Virtual PBX Service

We generally consider Centrex as providing a "virtual PBX" service, with multiple customers and many sites being served by the software that resides in the one CO system, as shown in the upper part of Figure 1.2. A standard characteristic of Centrex is that all its stations have direct inward dialing (DID) access, usually based on seven-digit numbers. Users can employ abbreviated dialing (e.g., four digits) between Centrex-based stations within a local calling area. These features minimize the need for operator consoles within a Centrex system, although some type of operator support, for the occasional caller who needs assistance, is still usually required.


PBX replacement and KTS support.

A business line package with a few popular features, which is available from carriers in some countries, clearly does not qualify as Centrex service when measured against the virtual PBX definition.