298:. Introduced in 1953, 1A1 key systems simplified wiring with a single KTU for both line and station termination, and increased 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 the 1980s when the arrival of electronic key systems with their easier installation and greater features signaled the end of electromechanical key systems.
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324:, 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 the modern hybrid telephone system, as the features of PBXs and key systems quickly merged. One of the most recognized such systems is the
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556:(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 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.
2792:
518:(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.
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Follow-me, also known as find-me: Determines the routing of incoming calls. The exchange is configured with a list of numbers for a person. When a call is received for that person, the exchange routes it to each number on the list in turn until either the call is answered or the list is exhausted (at
187:
A key telephone system 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
1320:
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
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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 is possible to get
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1A family of key telephone units (KTUs) was introduced in 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
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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 the public network,
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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
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with central office telephone systems, and in larger or more complex systems, may rival a central office system in capacity and features. With 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.
183:
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
626:. 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.
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Historically, 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
618:. 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
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or the provider's data center. This means the customer does not need to buy or install PBX equipment. Generally, 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.
1180:– the most common digital standard for fixed telephony devices. This can be supplied in either Basic (2-circuit capacity) or Primary (24- or 30-circuit capacity) versions. Most medium to large companies would use Primary ISDN circuits carried on T1 or E1 physical connections.
412:, 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 the
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determines whether additional digit sequences must be prefixed when dialing to obtain access to 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.
764:, call forwarding, and programmable caller ID. As of 2015, ISDN 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
603:. 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 the
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supports integration with custom toll plans (that allow intra-company calls, even from private premises, to be dialed at a cheaper rate) and integrated billing and accounting (where calls made on a private line but on the company's behalf are billed centrally to the
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allows a single number to be presented for the entire company, despite its being geographically distributed. A company could even choose to have no premises, with workers connected from home using their domestic telephones but receiving the same features as any PBX
380:; 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.
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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.
671:
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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
1347:(CTI). An IP-PBX can exist as physical hardware or can carry out its 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".
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allows multimodal access, where employees access the network via a variety of telecommunications systems, including POTS, ISDN, cellular phones, and VOIP. This allows one extension to ring in multiple locations (either concurrently or
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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
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Local connection: Another useful attribute of a hosted PBX is the ability to have a local number in cities in which you are not physically present. This service essentially lets you create a virtual office presence anywhere in the
263:
1194:) lines – the common two-wire interface used in most domestic homes. This is adequate only for smaller systems and can suffer from not being able to detect incoming calls when trying to make an outbound call (commonly called
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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.
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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
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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):
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Into 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
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and switches. Additionally, many telecommunications providers now offer hosted PBX systems where the provider actually hosts the PBX and the phone handsets are connected to it through an internet connection.
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proprietary – the manufacturer has defined a protocol. One can only connect the manufacturer's sets to their PBX, but the benefit is more visible information displayed and/or specific function buttons.
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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
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managed company switchboards manually using cord circuits. As automated electromechanical switches and later electronic switching systems gradually replaced the manual systems, the terms
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also produced 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.
659:
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LSI also allowed smaller systems to distribute the control (and features) into individual telephone sets that don't require any single shared control unit. Such systems were dubbed
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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.
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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.
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handling. Business telephone systems are often broadly classified into key telephone systems and private branch exchanges, but many combinations (hybrid telephone systems) exist.
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Key telephone systems are primarily defined by arrangements with individual line selection buttons for each available telephone line. The earliest systems were known as
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Establishing connections (circuits) between the telephone sets of two users (e.g. mapping a dialed number to a physical phone, ensuring the phone isn't already busy)
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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
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services. Effectively, the aspects that distinguish a PBX from a hybrid key system are the amount, scope, and complexity of the features and facilities offered.
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allows scalability so that a larger system is not needed if new employees are hired, and so that resources are not wasted if the number of employees is reduced.
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interface – historically used to print every call record to a serial printer. In modern systems, a software application connects via serial cable to this port.
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596:. 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.
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network remains the core of communications, and the existing PBX systems are competitive in services with modern IP systems. Five distinct scenarios exist:
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The wiring plans evolved into modular hardware building blocks with a variety of functionality and services in the 1A key telephone system developed in the
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1092:) – the common two-wire interface used in most homes. This is cheap and effective and allows almost any standard phone to be used as an extension.
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A mobile PBX may exploit the functionality available in smartphones to run custom applications to implement the PBX-specific functionality.
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provides two logical phone lines (via two ISDN B channels) that can be used in parallel. With the adoption of VoIP by consumers, consumer
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Many manufacturers provided manually operated private branch exchange systems in various sizes and features; examples are pictured here:
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Automated directory services (where callers can be routed to a given employee by keying or speaking the letters of the employee's name)
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A typical rotary-dial key telephone: the
Western Electric eighteen-button Call Director, manufactured from 1958 to the early 1980s
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A data record from a PBX or other telecommunication system that provides the statistics for a telephone call is usually termed a
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1542:
Ng, John (June 16, 1986). "Fish, Fowl, or
Neither?: Quick, what's the difference between a key telephone system and a hybrid?".
