SXS(Step-by-Step) Exchange

As the number of telephone sets increased in service, manual switchboards requiring many operators were replaced by automatic switching systems. With the step-by-step (SXS) exchange, the selectors in the exchange rises while rotating under the control of the dial pulses sent from the calling telephone, stepping to the level dialed then automatically selecting a telephone line to connect the calling subscriber to the called one. The step-by-step exchange was a typical exchange which, in Japan, aliased "dan-dan-shiki" (staged type) because it used a combination of those selectors at several stages which operate sequentially based on the decimal notation for each digit in the dialed number.