ITU-T Rec. E.164 NUMBERING PLAN FOR THE ISDN ERA
1 Introduction
2 Definitions
3 ISDN numbering plan principles
    3.1 General
    3.2 Structure of the international ISDN number
    3.3 Number length
    3.4 Number analysis
4 Number allocation principles
5 Network identification
6 Service identification
7 Calling/called line identity6)
8 Dialling procedures
9 Prefixes
10 Escape code
11 Address information
    11.1 Direct dialling-in
    11.2 Sub-addressing (network address extension)
    11.3 Combination of sub-addressing and direct dialling-in
    11.4 Address delimiters