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projects have provided PBX-style features since the 1990s. These projects provide flexibility, features, and programmability.
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Proprietary protocols – if equipment from several manufacturers is on-site, the use of a standard protocol is required.
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839:) telephone lines, typically supporting four private analog and one public analog line. They were the size of a small
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Maintaining such connections as long as the users require them (i.e. channeling voice signals between the users)
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The ongoing migration of most major telecommunication carriers to IP-based networks, coupled with the rise in
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A PBX, in contrast to a key system, employs an organizational numbering plan for its stations. In addition, a
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The modern key system is usually fully digital, although analog variants persist and some systems implement
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hosted PBX services that include feature sets from minimal functionality to advanced feature combinations.
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Direct inward system access (DISA) (the ability to access internal features from an outside telephone line)
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Logic cards, switching and control cards, power cards, and related devices that facilitate PBX operation
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Racks of a
Strowger telephone exchange from 1989, showing two-motion selectors in the United Kingdom
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and has a designated extension telephone number that may or may not be mapped automatically to the
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have appeared, with PBX functions becoming simple additional software features of consumer-grade
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service provided by telcos since the 1960s; later competitive offerings evolved into the modern
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PBX systems also replaced some traditional PBXs in the 1990s, as ISDN offers features such as
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system typically used in business environments, encompassing the range of technology from the
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Manual cord telephone exchange exhibited in
Ainokura Traditional Industry Museum in Japan
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1130:(ISDN) – Provided over T1 (23 bearer channels and 1 signaling channel) or E1 carriers.
843:. In Europe, these systems for analog phones were followed by consumer-grade PBXs for
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Mobile PBX solution (mobile phones replacing or used in combination with fixed phones)
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Additionally, these more modern systems allowed a diverse set of features including:
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eliminates the need for companies to manage or pay for on-site hardware maintenance.
541:, call forwarding, and extension dialing. From the 1960s, a simulated PBX, known as
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In addition to the features available from premises-based PBX systems, hosted PBX:
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1721:"On-Premise [ sic] vs Hosted PBX: Blockbuster or Netflix? - Blog - 1stel"
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Network port (server mode) – the PBX connects to another application or buffer.
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differentiated them. Solid-state digital systems were sometimes referred to as
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Even though VoIP is considered by many people as the future of telephony, the
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1978:
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Early 1945 telephone exchange model N935 system featuring cordless operation
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of the central office and the telephone number block allocated to the PBX.
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Station-specific limitations (such as no long-distance access or no paging)
274:, key systems typically consisted of electromechanical components, such as
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has resulted in a significant rise in the uptake of hosted PBX solutions.
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Outside trunks connecting the PBX to the public switched telephone network
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File – the PBX generates a file containing the call records from the PBX.
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Shared message boxes (where a department can have a shared voicemail box)
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306:) or ground control approach (GCA) and included radio line connections.
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Hosted/virtual PBX (hosted and circuit-switched) or traditional
Centrex
619:
542:
465: in this section. Unsourced material may be challenged and removed.
289:, and the 6A, are typical examples and were sold for many decades. The
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protocols operate over IP and are supported by some network providers.
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Console or switchboard allowing an operator to control incoming calls
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shared-control, electronic shared-control, or independent key sets.
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Providing information for accounting purposes (e.g. metering calls)
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For the option to call from the IP network to the circuit-switched
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and simply consisted of telephone sets, keys, lamps, and wiring.
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1187:) – delivers 24 digital circuits over a four-wire (T1) interface
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823:), the hosted solutions include interconnecting media gateways.
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centers that are hosted by the operators or even manufacturers.
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An Avaya G3si PBX with front cover removed (view from the top)
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Key systems can be built using three principal architectures:
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847:. Using small PBXs for ISDN is a logical step since the ISDN
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In addition to these basic functions, PBXs offer many other
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IP Centrex or hosted/virtual IP (hosted and packet-switched)
1139:– for connecting PBXs to each other, usually runs over T1 (
1703:"Why Hosted PBX is the Better Choice For Small Businesses"
1110:, this usually runs over E1 (E-carrier) physical circuits.
521:
Each device connected to the PBX, such as a telephone, a
1213:(listen mode) – an external application connects to the
832:
commercial-grade PBXs, but still provide many features.
