287:. 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.
661:
134:
122:
186:
630:
649:
557:
491:
483:
1348:
313:, 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
386:
2792:
430:
25:
2802:
545:(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.
2781:
507:(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.
2812:
1000:
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
176:
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
1309:
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
1261:
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
282:
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
525:
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,
502:
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
177:
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.
172:
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
615:. 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.
820:
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
607:. 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
1253:
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.
1169:– 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.
401:, 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
552:
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.
753:, 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
592:. 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
1283:
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
1269:
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
369:; 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.
1310:
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.
660:
1248:
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
1336:(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".
1273:
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
290:
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
1013:
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
252:
1183:) 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
408:
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.
351:
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
891:
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):
377:
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
1585:
848:
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.
1084:
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.
210:
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
573:
managed company switchboards manually using cord circuits. As automated electromechanical switches and later electronic switching systems gradually replaced the manual systems, the terms
301:
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.
648:
363:
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
1316:
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.
243:
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.
173:
handling. Business telephone systems are often broadly classified into key telephone systems and private branch exchanges, but many combinations (hybrid telephone systems) exist.
193:
Key telephone systems are primarily defined by arrangements with individual line selection buttons for each available telephone line. The earliest systems were known as
1593:
871:
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)
588:
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
416:
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.
1277:
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.
1219:
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.
2764:
2736:
2731:
1756:
585:. 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.
780:
network remains the core of communications, and the existing PBX systems are competitive in services with modern IP systems. Five distinct scenarios exist:
229:
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
447:
42:
629:
2841:
1081:) – 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.
2758:
2836:
2753:
2743:
2723:
2525:
1313:
A mobile PBX may exploit the functionality available in smartphones to run custom applications to implement the PBX-specific functionality.
133:
840:
provides two logical phone lines (via two ISDN B channels) that can be used in parallel. With the adoption of VoIP by consumers, consumer
623:
Many manufacturers provided manually operated private branch exchange systems in various sizes and features; examples are pictured here:
2748:
2594:
1166:
994:
89:
906:
Automated directory services (where callers can be routed to a given employee by keying or speaking the letters of the employee's name)
2520:
612:
61:
2614:
1488:
1449:
504:
469:
121:
108:
1642:
556:
255:
A typical rotary-dial key telephone: the
Western Electric eighteen-button Call Director, manufactured from 1958 to the early 1980s
2399:
1947:
1749:
1616:
1223:
A data record from a PBX or other telecommunication system that provides the statistics for a telephone call is usually termed a
68:
1531:
Ng, John (June 16, 1986). "Fish, Fowl, or
Neither?: Quick, what's the difference between a key telephone system and a hybrid?".
2510:
1230:
855:
projects have provided PBX-style features since the 1990s. These projects provide flexibility, features, and programmability.
2505:
2056:
1333:
1156:
451:
46:
75:
2530:
1691:
1203:
877:
2815:
1563:
2846:
2805:
2566:
2463:
2006:
1773:
718:
126:
1122:
Proprietary protocols – if equipment from several manufacturers is on-site, the use of a standard protocol is required.
2795:
2302:
1742:
1180:
1152:
1110:
1078:
1071:
828:) telephone lines, typically supporting four private analog and one public analog line. They were the size of a small
825:
394:
57:
185:
2654:
2576:
2515:
2222:
1008:
909:
298:
440:
35:
2426:
2387:
2232:
2132:
2061:
1994:
1821:
1022:
874:
Maintaining such connections as long as the users require them (i.e. channeling voice signals between the users)
2785:
2027:
1962:
1915:
1801:
519:
1293:
The ongoing migration of most major telecommunication carriers to IP-based networks, coupled with the rise in
548:
A PBX, in contrast to a key system, employs an organizational numbering plan for its stations. In addition, a
490:
2624:
2609:
2453:
2404:
2327:
2227:
1905:
1791:
1786:
1160:
805:
412:
The modern key system is usually fully digital, although analog variants persist and some systems implement
357:
292:
1262:
hosted PBX services that include feature sets from minimal functionality to advanced feature combinations.
