What is the E.164 numbering plan?

A.
A proprietary PBX number plan.

B.
The IETF North American number plan.

C.
The European PBX standard telephony number plan.

D.
The ITU worldwide number plan.

Explanation:

Numbering Scheme The standard PSTN is a large, circuit-switched network. It uses a specific numbering scheme, which complies with theITU-Tinternational public telecommunications numbering plan(E.164)recommendations. For example, inNorth America, theNorth American Numbering Plan (NANP) is used, which consists of an area code, an office code, and a station code. Area codes are assigned geographically, office codes are assigned to specific switches, and station codes identify a specific port on that switch. The format inNorth Americais 1Nxx-Nxx-xxxx, with N = digits 2 through 9 and x = digits 0 through 9. Internationally, each country is implementations, numbering schemes are configured using thedestination-patterncommand.
E.164is an ITU-T recommendation which defines the international public telecommunication numbering plan used in the PSTN and some other data networks.