Information Technology Reference
In-Depth Information
PSTN Numbering Plans
Just as data networks use IP addressing to organize and locate resources, voice networks
use a numbering plan to organize and locate telephones all around the world. Organiza-
tions managing their own internal telephony systems can develop any internal number
scheme that best fits the company needs (similar to private IP addressing). However, when
connecting to the PSTN, you must use a valid, E.164 standard address for your telephone
system. E.164 is an international numbering plan created by the International Telecommu-
nication Union (ITU). Each number in the E.164 numbering plan contains the following
components:
Country code
■
National destination code
■
Subscriber number
■
Note:
E.164 numbers are limited to a maximum length of 15 digits.
As an example, the North American Numbering Plan (NANP) uses the E.164 standard to
break numbers down into the following components:
Country code
■
Area code
■
Central office or exchange code
■
Station code
■
For example, the NANP number 1-602-555-1212 breaks down as shown in Figure 1-11.
1 - 602 - 555 - 1212
Country Code
Area Code
Central Office Code
Station Code
(E.164 Country Code)
(E.164 National Destination Code)
(E.164 Subscriber Number)
Figure 1-11
NANP Phone Number Example
