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64-548: A business telephone system differs from an installation of several telephones with multiple central office (CO) lines in that the CO lines used are directly controllable in key telephone systems from multiple telephone stations, and that such a system often provides additional features for call handling. Business telephone systems are often broadly classified into key telephone systems and private branch exchanges, but many combinations (hybrid telephone systems) exist. A key telephone system

128-522: A Station Messaging Detail Record (SMDR). Virtual PBX systems or hosted PBX systems deliver PBX functionality as a service, available over the public switched telephone network (PSTN) or the Internet. Hosted PBXs are typically provided by a telephone company or service provider, using equipment located in the premises of a telephone exchange or the provider's data center. This means the customer does not need to buy or install PBX equipment. Generally,

192-463: A PBX from a hybrid key system are the amount, scope, and complexity of the features and facilities offered. A PBX is a telephone exchange or switching system that serves a private organization. A PBX permits the sharing of central office trunks between internally installed telephones, and provides intercommunication between those internal telephones within the organization without the use of external lines. The central office lines provide connections to

256-411: A central office trunk. Modern number-analysis systems permit users to dial internal and external telephone numbers without special codes to distinguish the intended destination. The term PBX originated when switchboard operators managed company switchboards manually using cord circuits. As automated electromechanical switches and later electronic switching systems gradually replaced the manual systems,

320-467: A different name for each capability): 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: A data record from a PBX or other telecommunication system that provides the statistics for a telephone call is usually termed a call detail record (CDR) or

384-514: A family of key telephone equipment, some of it compatible with Western Electric equipment, but it did not gain the widespread use enjoyed by Western Electric equipment. With the advent of LSI ICs , the same architecture could be implemented much less expensively than was possible using relays. In addition, it was possible to eliminate the many-wire cabling and replace it with much simpler cable similar to (or even identical to) that used by non-key systems. Electronic shared-control systems led quickly to

448-412: A key telephone system, a station user could control the connections directly using line buttons, which indicated the status of lines with built-in lamps. Key telephone systems are primarily defined by arrangements with individual line selection buttons for each available telephone line. The earliest systems were known as wiring plans and simply consisted of telephone sets, keys, lamps, and wiring. Key

512-542: A post- World War II reconstruction relationship with state-owned Nippon Telegraph and Telephone (NTT) before the 1956 boundaries were emplaced. Before 1956, the Bell System's reach was truly gargantuan. Even during the period from 1956 to 1984, the Bell System's dominant reach into all forms of communications was pervasive within the United States and influential in telecommunication standardization throughout

576-404: A result of this vertical monopoly , the Bell System effectively owned most telephone service in the United States by 1940, from local and long-distance service to the telephones. This allowed Bell to prohibit its customers from connecting equipment not made or sold by Bell to the system without paying fees. For example, if a customer desired a style of telephone not leased by the local Bell company,

640-401: A single Bell System trademark. For each regional operating company, its name was placed where "name of associated company" appears in this template version of the trademark. Bell system telephones and related equipment were made by Western Electric , a wholly owned subsidiary of AT&T Co. Member telephone companies paid a fixed fraction of their revenues as a license fee to Bell Labs . As

704-601: A term that referred generally to all AT&T companies, of which there were five major divisions: In 1913, the federal government challenged the Bell System's growing monopoly over the phone system under AT&T ownership in an anti-trust suit, leading to the Kingsbury Commitment . Under the commitment, AT&T escaped break-up or nationalization in exchange for divesting itself of Western Union and allowing non-competing independent telephone companies to interconnect with its long-distance network. After 1934,

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768-517: A variety of functionality and services in the 1A key telephone system developed in the Bell System in the 1930s. Key systems can be built using three principal architectures: electromechanical shared-control, electronic shared-control, or independent key sets. New installations of key telephone systems have become less common, as hybrid systems and private branch exchanges of comparable size have similar costs and greater functionality. Before

832-530: 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

896-425: Is being phased out by most major telecommunication carriers throughout Europe in favor of all-IP networks, with some expecting complete migration by 2025. Originally having started as an organization's manual switchboard or attendant console operated by a telephone operator or just simply the operator , PBXs have evolved into VoIP centers that are hosted by the operators or even manufacturers. Even though VoIP

