Stored program control: Difference between revisions

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Revision as of 00:59, 27 March 2017

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There is an inter processor link through which the processors exchange information needed for mutual coordination and verifying the 'state of health’ of the other. If the exchange of information fails, one of the processors which detect the same takes over the entire load including the calls that are already set up by the failing processor. However, the calls that were being established by the failing processor are usually lost. Sharing of resources calls for an exclusion mechanism so that both the processors do not seek the same resource at the same time. The mechanism may be implemented in software or hardware or both. Figure shows a hardware exclusion device which, when set by one of the processors, prohibits access to a particular resource by the other processor until it is reset by the first processor.

=== Distributed control ===

Distributed SPC is both more available and more reliable than centralized SPC. In this, theThe control function are shared by many processors within the exchange itself. It uses low cost [[microprocessor]]<nowiki/>s. Exchange control may decomposed either horizontally or vertically for distributed processing. <ref>[https://books.google.com/books?id=ghCiNHzWvL4C&pg=PA96&dq=4.3+Distributed+SPC&hl=en&sa=X&ei=ToAhT6fJAsHL0QHhr4zVCA&ved=0CDIQ6AEwAA#v=onepage&q=4.3%20Distributed%20SPC&f=false] T Wiswanathan</ref>

*:Whole In vertical decomposition the whole exchange is divided into several blocks and a processor is assigned to each block. This processor performperforms all the tasktasks related to that specific blocksblock. Therefore, the total control system consists of several control units coupled together. For redundancy, purpose processorprocessors may be duplicated in each blocksblock.

*Vertical decomposition:

*: In thishorizontal type of decompositionDecomposition each processor performs only one or only some exchange functionfunctions.

*:Whole exchange is divided into several blocks and a processor is assigned to each block. This processor perform all the task related to that specific blocks. Therefore, the total control system consists of several control units coupled together. For redundancy purpose processor may be duplicated in each blocks.

*Horizontal Decomposition:

*:In this type of decomposition each processor performs only one or some exchange function.

== See also ==

* [[List of telephone switches]]

== References ==

{{reflist}}