Extension dialing via the PNP (Private Numbering Plan) allows extension-based dialing to be kept and controlled within the logical confines of the PNP in which the calling subscriber is defined.
It uses the PAC (Prefix Access Code) prefix type of Extension Dialing to mark this call type as extension-to-extension calling within the home extension tables defined in the PNP.
There may be applications and configurations that prefer this type of digit routing and information to allow feature access and processing.This type of strategy retains the legacy extension format that traditional PABX systems do-that is, the maximum length of the extension field entering the home extension table must be between 3 and 8 digits.
Regardless of the digit translation done in the PNP PAC and extended through the PNP destination code and location code translation, the extension table only accepts this range of digit lengths to process and normalize to a fully qualified E.164 number, then sends it to the global home DN (Directory Number) table for analysis and EPP (Endpoint Profile) matching.This method allows the inclusion of an optional component, the location code, if manipulation of digits and locations is necessary when either of the following occurs:
The subscriber home DN does not match the DID (Direct Inward Dialing) number provided by the PSTN (Public Switched Telephone Network).
The digits dialed by a subscriber, based on location requirements, do not allow easy translation via the PNP PAC alone.
When this option is implemented, it allows digits received by the PNP PAC to match with a PNP destination code, then proceed to a location code table where the digits can be translated further, as required, before entering the PNP Extension table for normalization and extension to the home DN table containing the EPP for the dialed subscriber. Without this optional component, the routing proceeds from the PNP PAC, to the PNP destination code, then directly to the PNP extension table where it is normalized to the full E.164 address necessary to route the digits to the Home DN for a match and EPP information on the dialed party.
Parent topic: Routing and Translation