960-452: Is considered by many people as the future of telephony, the circuit switched network remains the core of communications, and the existing PBX systems are competitive in services with modern IP systems. Five distinct scenarios exist: For the option to call from the IP network to the circuit-switched PSTN ( SS7 / ISUP ), the hosted solutions include interconnecting media gateways. Historically,

1024-506: Is possible to get hosted PBX services that include feature sets from minimal functionality to advanced feature combinations. In addition to the features available from premises-based PBX systems, hosted PBX: The ongoing migration of most major telecommunication carriers to IP-based networks, coupled with the rise in Cloud Communications has resulted in a significant rise in the uptake of hosted PBX solutions. A mobile PBX

1088-536: The Antitrust Division of the U.S. Department of Justice brought a lawsuit against Bell claiming violations of the Sherman Act . In 1982, anticipating that it could not win, AT&T agreed to a Justice Department-mandated consent decree that settled the lawsuit and ordered it to break itself up into seven " Regional Bell Operating Companies " (known as "The Baby Bells"). This ended the existence of

1152-492: The Baby Bells and do not provide telephone service. Beginning in 1991, the Baby Bells began to consolidate operations or rename their Bell Operating Companies according to the parent company name, such as "Bell Atlantic – Delaware, Inc." or "U S WEST Communications, Inc.", to unify their corporate images. The Bell System service marks, including the circled-bell logo, especially as redesigned by Saul Bass in 1969, and

1216-635: The Bell Telephone Company and later by the American Telephone and Telegraph Company (AT&T), that dominated the telephone services industry in North America for over 100 years from its creation in 1877 until its antitrust breakup in 1983. The system of companies was often colloquially called Ma Bell (as in "Mother Bell"), as it held a vertical monopoly over telecommunication products and services in most areas of

1280-583: The Federal Communications Commission (FCC) assumed regulation of AT&T. Proliferation of telephone service allowed the company to become the largest corporation in the world until its dismantling by the United States Department of Justice in 1984, at which time the Bell System ceased to exist. Receiving a U.S. patent for the invention of the telephone on March 7, 1876, Alexander Graham Bell formed

1344-421: The hybrid designation. A hybrid system typically has some call appearance buttons that directly correspond to individual lines and/or stations, but may also support direct dialing to extensions or outside lines without selecting a line appearance. The modern key system is usually fully digital, although analog variants persist and some systems implement VOIP services. Effectively, the aspects that distinguish

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1408-507: The post-World War II occupation was considered an administrative adjunct to the North American Bell System. Immediately before the 1984 break-up, the Bell System had the following corporate structure : On January 1, 1984, the former components of the Bell System were structured into the following Regional Bell Operating Companies (RBOCs), which became known as Baby Bells. After 1984, multiple mergers occurred of

1472-436: The public switched telephone network (PSTN) and the concentration aspect of a PBX permits the shared use of these lines between all stations in the organization. Its intercommunication ability allows two or more stations to directly connect while not using the public switched telephone network. This method reduces the number of lines needed from the organization to the public switched telephone network. Each device connected to

1536-485: The voice over IP PBX, or IP PBX . The other trend involved the idea of focusing on core competence . 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 the hosted PBX. In wireline telephony, the original hosted PBX was the Centrex service provided by telcos since

1600-607: The 1960s; later competitive offerings evolved into the modern competitive local exchange carrier . In voice-over IP, hosted solutions are easier to implement as the PBX may be located at and managed by any telephone service provider, connecting to the individual extensions via the Internet. The upstream provider no longer needs to run direct, local leased lines to the served premises. Many manufacturers provided manually operated private branch exchange systems in various sizes and features; examples are pictured here: A PBX system often includes

1664-516: The 1980s when the arrival of electronic key systems with their easier installation and greater features signaled the end of electromechanical key systems. Two lesser-known key systems were used at airports for air traffic control communications, the 102 and 302 key systems. These were uniquely designed for communications between the air traffic control tower and radar approach control ( RAPCON ) or ground control approach (GCA) and included radio line connections. Automatic Electric Company also produced

1728-410: The 1990s led to new types of PBX systems. One was the massive growth of data networks and increased public understanding of packet switching . Companies needed packet-switched networks for data, so using them for telephone calls proved 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

1792-557: The 21st century, the distinction between key systems and PBX systems has become increasingly blurred. Early electronic key systems used dedicated handsets which displayed and allowed access to all connected PSTN lines and stations. The modern key system now supports SIP , ISDN , analog handsets (in addition to its own proprietary handsets – usually digital) as well as a raft of features more traditionally found on larger PBX systems. Their support for both analog and digital signaling, and of some PBX functionality gives rise to

