Automatic telephone exchange

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Automatic (non-computerized) telephone exchange came into existence in the early 1900's. Designed to replace the need for human operators to complete the connections required for a telehone call, they have for the most part been replaced by computerized exchanges in most moderized countries, but may still exist elsewhere. Using motors, shaft drives, rotating switches and relays, the exchange can automatically sense an off hook telephone condition, provide dial tone to that phone, receive the pulses generated by the phone and then complete a connection to the called phone within the same exchange or to another distant exchange. The exchnage then maintains the connection until the parties hangup, and the connection is disconnected. Additional features, such as billing euipment, may also be incorporated into the exchnage. Some types of automatic exchanges were Stroger,All Relay, X-Y, Panel and Crossbar