27:
Telephone system typically used in business environments
1151:
Interfaces for connecting PBXs to trunk lines include:
1064:
Interfaces for connecting extensions to a PBX include:
505:
An
Alcatel Lucent PABX Omni PCX Enterprise (front view)
1106:– for connecting PBXs to trunk lines. Standardized by
1099:
Interfaces for connecting PBXs to each other include:
748:) technologies, PBX development has tended toward the
285:
The systems marketed in North
America as the 1A, 1A1,
1221:
port. The PBX streams information to the application.
1124:(SIP) are IP-based solutions for multimedia sessions.
594:
electronic private automatic branch exchanges (EPABX)
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2586:
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2091:
1783:
1597:"BT Prepare to Switch to an All IP Network by 2025"
1575:"Big Changes Coming for SMBs in 2014 (Infographic)"
200:
A 1930s key telephone for a private branch exchange
60:. Unsourced material may be challenged and removed.
732:(UPS) consisting of sensors, power switches, and
614:The other trend involved the idea of focusing on
710:for arbitrary data processing, control and logic
891:those connections as per the user's requirement
756:to carry calls. Most modern PBXs support VoIP.
716:Stations, or telephone sets, sometimes called
1761:
1477:Engineering and Operations in the Bell System
1439:, Bell Laboratories Record, March 1966, pp.85
1202:Interfaces for collecting data from the PBX:
691:Cabinets, closets, vaults, and other housings
545:, provided similar features from the central
229:are housed in a panel or cabinet, called the
8:
1071:– a standard for connecting cordless phones.
835:The first consumer PBX systems used analog (
525:, or a computer modem, is referred to as an
2776:Global telecommunications regulation bodies
687:A PBX system often includes the following:
258:Electromechanical shared-control key system
2812:
1768:
1754:
1746:
1628:"The Big Guide To VOIP For Small Business"
1437:Key Telephone Systems: The Latest Chapter
874:Functionally, the PBX performs four main
481:Learn how and when to remove this message
120:Learn how and when to remove this message
1012:which point the call may be routed to a
744:Since the advent of Internet telephony (
586:private automatic branch exchange (PABX)
1428:
636:
349:Remote supervision of the entire system
1681:"Features of a Business Phone System"
590:private manual branch exchange (PMBX)
136:Early-1970s Telephone Exchange model
7:
2822:
801:IP PBX (private and packet-switched)
726:The PBX's internal switching network
463:adding citations to reliable sources
400:Nortel T Series Key System Telephone
58:adding citations to reliable sources
1452:Fiber Optics Illustrated Dictionary
1268:The first hosted PBX services were
404:The modern key system now supports
807:PBX (private and circuit-switched)
624:competitive local exchange carrier
25:
516:public switched telephone network
2821:
2811:
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2801:
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2411:Free-space optical communication
1679:Wright, Ian (13 December 2013).
1515:Marcus, Michael N. (June 1995).
1357:
989:Customized abbreviated dialing (
697:Interconnecting wires and cables
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658:
639:
439:
316:Electronic shared-control system
34:
1242:Station Messaging Detail Record
450:needs additional citations for
272:large-scale integrated circuits
45:needs additional citations for
2853:Computer telephony integration
1345:computer telephony integration
1:
1339:handles voice calls over the
827:Home and small-business usage
647:
580:The term PBX originated when
352:Selection of signaling sounds
2848:Telephone exchange equipment
2797:Telecommunication portal
2578:Telecommunications equipment
1517:"KSU-less Key System Update"
1343:(IP), bringing benefits for
730:Uninterruptible power supply
371:for line status indication.
2314:Alexander Stepanovich Popov
1656:. About.com. Archived from
1455:. CRC Press. p. 1151.
1192:plain old telephone service
1122:Session Initiation Protocol
1090:plain old telephone service
514:provide connections to the
384:Hybrid key telephone system
69:"Business telephone system"
2874:
2018:Telecommunications history
1601:Yoozoom Telecommunications
1494:. Que. pp. 165, 169.
1052:Voice message broadcasting
1020:Interactive voice response
921:Automatic call distributor
310:Automatic Electric Company
270:Before the development of
2785:
2626:Public Switched Telephone
2438:telecommunication circuit
2399:Fiber-optic communication
2144:Francis Blake (telephone)
1939:Optical telecommunication
1707:Unity Connected Solutions
1504:– via Google Books.
1465:– via Google Books.
780:, PBXs have evolved into
341:Automatic call accounting
158:business telephone system
2537:Orbital angular-momentum
1974:Satellite communications
1813:Communications satellite
1654:"The Functions of a PBX"
1577:. eFax. 17 December 2013
369:incandescent light bulbs
296:300/400-series telephone
294:1A systems was the WECo
2416:Molecular communication
2239:Gardiner Greene Hubbard
2068:Undersea telegraph line
1803:Cable protection system
1449:Petersen, J.K. (2018).