991:
Direct inward system access (DISA) (the ability to access internal features from an outside telephone line)
2546:
2332:
2147:
2092:
2087:
1900:
1865:
1709:
1207:
1116:
2448:
2252:
2217:
2137:
2117:
2039:
1927:
1848:
1406:
1216:
985:
754:
722:
689:
Logic cards, switching and control cards, power cards, and related devices that facilitate PBX operation
515:
482:
207:
758:
82:
2362:
2322:
2292:
2049:
1984:
1875:
1396:
1381:
1371:
1294:
1173:
837:
762:
570:
542:
560:
Racks of a
Strowger telephone exchange from 1989, showing two-motion selectors in the United Kingdom
2372:
2312:
2071:
2033:
1890:
1831:
1816:
914:
896:
527:
518:
and has a designated extension telephone number that may or may not be mapped automatically to the
284:
268:
2599:
2556:
2487:
2357:
2287:
2262:
2197:
2044:
1765:
1401:
1386:
1376:
1250:
1225:
845:
844:
have appeared, with PBX functions becoming simple additional software features of consumer-grade
750:
535:
499:
310:
260:
611:
service provided by telcos since the 1960s; later competitive offerings evolved into the modern
2639:
2561:
2475:
2458:
2421:
2307:
2267:
2097:
2066:
1932:
1826:
1484:
1445:
1353:
1329:
1144:
1102:
1063:
749:
PBX systems also replaced some traditional PBXs in the 1990s, as ISDN offers features such as
742:
324:
153:
system typically used in business environments, encompassing the range of technology from the
2644:
2604:
2584:
2551:
2480:
2438:
2352:
2207:
2192:
2167:
2142:
2102:
1952:
1811:
1806:
1796:
1199:
777:
589:
279:
237:
211:
138:
1505:
2272:
2127:
1895:
1858:
1096:
970:
929:
888:
864:
692:
604:
365:
1870:
666:
Manual cord telephone exchange exhibited in
Ainokura Traditional Industry Museum in Japan
2470:
2342:
2317:
2277:
2247:
2122:
1957:
1843:
1646:
1184:
1027:
809:
385:
314:
275:
1119:(ISDN) – Provided over T1 (23 bearer channels and 1 signaling channel) or E1 carriers.
832:. In Europe, these systems for analog phones were followed by consumer-grade PBXs for
793:
Mobile PBX solution (mobile phones replacing or used in combination with fixed phones)
2830:
2619:
2392:
2382:
2297:
2187:
2182:
2172:
2157:
1979:
1838:
1669:
1017:
979:
950:
924:
919:
734:
696:
593:
320:
Additionally, these more modern systems allowed a diverse set of features including:
1280:
eliminates the need for companies to manage or pay for on-site hardware maintenance.
530:, call forwarding, and extension dialing. From the 1960s, a simulated PBX, known as
2497:
2337:
2282:
2212:
2177:
2112:
2011:
2001:
1853:
1265:
In addition to the features available from premises-based PBX systems, hosted PBX:
1258:
960:
955:
945:
935:
1710:"On-Premise [ sic] vs Hosted PBX: Blockbuster or Netflix? - Blog - 1stel"
1478:
1439:
2697:
2347:
2257:
2242:
2202:
2162:
2021:
901:
852:
511:
429:
230:
204:
24:
1213:
Network port (server mode) – the PBX connects to another application or buffer.
581:
differentiated them. Solid-state digital systems were sometimes referred to as
2702:
2409:
2107:
2016:
1972:
1942:
1920:
1910:
1885:
1366:
1343:
1036:
1002:
776:
Even though VoIP is considered by many people as the future of telephony, the
2687:
2152:
1967:
1133:
1129:
940:
829:
654:
Early 1945 telephone exchange model N935 system featuring cordless operation
549:
333:
150:
522:
of the central office and the telephone number block allocated to the PBX.
347:
Station-specific limitations (such as no long-distance access or no paging)
263:, key systems typically consisted of electromechanical components, such as
1297:
has resulted in a significant rise in the uptake of hosted PBX solutions.
702:
Outside trunks connecting the PBX to the public switched telephone network
2682:
2672:
2589:
2414:
2237:
1195:
File – the PBX generates a file containing the call records from the PBX.
1033:
Shared message boxes (where a department can have a shared voicemail box)
710:
215:
295:) or ground control approach (GCA) and included radio line connections.
2677:
2662:
1361:
965:
784:
Hosted/virtual PBX (hosted and circuit-switched) or traditional
Centrex
608:
531:
454: in this section. Unsourced material may be challenged and removed.
278:, and the 6A, are typical examples and were sold for many decades. The
1163:
protocols operate over IP and are supported by some network providers.
2707:
2667:
1989:
1781:
1734:
1325:
841:
738:
683:
Console or switchboard allowing an operator to control incoming calls
597:
251:
240:
shared-control, electronic shared-control, or independent key sets.
883:
Providing information for accounting purposes (e.g. metering calls)
800:
For the option to call from the IP network to the circuit-switched
2692:
2629:
1937:
1148:
1106:
1092:
1067:
555:
489:
481:
384:
264:
250:
184:
132:
120:
197:
and simply consisted of telephone sets, keys, lamps, and wiring.
2634:
1391:
1176:) – delivers 24 digital circuits over a four-wire (T1) interface
1125:
1057:
833:
812:), the hosted solutions include interconnecting media gateways.
801:
773:
centers that are hosted by the operators or even manufacturers.
770:
746:
413:
398:
379:
1738:
1880:
486:
An Avaya G3si PBX with front cover removed (view from the top)
423:
353:
236:
Key systems can be built using three principal architectures:
18:
836:. Using small PBXs for ISDN is a logical step since the ISDN
887:
In addition to these basic functions, PBXs offer many other
787:
IP Centrex or hosted/virtual IP (hosted and packet-switched)
1128:– for connecting PBXs to each other, usually runs over T1 (
1692:"Why Hosted PBX is the Better Choice For Small Businesses"
1099:, this usually runs over E1 (E-carrier) physical circuits.
510:
Each device connected to the PBX, such as a telephone, a
1202:(listen mode) – an external application connects to the
821:
commercial-grade PBXs, but still provide many features.
