Numbering Plan Categories
Types of numbering plans include the following:
■ Private numbering plans: Private numbering plans are used to address endpoints and
applications within private networks. Private numbering plans are not required to
adhere to any specific format and can be created to accommodate the needs of the
network. Because most private telephone networks connect to the PSTN at some
point in the design, it is good practice to plan the private numbering plan to coincide
with publicly assigned number ranges. Number translation might be required when
connecting private voice networks to the PSTN.
■ 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. The E.164 plan was originally
developed by the International Telecommunication Union (ITU).
■ National numbering plans: A national numbering plan defines the numbering
structure for a specific country or group of countries. One example is the NANP.
It defines a 10-digit numbering plan. This number is represented as XXX XXXXXXX.
First is a three-digit Numbering Plan Area (NPA) code (commonly
referred to as the area code). Next is a three-digit central office code. Last is a
four-digit subscriber line number. The United States, Canada, and parts of the
Caribbean all use the NANP for number assignment. Other countries have differing
national numbering plans.