1172:Inter-Asterisk eXchange
431:Private branch exchange
174:private branch exchange
18:Private branch exchange
2558:Communication protocol
2344:Charles Sumner Tainter
2159:Walter Houser Brattain
2104:Edwin Howard Armstrong
1912:Information revolution
1418:Telephone switchboards
1128:Primary rate interface
646:Cord PBX switchboard (
572:
506:
498:
401:
267:
201:
153:
141:
2532:Polarization-division
2264:Narinder Singh Kapany
2229:Erna Schneider Hoover
2149:Jagadish Chandra Bose
2129:Alexander Graham Bell
1860:online video platform
997:Direct inward dialing
582:switchboard operators
570:
552:A PBX differs from a
504:
496:
399:
393:lines and stations.
265:
199:
147:
135:
2374:Vladimir K. Zworykin
2334:Almon Brown Strowger
2304:Charles Grafton Page
1959:Prepaid mobile phone
1887:Electrical telegraph
1607:on 13 September 2015
1562:Notes on the Network
1408:Switchboard operator
1393:List of SIP software
1383:Cloud communications
1306:Cloud Communications
1300:Hosted PBX providers
1185:robbed bit signaling
1147:) physical circuits.
849:basic rate interface
554:key telephone system
459:improve this article
192:Key telephone system
166:key telephone system
54:improve this article
2858:Telephony equipment
2324:Johann Philipp Reis
2083:Wireless revolution
2045:The Telephone Cases
1902:Hydraulic telegraph
1660:on 27 February 2014
1253:Virtual PBX systems
1060:Interface standards
926:Automatic ring back
776:or just simply the
320:With the advent of
280:telephone switching
2522:Frequency-division
2499:Telephone exchange
2369:Charles Wheatstone
2299:Jun-ichi Nishizawa
2274:Innocenzo Manzetti
2209:Reginald Fessenden
1944:Optical telegraphy
1777:Telecommunications
1709:. Unity Connected.
1527:(6). UBM LLC: 117
1488:Main, Max (2003).
1413:Telephone exchange
1398:Reference computer
1388:Ground start trunk
1262:telephone exchange
1257:hosted PBX systems
1248:Hosted PBX systems
1237:call detail record
943:on busy or absence
774:telephone operator
762:conference calling
573:
547:telephone exchange
511:telephone exchange
507:
499:
402:
268:
202:
154:
142:
2835:
2834:
2573:Store and forward
2568:Data transmission
2482:Network switching
2433:Transmission line
2279:Guglielmo Marconi
2244:Internet pioneers
2109:Mohamed M. Atalla
2078:Whistled language
1531:– via Gale.
1365:Telephones portal
1341:Internet Protocol
1156:Internet Protocol
1114:Internet Protocol
1075:Internet Protocol
770:attendant console
754:Internet Protocol
752:, which uses the
683:System components
491:
490:
483:
336:Answering machine
278:, as were larger
249:electromechanical
152:key telephone set
148:Early model 464G
140:Automatic system
130:
129:
122:
104:
16:(Redirected from
2865:
2825:
2824:
2815:
2814:
2805:
2804:
2795:
2794:
2793:
2666:Notable networks
2656:Wireless network
2596:Cellular network
2588:Types of network
2563:Computer network
2450:Network topology
2364:Thomas A. Watson
2219:Oliver Heaviside
2204:Philo Farnsworth
2179:Daniel Davis Jr.
2154:Charles Bourseul
2114:John Logie Baird
1823:Data compression
1818:Computer network
1770:
1763:
1756:
1747:
1736:
1735:
1733:
1732:
1717:
1711:
1710:
1699:
1693:
1692:
1690:
1688:
1676:
1670:
1669:
1667:
1665:
1649:
1643:
1642:
1640:
1638:
1626:Sullivan, Mark.
1623:
1617:
1616:
1614:
1612:
1603:. Archived from
1593:
1587:
1586:
1584:
1582:
1571:
1565:
1558:
1552:
1551:
1539:
1533:
1532:
1512:
1506:
1505:
1485:
1479:
1475:AT&T (1984)
1473:
1467:
1466:
1446:
1440:
1433:
1367:
1362:
1361:
1360:
986:Custom greetings
900:calling features
789:circuit switched
674:
662:
652:
649:
643:
601:packet switching
486:
479:
475:
472:
466:
443:
435:
291:Western Electric
231:key service unit
150:Western Electric
125:
118:
114:
111:
105:
103:
62:
38:
30:
21:
2873:
2872:
2868:
2867:
2866:
2864:
2863:
2862:
2838:
2837:
2836:
2831:
2791:
2789:
2781:
2723:
2660:
2582:
2546:
2503:
2452:
2444:
2385:
2378:
2284:Robert Metcalfe
2139:Tim Berners-Lee
2087:
1907:Information Age
1779:
1774:
1744:
1739:
1730:
1728:
1719:
1718:
1714:
1701:
1700:
1696:
1686:
1684:
1683:. Expert Market
1678:
1677:
1673:
1663:
1661:
1652:Unuth, Nadeem.
