QoS management for duplex multicast transport
X.608    | ISO/IEC 14476-5 | X.608 (02/2007)    | ECTS: Specification of N-plex multicast transport
X.608.1  | ISO/IEC 14476-6 | X.608.1 (02/2007)  | ECTS: Specification of QoS management for n-plex multicast transport
X.609    | (none)          | X.609 (06/2015)    | Managed peer-to-peer (P2P) communications: Functional architecture
X.609.1  | (none)          | X.609.1 (06/2016)  | Managed P2P communications: Peer activity management protocol (PAMP)
X.609.2  | (none)          | X.609.2 (06/2016)  | Managed P2P communications: Overlay resource control protocol (ORCP)
X.609.3  | (none)          | X.609.3 (08/2017)  | Managed P2P communications: Multimedia streaming signalling requirements
X.609.4  | (none)          | X.609.4 (01/2018)  | Managed P2P communications: Multimedia streaming peer protocol
X.609.5  | (none)          | X.609.5 (12/2018)  | Managed P2P communications: Overlay management protocol
X.609.6  | (none)          | X.609.6 (12/2018)  | Managed P2P communications: Content distribution signalling requirements
X.609.7  | (none)          | X.609.7 (12/2018)  | Managed P2P communications: Content distribution peer protocol
X.609.8  | (none)          | X.609.8 (12/2019)  | Managed P2P communications: Management protocol for live data sources
X.609.9  | (none)          | X.609.9 (09/2020)  | Managed P2P communications: Overlay content management protocol
X.609.10 | (none)          | X.609.10 (09/2020) | Managed P2P communications: Signalling requirements for data streaming
X.800    | ISO/IEC 7498-2  | X.800 (03/1991)    | Security architecture for open systems interconnection for CCITT applications
Z.100    | (none)          | Z.100 (06/2021)    | Specification and Description Language (SDL)
Z.101    | (none)          | Z.101 (06/2021)    | Specification and Description Language – Basic SDL-2010
Z.102    | (none)          | Z.102 (06/2021)    | Specification and Description Language – Comprehensive SDL-2010
Z.103    | (none)          | Z.103 (06/2021)    | Specification and Description Language – Shorthand notation and annotation features of SDL
Z.104    | (none)          | Z.104 (06/2021)    | Specification and Description Language – Data and expressions
Z.105    | (none)          | Z.105 (07/2003)    | SDL combined with ASN.1 modules (SDL/ASN.1)
Z.106    | (none)          | Z.106 (08/2002)    | Common interchange format for SDL
Z.107    | (none)          | Z.107 (10/2019)    | Specification and Description Language – Object-oriented data in SDL-2010
Z.109    | (none)          | Z.109 (11/1999)    | SDL combined with UML
Z.110    | (none)          | Z.110 (11/2000)    | Criteria for use of formal description techniques by ITU-T
Z.120    | (none)          | Z.120 (11/1999)    | Message sequence chart (MSC)
Z.140    | (none)          | Z.140 (04/2003)    | Testing and Test Control Notation version 3 (TTCN-3): Core language
Z.141    | (none)          | Z.141 (02/2003)    | Testing and Test Control Notation version 3 (TTCN-3): Tabular presentation format
Z.200    | ISO/IEC 9496    | Z.200 (11/1999)    | CHILL – The ITU-T Programming Language
Z.400    | (none)          | Z.400 (03/1993)    | Structure and format of quality manuals for telecommunications software