Typical standard phone used with Centrex. Note the "Recall" button and the Message Waiting Lamp.

Centrex is a contraction of central exchange, a kind of telephone exchange. Conventional telephone from AT&T. Photo by Dante Alighieri | Talk. ... Conventional telephone from AT&T. Photo by Dante Alighieri | Talk. ... A telephone operator manually connecting calls with patch cables at a telephone switchboard. ...

Use of Centrex

Centrex is 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. PBX redirects here. ... A telephone company (or telco) provides telecommunications services such as telephony and data communications. ...

in the United Kingdom, British Telecom markets this service as FeatureLine (although refers to it internally as Centrex) BT Group plc (which trades as just BT, and is commonly known by its former name, British Telecom) is the privatised former British state telecommunications operator. ...

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 by multiplexing a number of lines over a single fiber optic or copper link. In effect, Centrex provides an emulation of a hardware PBX, by using special software programming at the central office, which can be customized to meet a particular customer's needs. As with a PBX, stations inside the group can call each other with 3, 4 or 5 digits, depending on how large the group, instead of an entire telephone number. In telecommunications, multiplexing (also muxing or MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ... In the field of telecommunications, a central office or telephone exchange houses equipment that is commonly known as simply a switch, which is a piece of equipment that connects phone calls. ...

Centrex obviates separate exchange lines delivered to a site for use with a 1A2 Key System or similar, or PBX. Instead, telephone extensions, called Centrex lines, are delivered directly from the local exchange to the user. Some customers, however, still like to use a key telephone system for a small office within the large corporate Centrex. Unlike with a conventional PBX, it is a simple matter to have extensions at different locations while allowing them to function as if they were within the same building. Newer IP PBX systems also allow phones at any location with a WAN or Internet connection to act as a local extension. Facilities such as Direct Inward Dialing (DID), where individual extensions are offered a direct and unique telephone number for incoming calls, are 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. A typical rotary dial key telephone: the Western Electric eighteen button Call Director, manufactured from 1958 to the early 80s. ... A telephone extension is an internal telephone line attached to a PBX or Centrex system. ... Early model 464G Western Electric Key Telephone Set A key system or key telephone system is a multiline telephone system typically used in small office environments. ... The Internet Protocol Private Branch eXchange (IP PBX) is telephone switching equipment that resides in a private business instead of the telephone company. ... WAN MEANS WHAT A NOOB BY ZACH THE GOOSE EPPS AKA FOUNDER OF WAN Look up wan in Wiktionary, the free dictionary. ... Direct Inward Dialing (DID, also called DDI in Europe) is a feature offered by telephone companies for use with their customers PBX system, whereby the telephone company (telco) allocates a range of numbers all connected to their customers PBX. As calls are presented to the PBX, the number that...

With the high price of Long Distance service, many large companies had their own network of private lines crossing the country or to distant countries. Managing these networks of 'Tie Lines' and connecting users to them was also an important part of Centrex. Long distance in telecommunications, refers to telephone calls made outside a certain area, usually characterized by an area code outside of a local call area. ... Private Line are a hard rock/sleaze glam band from Helsinki, Finland, formed during the mid-1990s and continuing today. ...

Birth of Centrex

Centrex was invented in the middle 1960s by the Engineering Department of New York Telephone to replace the PBX switchboards of large customers. It was a feature package of the 5XB crossbar system. Much equipment had to be redesigned, including incoming trunks and markers. The redesigned equipment was so expensive that usually a separate 5XB switch was used just for Centrex customers, while POTS (Plain Old Telephone Service) customers were wired to an unmodified exchange. The New York Telephone Company (NYTel) was organized in 1896, taking over the New York City operations of the American Bell Telephone Company. ... A marker is a type of special purpose control system that was used in electromechanical telephone central office switches. ... The Number Five Crossbar Switching System, designed by Bell Labs and made by Western Electric was in use in Bell System telephone exchanges from 1948 to the 1980s. ... Plain old telephone service, or POTS, are the services available from analogue telephones prior to the introduction of electronic telephone exchanges into the public switched telephone network. ...

