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level of contacts, by engaging a pawl with the upper ratchet. Another pawl, pivoting on the frame, holds the shaft at that height as it rotates. The second set of pulses, from the second key, operates another electromagnet. Its pawl engages the (hidden) vertical teeth in the lower ratchet to rotate the shaft to the required position. It is kept there against spring tension by a pawl pivoted on the frame. When the switch returns to its home position, typically when a call is complete, a release magnet disengages the pawls that hold the shaft in position. An interlock ensures that the spring on the shaft rotates it to angular home position before it drops to its home position by gravity.
245:, which Strowger was involved in founding, although Strowger himself seems not to have been involved in further developments. The Strowger patents were exclusively licensed to the Automatic Electric Company. Strowger sold his patents in 1896 for US$ 1,800 (equivalent to $ 57,000 in 2023) and sold his share in Automatic Electric in 1898 for $ 10,000 (equivalent to $ 310,000 in 2023). His patents subsequently sold for $ 2,500,000 (equivalent to $ 48,000,000 in 2023) in 1916. Company engineers continued development of the Strowger designs and submitted several patents in the names of its employees.
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290:. A contact arm is moved up to select one of ten rows of contacts, and then rotated clockwise to select one of ten contacts in that row, a total of 100 choices. The stepping motion is controlled by the current pulses coming from the originating customer's telegraph keys, and later from the rotary dial.
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The
Strowger switch uses two telegraph-type keys on a telephone set for dialing. Each key requires a separate wire to the exchange. The keys are tapped to step the switch in two stages. The first set of incoming pulses raises the armature of an electromagnet to move a shaft which selects the desired
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was founded in 1891. In the original design patent, four keys were added near the telephone, one each for thousands, hundreds, tens and units, with each key having an additional wire connection to the central exchange. Each key had to be tapped the correct number of times to step the switch and make
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manager Herman
Ritterhoff, Strowger swore to "get even" with the telephone operators and "put every last one of them out of a job." Ritterhoff claimed that the real cause of Strowger's difficulties was a metal sign hung on his wall over his telephone, causing an intermittent short circuit when blown
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as part of the line equipment individual to each line, which searches "forward" for a first selector. This is more economical for higher calling-rate domestic or business customers, and has the advantage that access to additional switches can readily be added if the traffic increases (the number of
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for signalling to the exchange. The original final selector (connector) switch which connected to 100 customers was supplemented by preceding group selector stages, as the "cascading" enabled connection to many more customers, and to customers at other exchanges. Another requirement for commercial
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The fundamental modularity of the system combined with its step-by-step (hence the alternative name) selection process and an almost unlimited potential for expansion gives the
Strowger system its technical advantage. Previous systems had all been designed for a fixed number of subscribers to be
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was adopted. The
Director systems used SXS switches for destination routing and number translation facilities similar to the register used in common-control exchanges. Using similar equipment as in the rest of the network was deemed beneficial and the equipment could be manufactured in Britain.
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switched directly to each other in a mesh arrangement. This became quadratically more complex as each new customer was added, as each new customer needed a switch to connect to every other customer. In modern terminology, the previous systems were not "
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While Almon
Strowger devised the initial concept, he was not alone in his endeavors and sought the assistance of his brother Arnold, nephew William, and others with a knowledge of electricity and financing to realize the concept. The
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419:), Fleetwood (relay exchange from Sweden), Grimsby (Siemens), Hereford (Lorimer) and Leeds (Strowger). The GPO selected the Strowger switches for small and medium-sized cities and towns. The selection of switching systems for
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on
November 3, 1892. The exchange had around 75 subscribers. The installation followed the original patented design, with four keys and four additional line wires connected to the exchange, but not all of the keys were used.
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linefinders serving a group is limited by the wiring multiple installed). Hence exchanges with subscriber uniselectors were usually used at
British exchanges with a high proportion of business customers, e.g.
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Western
Electric 7A Rotary, friction drive (Bird-cage), No. 7001 Line Finder. Note the driven bevel gear on the right-hand side; this type has a steady rotary motion and does not employ an electromagnet for
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Instead of dedicating an expensive first-stage selector switch to each customer as in the first exchange, the customer was given access to the first-stage switch of a telephone network, often by a
415:, which also operated the British telephone system, installed several automatic telephone exchanges from several vendors in trials at Darlington on 10 October 1914 and Dudley on 9 September 1916 (
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which searches "backward" for the calling line; so requiring only a few relays (in most cases two, a Line, and a Cut-off relay), for the equipment required for each customer line.
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the desired connection. To connect to number 1256, the user would press the first key once, the second key twice, the third key five times and the final key six times.
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199:, was motivated to invent an automatic telephone exchange after having difficulties with his telephone service. He became convinced that the
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exchanges, or in New
Zealand where the provision of local free calling meant that residential customers had a relatively high calling rate.
