What is store program control (SPC)? Give the organization of centralized SPC. Discuss the advantages of SPC automation in telephone switching.

What is store program control (SPC)? Give the organization of centralized SPC. Discuss the advantages of SPC automation in telephone switching.
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1 Answer

Answer :

 In stored program control systems, a program or set of instructions to the computer is stored in its memory and the instructions are executed automatically one by one by the processor. Carrying out the exchange control functions through programs stored in the memory of a computer led to this name.

 There are two approaches to organizing stored program control:

1. Centralized: In this control, all the control equipment is replaced by a single processor which must be quite powerful.

2. Distributed: In this control, the control functions are shared by many processors within the exchange itself. 

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In centralized SPC, dual processor architecture may be configured to operate in one of three modes:

1. Standby mode: In this mode, one processor is active and the other is on standby, both hardware and software wise. The standby processor brought online when active processor fails. An important requirement of this configuration is the ability of the standby processor to reconstitute the state of the exchange system when it takes over the control.

2. Synchronous duplex mode: In synchronous duplex mode, hardware coupling is provided between the two processors which execute the same set of instructions and compare the results continuously. If a mismatch occurs, the faculty processor is identified and taken out of service immediately. When the system is operating normally, the two processors have the same data in their memories at all the times and receive all information from the exchange environment.

3. Load Sharing mode; In load sharing operation, an incoming call is assigned randomly or in a predetermined order to one of the processors which then handles the call right through completion. Thus both the processors are active simultaneously and share the load and the resources dynamically.


 Advantages of SPC:

(i) Easy to control

 (ii) Easy to maintain

 (iii) Flexible

 (iv) Wide range of services can be provided to customers. 

(v) Increase level of automotive in switching 

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