1651:
1650:
1646:
1636:
1634:
1625:
1624:
1620:
1610:
1608:
1595:
1594:
1590:
1580:
1578:
1573:
1572:
1568:
1559:
1555:
1541:
1540:
1536:
1514:
1513:
1509:
1502:
1487:
1486:
1482:
1474:
1470:
1463:
1448:
1447:
1443:
1434:
1430:
1426:
1363:
1358:
1356:
1353:
1333:
1314:
1302:
1250:
1190:standard POTS (
1108:British Telecom
1077:– For example,
1062:
1055:Welcome message
982:Conference call
941:Call forwarding
876:call processing
872:
829:
742:
704:Microcontroller
685:
678:
675:
666:
663:
654:
650:
644:
632:
616:core competence
578:
487:
476:
470:
467:
456:
444:
433:
386:
326:AT&T Merlin
318:
260:
235:key system unit
194:
126:
115:
109:
106:
63:
61:
51:
39:
28:
23:
22:
15:
12:
11:
5:
2871:
2869:
2861:
2860:
2855:
2850:
2840:
2839:
2833:
2832:
2830:
2829:
2819:
2809:
2799:
2786:
2783:
2782:
2780:
2779:
2772:
2767:
2762:
2757:
2752:
2751:
2750:
2745:
2737:
2731:
2729:
2725:
2724:
2722:
2721:
2716:
2711:
2706:
2701:
2696:
2691:
2686:
2681:
2676:
2670:
2668:
2662:
2661:
2659:
2658:
2653:
2648:
2643:
2638:
2633:
2628:
2623:
2618:
2613:
2608:
2603:
2598:
2592:
2590:
2584:
2583:
2581:
2580:
2575:
2570:
2565:
2560:
2554:
2552:
2548:
2547:
2545:
2544:
2539:
2534:
2529:
2524:
2519:
2517:Space-division
2513:
2511:
2505:
2504:
2502:
2501:
2496:
2495:
2494:
2489:
2479:
2478:
2477:
2467:
2462:
2456:
2454:
2446:
2445:
2443:
2442:
2441:
2440:
2430:
2429:
2428:
2418:
2413:
2408:
2407:
2406:
2396:
2390:
2388:
2380:
2379:
2377:
2376:
2371:
2366:
2361:
2356:
2354:Camille Tissot
2351:
2346:
2341:
2336:
2331:
2329:Claude Shannon
2326:
2321:
2319:Tivadar Puskás
2316:
2311:
2306:
2301:
2296:
2291:
2289:Antonio Meucci
2286:
2281:
2276:
2271:
2266:
2261:
2259:Charles K. Kao
2256:
2251:
2246:
2241:
2236:
2234:Harold Hopkins
2231:
2226:
2221:
2216:
2211:
2206:
2201:
2196:
2191:
2186:
2181:
2176:
2171:
2166:
2161:
2156:
2151:
2146:
2141:
2136:
2134:Emile Berliner
2131:
2126:
2121:
2116:
2111:
2106:
2101:
2095:
2093:
2089:
2088:
2086:
2085:
2080:
2075:
2073:Videotelephony
2070:
2065:
2064:
2063:
2058:
2048:
2041:
2036:
2030:
2025:
2020:
2015:
2010:
2009:
2008:
2003:
1998:
1988:
1987:
1986:
1976:
1971:
1969:Radiotelephone
1966:
1961:
1956:
1951:
1946:
1941:
1936:
1935:
1934:
1924:
1919:
1914:
1909:
1904:
1899:
1894:
1889:
1884:
1879:
1874:
1873:
1872:
1867:
1862:
1857:
1855:Internet video
1847:
1846:
1845:
1840:
1835:
1830:
1820:
1815:
1810:
1805:
1800:
1795:
1789:
1787:
1781:
1780:
1775:
1773:
1772:
1765:
1758:
1750:
1743:
1742:External links
1740:
1738:
1737:
1712:
1694:
1671:
1644:
1618:
1588:
1566:
1553:
1534:
1507:
1500:
1480:
1468:
1461:
1441:
1427:
1425:
1422:
1421:
1420:
1415:
1410:
1405:
1400:
1395:
1390:
1385:
1380:
1375:
1369:
1368:
1352:
1349:
1332:
1329:
1313:
1310:
1301:
1298:
1297:
1296:
1292:
1289:
1286:
1285:sequentially).