16:
Telephone system typically used in business environments
1140:
Interfaces for connecting PBXs to trunk lines include:
1053:
Interfaces for connecting extensions to a PBX include:
494:
An
Alcatel Lucent PABX Omni PCX Enterprise (front view)
1095:– for connecting PBXs to trunk lines. Standardized by
1088:
Interfaces for connecting PBXs to each other include:
737:) technologies, PBX development has tended toward the
274:
The systems marketed in North
America as the 1A, 1A1,
1210:
port. The PBX streams information to the application.
1113:(SIP) are IP-based solutions for multimedia sessions.
583:
electronic private automatic branch exchanges (EPABX)
2716:
2653:
2575:
2539:
2496:
2437:
2371:
2080:
1772:
1586:"BT Prepare to Switch to an All IP Network by 2025"
1564:"Big Changes Coming for SMBs in 2014 (Infographic)"
189:
A 1930s key telephone for a private branch exchange
49:. Unsourced material may be challenged and removed.
721:(UPS) consisting of sensors, power switches, and
603:The other trend involved the idea of focusing on
699:for arbitrary data processing, control and logic
880:those connections as per the user's requirement
745:to carry calls. Most modern PBXs support VoIP.
705:Stations, or telephone sets, sometimes called
1750:
1466:Engineering and Operations in the Bell System
1428:, Bell Laboratories Record, March 1966, pp.85
1191:Interfaces for collecting data from the PBX:
680:Cabinets, closets, vaults, and other housings
534:, provided similar features from the central
218:are housed in a panel or cabinet, called the
8:
1060:– a standard for connecting cordless phones.
824:The first consumer PBX systems used analog (
514:, or a computer modem, is referred to as an
2765:Global telecommunications regulation bodies
676:A PBX system often includes the following:
247:Electromechanical shared-control key system
2801:
1757:
1743:
1735:
1617:"The Big Guide To VOIP For Small Business"
1426:Key Telephone Systems: The Latest Chapter
863:Functionally, the PBX performs four main
470:Learn how and when to remove this message
109:Learn how and when to remove this message
1001:which point the call may be routed to a
733:Since the advent of Internet telephony (
575:private automatic branch exchange (PABX)
1417:
625:
338:Remote supervision of the entire system
1670:"Features of a Business Phone System"
579:private manual branch exchange (PMBX)
125:Early-1970s Telephone Exchange model
7:
2811:
790:IP PBX (private and packet-switched)
715:The PBX's internal switching network
452:adding citations to reliable sources
389:Nortel T Series Key System Telephone
47:adding citations to reliable sources
1441:Fiber Optics Illustrated Dictionary
1257:The first hosted PBX services were
393:The modern key system now supports
796:PBX (private and circuit-switched)
613:competitive local exchange carrier
14:
505:public switched telephone network
2810:
2800:
2791:
2790:
2779:
2400:Free-space optical communication
1668:Wright, Ian (13 December 2013).
1504:Marcus, Michael N. (June 1995).
1346:
978:Customized abbreviated dialing (
686:Interconnecting wires and cables
659:
647:
628:
428:
305:Electronic shared-control system
23:
1231:Station Messaging Detail Record
439:needs additional citations for
261:large-scale integrated circuits
34:needs additional citations for
2842:Computer telephony integration
1334:computer telephony integration
1:
1328:handles voice calls over the
816:Home and small-business usage
636:
569:The term PBX originated when
341:Selection of signaling sounds
2837:Telephone exchange equipment
2786:Telecommunication portal
2567:Telecommunications equipment
1506:"KSU-less Key System Update"
1332:(IP), bringing benefits for
719:Uninterruptible power supply
360:for line status indication.
2303:Alexander Stepanovich Popov
1645:. About.com. Archived from
1444:. CRC Press. p. 1151.
1181:plain old telephone service
1111:Session Initiation Protocol
1079:plain old telephone service
503:provide connections to the
373:Hybrid key telephone system
58:"Business telephone system"
2863:
2007:Telecommunications history
1590:Yoozoom Telecommunications
1483:. Que. pp. 165, 169.
1041:Voice message broadcasting
1009:Interactive voice response
910:Automatic call distributor
299:Automatic Electric Company
259:Before the development of
2774:
2615:Public Switched Telephone
2427:telecommunication circuit
2388:Fiber-optic communication
2133:Francis Blake (telephone)
1928:Optical telecommunication
1696:Unity Connected Solutions
1493:– via Google Books.
1454:– via Google Books.
769:, PBXs have evolved into
330:Automatic call accounting
147:business telephone system
2526:Orbital angular-momentum
1963:Satellite communications
1802:Communications satellite
1643:"The Functions of a PBX"
1566:. eFax. 17 December 2013
358:incandescent light bulbs
285:300/400-series telephone
283:1A systems was the WECo
2405:Molecular communication
2228:Gardiner Greene Hubbard
2057:Undersea telegraph line
1792:Cable protection system
1438:Petersen, J.K. (2018).
