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"PBX" redirects here. For the type of explosive, see Polymer-bonded explosive. A polymer-bonded explosive, also called PBX or plastic-bonded explosive, is an Explosive material in which explosive powder is bound together in a matrix
An Avaya G3R PBX with front cover removed (view from the top).
An Avaya G3R PBX with front cover removed (view from the top).

A Private Branch eXchange (PBX) is a telephone exchange that serves a particular business or office, as opposed to one that a common carrier or telephone company operates for many businesses or for the general public. In the field of Telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls A common carrier is a business that transports people goods or services and offers its services to the general public under license or authority provided by a regulatory body PBXs are also referred to as:

Contents

Overview

PBXs make connections among the internal telephones of a private organization — usually a business — and also connect them to the public switched telephone network (PSTN) via trunk lines. The public switched telephone network ( PSTN) is the network of the world's public circuit-switched Telephone networks in much the same way that the This is about the network-design strategies for riding in auto cargo space see Trunking (auto, and for the UK term for electrical wireways see Electrical conduit#Trunking Because they incorporate telephones, fax machines, modems, and more, the general term "extension" is used to refer to any end point on the branch. Fax (short for facsimile, from Latin fac simile, "make similar" i Modem (from mo dulator- dem odulator is a device that modulates an analog carrier signal to encode Digital information An extension telephone is an additional Telephone wired to the same Telephone line as another

PBXs are differentiated from "key systems" in that users of key systems manually select their own outgoing lines, while PBXs select the outgoing line automatically. A key system or key telephone system is a multiline Telephone system typically used in small office environments Hybrid systems combine features of both.

Initially, the primary advantage of PBXs was cost savings on internal phone calls: handling the circuit switching locally reduced charges for local phone service. As PBXs gained popularity, they started offering services that were not available in the operator network, such as hunt groups, call forwarding, and extension dialing. In the 1960s a simulated PBX known as Centrex provided similar features from the central telephone exchange. Centrex is a contraction of centr al ex change a kind of Telephone exchange. In the field of Telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls

Two significant developments during the 1990s led to new types of PBX systems. One was the massive growth of data networks and increased public understanding of packet switching. Packet switching is a network communications method that splits data traffic (digital representations of text sound or video data into chunks called packets, that are then Companies needed packet switched networks for data, so using them for telephone calls was tempting, and the availability of the Internet as a global delivery system made packet switched communications even more attractive. These factors led to the development of the VoIP PBX. Voice-over-Internet protocol ( VoIP, vɔɪp is a protocol optimized for the transmission of voice through the Internet (Technically, nothing was being "exchanged" any more, but the abbreviation PBX was so widely understood that it remained in use. )

The other trend was the idea of focusing on core competence. Core competency is something that a firm can do well and that meets the following three conditions It provides consumer benefits It is not easy for competitors to imitate PBX services had always been hard to arrange for smaller companies, and many companies realized that handling their own telephony was not their core competence. These considerations gave rise to the concept of hosted PBX. In a hosted setup, the PBX is located at and managed by the telephone service provider, and features and calls are delivered via the Internet. The customer just signs up for a service, rather than buying and maintaining expensive hardware. This essentially removes the branch from the private premises, moving it to a central location.

History

Operator mannequins, Telecommunications Museum, Madrid, Spain
Operator mannequins, Telecommunications Museum, Madrid, Spain

The term PBX was first applied when switchboard operators ran company switchboards by hand. Medium-to-large organizations often employ switchboard operators &mdashspecialised staff who answer general Telephone calls to the organization and usually maintain As automated electromechanical and then electronic switching systems gradually began to replace the manual systems, the terms PABX (Private Automatic Branch eXchange) and PMBX (Private Manual Branch eXchange) were used to differentiate them. Solid state digital systems were sometimes referred to as EPABXs (Electronic Private Automatic Branch eXchange). Now, the term PBX is by far the most widely recognized. The acronym is now applied to all types of complex, in-house telephony switching systems, even if they are not Private, Branches, or eXchanging anything.

