SPC Control Systems: Centralized vs. Distributed

SPC Control System

SPC Control System refers to the method of controlling a switching system.

• Centralized SPC Control: If a given processor has direct access to all resources of the node and performs all system functions. This usually means the node has a single central computer (doubled for security).
• Distributed SPC Control: If a processor is in a given state but does not have access to some of the resources and/or is not able to run only some of the functions of the system. In practice, this leads to an existing digital system with a high number of microprocessors that perform the control node as a whole.

Functions of Switching Systems

Switching systems provide power and signaling with user terminals. The user, via the wire pair of the switching system, receives the supply current required for operation: -48V DC at terminal access points. When performing the hook, establishing a current around 30 mA, depending upon the distance of the plant, its impedance, and so on. When the node detects the presence of a user request for communication, the establishment of the stream, picking up the handset, is assigned the device to receive the necessary signaling for the start of communication. This process is completed with the hook in the distant user. In this process the user must be informed, and to this end, by establishing a code or signaling tones:

• Invitation to dial tone: The devices send the dial tone (continuous, 400 Hz).
• Pulse dialing: As many openings as dialed digits loop.
• Multi-frequency dialing: Combination of two frequencies assigned to matrix form.
• Ring tone: Towards the user calls, a discontinuous signal tone of 0.2 seconds and 3 seconds of silence, 400 Hz.
• Busy tone: Calls to the user when the call is not free. Discontinuous signal tone and 0.2 seconds of silence, 400 Hz.
• Communication tone not completed: When circumstances prevent selection techniques. Discontinuous signal of 0.6 seconds of silence and 1 tone, 400 Hz.
• Call sign: Discontinuous 75 Vac and 25 Hz was superimposed on the power of the loop.
• Tone of invitation to international dialing: Continuous 600 Hz.