Centrex is a contraction of central exchange, a kind of telephone exchange.
A PBX-like service providing switching at the central office instead of at the customer's premises. Typically, the telephone company owns and manages all the communications equipment and software necessary to implement the Centrex service and then sells various services to the customer.
However no switching equipment resides on the customer premise as the service is supplied and managed directly from the phone company's exchange site, with lines being delivered to the premises either as individual lines over traditional copper pairs, or delivering many lines multiplexed to the premises over fibre optic or copper links, eliminating the need to bring many individual pairs from the exchange to the premises. In effect, Centrex provides an emulation of a hardware PBX, by using special software programming at the telephone exchange, which can be customized to meet a particular customer's needs.
Centrex obviates the need to use separate exchange lines delivered to a site for use with a Key System or PBX. Instead, telephone extensions, called Centrex lines, are delivered directly from the local exchange to the user. Unlike with a conventional PBX, it is a simple matter to have extensions at different locations, yet allow them to function as if they were within the same building. Facilities such as Direct Inward Dial (DID), where individual extensions are offered a direct and unique telephone number for incoming calls, become standard features in a Centrex environment. Stations may also be part of a hunt group, allowing for automatic distribution of incoming calls to two or more extensions.
Applications offered by Centrex:
- Small business start-ups (growth and costs)
- Banks and financial institutions (branch offices/multi-departmental branches)
- Professional offices (reliability, connectivity and customer service)
- Local government (reliability, cost, multi-location)
- Hotels and guest houses (customer service)
- Colleges and Universities (reliability, cost, multi-location, growth)
- Temporary Locations where permanent PBX services are impractical, such as a campaign office.
- Call Transfer
- Call Divert - on no reply /on busy
- Call Waiting
- Three Party Conference
- Call Pick Up (Group)
- Ring Back
- Reminder / Alarm Call
- Last Number Redial
- Centrex Hotline (non-dialed connection)
- Centrex Warm Line (delayed Hotline)
- Centrex Hunt Groups, with optional bypass numbers