Committed to connecting the world


ITU-T Recommendations

Search by number:
Skip Navigation Links
Content search
Advanced search
Provisional name
ISO/IEC number
Formal description
Study Groups tree viewExpand Study Groups tree view

ITU-T X.121 (10/2000)

عربي | 中文 | English | Español | Français | Русский
International numbering plan for public data networks
This Recommendation defines the design, characteristics and application of the Numbering Plan for Public Data Networks. The International Numbering Plan for Public Data Networks has been developed in order to facilitate the operation of public data networks and provide for their interworking on a worldwide basis. The numbering plan allows for the identification of a country as well as a specific public data network in that country by means of Data Country Codes and Data Network Identification Codes. Additionally the numbering plan also allows for the identification of Global public data networks by means of a Global Data Network Identification Code. Interworking with other numbering plans can be achieved by use of an escape code mechanism.In order to conserve the valuable numbering resource, guidance is provided on the efficient use of Data Country codes for the creation of Data Network Identification Codes, and on the use of variable length Private Network Identification Codes for the numbering of private data networks in harmony with the Public Network Numbering Plan. Procedures for the allocation of Data Country Codes are defined. The eligibility criteria and procedures for the allocation of Data Network Identification Codes to Global public data networks are also defined. Guidance is also provided on the numbering of global networks.
Series title: X series: Data networks, open system communications and security
  X.1-X.199: Public data networks
  X.90-X.149: Network aspects
Approval date: 2000-10-06
Approval process:WTSA
Status: In force
Maintenance responsibility: ITU-T Study Group 13
Further details: Patent statement(s)
Ed. ITU-T Recommendation Status Summary Table of Contents Download
7 X.121 (10/2000) In force
6 X.121 (10/1996) Superseded
5 X.121 (09/1992) Superseded -
4 X.121 (11/1988) Superseded -
3 X.121 (10/1984) Superseded - - Not available
2 X.121 (11/1980) Superseded - - Not available
1 X.121 (09/1978) Superseded - - Not available