1856-488: The Bell System's Caribbean regional operating companies. The consent decree also forced Bell to make all of its patents royalty-free . This led to substantial increases in innovation, in particular in the electronics and computer sectors. Steven Weber 's The Success of Open Source characterizes the consent decree as important in fostering the open source movement. The Bell System also owned various Caribbean regional operating companies, as well as 54% of Japan's NEC and

1920-597: The Bell Telephone Company in 1877, which in 1885 became AT&T. When Bell's original patent expired 15 years later in 1894, the telephone market opened to competition and 6,000 new telephone companies started while the Bell Telephone company took a significant financial downturn. On April 30, 1907, Theodore Newton Vail returned as President of AT&T. Vail believed in the superiority of one national telephone system and AT&T adopted

1984-548: The Bell name and the circled-bell trademark until SBC opted for all of its companies to do business under the "SBC" name in 2002. Bell Atlantic used the Bell name and circled-bell trademark until renaming itself Verizon in 2000. Pacific Bell continued operating in California under that name (or the shortened "PacBell" nickname) until SBC purchased it. In Canada, Bell Canada ( divested from AT&T in 1975) continues to use

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2048-530: The Bell name. For the decades that Nortel was named Northern Telecom, its research and development arm was Bell Northern Research. Bell Canada and its holding-company parent, Bell Canada Enterprises , still use the Bell name. They used variations of the circled-bell logo until 1977, which until 1976 strongly resembled the 1921 to 1939 Bell System trademark shown above. AT%26T Merlin Too Many Requests If you report this error to

2112-525: The DOJ had agreed upon in 1956. Before the 1956 break-up, the Bell System included the companies listed below, plus those listed in the pre-1984 section. Northern Electric and the Caribbean regional operating companies were considered part of the Bell System proper before the break-up. Nippon Electric was considered a more distant affiliate of Western Electric, and through its own research and development adapted

2176-715: The Department of Justice in 1913. AT&T committed to sell its $ 30 million in Western Union capital stock, allow competitors to interconnect with its long-distance telephone network, and not acquire other independent companies without permission from the Interstate Commerce Commission . The Bell trademark was used from 1921 through 1969 by both the AT&;T corporation and the regional operating corporations to co-brand themselves under

2240-511: The Northwestern Bell name. In 1984, each regional Bell operating company was assigned a set list of names it was allowed to use in combination with the Bell marks. By 2022, all these Bell System names had disappeared from the United States business landscape. Cincinnati Bell was the last to use the name, until 2022 when it rebranded to Altafiber , though it still has Cincinnati Bell as its corporate name. Southwestern Bell used both

2304-573: The PBX, such as a telephone, a fax machine , or a computer modem, is referred to as an extension and has a designated extension telephone number that may or may not be mapped automatically to the numbering plan of the central office and the telephone number block allocated to the PBX. Initially, PBX systems offered the primary advantage of cost savings for internal phone calls: handling the circuit switching locally reduced charges for telephone service via central-office lines. As PBX systems gained popularity, they began to feature services not available in

2368-407: The United States and Canada. At the time of the breakup of the Bell System in the early 1980s, it had assets of $ 150 billion (equivalent to $ 440 billion in 2023) and employed over one million people. Beginning in the 1910s, American antitrust regulators had been observing and accusing the Bell System of abusing its monopoly power, and had brought legal action multiple times over the decades. In 1974

2432-634: The assets of its parent, the American Bell Telephone Company. American Bell had created AT&T to provide long-distance calls between New York and Chicago and beyond. AT&T became the parent of American Bell Telephone Company, and thus the head of the Bell System, because regulatory and tax rules were leaner in New York than in Boston, where American Bell was headquartered. Later, the Bell System and its moniker "Ma Bell" became

2496-803: The conglomerate in 1984. The Baby Bells became independent companies and several of them are large corporations today. In 1877, the American Bell Telephone Company, named after Alexander Graham Bell , opened the first telephone exchange in New Haven, Connecticut . Within a few years local exchange companies were established in every major city in the United States. Use of the Bell System name initially referred to those early telephone franchises and eventually comprised all telephone companies owned by American Telephone & Telegraph , referred to internally as associated companies , regional holding companies , or later Bell operating companies (BOCs). In 1899, American Telephone & Telegraph (AT&T) acquired