1282:
1249:
1246:
1232:
1231:
1225:
1222:
1207:
1200:
1199:
1188:
1181:
1175:
1149:
1148:
1134:
1131:
1125:
1111:
1097:
1096:
1093:
1086:
1072:
1061:
1058:
1057:
1056:
1053:
1050:
1045:
1042:
1039:Public address
1036:
1031:
1026:
1022:
1017:
1009:
1006:Do not disturb
1003:
1000:
994:
987:
984:
979:
974:
969:
964:
959:
954:
949:
944:
938:
933:
928:
923:
918:
915:
910:
908:Auto attendant
896:
895:
892:
886:
883:
871:
868:
828:
825:
809:
808:
805:
802:
799:
796:
772:operated by a
741:
740:Current trends
738:
737:
736:
727:
724:
714:
711:
701:
698:
695:
692:
684:
681:
680:
679:
676:
669:
667:
664:
657:
655:
645:
638:
631:
628:
577:
574:
531:numbering plan
489:
488:
471:September 2017
447:
445:
438:
432:
429:
385:
382:
360:
359:
356:
353:
350:
347:
342:
339:
317:
314:
287:1A2 Key System
259:
256:
244:in the 1930s.
193:
190:
128:
127:
42:
40:
33:
26:
24:
14:
13:
10:
9:
6:
4:
3:
2:
2870:
2859:
2856:
2854:
2851:
2849:
2846:
2845:
2843:
2828:
2820:
2818:
2810:
2808:
2800:
2798:
2788:
2787:
2784:
2777:
2773:
2771:
2768:
2766:
2763:
2761:
2758:
2756:
2753:
2749:
2746:
2744:
2741:
2740:
2738:
2736:
2733:
2732:
2730:
2726:
2720:
2717:
2715:
2712:
2710:
2707:
2705:
2702:
2700:
2697:
2695:
2692:
2690:
2687:
2685:
2682:
2680:
2677:
2675:
2672:
2671:
2669:
2667:
2663:
2657:
2654:
2652:
2649:
2647:
2644:
2642:
2639:
2637:
2634:
2632:
2629:
2627:
2624:
2622:
2619:
2617:
2614:
2612:
2609:
2607:
2604:
2602:
2599:
2597:
2594:
2593:
2591:
2589:
2585:
2579:
2576:
2574:
2571:
2569:
2566:
2564:
2561:
2559:
2556:
2555:
2553:
2549:
2543:
2542:Code-division
2540:
2538:
2535:
2533:
2530:
2528:
2527:Time-division
2525:
2523:
2520:
2518:
2515:
2514:
2512:
2510:
2506:
2500:
2497:
2493:
2490:
2488:
2485:
2484:
2483:
2480:
2476:
2473:
2472:
2471:
2468:
2466:
2463:
2461:
2458:
2457:
2455:
2453:and switching
2451:
2447:
2439:
2436:
2435:
2434:
2431:
2427:
2424:
2423:
2422:
2419:
2417:
2414:
2412:
2409:
2405:
2404:optical fiber
2402:
2401:
2400:
2397:
2395:
2394:Coaxial cable
2392:
2391:
2389:
2387:
2381:
2375:
2372:
2370:
2367:
2365:
2362:
2360:
2357:
2355:
2352:
2350:
2347:
2345:
2342:
2340:
2337:
2335:
2332:
2330:
2327:
2325:
2322:
2320:
2317:
2315:
2312:
2310:
2309:Radia Perlman
2307:
2305:
2302:
2300:
2297:
2295:
2292:
2290:
2287:
2285:
2282:
2280:
2277:
2275:
2272:
2270:
2267:
2265:
2262:
2260:
2257:
2255:
2252:
2250:
2247:
2245:
2242:
2240:
2237:
2235:
2232:
2230:
2227:
2225:
2222:
2220:
2217:
2215:
2212:
2210:
2207:
2205:
2202:
2200:
2199:Lee de Forest
2197:
2195:
2194:Thomas Edison
2192:
2190:
2187:
2185:
2184:Donald Davies
2182:
2180:
2177:
2175:
2172:
2170:
2169:Claude Chappe
2167:
2165:
2162:
2160:
2157:
2155:
2152:
2150:
2147:
2145:
2142:
2140:
2137:
2135:
2132:
2130:
2127:
2125:
2122:
2120:
2117:
2115:
2112:
2110:
2107:
2105:
2102:
2100:
2097:
2096:
2094:
2090:
2084:
2081:
2079:
2076:
2074:
2071:
2069:
2066:
2062:
2059:
2057:
2054:
2053:
2052:
2049:
2047:
2046:
2042:
2040:
2037:
2034:
2031:
2029:
2026:
2024:
2021:
2019:
2016:
2014:
2013:Smoke signals
2011:
2007:
2004:
2002:
1999:
1997:
1994:
1993:
1992:
1991:Semiconductor
1989:
1985:
1982:
1981:
1980:
1977:
1975:
1972:
1970:
1967:
1965:
1962:
1960:
1957:
1955:
1952:
1950:
1947:
1945:
1942:
1940:
1937:
1933:
1930:
1929:
1928:
1925:
1923:
1920:
1918:
1915:
1913:
1910:
1908:
1905:
1903:
1900:
1898:
1895:
1893:
1890:
1888:
1885:
1883:
1880:
1878:
1875:
1871:
1868:
1866:
1863:
1861:
1858:
1856:
1853:
1852:
1851:
1850:Digital media
1848:
1844:
1841:
1839:
1836:
1834:
1831:
1829:
1826:
1825:
1824:
1821:
1819:
1816:
1814:
1811:
1809:
1806:
1804:
1801:
1799:
1796:
1794:
1791:
1790:
1788:
1786:
1782:
1778:
1771:
1766:
1764:
1759:
1757:
1752:
1751:
1748:
1741:
1726:
1722:
1716:
1713:
1708:
1704:
1698:
1695:
1682:
1675:
1672:
1659:
1655:
1648:
1645:
1633:
1629:
1622:
1619:
1606:
1602:
1598:
1592:
1589:
1576:
1570:
1567:
1563:
1557:
1554:
1549:
1545:
1544:Network World
1538:
1535:
1530:
1526:
1522:
1518:
1511:
1508:
1503:
1501:9780789729378
1497:
1493:
1492:
1484:
1481:
1478:
1472:
1469:
1464:
1462:9781351836166
1458:
1454:
1453:
1445:
1442:
1438:
1435:W.F.B. Wood,
1432:
1429:
1423:
1419:
1416:
1414:
1411:
1409:
1406:
1404:
1401:
1399:
1396:
1394:
1391:
1389:
1386:
1384:
1381:
1379:
1376:
1374:
1371:
1370:
1366:
1355:
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1346:
1342:
1338:
1330:
1328:
1325:
1322:
1319:
1311:
1309:
1307:
1299:
1293:
1290:
1287:
1283:
1279:
1278:
1277:
1274:
1271:
1266:
1263:
1258:
1254:
1247:
1245:
1243:
1239:
1238:
1229:
1226:
1223:
1220:
1216:
1212:
1208:
1205:
1204:
1203:
1197:
1193:
1189:
1186:
1182:
1179:
1176:
1173:
1169:
1165:
1161:
1157:
1154:
1153:
1152:
1146:
1142:
1138:
1135:
1132:
1129:
1126:
1123:
1119:
1115:
1112:
1109:
1105:
1102:
1101:
1100:
1094:
1091:
1087:
1084:
1080:
1076:
1073:
1070:
1067:
1066:
1065:
1059:
1054:
1051:
1049:
1046:
1043:
1040:
1037:
1035:
1034:Night service
1032:
1030:
1029:Music on hold
1027:
1023:
1021:
1018:
1015:
1010:
1007:
1004:
1001:
998:
995:
992:
991:speed dialing
988:
985:
983:
980:
978:
975:
973:
970:
968:
965:
963:
962:Call transfer
960:
958:
955:
953:
950:
948:
945:
942:
939:
937:
936:Call blocking
934:
932:
931:Busy override
929:
927:
924:
922:
919:
916:
914:
911:
909:
906:
905:
904:
901:
893:
890:
889:Disconnecting
887:
884:
881:
880:
879:
877:
870:PBX functions
869:
867:
865:
861:
858:
854:
850:
846:
842:
838:
833:
826:
824:
822:
818:
814:
806:
803:
800:
797:
794:
793:
792:
790:
785:
783:
779:
775:
771:
767:
763:
759:
755:
751:
747:
746:Voice over IP
739:
735:
731:
728:
725:
723:
719:
715:
712:
709:
708:microcomputer
705:
702:
699:
696:
693:
690:
689:
688:
682:
673:
668:
661:
656:
642:
637:
635:
629:
627:
625:
621:
617:
612:
610:
606:
605:voice over IP
602:
597:
595:
591:
587:
583:
575:
569:
565:
562:
557:
555:
550:
548:
544:
540:
534:
532:
528:
524:
519:
517:
512:
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65:Find sources:
59:
55:
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43:This article
41:
37:
32:
31:
19:
2509:Multiplexing
2384:Transmission
2349:Nikola Tesla
2339:Henry Sutton
2294:Samuel Morse
2224:Robert Hooke
2189:Amos Dolbear
2124:John Bardeen
2043:
2023:Telautograph
1927:Mobile phone
1882:Edholm's law
1865:social media
1798:Broadcasting
1729:. Retrieved
1727:. 2016-03-01
1725:Blog - 1stel
1724:
1715:
1706:
1697:
1685:. Retrieved
1674:
1662:. Retrieved
1658:the original
1647:
1635:. Retrieved
1631:
1621:
1609:. Retrieved
1605:the original
1600:
1591:
1579:. Retrieved
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1275:
1270:feature-rich
1267:
1256:
1252:
1251:
1235:
1233:
1201:
1150:
1098:
1063:
1041:voice paging
972:Call whisper
967:Call waiting
957:Call pick-up
947:Call logging
913:Auto dialing
897:
873:
862:
834:
830:
810:
786:
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686:
633:
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598:
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477:
468:
457:Please help
452:verification
449:
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361:
330:
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308:
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206:wiring plans
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52:Please help
47:verification
44:
2709:NPL network
2421:Radio waves
2359:Alfred Vail
2269:Hedy Lamarr
2254:Dawon Kahng
2214:Elisha Gray
2174:Yogen Dalal
2099:Nasir Ahmed
2033:Teleprinter
1897:Heliographs
1664:23 February
1581:23 February
1521:Teleconnect
1240:(CDR) or a
864:Open source
766:switchboard
651: 1975
539:hunt groups
523:fax machine
509:A PBX is a
367:instead of
242:Bell System
219:term of art
216:Bell System
2842:Categories
2755:Antarctica
2714:Toasternet
2636:Television
2119:Paul Baran
2051:Television
2035:(teletype)
2028:Telegraphy
2006:transistor
1984:Phryctoria
1954:Photophone
1932:Smartphone
1922:Mass media
1731:2016-05-02
1632:Forbes.com
1564:(1980) p.3
1560:AT&T,
1424:References
1378:Circuit ID
1318:mobile PBX
1312:Mobile PBX
1048:Voice mail
1014:voice mail
630:Manual PBX
80:newspapers
2739:Americas
2728:Locations
2699:Internet2
2460:Bandwidth
2164:Vint Cerf
2061:streaming
2039:Telephone
1979:Semaphore
1870:streaming
1611:8 October
1295:company).
1145:E-carrier
1143:) or E1 (
1141:T-carrier
952:Call park
853:VoIP PBXs
841:cigar box
734:batteries
561:dial plan
527:extension
345:Caller ID
338:functions
282:systems.
172:) to the
162:telephone
110:June 2013
2807:Category
2694:Internet
2684:CYCLADES
2601:Ethernet
2551:Concepts
2475:terminal
2426:wireless
2249:Bob Kahn
2092:Pioneers
1917:Internet
1808:Cable TV
1687:23 April
1637:23 April
1351:See also
1244:(SMDR).
1209:Network
1120:and the
1016:system).
878:duties:
778:operator
722:metonymy
607:PBX, or
537:such as
377:KSU-less
227:intercom
2827:Commons
2817:Outline
2770:Oceania
2689:FidoNet
2674:ARPANET
2487:circuit
2056:digital
1785:History
1373:Centrex
977:Camp-on
857:routers
620:Centrex
576:History
543:Centrex
322:LSI ICs
237:(KSU).
94:scholar
2765:Europe
2735:Africa
2719:Usenet
2679:BITNET
2616:Mobile
2492:packet
2001:MOSFET
1996:device
1793:Beacon
1529:et seq
1498:
1459:
1337:IP PBX
1331:IP-PBX
1228:Serial
1170:, and
1088:POTS (
1025:world.
750:IP PBX
609:IP PBX
414:hybrid
304:RAPCON
276:relays
214:was a
96:
89:
82:
75:
67:
2748:South
2743:North
2704:JANET
2641:Telex
2631:Radio
2470:Nodes
2465:Links
2386:media
1964:Radio
1949:Pager
1877:Drums
1843:video
1838:image
1828:audio
1550:(15).
1281:user.
1196:glare
1183:RBS (
1160:H.323
1118:H.323
1104:DPNSS
1079:H.323
1008:(DND)
999:(DID)
718:lines
160:is a
138:TESLA
101:JSTOR
87:books
2760:Asia
2646:UUCP
2606:ISDN
1689:2014
1666:2014
1639:2014
1613:2015
1583:2014
1496:ISBN
1491:HTI+
1457:ISBN
1403:RJ21
1211:port
1178:ISDN
1168:MGCP
1137:QSIG
1081:and
1069:DECT
845:ISDN
837:POTS
821:ISUP
813:PSTN
782:VoIP
758:ISDN
588:and
425:VOIP
410:ISDN
391:PSTN
365:LEDs
225:and
223:hold
73:news
2651:WAN
2621:NGN
2611:LAN
1892:Fax
1833:DCT
1335:An
1255:or
1219:UDP
1217:or
1215:TCP
1164:SIP
1083:SIP
817:SS7
768:or
720:by
706:or
461:by
406:SIP
233:or
212:Key
180:).
178:PBX
170:KTS
56:by
2844::
1723:.
1705:.
1630:.
1599:.
1546:.
1525:13
1523:.
1519:.
1316:A
1198:).
1166:,
1162:,
1158:–
1116:–
648:c.
611:.
549:.
408:,
328:.
156:A
2778:)
2774:(
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98:·
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20:)
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