Stored program control: Difference between revisions

Revision as of 05:27, 23 November 2019

Revision as of 22:05, 18 December 2019

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'''Stored program control''' (SPC) wasis a telecommunications technology used for [[telephone exchanges]] controlled by a computer program stored in the memory of the switching system. SPC was the enabling technology of [[electronic switching system]]s (ESS) developed in the [[Bell System]] in the 1950s, and may be considered the third generation of switching technology. Stored program control was invented by [[Bell Labs]] scientist [[Erna Schneider Hoover]] in 1954 who reasoned that computer software could control the connection of telephone calls.<ref name=tws2Q312>{{cite news

|author= Alpha Doggs

|title= Phone switching pioneers to be inducted in National Inventors Hall of Fame

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Proposed and developed in the 1950s, SPC was introduced in production [[electronic switching system]]s in the 1960s. The 101ESS [[Private branch exchange|PBX]] was a transitional switching system in the Bell System to provide expanded services to business customers that were otherwise still served by an electromechanical central office switch. The first central office switch with SPC was installed at Morris, IL in a 1960 trial of electronic switching, followed shortly thereafter by the first Western Electric [[1ESS switch]] at Succasunna, NJ in 1965. Other examples of SPC-based third generation switching systems include: British GPO [[TXE]] (various manufacturers), Metaconta 11 (ITT Europe) and the AKE, ARE and pre-digital (1970s) versions of the [[AXE telephone exchange]] by [[Ericsson]] and [[Philips]] [[PRX (telephony)|PRX]] were large-scale systems in the [[public switched telephone network]].

SPC enabledenables sophisticated [[calling feature]]s. As SPC exchanges evolved, reliability and versatility increased.

Second generation exchanges such as [[Strowger switch|Strowger]], [[Panel switch|panel]], rotary, and [[Crossbar switch|crossbar]] switches were constructed purely from electromechanical switching components with [[combinational logic]] control, and had no computer software control. The first generation were the manual switchboards operated by attendants and operators.

Later crossbar systems also used computer control of their switching matrices and may be considered SPC systems as well. Examples include the Ericsson ARE 11 (local) and ARE 13 (transit) as well as the North Electric NX-1E & D Switches and the ITT Metaconta 11, once found throughout Western Europe and in many countries around the world. SPC technology using analog switching matrices was largely phased out in the 1980s and had disappeared from most modern networks by the late 1990s., There may still be SPC Switches in some countries like Russia or Ukraine{{citation needed|date=Dec 2019}})

The addition of [[time-division multiplexing]] (TDM) decreased subsystem sizes and dramatically increased the capacity of the telephone network. By the 1980s, SPC technology dominated the telecommunications industry.