online telephone directory use case diagram

The International Telecommunication Union (ITU) has established a comprehensive numbering plan, designated E.164, for uniform interoperability of the networks of its member state or regional administrations. The latter type developed predominantly in Europe. A closed numbering plan, as found in North America, features fixed-length area codes and local numbers, while an open numbering plan has a variance in the length of the area code, local number, or both of a telephone number assigned to a subscriber line. A broad division is commonly recognized between closed and open numbering plans. Numbering plans may follow a variety of design strategies which have often arisen from the historical evolution of individual telephone networks and local requirements. Many numbering plan administrators subdivide their territory of service into geographic regions designated by a prefix, often called an area code or city code, which is a set of digits forming the most-significant part of the dialing sequence to reach a telephone subscriber. Telephone numbering plans are defined in each of the administrative regions of the public switched telephone network (PSTN) and in private telephone networks.įor public numbering systems, geographic location typically plays a role in the sequence of numbers assigned to each telephone subscriber. Telephone numbers are the addresses of participants in a telephone network, reachable by a system of destination code routing.

For the songs, see Area Codes (Ludacris song) and Area Codes (Kali song).Ī telephone numbering plan is a type of numbering scheme used in telecommunication to assign telephone numbers to subscriber telephones or other telephony endpoints.

Online telephone directory use case diagram