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ITU-T Recommendations
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ITU-T Recommendations
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ITU-T Recommendations by series
Select a series of Recommendations
A series: Organization of the work of ITU-T
D series: Tariff and accounting principles and international telecommunication/ICT economic and policy issues
E series: Overall network operation, telephone service, service operation and human factors
F series: Non-telephone telecommunication services
G series: Transmission systems and media, digital systems and networks
H series: Audiovisual and multimedia systems
I series: Integrated services digital network
J series: Cable networks and transmission of television, sound programme and other multimedia signals
K series: Protection against interference
L series: Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant
M series: Telecommunication management, including TMN and network maintenance
N series: Maintenance: international sound programme and television-transmission circuits
O series: Specifications of measuring equipment
P series: Telephone transmission quality, telephone installations, local line networks
Q series: Switching and signalling, and associated measurements and tests
R series: Telegraph transmission
S series: Telegraph services terminal equipment
T series: Terminals for telematic services
U series: Telegraph switching
V series: Data communication over the telephone network
X series: Data networks, open system communications and security
Y series: Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities
Z series: Languages and general software aspects for telecommunication systems
X series
: Data networks, open system communications and security
X.1-X.199
: Public data networks
X.200-X.299
: Open Systems Interconnection
X.300-X.399
: Interworking between networks
X.400-X.499
: Message Handling Systems
X.500-X.599
: Directory
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.900-X.999
: Open distributed processing
X.1000-X.1099
: Information and network security
X.1100-X.1199
: Secure applications and services (I)
X.1200-X.1299
: Cyberspace security
X.1300-X.1499
: Secure applications and services (II)
X.1500-X.1599
: Cybersecurity information exchange
X.1600-X.1699
: Cloud computing security
X.1700-X.1729
: Quantum communication
X.1750-X.1799
: Data security
X.1800-X.1839
: International Mobile Telecommunications (IMT) security
X.2000-X.2199
: Metaverse and digital twin security
X.2150-X.2199
: Software supply chain security
[Empty]
X.2200-X.2249
: Artificial Intelligence (AI) / Machine Learning (ML) security
[Empty]
X supplements
: Supplements to ITU-T X-series Recommendations
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