1161:Inter-Asterisk eXchange
420:Private branch exchange
163:private branch exchange
2547:Communication protocol
2333:Charles Sumner Tainter
2148:Walter Houser Brattain
2093:Edwin Howard Armstrong
1901:Information revolution
1407:Telephone switchboards
1117:Primary rate interface
635:Cord PBX switchboard (
561:
495:
487:
390:
256:
190:
142:
130:
2521:Polarization-division
2253:Narinder Singh Kapany
2218:Erna Schneider Hoover
2138:Jagadish Chandra Bose
2118:Alexander Graham Bell
1849:online video platform
986:Direct inward dialing
571:switchboard operators
559:
541:A PBX differs from a
493:
485:
388:
382:lines and stations.
254:
188:
136:
124:
2363:Vladimir K. Zworykin
2323:Almon Brown Strowger
2293:Charles Grafton Page
1948:Prepaid mobile phone
1876:Electrical telegraph
1596:on 13 September 2015
1551:Notes on the Network
1397:Switchboard operator
1382:List of SIP software
1372:Cloud communications
1295:Cloud Communications
1289:Hosted PBX providers
1174:robbed bit signaling
1136:) physical circuits.
838:basic rate interface
543:key telephone system
448:improve this article
181:Key telephone system
155:key telephone system
43:improve this article
2847:Telephony equipment
2313:Johann Philipp Reis
2072:Wireless revolution
2034:The Telephone Cases
1891:Hydraulic telegraph
1649:on 27 February 2014
1242:Virtual PBX systems
1049:Interface standards
915:Automatic ring back
765:or just simply the
309:With the advent of
269:telephone switching
2511:Frequency-division
2488:Telephone exchange
2358:Charles Wheatstone
2288:Jun-ichi Nishizawa
2263:Innocenzo Manzetti
2198:Reginald Fessenden
1933:Optical telegraphy
1766:Telecommunications
1698:. Unity Connected.
1516:(6). UBM LLC: 117
1477:Main, Max (2003).
1402:Telephone exchange
1387:Reference computer
1377:Ground start trunk
1251:telephone exchange
1246:hosted PBX systems
1237:Hosted PBX systems
1226:call detail record
932:on busy or absence
763:telephone operator
751:conference calling
562:
536:telephone exchange
500:telephone exchange
496:
488:
391:
257:
191:
143:
131:
2824:
2823:
2562:Store and forward
2557:Data transmission
2471:Network switching
2422:Transmission line
2268:Guglielmo Marconi
2233:Internet pioneers
2098:Mohamed M. Atalla
2067:Whistled language
1520:– via Gale.
1354:Telephones portal
1330:Internet Protocol
1145:Internet Protocol
1103:Internet Protocol
1064:Internet Protocol
759:attendant console
743:Internet Protocol
741:, which uses the
672:System components
480:
479:
472:
325:Answering machine
267:, as were larger
238:electromechanical
141:key telephone set
137:Early model 464G
129:Automatic system
119:
118:
111:
93:
2854:
2814:
2813:
2804:
2803:
2794:
2793:
2784:
2783:
2782:
2655:Notable networks
2645:Wireless network
2585:Cellular network
2577:Types of network
2552:Computer network
2439:Network topology
2353:Thomas A. Watson
2208:Oliver Heaviside
2193:Philo Farnsworth
2168:Daniel Davis Jr.
2143:Charles Bourseul
2103:John Logie Baird
1812:Data compression
1807:Computer network
1759:
1752:
1745:
1736:
1725:
1724:
1722:
1721:
1706:
1700:
1699:
1688:
1682:
1681:
1679:
1677:
1665:
1659:
1658:
1656:
1654:
1638:
1632:
1631:
1629:
1627:
1615:Sullivan, Mark.
1612:
1606:
1605:
1603:
1601:
1592:. Archived from
1582:
1576:
1575:
1573:
1571:
1560:
1554:
1547:
1541:
1540:
1528:
1522:
1521:
1501:
1495:
1494:
1474:
1468:
1464:AT&T (1984)
1462:
1456:
1455:
1435:
1429:
1422:
1356:
1351:
1350:
1349:
975:Custom greetings
889:calling features
778:circuit switched
663:
651:
641:
638:
632:
590:packet switching
475:
468:
464:
461:
455:
432:
424:
280:Western Electric
220:key service unit
139:Western Electric
114:
107:
103:
100:
94:
92:
51:
27:
19:
2862:
2861:
2857:
2856:
2855:
2853:
2852:
2851:
2827:
2826:
2825:
2820:
2780:
2778:
2770:
2712:
2649:
2571:
2535:
2492:
2441:
2433:
2374:
2367:
2273:Robert Metcalfe
2128:Tim Berners-Lee
2076:
1896:Information Age
1768:
1763:
1733:
1728:
1719:
1717:
1708:
1707:
1703:
1690:
1689:
1685:
1675:
1673:
1672:. Expert Market
1667:
1666:
1662:
1652:
1650:
1641:Unuth, Nadeem.