2560-470: The control (and features) into individual telephone sets that don't require any single shared control unit. Such systems were dubbed KSU-less ; the first such phone was introduced in 1975 with the Com Key 416. Generally, these systems are used with relatively few telephone sets and it is often more difficult to keep the feature set (such as speed-dialing numbers) in synchrony between the various sets. Into

2624-445: The customer was required to purchase the instrument at cost, furnish it to the telephone company for rewiring, pay a service charge, and a monthly lease fee for using it. In 1949, the United States Department of Justice alleged in an antitrust lawsuit that AT&T and the Bell System operating companies were using their near-monopoly in telecommunications to attempt to establish unfair advantage in related technologies. The outcome

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2688-535: The designs of Western Electric's North American telecommunications equipment for use in Japan, which to this day gives much of Japan's telephone equipment and network a closer resemblance to North American ANSI and iconectiv standards than to European-originated ITU-T standards. Before the 1956 break-up, Northern Electric was focused on manufacturing, without significant telecommunication-equipment research & development of its own. The operation of Japan's NTT during

2752-402: The development of large-scale integrated circuits , key systems typically consisted of electromechanical components, such as relays , as were larger telephone switching systems. The systems marketed in North America as the 1A, 1A1, 1A2 Key System , and the 6A, are typical examples and were sold for many decades. The Western Electric 1A family of key telephone units (KTUs) was introduced in

2816-479: The expense of full-fledged PBX systems has put them out of reach of small businesses and individuals. However, since the 1990s many small, consumer-grade, and consumer-size PBXs have become available. These systems are not comparable in size, robustness, or flexibility to commercial-grade PBXs, but still provide many features. The first consumer PBX systems used analog ( POTS ) telephone lines, typically supporting four private analog and one public analog line. They were

2880-573: The features available. As the 1A1 systems became commonplace, requirements for intercom features grew. The original intercom KTUs, WECo Model 207, were wired for a single talk link, that is, a single conversation on the intercom at a time. The WECo 6A dial intercom system provided two talk links and was often installed as the dial intercom in a 1A1 or 1A2 key system. The 6A systems were complex, troublesome, and expensive, and never became popular. The advent of 1A2 technology in 1964 simplified key system setup and maintenance. These continued to be used throughout

2944-521: The following: Since the advent of Internet telephony ( Voice over IP ) technologies, PBX development has tended toward the IP PBX , which uses the Internet Protocol to carry calls. 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. As of 2015, ISDN

3008-438: The industrialized world. The 1984 Bell System divestiture brought an end to the affiliation branded as the Bell System. It resulted from another antitrust lawsuit filed by the U.S. Department of Justice in 1974, alleging illegal practices by the Bell System companies to stifle competition in the telecommunications industry. The parties settled the lawsuit on January 8, 1982, superseding the former restrictions that AT&T and

3072-470: The late 1930s and remained in use until the 1950s. 1A equipment was primitive and required at least two KTUs per line; one for line termination and one for station (telephone instrument) termination. The telephone instrument commonly used by 1A systems was the WECo 300/400-series telephone . Introduced in 1953, 1A1 key systems simplified wiring with a single KTU for both line and station termination, and increased

3136-477: The marks on rare occasions to maintain their trademark rights, even less now that they have adopted names conceived long after divestiture. Examples include Verizon, which still used the Bell logo on its trucks and payphones until it updated its own logo in 2015, and Qwest, formerly US West , which licenses the Northwestern Bell and Mountain Bell names to Unical Enterprises, who makes telephones under

3200-634: The modern hybrid telephone system, as the features of PBXs and key systems quickly merged. One of the most recognized such systems is the AT&;T Merlin . Additionally, these more modern systems allowed a diverse set of features including: Features could be added or modified simply using software, allowing easy customization of these systems. The stations were easier to maintain than the previous electromechanical key systems, as they used efficient LEDs instead of incandescent light bulbs for line status indication. LSI also allowed smaller systems to distribute

3264-416: The operating companies and between them, so that some components of the former Bell System are now owned by companies independent of the historic Bell System, including foreign telecommunications firms. The structure of the companies today is as follows. The following telephone companies are considered independent of the Baby Bells : The following companies were divested after 1984 from AT&T Corp. or

