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Consumer Electronics by S. P. Bali

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FUNCTIONS OF A SWITCHING OFFICE

The basic functions performed by a switching office are the same, whether it is manual, electromechanical, or electronic. The basic stages that a call must go through are as follows :

  1. When the subscriber picks up her telephone, the office must detect that service is needed. In an automatic office, the dialing tone is switched to that line, and the mechanism waits for the subscriber to dial.
  2. The dialed telephone number must now be used to set up an interconnection path. The number is received as a train of pulses from a rotary dial or a train of frequency pairs from a push-button telephone. These signals cause the equipment to set up a path through the exchange to the appropriate outgoing line.
  3. A central office ...

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