The rapid development of electronic communications technologies, as well as the enlarging diversity of the demand featured by the users of the public networks of electronic communications triggered the necessity of offering these users uniform access to various network structures (ISDN, intelligent networks etc.). As the numbering resources had to be up to the above mentioned development, the existing formats were extended to correspond to the new types of networks and to international telephone services, nevertheless maintaining compatibility with the previous formats.
Based on these general considerations, the International Telecommunications Union, a specialized agency of the United Nations Organisation in the telecommunications field, elaborated by means of its telecommunications standardization section (ITU – T), Recommendation E.164 regarding the "Numbering Plan for public international telecommunications ", specifying the structure and functionality of three numbering resource categories:
- geographical numbering resources,
- global service numbering resources,
- network numbering resources.
One can appreciate that E.164 numbering comprises numbers used in the networks presenting circuit switching (telephony), without excluding however the networks with packet switching (frame relay). These numbers are hierarchically structured in international numbers, national numbers and local numbers, being differentiated by the prefixes used. These contain information on the geographic area, the services provided and the corresponding tariffs.
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