1640:
1639:
1635:
1625:
1623:
1614:
1613:
1609:
1599:
1597:
1584:
1583:
1579:
1569:
1567:
1562:
1561:
1557:
1548:
1544:
1530:
1529:
1525:
1503:
1502:
1498:
1491:
1476:
1475:
1471:
1463:
1459:
1452:
1437:
1436:
1432:
1423:
1419:
1415:
1352:
1347:
1345:
1342:
1322:
1303:
1291:
1239:
1179:standard POTS (
1097:British Telecom
1066:– For example,
1051:
1044:Welcome message
971:Conference call
930:Call forwarding
865:call processing
861:
818:
731:
693:Microcontroller
674:
667:
664:
655:
652:
643:
639:
633:
621:
605:core competence
567:
476:
465:
459:
456:
445:
433:
422:
375:
315:AT&T Merlin
307:
249:
224:key system unit
183:
115:
104:
98:
95:
52:
50:
40:
28:
17:
12:
11:
5:
2860:
2858:
2850:
2849:
2844:
2839:
2829:
2828:
2822:
2821:
2819:
2818:
2808:
2798:
2788:
2775:
2772:
2771:
2769:
2768:
2761:
2756:
2751:
2746:
2741:
2740:
2739:
2734:
2726:
2720:
2718:
2714:
2713:
2711:
2710:
2705:
2700:
2695:
2690:
2685:
2680:
2675:
2670:
2665:
2659:
2657:
2651:
2650:
2648:
2647:
2642:
2637:
2632:
2627:
2622:
2617:
2612:
2607:
2602:
2597:
2592:
2587:
2581:
2579:
2573:
2572:
2570:
2569:
2564:
2559:
2554:
2549:
2543:
2541:
2537:
2536:
2534:
2533:
2528:
2523:
2518:
2513:
2508:
2506:Space-division
2502:
2500:
2494:
2493:
2491:
2490:
2485:
2484:
2483:
2478:
2468:
2467:
2466:
2456:
2451:
2445:
2443:
2435:
2434:
2432:
2431:
2430:
2429:
2419:
2418:
2417:
2407:
2402:
2397:
2396:
2395:
2385:
2379:
2377:
2369:
2368:
2366:
2365:
2360:
2355:
2350:
2345:
2343:Camille Tissot
2340:
2335:
2330:
2325:
2320:
2318:Claude Shannon
2315:
2310:
2308:Tivadar Puskás
2305:
2300:
2295:
2290:
2285:
2280:
2278:Antonio Meucci
2275:
2270:
2265:
2260:
2255:
2250:
2248:Charles K. Kao
2245:
2240:
2235:
2230:
2225:
2223:Harold Hopkins
2220:
2215:
2210:
2205:
2200:
2195:
2190:
2185:
2180:
2175:
2170:
2165:
2160:
2155:
2150:
2145:
2140:
2135:
2130:
2125:
2123:Emile Berliner
2120:
2115:
2110:
2105:
2100:
2095:
2090:
2084:
2082:
2078:
2077:
2075:
2074:
2069:
2064:
2062:Videotelephony
2059:
2054:
2053:
2052:
2047:
2037:
2030:
2025:
2019:
2014:
2009:
2004:
1999:
1998:
1997:
1992:
1987:
1977:
1976:
1975:
1965:
1960:
1958:Radiotelephone
1955:
1950:
1945:
1940:
1935:
1930:
1925:
1924:
1923:
1913:
1908:
1903:
1898:
1893:
1888:
1883:
1878:
1873:
1868:
1863:
1862:
1861:
1856:
1851:
1846:
1844:Internet video
1836:
1835:
1834:
1829:
1824:
1819:
1809:
1804:
1799:
1794:
1789:
1784:
1778:
1776:
1770:
1769:
1764:
1762:
1761:
1754:
1747:
1739:
1732:
1731:External links
1729:
1727:
1726:
1701:
1683:
1660:
1633:
1607:
1577:
1555:
1542:
1523:
1496:
1489:
1469:
1457:
1450:
1430:
1416:
1414:
1411:
1410:
1409:
1404:
1399:
1394:
1389:
1384:
1379:
1374:
1369:
1364:
1358:
1357:
1341:
1338:
1321:
1318:
1302:
1299:
1290:
1287:
1286:
1285:
1281:
1278:
1275:
1274:sequentially).
1271:
1238:
1235:
1221:
1220:
1214:
1211:
1196:
1189:
1188:
1177:
1170:
1164:
1138:
1137:
1123:
1120:
1114:
1100:
1086:
1085:
1082:
1075:
1061:
1050:
1047:
1046:
1045:
1042:
1039:
1034:
1031:
1028:Public address
1025:
1020:
1015:
1011:
1006:
998:
995:Do not disturb
992:
989:
983:
976:
973:
968:
963:
958:
953:
948:
943:
938:
933:
927:
922:
917:
912:
907:
904:
899:
897:Auto attendant
885:
884:
881:
875:
872:
860:
857:
817:
814:
798:
797:
794:
791:
788:
785:
761:operated by a
730:
729:Current trends
727:
726:
725:
716:
713:
703:
700:
690:
687:
684:
681:
673:
670:
669:
668:
665:
658:
656:
653:
646:
644:
634:
627:
620:
617:
566:
563:
520:numbering plan
478:
477:
460:September 2017
436:
434:
427:
421:
418:
374:
371:
349:
348:
345:
342:
339:
336:
331:
328:
306:
303:
276:1A2 Key System
248:
245:
233:in the 1930s.
