Systems : Central Exchange (Centrex) Features

Systems
The different types of systems used in private telephone networks include key telephone systems (KTS), private branch exchange (PBX), Centrex, and computer telephony integration (CTI). Key telephone and PBX systems often use proprietary specifications. There are several industry standards that are used for computer telephony and LAN telephony system.

Central Exchange (Centrex) Features
Centrex is a service offered by a local telephone service provider that allows the customer to have features that are typically associated with a PBX. These features include 3 or 4 digit dialing, intercom features, distinctive line ringing for inside and outside lines, voice mail waiting indication, and others. Centrex services are provided by the central office switching facilities in the telephone network.

Centrex systems are EO switches that have software installed to enable advanced call processing features. The software applies to specific ports on the EO switch. This allows these ports on the standard EO switch to operate more like private telephone systems.

Figure 1 shows a typical Centrex system. This diagram shows that the EO switch is equipped with Centrex software. Individual ports from the switch are connected to individual telephones at a company. The public telephone company programs the Centrex features for specific companies into the switch software. The Centrex software monitors the ports so advanced features such as abbreviated dialing can be performed. This example shows that a telephone that is used in a Centrex system can dial a 4 digit dialing number to reach a telephone connected within the companies Centrex telephone network.


Figure 1: Centrex System