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corresponding to the digits 1–9, and 0 (which sends 10 pulses). This equipment originally consisted of two telegraph keys engaged by
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Strowger's patent specifies dialing equipment at the customer location and the switching equipment at the central office.
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The commercial version of the
Strowger switch, as developed by the Strowger Automatic Telephone Exchange Company, used a
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Early advertising called the new invention the "girl-less, cuss-less, out-of-order-less, wait-less telephone".
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operators were deliberately interfering with his calls, leading to loss of business. According to the local
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In 1896 the company patented the finger-wheel dial as an improvement to the existing four-key design.
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The Strowger switch has three banks of contacts. Toward the upper end of each shaft are two
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The company installed and opened the first commercial exchange in his then-home town of
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in 1891. The initial model was made from a round collar box and some straight pins.
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The Strowger system was widely used until the development of the more reliable
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Strowger conceived his invention in 1888, and was awarded a patent for an
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AT&T Archives: 1951 Training Video Regarding the Step-by-Step Switch
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systems was a circuit to detect a busy connection (line) and return a
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The telegraph keys or telephone dial creates trains of on-off current
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Hill, R. B. (March 1953). "The Early Years of the Strowger System".
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and other large cities was not decided until the 1920s, when the
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The Strowger Automatic Telephone Exchange Company became the
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Telephone Systems Training Course: Central Office Equipment
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The sound of a step-by-step call reaching a busy circuit.
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19:"SXS" redirects here. For the flash memory standard, see
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The central office switching equipment has a two-motion
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Later Strowger (SXS) exchanges often use a subscriber
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64:. Unsourced material may be challenged and removed.
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264:British Strowger exchange, BPO 2000-type equipment
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592:By Donovan A. Shilling, Pancoast Publishing, 2011
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27:. For the Side by Side all terrain vehicle, see
622:Johnston, Louis; Williamson, Samuel H. (2023).
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472:"The Automatic Phone Sprang From a Collar Box"
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221:Strowger Automatic Telephone Exchange Company
169:Strowger Automatic Telephone Exchange Company
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1931:Global telecommunications regulation bodies
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700:Events in Telecommunications History – 1927
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747:Prof Mark Csele, Niagara College, Ontario
124:Learn how and when to remove this message
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549:Price, David A. (Fourth Quarter 2019).
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753:1954, Western Electric Hawthorne Works
569:"Telecommunications through the years"
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660:"Creatures of Thought – Only Connect"
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157:is the first commercially successful
23:. For the Microsoft Windows SxS, see
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62:adding citations to reliable sources
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573:Telephone Engineer & Management
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16:Electromechanical telephone switch
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1566:Free-space optical communication
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726:, McGraw, 1905, pp. 692ff.
662:. technicshistory. April 9, 2017
397:Problems playing this file? See
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167:system. It was developed by the
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652:
643:Gross Domestic Product deflator
49:needs additional citations for
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1:
864:Stromberg-Carlson/Siemens DCO
624:"What Was the U.S. GDP Then?"
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318:Télégraphie, Systeme Strowger
2003:Telephone exchange equipment
1952:Telecommunication portal
1733:Telecommunications equipment
874:Automatic Electric GTD-5 EAX
831:Electronic switching systems
722:Kempster, Blanchard Miller,
530:. 5 November 1892. p. 3
524:"How It Connects Telephones"
504:. 31 October 1891. p. 8
502:The Memphis Appeal-Avalanche
498:"The Telephone Girl Must Go"
213:automatic telephone exchange
7:
1469:Alexander Stepanovich Popov
839:Western Electric 1ESS/1AESS
724:American Telephone Practice
590:Rochester's Remarkable Past
452:. 19 March 1913. p. 11
446:"Originator Sought Revenge"
331:to the calling subscriber.