PBXs are distinguished from smaller "key systems" by the fact that external lines are not normally indicated or selectable at an individual extension. A key system or key telephone system is a multiline Telephone system typically used in small office environments From a user's point of view, calls on a key system are made by selecting a specific outgoing line and dialing the external number. A PBX, in contrast, has a Dial plan. A dial plan establishes the expected number and pattern of digits for a Telephone number. Users dial an escape code (usually a single digit; often the same as the first digit of the local emergency telephone number) that connects them to an outside line (DDCO or Direct Dial Central Office in Bell System jargon), followed by the external number. Many countries' public telephone networks have a single emergency telephone number, sometimes known as the universal emergency telephone number or occasionally the Some modern number analysis systems allow users to dial internal and external numbers without escape codes.

System components

A PBX will often include:

Current trends

One of the latest trends in PBX development is the VoIP PBX, also known as an IP-PBX or IPBX, which uses the Internet Protocol to carry calls. Voice-over-Internet protocol ( VoIP, vɔɪp is a protocol optimized for the transmission of voice through the Internet An IP ( Internet Protocol) PBX ( Private branch exchange) is a business telephone system designed to deliver voice over a data network and interoperate with the normal Public Switched The Internet Protocol ( IP) is a protocol used for communicating data across a Packet-switched Internetwork using the Internet Protocol Most modern PBXs support VoIP. ISDN PBX systems also replaced some traditional PBXs in the 1990s, as ISDN offers features such as conference calling, call forwarding, and programmable caller ID. A Conference call is a Telephone call in which the Calling party wishes to have more than one Called party listen in to the audio portion However, recent open source projects combined with cheap modern hardware are sharply reducing the cost of PBX ownership. Open source is a development methodology which offers practical accessibility to a product's source (goods and knowledge

For some users, the Private Branch eXchange has gone full circle as a term. Originally having started as an organization's manual switchboard or attendant console operated by a telephone operator or just simply the operator, they have evolved into VoIP centres that are hosted by the operators or even hardware manufacturers. A switchboard (also called a manual exchange) was a device used to connect a group of Telephones manually to one another or to an outside connection within and between An attendant console is a Telephone station that is generally part of a Private branch exchange (PBX or A telephone operator is either a person who provides assistance to a Telephone caller usually in the placing of Operator assisted telephone Voice-over-Internet protocol ( VoIP, vɔɪp is a protocol optimized for the transmission of voice through the Internet These modern IP Centrex systems offer essentially the same service, but they have moved so far from the original concept of the PBX that the term hardly applies at all. Centrex is a contraction of centr al ex change a kind of Telephone exchange.

Even though VoIP gets a great deal of press, the old circuit switched network is alive and well, and the already bought PBX's are very competitive in services with modern IP Centrexes. In Telecommunications a circuit switching network is one that establishes a fixed bandwidth circuit (or channel) between nodes and terminals Centrex is a contraction of centr al ex change a kind of Telephone exchange. Currently, there are four distinct scenarios in use:

Since in reality people want to call from the IP side to the circuit switched PSTN (SS7/ISUP), the hosted solutions usually have to maneuver in both realms in one way or another. Centrex is a contraction of centr al ex change a kind of Telephone exchange. Centrex is a contraction of centr al ex change a kind of Telephone exchange. The public switched telephone network ( PSTN) is the network of the world's public circuit-switched Telephone networks in much the same way that the The ISDN User Part or ISUP is part of the Signaling System #7 which is used to set up Telephone calls in Public Switched Telephone Networks. The distinctions are seldom visible to the end user.

Home and small business usage

Historically, the expense of full-fledged PBX systems has put them out of reach of small businesses and individuals. However, since the 1990s there has been a large set of small, consumer-grade and consumer-size PBXs available. These systems are not comparable in size, robustness or flexibility to commercial-grade PBXs, but still provide a surprising set of features.

The first consumer PBX systems were for the analog telephone systems, typically supporting four private analog and one public analog line. They are the size of a small cigar box or smaller and are inexpensive (e. g. US$50).

Particularly in Europe these systems for analog phones were followed by consumer-grade PBXs for ISDN. Using small PBXs for ISDN is a logical step, since already the Basic Rate Interface of ISDN (which is the phone interface individuals and small businesses typically get) provides two logical phone lines (two B channels) which can be used in parallel. Basic rate interface (BRI 2B+D 2B1D is an Integrated Services Digital Network (ISDN configuration defined in the physical layer standard I Small, entry-level systems are also extremely cheap (e. g. US$100).

