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Information about Strowger Switch

The Strowger switch, also known as Step-by-Step or SxS, is an early electromechanical telephone switching system invented by Almon Brown Strowger. It is a specialized version of a stepping switch.

History

According to legend, Almon Strowger was motivated to invent an automatic telephone exchange after having difficulties with the local telephone operators. He was said to be convinced that the local manual telephone exchange operators were sending calls to a competing undertaker business.

He first conceived his invention in 1888, and patented the automatic telephone exchange in 1891. It is reported that he initially constructed a model of his invention from a round collar box and some straight pins.

Details of the patent

US patent 447918 consists of:
  1. A device for use by the customer - this creates trains of on-off current pulses corresponding to the digits 0-9. This equipment originally consisted of two telegraph keys engaged by knife switches, and evolved into the rotary dial telephone.
  2. A two motion stepping switch at telephone exchange. A contact arm could be moved up and down in order to select one of ten rows of contacts, and then rotated to select one of one hundred contacts in that row. The stepping motion was controlled by the current pulses coming from the originating customer's telegraph keys, and later from the rotary dial.


This system was never put into service as described; the first commercial system was covered by US patent 540168.

Further development

Later systems cascaded Strowger-style switches, enabling connection among more customers. They also added a line finder selector, to connect a subscriber to any available switch rather than dedicating a single switch to each customer, reducing the number of switches needed. Another enhancement was the inclusion of circuits to detect busy connections and send the subscriber's call to a busy signal.

It is 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 that gives the Strowger system its technical advantage: previous systems had all been designed for a fixed number of subscribers to be switched directly to each other in a mesh arrangement. This became geometrically 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 simply not scalable.

Audio sample:
The sound of a step-by-step call reaching a busy circuit.
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While Almon Strowger may have come up with the idea, he was not alone in his endeavours and sought the assistance of his brother Arnold, nephew William and others with a knowledge of electricity and money to realise his concepts. With this help the Strowger Automatic Telephone Exchange Company was formed and it installed and opened the first commercial exchange in (his then home town of) La Porte, Indiana on November 3, 1892, with about 75 subscribers and capacity for 99. He married Susan A. (1846-1921) from Massachusetts in 1897 as his second wife. Strowger sold his patents in 1896 for $1,800 and sold his share in the Automatic Electric Company for $10,000 in 1898. His patents subsequently sold for $2.5 million in 1916.

The company's engineers continued development of Strowger's designs and submitted several patents in the names of its employees. It also underwent several name changes. Strowger himself seems to have not taken part in this further development. He subsequently moved to St. Petersburg, Florida and appears to have returned to being an undertaker, as H.P. Bussey Funeral Home records report an unidentified body being moved "for Mr. Strowger" in December 1899. The same funeral home subsequently buried Strowger himself. Strowger was a man of some wealth at his death and was reported as owning at least a city block of property.

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NANP Telephone Switches
Almon Brown Strowger (1839 – May 26, 1902) gave his name to the electromechanical telephone exchange technology that his invention and patent inspired.

Early years

He was born in Penfield, near Rochester, New York.
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In electrical controls, a stepping switch (also called a uniselector), is an electromechanical device which allows an input connection to be connected to one of a number of possible output connections, under the control of a series of electrical pulses.
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Almon Brown Strowger (1839 – May 26, 1902) gave his name to the electromechanical telephone exchange technology that his invention and patent inspired.

Early years

He was born in Penfield, near Rochester, New York.
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"Undertaker" and "Mortician" redirect here.

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In signal processing, the term pulse has the following meanings:
  1. A rapid, transient change in the amplitude of a signal from a baseline value to a higher or lower value, followed by a rapid return to the baseline value.

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rotary dial is a device mounted on or in a telephone or switchboard that is designed to send interrupted electrical pulses, known as pulse dialing, corresponding to the number dialed. The early form of the rotary dial used lugs on a finger plate instead of holes.
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In electrical controls, a stepping switch (also called a uniselector), is an electromechanical device which allows an input connection to be connected to one of a number of possible output connections, under the control of a series of electrical pulses.
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A busy signal (or engaged tone) in telephony is an audible or visual signal to the calling party that indicates failure to complete the requested connection of that particular telephone call.
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In telecommunications and software engineering, scalability is a desirable property of a system, a network, or a process, which indicates its ability to either handle growing amounts of work in a graceful manner, or to be readily enlarged.
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Automatic Electric Company was a telephone equipment supplier for independent phone companies similar in many ways to the Bell System's Western Electric. It was located in Northlake, Illinois.
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City of La Porte, Indiana
Nickname: The Maple City
LaPorte County Courthouse
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Country United States
State Indiana
County LaPorte
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November 3 is the 1st day of the year (2nd in leap years) in the Gregorian calendar. There are 0 days remaining.

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Automatic Electric Company was a telephone equipment supplier for independent phone companies similar in many ways to the Bell System's Western Electric. It was located in Northlake, Illinois.
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18th century - 19th century - 20th century
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crossbar switch is one of the principal architectures used to construct switches of many types. Originally the term was used literally, for a matrix switch controlled by a grid of crossing metal bars, and later was broadened to matrix switches in general.
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The Panel switching system was an early type of automatic telephone exchange, first put into urban service by the Bell System in the 1920s and removed during the 1970s.

The system was named for its tall panels covered with 500 rows of terminals.
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The Number One Crossbar Switching System was the primary urban local telephone exchange design used by the Bell System in the middle 20th century. Its switch fabric topology was based on the earlier urban Panel switch system, which in turn was based on the turn of the century
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The Number Five Crossbar Switching System, designed by Bell Labs and made by Western Electric, was in use in Bell System telephone exchanges from 1948 to the 1980s. Its principal use was as a Class 5 telephone switch, though variants were used as combined class 4/5 in rural areas
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In telecommunications, an electronic switching system (ESS) is:
  • A telephone exchange based on the principles of time-division multiplexing of digitized analog signals.

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The Number One Electronic Switching System was the first large scale Stored Program Control (SPC) telephone exchange or Electronic Switching System in the Bell System, was introduced in Succasunna, NJ, in May 1965.
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The Number One Electronic Switching System was the first large scale Stored Program Control (SPC) telephone exchange or Electronic Switching System in the Bell System, was introduced in Succasunna, NJ, in May 1965.
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The 5ESS Switch is the Class 5 telephone Electronic Switching System sold by Alcatel-Lucent. This digital central office telephone circuit switching system is used by many telecommunications service providers.
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