Nortel VoIP Gateway, Configuration Manual

Page: 147 / 220

147
Norstar VoIP Gateway Configuration Guide
Appendix A
Numbering and Dial Plans
One of the most important planning considerations in using the Norstar VoIP Gateway is to
determine the dial plan requirements of the overall enterprise voice network that is created. This
appendix will help you to understand the concepts and create the dialing plan that is right for your
system.
Public and Private Numbering Plans
Simply put, the public dialing plan is the numbering scheme that is used within the country that
you live for dialing calls through your phone company on the public phone network. Private
dialing plans are used within companies to create their own, private telephone network. Private
numbers are separate from public numbers, just as their phone systems are separated. Dialing a
number from a private dialing plan on a public phone network will not work because the networks
are separate.
Most companies with private telephone networks still require access to the public switched
telephone network, commonly called the PSTN. Therefore, your dialing plan must include both
private and public elements and the systems you use, such as the Norstar KSU and the Norstar
VoIP Gateway, must be configured correctly to route your calls based on this plan.
Public telephone numbers are, as you might suspect, controlled and regulated. The ITU
(International Telecommunications Union) has set a standard outlining how public telephone
numbers are formatted, called the "E.164 Numbering Plan". The general format of these numbers
is shown below.
Figure 41 E.164 Numbering Plan
The Country Code for North America (CC) is the digit "1". NDC is the "National Destination
Code (optional) and SN is the "Subscriber Number".
CC
NDC
SN
1 to 3 digits Max (15-n) digits
National (significant) number
Max 15 digits
International public telecommunication
number for geographic areas