Marker (telecommunications)

A marker is a type of special purpose control system that was used in electromechanical telephone central office switches.

5 Crossbar switches had dial tone markers to select one of a number of shared digit receivers (termed originating registers) and connect it to a subscriber who wished to make a telephone call.

In this case the Completing Marker would mark a proper path of idle links for the call to make through the mechanical voice switching matrix.

[5] During the middle 20th Century, markers in Bell System exchanges acquired other functions that were only needed once or twice per telephone call, including outgoing digit translation and enforcement of different policies upon different classes of service in the provision of features to customers.

Where those exchanges had markers, for example in the British TXK or the Ericsson ARM, they were simpler in design and function.

The digit translation jobs that were added to Bell System markers were handled by other equipment.