Rec. UIT-T X.121 (09/1992) INTERNATIONAL NUMBERING PLAN FOR PUBLIC DATA NETWORKS
FOREWORD
1 Design considerations
2 Characteristics and application of the Numbering Plan
    2.1 Number system
    2.2 Data network identification codes and data country codes
    2.3 International data number
    2.4 Number of digits
    2.5 Prefixes
    2.6 Escape codes
    2.7 Number analysis International calls between public data networks
    2.8 Numbering plan interworking
    2.9 Directories and letterheads
ANNEX A Development of data network identification codes
ANNEX B Development of network terminal numbers where a data network identification code is assigned to a group ...
ANNEX C List of DNICs for non-zoned systems public mobile satelite sistems
ANNEX D List of data country or geographical area codes
ANNEX E Definitions regarding the international numbering plan for public data networks
E.1 data country code
E.2 data network identification code
E.3 escape code
E.4 international data number
E.5 international data number format
E.6 international X.121 format
E.7 numbering plan
E.8 numbering plan interworking
E.9 prefix
ANNEX F Alphabetical list of abbreviations used in this Recommendation