With the pickup of VoIP by consumers, of course consumer VoIP PBXs have seen the light, and PBX functions have become simple additional features of consumer-grade routers and switches.

Open source projects have been available since the beginning of the 90s. Open source is a development methodology which offers practical accessibility to a product's source (goods and knowledge These projects provide flexibility and features (often not needed or understood by average users), plus the means to actually inspect and change the inner working of a PBX. They have also opened business opportunities for newcomers to the market of mid-size PBXs, since they have lowered the entry barrier for new manufacturers .

PBX functions

Functionally, the PBX performs four main call processing duties:

In addition to these basic functions, PBXs offer many other calling features and capabilities, with different manufacturers providing different features in an effort to differentiate their products. Common capabilities include (manufacturers may have a different name for each capability):

Interface standards

Interfaces for connecting extensions to a PBX include:

Interfaces for connecting PBXs to each other include:

Interfaces for connecting PBXs to trunk lines include:

Interfaces for collecting data from the PBX:

The call records from the PBX are called SMDR, CDR, or CIL. A Call Detail Record (CDR is the computer record produced by a Telephone exchange containing details of a call that passed through it A Call Detail Record (CDR is the computer record produced by a Telephone exchange containing details of a call that passed through it It is possible to use a Voice modem as FXO card. Modem (from mo dulator- dem odulator is a device that modulates an analog carrier signal to encode Digital information In telecommunications a Foreign Exchange Office, or FXO, is a Telephone signaling interface that receives POTS, or "plain old telephone service"

Hosted PBX systems

A hosted PBX system delivers PBX functionality as a service, available over the Public Service Telephone Network (PSTN) and/or the internet. Hosted PBXs are typically provided by the telephone company, using equipment located in the premises of the telephone company's exchange. In the field of Telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls This means the customer organization doesn't need to buy or install PBX equipment (generally the service is provided by a lease agreement) and the telephone company can (in some configurations) use the same switching equipment to service multiple PBX hosting accounts.

Instead of buying PBX equipment, users contract for PBX services from a hosted PBX service provider, a particular type of Application Service Provider (ASP). An application service provider (ASP is a business that provides computer-based services to customers over a network The first hosted PBX service was very feature-rich compared to most premise-based systems of the time. In fact, some PBX functions, such as follow-me calling, appeared in a hosted service before they became available in hardware PBX equipment. Since that introduction, updates and new offerings from several companies have moved feature sets in both directions. Today, it is possible to get hosted PBX service that includes far more features than were available from the first systems of this class, or to contract with companies that provide less functionality for more simple needs.

In addition to the features available from premises-based PBX systems, hosted-PBX:

Mobile PBX

A mobile PBX is a hosted PBX service that extends fixed-line PBX functionality to mobile devices such as cellular handsets, smartphones and PDA phones by provisioning them as extensions. Mobile PBX services also can include fixed-line phones. Mobile PBX systems are different from other hosted PBX systems that simply forward data or calls to mobile phones by allowing the mobile phone itself, through the use of buttons, keys and other input devices, to control PBX phone functions and to manage communications without having to call into the system first.

IP-PBX

An IP PBX handles voice signals under Internet protocol, bringing benefits for Computer telephony integration (CTI). An IP ( Internet Protocol) PBX ( Private branch exchange) is a business telephone system designed to deliver voice over a data network and interoperate with the normal Public Switched Computer telephony integration ( CTI) is technology that allows interactions on a Telephone and a Computer to be integrated or co-ordinated An IP-PBX can exist as physical hardware, or can carry out it functions virtually, performing the call-routing activities of the traditional PBX or key system as a software system. The virtual version is also called a "Soft PBX".

See also

Notes

External links

The Open Directory Project ( ODP) also known as dmoz (from directory

Dictionary

private branch exchange

-noun

  1. (idiomatic) A telecommunications switching system, physically located at a customer's place of business, that provides internal communication between users and also access to outside (trunk) telephone lines.
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