Marker (telecommunications)

For other meanings, see the disambiguation page Marker A marker is a type of special purpose control system that was used in electromechanical telephone central office switches.  Central office switches are the large devices that telephone companies use to make the connections that support telephone calls. So the switch will be used to make the voice connections between users, and to make connections to other equipment such as that used to detect the tones in DTMF (commonly called TouchTone) dialing.
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