149:Bank of two-motion switches
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478:. 27 May 1928. p. 71
425:Director telephone system
201:manual telephone exchange
1692:Orbital angular-momentum
1129:Satellite communications
968:Communications satellite
859:Northern Telecom DMS-100
604:Bell Laboratories Record
1571:Molecular communication
1394:Gardiner Greene Hubbard
1223:Undersea telegraph line
958:Cable protection system
411:From 1912, the British
279:, and evolved into the
1713:Communication protocol
1499:Charles Sumner Tainter
1314:Walter Houser Brattain
1259:Edwin Howard Armstrong
1067:Information revolution
796:Early automatic &
375:Strowger switch in use
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1419:Narinder Singh Kapany
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1304:Jagadish Chandra Bose
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892:Telephones portal
854:Northern Electric SP1
849:Western Electric 5ESS
844:Western Electric 4ESS
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25:Side-by-side assembly
1529:Vladimir K. Zworykin
1489:Almon Brown Strowger
1459:Charles Grafton Page
1114:Prepaid mobile phone
1042:Electrical telegraph
821:Western Electric 5XB
816:Western Electric 1XB
528:Akron Daily Democrat
476:The Kansas City Star
294:Two-motion mechanism
173:Almon Brown Strowger
58:improve this article
1479:Johann Philipp Reis
1238:Wireless revolution
1200:The Telephone Cases
1057:Hydraulic telegraph
645:figures follow the
551:"Goodbye, Operator"
413:General Post Office
171:founded in 1891 by
1677:Frequency-division
1654:Telephone exchange
1524:Charles Wheatstone
1454:Jun-ichi Nishizawa
1429:Innocenzo Manzetti
1364:Reginald Fessenden
1099:Optical telegraphy
932:Telecommunications
790:telephone switches
745:Telephone Switches
705:2016-06-22 at the
450:Sioux City Journal
407:British deployment
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1434:Guglielmo Marconi
1399:Internet pioneers
1264:Mohamed M. Atalla
1233:Whistled language
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579:: 244. June 1984.
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1605:Network topology
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1168:Smoke signals
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114:February 2008
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75: –
74:
70:
69:Find sources:
63:
59:
53:
52:
47:This article
45:
41:
36:
35:
30:
26:
22:
1664:Multiplexing
1539:Transmission
1504:Nikola Tesla
1494:Henry Sutton
1449:Samuel Morse
1379:Robert Hooke
1344:Amos Dolbear
1279:John Bardeen
1198:
1178:Telautograph
1082:Mobile phone
1037:Edholm's law
1020:social media
953:Broadcasting
869:Siemens EWSD
811:Panel Switch
805:
723:
695:
676:
664:. Retrieved
654:
646:
635:November 30,
633:. Retrieved
627:
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585:
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532:. Retrieved
527:
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506:. Retrieved
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480:. Retrieved
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454:. Retrieved
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180:
177:step-by-step
176:
154:
152:
120:
111:
101:
94:
87:
80:
68:
56:Please help
51:verification
48:
1864:NPL network
1576:Radio waves
1514:Alfred Vail
1424:Hedy Lamarr
1409:Dawon Kahng
1369:Elisha Gray
1329:Yogen Dalal
1254:Nasir Ahmed
1188:Teleprinter
1052:Heliographs
709:BT Archives
343:uniselector
336:line-finder
329:busy signal
324:rotary dial
310:Development
283:telephone.
281:rotary dial
1910:Antarctica
1869:Toasternet
1791:Television
1274:Paul Baran
1206:Television
1190:(teletype)
1183:Telegraphy
1161:transistor
1139:Phryctoria
1109:Photophone
1087:Smartphone
1077:Mass media
666:August 11,
555:Econ Focus
534:20 October
508:20 October
482:20 October
456:20 October
432:References
399:media help
197:undertaker
84:newspapers
1894:Americas
1883:Locations
1854:Internet2
1615:Bandwidth
1319:Vint Cerf
1216:streaming
1194:Telephone
1134:Semaphore
1025:streaming
728:full text
682:US 447918
606:: 95–103.
141:stepping.
1997:Category
1962:Category
1849:Internet
1839:CYCLADES
1756:Ethernet
1706:Concepts
1630:terminal
1581:wireless
1404:Bob Kahn
1247:Pioneers
1072:Internet
963:Cable TV
703:Archived
649:series.
557:: 18–20.
356:scalable
348:director
300:ratchets
1982:Commons
1972:Outline
1925:Oceania
1844:FidoNet
1829:ARPANET
1642:circuit
1211:digital
940:History
191:History
98:scholar
1920:Europe
1890:Africa
1874:Usenet
1834:BITNET
1771:Mobile
1647:packet
1156:MOSFET
1151:device
948:Beacon
688:
421:London
273:pulses
185:switch
100:
93:
86:
79:
71:
1903:South
1898:North
1859:JANET
1796:Telex
1786:Radio
1625:Nodes
1620:Links
1541:media
1119:Radio
1104:Pager
1032:Drums
998:video
993:image
983:audio
105:JSTOR
91:books
1915:Asia
1801:UUCP
1761:ISDN
788:NANP
668:2022
637:2023
536:2022
510:2022
484:2022
458:2022
153:The
77:news
1806:WAN
1776:NGN
1766:LAN
1047:Fax
988:DCT
358:".
181:SXS
60:by
21:SxS
1999::
626:.
612:^
577:88
575:.
571:.
553:.
526:.
500:.
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448:.
187:.
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1929:(
924:e
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179:(
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121:(
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112:(
102:·
95:·
88:·
81:·
54:.
31:.
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