182:
179:
117:
116:
31:
29:
22:
15:
13:
10:
9:
6:
4:
3:
2:
2859:
2848:
2845:
2843:
2840:
2838:
2835:
2834:
2832:
2817:
2809:
2807:
2799:
2797:
2789:
2787:
2777:
2776:
2773:
2766:
2762:
2760:
2757:
2755:
2752:
2750:
2747:
2745:
2742:
2738:
2735:
2733:
2730:
2729:
2727:
2725:
2722:
2721:
2719:
2715:
2709:
2706:
2704:
2701:
2699:
2696:
2694:
2691:
2689:
2686:
2684:
2681:
2679:
2676:
2674:
2671:
2669:
2666:
2664:
2661:
2660:
2658:
2656:
2652:
2646:
2643:
2641:
2638:
2636:
2633:
2631:
2628:
2626:
2623:
2621:
2618:
2616:
2613:
2611:
2608:
2606:
2603:
2601:
2598:
2596:
2593:
2591:
2588:
2586:
2583:
2582:
2580:
2578:
2574:
2568:
2565:
2563:
2560:
2558:
2555:
2553:
2550:
2548:
2545:
2544:
2542:
2538:
2532:
2531:Code-division
2529:
2527:
2524:
2522:
2519:
2517:
2516:Time-division
2514:
2512:
2509:
2507:
2504:
2503:
2501:
2499:
2495:
2489:
2486:
2482:
2479:
2477:
2474:
2473:
2472:
2469:
2465:
2462:
2461:
2460:
2457:
2455:
2452:
2450:
2447:
2446:
2444:
2442:and switching
2440:
2436:
2428:
2425:
2424:
2423:
2420:
2416:
2413:
2412:
2411:
2408:
2406:
2403:
2401:
2398:
2394:
2393:optical fiber
2391:
2390:
2389:
2386:
2384:
2383:Coaxial cable
2381:
2380:
2378:
2376:
2370:
2364:
2361:
2359:
2356:
2354:
2351:
2349:
2346:
2344:
2341:
2339:
2336:
2334:
2331:
2329:
2326:
2324:
2321:
2319:
2316:
2314:
2311:
2309:
2306:
2304:
2301:
2299:
2298:Radia Perlman
2296:
2294:
2291:
2289:
2286:
2284:
2281:
2279:
2276:
2274:
2271:
2269:
2266:
2264:
2261:
2259:
2256:
2254:
2251:
2249:
2246:
2244:
2241:
2239:
2236:
2234:
2231:
2229:
2226:
2224:
2221:
2219:
2216:
2214:
2211:
2209:
2206:
2204:
2201:
2199:
2196:
2194:
2191:
2189:
2188:Lee de Forest
2186:
2184:
2183:Thomas Edison
2181:
2179:
2176:
2174:
2173:Donald Davies
2171:
2169:
2166:
2164:
2161:
2159:
2158:Claude Chappe
2156:
2154:
2151:
2149:
2146:
2144:
2141:
2139:
2136:
2134:
2131:
2129:
2126:
2124:
2121:
2119:
2116:
2114:
2111:
2109:
2106:
2104:
2101:
2099:
2096:
2094:
2091:
2089:
2086:
2085:
2083:
2079:
2073:
2070:
2068:
2065:
2063:
2060:
2058:
2055:
2051:
2048:
2046:
2043:
2042:
2041:
2038:
2036:
2035:
2031:
2029:
2026:
2023:
2020:
2018:
2015:
2013:
2010:
2008:
2005:
2003:
2002:Smoke signals
2000:
1996:
1993:
1991:
1988:
1986:
1983:
1982:
1981:
1980:Semiconductor
1978:
1974:
1971:
1970:
1969:
1966:
1964:
1961:
1959:
1956:
1954:
1951:
1949:
1946:
1944:
1941:
1939:
1936:
1934:
1931:
1929:
1926:
1922:
1919:
1918:
1917:
1914:
1912:
1909:
1907:
1904:
1902:
1899:
1897:
1894:
1892:
1889:
1887:
1884:
1882:
1879:
1877:
1874:
1872:
1869:
1867:
1864:
1860:
1857:
1855:
1852:
1850:
1847:
1845:
1842:
1841:
1840:
1839:Digital media
1837:
1833:
1830:
1828:
1825:
1823:
1820:
1818:
1815:
1814:
1813:
1810:
1808:
1805:
1803:
1800:
1798:
1795:
1793:
1790:
1788:
1785:
1783:
1780:
1779:
1777:
1775:
1771:
1767:
1760:
1755:
1753:
1748:
1746:
1741:
1740:
1737:
1730:
1715:
1711:
1705:
1702:
1697:
1693:
1687:
1684:
1671:
1664:
1661:
1648:
1644:
1637:
1634:
1622:
1618:
1611:
1608:
1595:
1591:
1587:
1581:
1578:
1565:
1559:
1556:
1552:
1546:
1543:
1538:
1534:
1533:Network World
1527:
1524:
1519:
1515:
1511:
1507:
1500:
1497:
1492:
1490:9780789729378
1486:
1482:
1481:
1473:
1470:
1467:
1461:
1458:
1453:
1451:9781351836166
1447:
1443:
1442:
1434:
1431:
1427:
1424:W.F.B. Wood,
1421:
1418:
1412:
1408:
1405:
1403:
1400:
1398:
1395:
1393:
1390:
1388:
1385:
1383:
1380:
1378:
1375:
1373:
1370:
1368:
1365:
1363:
1360:
1359:
1355:
1344:
1339:
1337:
1335:
1331:
1327:
1319:
1317:
1314:
1311:
1308:
1300:
1298:
1296:
1288:
1282:
1279:
1276:
1272:
1268:
1267:
1266:
1263:
1260:
1255:
1252:
1247:
1243:
1236:
1234:
1232:
1228:
1227:
1218:
1215:
1212:
1209:
1205:
1201:
1197:
1194:
1193:
1192:
1186:
1182:
1178:
1175:
1171:
1168:
1165:
1162:
1158:
1154:
1150:
1146:
1143:
1142:
1141:
1135:
1131:
1127:
1124:
1121:
1118:
1115:
1112:
1108:
1104:
1101:
1098:
1094:
1091:
1090:
1089:
1083:
1080:
1076:
1073:
1069:
1065:
1062:
1059:
1056:
1055:
1054:
1048:
1043:
1040:
1038:
1035:
1032:
1029:
1026:
1024:
1023:Night service
1021:
1019:
1018:Music on hold
1016:
1012:
1010:
1007:
1004:
999:
996:
993:
990:
987:
984:
981:
980:speed dialing
977:
974:
972:
969:
967:
964:
962:
959:
957:
954:
952:
951:Call transfer
949:
947:
944:
942:
939:
937:
934:
931:
928:
926:
925:Call blocking
923:
921:
920:Busy override
918:
916:
913:
911:
908:
905:
903:
900:
898:
895:
894:
893:
890:
882:
879:
878:Disconnecting
876:
873:
870:
869:
868:
866:
859:PBX functions
858:
856:
854:
850:
847:
843:
839:
835:
831:
827:
822:
815:
813:
811:
807:
803:
795:
792:
789:
786:
783:
782:
781:
779:
774:
772:
768:
764:
760:
756:
752:
748:
744:
740:
736:
735:Voice over IP
728:
724:
720:
717:
714:
712:
708:
704:
701:
698:
697:microcomputer
694:
691:
688:
685:
682:
679:
678:
677:
671:
662:
657:
650:
645:
631:
626:
624:
618:
616:
614:
610:
606:
601:
599:
595:
594:voice over IP
591:
586:
584:
580:
576:
572:
564:
558:
554:
551:
546:
544:
539:
537:
533:
529:
523:
521:
517:
513:
508:
506:
501:
492:
484:
474:
471:
463:
453:
449:
443:
442:
437:This section
435:
431:
426:
425:
419:
417:
415:
410:
406:
405:designation.
404:
400:
396:
387:
383:
381:
372:
370:
368:
367:
361:
359:
355:
346:
344:Speed dialing
343:
340:
337:
335:
332:
329:
326:
323:
322:
321:
318:
316:
312:
304:
302:
300:
296:
294:
288:
286:
281:
277:
272:
270:
266:
262:
253:
246:
244:
241:
239:
234:
232:
227:
225:
221:
217:
213:
209:
206:
202:
198:
196:
187:
180:
178:
174:
170:
168:
164:
160:
156:
152:
148:
140:
135:
128:
123:
113:
110:
102:
91:
88:
84:
81:
77:
74:
70:
67:
63:
60: –
59:
55:
54:Find sources:
48:
44:
38:
37:
32:This article
30:
26:
21:
20:
2498:Multiplexing
2373:Transmission
2338:Nikola Tesla
2328:Henry Sutton
2283:Samuel Morse
2213:Robert Hooke
2178:Amos Dolbear
2113:John Bardeen
2032:
2012:Telautograph
1916:Mobile phone
1871:Edholm's law
1854:social media
1787:Broadcasting
1718:. Retrieved
1716:. 2016-03-01
1714:Blog - 1stel
1713:
1704:
1695:
1686:
1674:. Retrieved
1663:
1651:. Retrieved
1647:the original
1636:
1624:. Retrieved
1620:
1610:
1598:. Retrieved
1594:the original
1589:
1580:
1568:. Retrieved
1558:
1550:
1545:
1536:
1532:
1526:
1517:
1513:
1509:
1499:
1479:
1472:
1465:
1460:
1440:
1433:
1425:
1420:
1323:
1315:
1312:
1306:
1304:
1292:
1264:
1259:feature-rich
1256:
1245:
1241:
1240:
1224:
1222:
1190:
1139:
1087:
1052:
1030:voice paging
961:Call whisper
956:Call waiting
946:Call pick-up
936:Call logging
902:Auto dialing
886:
862:
851:
823:
819:
799:
775:
766:
732:
706:
675:
622:
602:
587:
582:
578:
574:
568:
547:
540:
524:
509:
497:
466:
457:
446:Please help
441:verification
438:
411:
407:
402:
392:
376:
364:
362:
350:
319:
308:
297:
289:
273:
258:
242:
235:
228:
223:
219:
200:
199:
195:wiring plans
194:
192:
175:
171:
166:
162:
158:
154:
146:
144:
105:
96:
86:
79:
72:
65:
53:
41:Please help
36:verification
33:
2698:NPL network
2410:Radio waves
2348:Alfred Vail
2258:Hedy Lamarr
2243:Dawon Kahng
2203:Elisha Gray
2163:Yogen Dalal
2088:Nasir Ahmed
2022:Teleprinter
1886:Heliographs
1653:23 February
1570:23 February
1510:Teleconnect
1229:(CDR) or a
853:Open source
755:switchboard
640: 1975
528:hunt groups
512:fax machine
498:A PBX is a
356:instead of
231:Bell System
208:term of art
205:Bell System
2831:Categories
2744:Antarctica
2703:Toasternet
2625:Television
2108:Paul Baran
2040:Television
2024:(teletype)
2017:Telegraphy
1995:transistor
1973:Phryctoria
1943:Photophone
1921:Smartphone
1911:Mass media
1720:2016-05-02
1621:Forbes.com
1553:(1980) p.3
1549:AT&T,
1413:References
1367:Circuit ID
1307:mobile PBX
1301:Mobile PBX
1037:Voice mail
1003:voice mail
619:Manual PBX
69:newspapers
2728:Americas
2717:Locations
2688:Internet2
2449:Bandwidth
2153:Vint Cerf
2050:streaming
2028:Telephone
1968:Semaphore
1859:streaming
1600:8 October
1284:company).
1134:E-carrier
1132:) or E1 (
1130:T-carrier
941:Call park
842:VoIP PBXs
830:cigar box
723:batteries
550:dial plan
516:extension
334:Caller ID
327:functions
271:systems.
161:) to the
151:telephone
99:June 2013
2796:Category
2683:Internet
2673:CYCLADES
2590:Ethernet
2540:Concepts
2464:terminal
2415:wireless
2238:Bob Kahn
2081:Pioneers
1906:Internet
1797:Cable TV
1676:23 April
1626:23 April
1340:See also
1233:(SMDR).
1198:Network
1109:and the
1005:system).
867:duties:
767:operator
711:metonymy
596:PBX, or
526:such as
366:KSU-less
216:intercom
2816:Commons
2806:Outline
2759:Oceania
2678:FidoNet
2663:ARPANET
2476:circuit
2045:digital
1774:History
1362:Centrex
966:Camp-on
846:routers
609:Centrex
565:History
532:Centrex
311:LSI ICs
226:(KSU).
83:scholar
2754:Europe
2724:Africa
2708:Usenet
2668:BITNET
2605:Mobile
2481:packet
1990:MOSFET
1985:device
1782:Beacon
1518:et seq
1487:
1448:
1326:IP PBX
1320:IP-PBX
1217:Serial
1159:, and
1077:POTS (
1014:world.
739:IP PBX
598:IP PBX
403:hybrid
293:RAPCON
265:relays
203:was a
85:
78:
71:
64:
56:
2737:South
2732:North
2693:JANET
2630:Telex
2620:Radio
2459:Nodes
2454:Links
2375:media
1953:Radio
1938:Pager
1866:Drums
1832:video
1827:image
1817:audio
1539:(15).
1270:user.
1185:glare
1172:RBS (
1149:H.323
1107:H.323
1093:DPNSS
1068:H.323
997:(DND)
988:(DID)
707:lines
149:is a
127:TESLA
90:JSTOR
76:books
2749:Asia
2635:UUCP
2595:ISDN
1678:2014
1655:2014
1628:2014
1602:2015
1572:2014
1485:ISBN
1480:HTI+
1446:ISBN
1392:RJ21
1200:port
1167:ISDN
1157:MGCP
1126:QSIG
1070:and
1058:DECT
834:ISDN
826:POTS
810:ISUP
802:PSTN
771:VoIP
747:ISDN
577:and
414:VOIP
399:ISDN
380:PSTN
354:LEDs
214:and
212:hold
62:news
2640:WAN
2610:NGN
2600:LAN
1881:Fax
1822:DCT
1324:An
1244:or
1208:UDP
1206:or
1204:TCP
1153:SIP
1072:SIP
806:SS7
757:or
709:by
695:or
450:by
395:SIP
222:or
201:Key
169:).
167:PBX
159:KTS
45:by
2833::
1712:.
1694:.
1619:.
1588:.
1535:.
1514:13
1512:.
1508:.
1305:A
1187:).
1155:,
1151:,
1147:–
1105:–
637:c.
600:.
538:.
397:,
317:.
145:A
2767:)
2763:(
1758:e
1751:t
1744:v
1723:.
1680:.
1657:.
1630:.
1604:.
1574:.
1537:3
1074:.
982:)
808:/
804:(
642:)
473:)
467:(
462:)
458:(
444:.
291:(
165:(
157:(
112:)
106:(
101:)
97:(
87:·
80:·
73:·
66:·
39:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