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3328-445: The outgoing line automatically. The telephone sets connected to a PBX do not normally have special keys for central-office line control, but it is not uncommon for key systems to be connected to a PBX to extend its services. A PBX, in contrast to a key system, employs an organizational numbering plan for its stations. In addition, a dial plan determines whether additional digit sequences must be prefixed when dialing to obtain access to

3392-576: The provider actually hosts the PBX and the phone handsets are connected to it through an internet connection. Open source projects have provided PBX-style features since the 1990s. These projects provide flexibility, features, and programmability. 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

3456-406: The public network, such as hunt groups , call forwarding, and extension dialing. From the 1960s, a simulated PBX, known as Centrex , provided similar features from the central telephone exchange . A PBX differs from a key telephone system (KTS) in that users of a key system manually select their own outgoing lines on special telephone sets that control buttons for this purpose, while PBXs select

3520-499: The service is provided by a lease agreement and the provider can, in some configurations, use the same switching equipment to service multiple hosted PBX customers. The first hosted PBX services were feature-rich compared to most premises-based systems of the time. Some PBX functions, such as follow-me calling, appeared in a hosted service before they became available in hardware PBX equipment. Since its introduction, updates and new offerings have moved feature sets in both directions. It

3584-611: The size of a small cigar box . 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 the ISDN basic rate interface provides two logical phone lines (via two ISDN B channels) that can be used in parallel. With the adoption of VoIP by consumers, consumer VoIP PBXs have appeared, with PBX functions becoming simple additional software features of consumer-grade routers and switches. Additionally, many telecommunications providers now offer hosted PBX systems where

3648-489: The slogan One Policy, One System, Universal Service. This became the company's philosophy for the next 70 years. Under Vail, AT&T began acquiring many of the smaller telephone companies including the Western Union Telegraph Company . In response to the threat of antitrust action from government, AT&T entered into an out-of-court agreement, known as the Kingsbury Commitment with

3712-498: The system first. A mobile PBX may exploit the functionality available in smartphones to run custom applications to implement the PBX-specific functionality. In addition, a mobile PBX may create extension identifiers for each handset that allow to dial other cell phones in the PBX via their extension shortcut, instead of a PSTN number. Bell System The Bell System was a system of telecommunication companies, led by

3776-425: The terms private automatic branch exchange (PABX) and private manual branch exchange (PMBX) differentiated them. Solid-state digital systems were sometimes referred to as electronic private automatic branch exchanges (EPABX) . As of 2021, the term PBX is by far the most widely recognized. The abbreviation now applies to all types of complex, in-house telephony switching systems. Two significant developments during

3840-414: The various resulting 1984 spinoffs, only BellSouth actively used and promoted the Bell name and logo during its entire history, from the 1984 break-up to its reunion with the new AT&T in 2006. Similarly, cessation of using either the Bell name or logo occurred for many of the other companies more than a decade after the 1984 break-up as part of an acquisition-related rebranding. The others have only used

3904-448: The words Bell System in text, were used before January 1, 1984, when the AT&T divestiture of its regional operating companies took effect. The word mark Bell , the logo, and other related trademarks, are held by each of the remaining Bell companies, namely AT&T, Verizon , CenturyLink , and Altafiber . International rights to the marks, except for Canada , are held by a joint venture of these companies, Bell IP Holdings . Of

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3968-848: Was a 1956 consent decree limiting AT&T to 85% of the United States' national telephone network and certain government contracts, and from continuing to hold interests in Canada and the Caribbean . The Bell System's Canadian operations included the Bell Canada regional operating company and the Northern Electric manufacturing subsidiary of the Bell System's Western Electric equipment manufacturer. Western Electric divested Northern Electric in 1956, but AT&T did not divest itself of Bell Canada until 1975. ITT Inc. , then known as International Telephone & Telegraph Co. , purchased

4032-414: Was a Bell System term of art for a customer-controlled switching system such as the line buttons on the phones associated with such systems. The electrical components that allow for the selection of lines and features such as hold and intercom are housed in a panel or cabinet, called the key service unit or key system unit (KSU). The wiring plans evolved into modular hardware building blocks with

4096-421: Was originally distinguished from a private branch exchange in that it did not require an operator or attendant at a switchboard to establish connections between the central office trunks and stations, or between stations. Technologically, private branch exchanges share lineage with central office telephone systems, and in larger or more complex systems, may rival a central office system in capacity and features. With

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