PBX or private branch exchange is also referred to as private automatic branch exchange (PABX) or electronic private automatic branch exchange (EPABX). It is a telephone exchange for a particular office or business. Centrex or Central Office Exchange Service is also a kind of telephone exchange but differs from PBX in that it provides its services from a central office as opposed to the customer’s premises.
Differences in Hardware and Equipment
PBX systems usually hook up and connect the company’s internal telephones to the public switched telephone network (PSTN), and incorporate fax machines, modems and other extensions. In case of the Centrex services, the equipment and software is owned by the telephone company and services are sold to the customer.
The term "PBX" started being used when switchboards were operated by hand. Gradually, this system evolved from manual to automatic switching and digital systems. This acronym has now become a widely used and recognized term for all in house telephone switching systems. Centrex system was invented in the late 1960s and targeted to replace the PBX switchboards of large organizations.
Components of PBX vs Centrex
PBX includes an internal switching network, a microcomputer for data control and processing, devices to control switching, telephone lines, switchboards, uninterrupted power supply, wiring to connect components internally and other storage. Customers do not have to buy any of the components necessary for a Centrex system.
Usage and Functions
Due to the large expense incurred, small businesses are unable to afford PBX systems. However, a small set of PBX features can be provided for such businesses. The main functions that a PBX system performs include successfully connecting two telephone users till required, disconnecting connections when the call ends, and keeping an account of calls connected (metering calls). In addition, the other functions provided are auto dialling, automatic directory services, call blocking and forwarding, call waiting, conference call facility, voice mail, welcome message and others.
Centrex is ideal for small and start-up businesses, banks, financial institutions, colleges, and other temporary locations. The services available depends on the type of package and can include call transfer and waiting, three-party conference, ring back, reminder and alarm and other features.
Types of PBX and Centrex
Customers can choose from various features and services offered by telecommunication services. Different services available are Packaged Centrex, Centrex Data and Customized Centrex. Packaged Centrex service includes a fixed set of features. The customers can choose from the various packages available. Centrex data services offer flexible low speed connections within the telephone network. Customized Centrex is the most expensive of the services available and allows customizable options to the customers.
The traditional PBX system has been somewhat replace by VoIP (Voice over Internet protocol). The types of PBX include Hosted PBX systems, Mobile PBX, and IP-PBX. Hosted PBX service is delivered by the telephone company using the company’s equipment over the Public Switched Telephone Network and/or the internet. Mobile PBX services extend the PBX functions to mobile devices like mobile phones, PDA and soon. IP-PBX also called “Soft PBX” manages voice signals under IP or Internet protocol.