Multi-Site Customer with Extension Prefix and no ISP
----------------------------------------------------

In order to support Inter-Site calls without an Inter-Site Prefix (ISP), the first
digit of site codes do not have match. The only requirement is that site codes
should not conflict with extension or PSTN dialing. Customers use an extension
prefix for intrasite calls.

Extension prefixes are useful when there is a conflict with PSTN Prefix or other
Site Codes. They are also useful when you need to go from four- to five-digit
dialing. This extension is still the last four digits of the E.164 number, but
the last digit of an NXX code can be used as an extension prefix.

Multi-Site Customer with Extension Prefix and no ISP

+------------+----------------+----------------+-------------------------+
|            | Dialing Format | Display Format | Notes                   |
|            | (A-Party)      | (B-Party)      |                         |
+============+================+================+=========================+
| Intra-Site | * Extension    | * Site Code +  | Site Code = 255         |
| Dialing    |   Prefix +     |   Extension    |                         |
|            |   Extension    |                | Extension Prefix = 5    |
|            |   (for example |                |                         |
|            |   example,     |                | Number of extension     |
|            |   51234)       |                | digits = 4              |
|            | * Site Code +  |                |                         |
|            |   Extension    |                | Note:                   |
|            |   (for example,|                |                         |
|            |   2551234)     |                | Even though the         |
|            |                |                | extension is dialed, the|
|            |                |                | calling party number is |
|            |                |                | displayed as a DN.      |
|            |                |                | Displaying the extension|
|            |                |                | causes issues during    |
|            |                |                | Call Forwarding.        |
+------------+----------------+----------------+-------------------------+
| Inter-Site | Site Code +    | Site Code +    | \-                      |
| Dialing    | Extension (for | Extension      |                         |
|            | example,       |                |                         |
|            | 2551234)       |                |                         |
+------------+----------------+----------------+-------------------------+
| DN Format  | Site Code +    |                | \-                      |
|            | Extension (for |                |                         |
|            | example,       |                |                         |
|            | 2551234)       |                |                         |
+------------+----------------+----------------+-------------------------+