PSTN Numbering Plan

Abdul Rahim Rahem AtayeeMaqsood(dawood)

Farhad (siddiqi)Besmullah (sirdash)

Numbering Plan

A Numbering Plan specifies the format and structure of numbers including any segments used for identification, routing, and charging capabilities.

A numbering plan is a system that identifies communication points within a communications network through the structured use of numbers. It is important that all users connected to a telephone network agree on a specific numbering plan to be able to identify and route calls from one point to another. A well-designed numbering plan should evaluate both current requirements and potential growth requirements to avoid the need to renumber as more users connect to the voice network.

Numbering Plan Categories

• Private numbering plans: Private numbering plans are used to address endpoints and applications within private networks. Private numbering plans are not required to any specific format and can be created to accommodate the needs of the network

Private Numbering Plan Design Considerations

• When designing a private numbering plan, the following issues must be observed:

• Number of addressable devices: Try to use the fewest possible digits for internal dialing to make it easier for users to remember extensions.

• Number of locations: Use the fewest possible digits for calls within a location and site codes plus extensions for calls between locations.

• ■ Inbound call routing: Some companies buy a block of numbers from a service provider and Other companies prefer to use a single number for external callers and then route all calls to a receptionist or an auto attendant who then forwards the call to the intended party.

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• PSTN access codes: PSTN access codes differentiate internal from external calls. In the United States, we usually use 9 as a PSTN access code, although many other countries use 8. One effect of using PSTN access codes is that you cannot use the PSTN access code digit to begin an extension. In other words, if you use 9 as a PSTN access code, then you cannot have an extension range of 9XXX. The same thing goes for operator digits (for example, 0).

Public/PSTN numbering plans

• PSTN or public numbering plans are unique to the country in which they are implemented:

• ■ The international public telecommunication numbering plan (E.164): The E.164 standard is an international numbering plan for public telephone systems in which each assigned number contains a one-, two-, or three-digit country code (CC) followed by a national destination code (NDC) followed by a subscriber number (SN). There can be up to 15 digits in an E.164 number.

PSTN Numbering Plan Common Elements

• Emergency services

• Information or directory services

• Local calls

• Mobile calls

• Long distance or toll

• Toll free

• International

ITU

The ITU Telecommunication Standardization Sector (ITU-T) is one of the three Sectors of the International Telecommunication Union, a specialized agency of the United Nations with headquarters in Geneva, Switzerland. The ITU-T studies technical, operating and tariff questions and produces Recommendations and other publications that are used to guarantee the interconnectivity and interoperability of networks and enables telecommunication services to be provided worldwide. The ITU-T website is at http://www.itu.int/ITU-T/index.html.

E.164 Numbers - Format & Functions

World zone numbering plan• Country codes are a part of telephone numbering

plans and are necessary only when dialing a telephone number from another country. These are dialed before the

•  Zone 1: North American Numbering Plan Area•  Zone 2: mostly Africa•  Zones 3-4: Europe•  Zone 5: mostly Latin America•  Zone 6: Southeast Asia and Oceania•  Zone 7: Former  Soviet Union•  Zone 8: East Asia and special services•  Zone 9: mostly Asia

World zoon numbering plane

North American numbering plan

Historical References and Perspectives•AT&T developed and evolved the numbering portion of the NANP from its inception in 1947 until the breakup of AT&T The NANP was then managed by Bell Communications Research Corporation In this time period, Bellcore maintained and coordinated the evolution of the NANP by working with regulators and industry

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• 1947: Original NANP Format and Values = N (0 or 1) X – NNX – XXXX where N = digits 2 through 9 and X = any digit of 0 through 9.

• 1995: Interchangeable NPA codes implemented NANP format: NXX – NXX – XXXX

• The format of a NANP Number is NXX-NXX-XXXX where N = digits 2 through 9 and X = any digit of 0 through 9.

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The NANP is the basic numbering plan for the telecommunications networks in the following 19 countriesin Country Code 1: Anguilla, Antigua & Barbuda, Bahamas, Barbados, Bermuda, British Virgin Islands,Canada, Cayman Islands, Dominica, Dominican Republic, Grenada, Jamaica, Montserrat, St. Kitts &Nevis, St. Lucia, St. Vincent & the Grenadines, Trinidad & Tobago, Turks & Caicos Islands, and theUnited States of America

North American Numbering Plan Example

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• 1. A subscriber in Texas dials 1 703 555-0123.• 2. The local CO in Texas recognizes that the 1

means this is not a local call and forwards the call to a long-distance carrier in Texas.

• 3. The long-distance carrier in Texas recognizes 703 as an area code in Virginia and forwards the call to a long-distance carrier in Virginia.

• 4. The long-distance carrier in Virginia forwards the call to the local CO.

• 5. The local CO delivers the call to the correct subscriber.

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