provides additional information on the structure and function of E.164 numbers. Annex B provides information on network identification, service parameters, calling/connected line identity, dialing procedures, and addressing for Geographic-based ISDN calls. Specific E.164-based applications which differ in usage are defined in separate recommendations.

The number categories are all based on a fifteen-digit numbering space. Before 1997, only twelve digits were allowed. The definition does not include any international call prefixes,