What is a numbering plan?

A telephone numbering plan is a plan for allocating telephone number ranges to countries, regions, areas and exchanges and to non-fixed telephone networks such as mobile phone networks. Dial plans should not be confused with numbering plans. A closed numbering plan, such as found in North America, features fixed length area codes and local numbers. An open numbering plan, as found in assorted countries that have not yet standardized, features variance in length of area code or local number, or both. The rules for dialing the numbers assigned by the numbering plan vary by defining which digits need not always be dialed (codes) and digits that must always be dialed (local number). What is a numbering plan?

A.
numbering plan defines the path from one endpoint to another

B.
numbering plan defines the calling privileges of an endpoint

C.
numbering plan defines how digits are manipulated in processing a call.

D.
numbering plan defines the endpoint addressing used in a voice system