Stored program control: Difference between revisions

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'''Stored program control''' (SPC) was 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 couldmay 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

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. 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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|accessdate= 2012-06-17

}}</ref>

SPC was introduced in [[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. Examples of SPC based 3rd generation switching systems include: Western Electric [[1ESS switch]], 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 enabled sophisticated [[calling feature]]s. As SPC exchanges evolved, reliability and versatility increased.

== History ==

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. ExamplesThe offirst central office switch with SPC basedwas 3rdinstalled generationat Morris, IL in a 1960 trial of electronic switching, systemsfollowed include:shortly thereafter by the first Western Electric [[1ESS switchsiwtch]] 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 enabled sophisticated [[calling feature]]s. As SPC exchanges evolved, reliability and versatility increased.

These systems could be considered the 3rd generation of public telephony switching technology, following on from 1st generation manual switch boards and 2nd generation step-by-step, rotary, crossbar and similar electromechanical technologies.

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

However, later crossbar systems used computer control of their switching matrices and would be considered full SPC systems. Examples include the Ericsson ARE 11 (local) and ARE 13 (transit) and the ITT Metaconta 11, once found throughout Western Europe and in many countries around the world.

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. StoredThe programfirst controlgeneration waswere inventedthe bymanual [[Bellswitchboards Labs]]operated scientistby [[Ernaattendants Schneiderand Hoover]] in 1954 who reasoned that computer software could control the connection of telephone callsoperators.<ref name=tws2Q312>{{cite news

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.

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) and the ITT Metaconta 11, once found throughout Western Europe and in many countries around the world. SPC technology using analog switching matrices began to bewas phased out in the 1980s and had disappeared from most modern networks by the late 1990s.

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.

Viable, fully digital switches emerged in the 1970s, with early systems, such likeas the French [[Alcatel-Lucent|Alcatel]] E10 and Canadian Nortel DMS series going liveinto production during that decade. Other widely adopted systems hitbecame the marketavailable in the early 1980s. These included Ericsson AXE 10, which would becomebecame the world's most popular switching platform, the [[Western Electric]] [[5ESS]] used through the US and in many other countries, the German designed Siemens ESWD, the ITT System 12 (later rebranded [[Alcatel (mobile device brand)|Alcatel]] S12) and [[NEC]] NEAX all of which were widely used around the world. The British developed [[System X (telephony)]], and other smaller systems also emerged in the early 1980s.

Some digital switches, (notably the 5ESS and very early versions of Ericsson AXE 10), continued to use analog concentrator stages, using SPC -like technologies, rather than direct connections to the digital line cards containing the [[CODEC]].

Early in the 21st century the industry began using a 5th generation of telephony switching, as [[Time-division multiplexing|TDM]] and specialist hardware based digital circuit switching is being replaced by [[softswitch]]<nowiki/>es and voice over IP [[VoIP]] technologies.