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.
These categories are known as E.164 numbering resources. The recommendation considers E.164 numbering resources to be the basis of global addressing in the fixed (PSTN and ISDN) and mobile terminal networks. The same term covers a couple of other categories, according to Completion no.1 of Recommendation E.164 (such as carrier selection numbering resources and network identification 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.
Number, name, address - definitions
Recommendation E.164 defines a number as being a set of decimal digits corresponding to one and only one terminal point in a public network. The number contains the data required for routing a call to the respective terminal point. A number has a national/international format.
The definitions above may be extended to include a wider range of applications which are the object of numbering allotments.
Therefore, a number may be defined as an alpha-numeric label used for the identification of electronic communications users (or of their equipment), provided that this label may be portable. Meanwhile, for monitored generalisation, the concept of address is used, defined as a set of decimal digits and symbols identifying a terminal point of in a network, as it is used for routing.
In this wider context, a number is defined as a name, an address, or a combination of a name and address.
Non – E.164 numbers
The Annex of the Recommendation E.164 stipulates the types of numbers that do not correspond to the E.164 numbering as concerns structure, length or unique character. Such types of numbers are represented by the special local numbers (also known as “short” local numbers), whose use is restricted to a certain NDC area and short national numbers, e.g. the emergency unique European number 112.
National Numbering Plan
Recommendation E.164 of the International Telecommunications Union (ITU) also defines the National Numbering plan as the document specifying the format and structure of the numbers used within this plan. It stipulates the distribution of the digit groups, so as to highlight the specific elements by which the functions of identification, routing and tariff-charging could be implemented (for example, within E.164: identification of the country, of the national called points, and of the subscribers). The national numbering plan does not comprise the prefixes, suffixes and additional information required for initiating a call. The numbering plan comprises E.164 numbers, prefixes (national, international and carrier selection indicatives) and “non-E.164” numbers (e.g.: “short” local numbers). For the provision of additional information, one may use the codes * and #. These are used in the control procedures initiated by a subscriber (e.g.: call re-routing). Although these codes do not identify the network terminal points and have only a local significance, they may be included in the national numbering plan. For the terminals that do not have the * and # keys, these codes may be replaced by digit sequences. The national numbering plan (NNP) transposes, according to the same document, on national level, the E.164 numbering plan. NNP types: closed / open. The NNP deals with two categories of numbers, considering the digit sequence dialled for initiating a call: closed NNP – dialling the whole national significant number, disregarding the calling or the called telephone set (including local calls). Closed numbering is used, for example, in the mobile telephone networks. Open numbering and, respectively, the open NNP do not correspond to the above specifications. Geographic and non-geographic numbers. A geographic number is a number established according to the National Numbering Plan, within which one or several digits contribute to identifying the geographic location of the network terminal point. A non-geographic number is a number established according to the National Numbering Plan, which is not a geographic number; non-geographic numbers are, among others, the numbers allotted to mobile telephony services, green numbers and premium rate numbers. Dialling Plan. Taking into account the open character of the Romanian NNP, the method of dialling the digit sequence for initiating calls is presented in the so-called dialling plan. Generally, this sequence has the following structure: ICSP IP CC NDC SN, where: ICSP (International Carrier Selection Prefix) IP (International Prefix) CC (Country Code) NDC (National Destination Code) SN (Subscriber Number) e.g. A call towards a certain provider’s subscriber, located in Bucharest, having the (fictive) number 501 23 45, may be initiated by dialling: – 021 501 23 45 if the caller is from Romania – (1099) 021 501 23 45 if the caller is from one of Romania’s counties (excluding Ilfov county) and appeals to a carrier service with the individual indicative 1099 – 0040 21 501 23 45 if the caller is from outside Romania, 0040 being the combination between the international prefix “00” + Romania’s country code – (ISCP) 0040 21 501 23 45 if the caller is from outside Romania and appeals to a carrier service which was allotted the ICSP indicative.