The PBX had the important feature that someone who received a call in error could jiggle the switchhook, causing a light to flash to recall the operator to connect the caller to the desired extension. This feature was implemented in Centrex with a timing circuit to detect a hook flash and set up a three way connection among outside party, inside party and operator. The operator or "attendant" had a large and complex console, replacing the old, larger and even more complex switchboard and giving additional control of a connection. Its buttons and lights needed approximately fifty pairs of wires. Incoming calls arrived on an Attendant Trunk which, for customers with more than one console, waited for one to become idle and then connected to it, initially via Step by Step switches arranged as a Trunk Finder and Position Finder. Customers who preferred the old cord switchboards could use an adapted "608" board. In either case the console communicated with the incoming trunk with coded plus and minus 130 volt DC signals on Tip, Ring or both wires. Usually a button that simulates a quick off-hook/on-hook/off-hook cycle. ... The word Strowger when used alone, has several possible meanings in the English language. ...

Bell Labs took over Centrex development in the late 1960s. The NYTel version was designated Centrex I, and the Bell Labs revision Centrex II with additional features. The unreliable Step switches were replaced by a Centrex Position Link Circuit (CXPL), a small, dedicated two stage crossbar network. In the early 1970s Centrex III arrived, a complete redesign bringing more versatility to the old 5XB system. The Centrex product line was also extended down-market, with Centrex Small Business for customers having mere dozens of lines and no attendant console. Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) was the main research and development arm of the United States Bell System. ...

Meanwhile Stored Program Control came to live up to its promise of versatility, and Centrex customers were among the first in the middle 1970s to be removed from 5XB to 1ESS switch. Complex logic and storage was cheaper in a central computer than in individual trunk circuits, hence outgoing calls could be transferred as easily as incoming. Other manufacturers produced similar services, usually calling them something else due to trademark considerations. Northern Electric, later Nortel, called their version IBN or Integrated Business Network and enhanced the service with their proprietary P-phone sets in the 1980s. Stored Program Control exchange (SPC) is the technical name used for telephone exchanges controlled by a program stored in the memory of the system. ... The Number One Electronic Switching System was the first large scale Stored Program Control (SPC) telephone exchange or Electronic Switching System in the Bell System, entering service in the late 1960s. ... Northern Telecommunications Networks, commonly known as Nortel, is a telecommunications equipment manufacturer headquartered in Canada. ...

Types of Centrex Service

The Centrex customer is not restricted to using the features available to POTS customers, but can choose from a wide variety of special services and features. In fact, telecommunications companies generally offer numerous types of Centrex service, including "Packaged Centrex", "Centrex Data", and "Customized Centrex". Plain old telephone service, or POTS, are the services available from analogue telephones prior to the introduction of electronic telephone exchanges into the public switched telephone network. ...

Packaged Centrex

Packaged Centrex customers could be offered a fixed set of features in package "A", a different set of features in package "B", and so on. These packages can be offered at a relatively low cost as little or no customization is permitted, minimizing the operational costs of programming and maintaining the services for the telephone company.

Centrex Data

Centrex Data services can provide relatively low speed (56 and 64 kbit/s) data services utilizing the circuit-switched telephone network. Although they are now overshadowed by the internet and other data networks, Centrex Data services can offer very flexible and wide-reaching network configurations since connections can be made almost anywhere within the reach of the telephone network. The public switched telephone network (PSTN) is the network of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the network of the worlds public IP-based packet-switched networks. ...

Customized Centrex

Customized Centrex is the most flexible (and most expensive) Centrex service as it offers a highly customizable set of options that require specialized programming and troubleshooting skills to maintain. A typical Customized Centrex setup will allow 4 digit dialing between "locals" (perhaps even if they are located in different parts of the city), customized routing through the telephone network (such as Least Cost Routing or Time of Day Routing), and customized codes for invoking features. In international voice telecommunications, least cost routing (LCR) is the process that provides customers with cheap telephone calls. ...

Example Applications

• 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.

Services

• 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