Crossbar Dial System

Two outstanding features of the crossbar system are the crossbar switch, which is used for all major switching operations, and the marker system of control, which is used in establishing connections. The advantages of the crossbar switch are the high speed relay-like operating characteristics and the use of a few common control circuits having the selecting and trunk-hunting features. These control circuits are used for only a few seconds in setting up a connection and then are released for use on another call. The advantage of the marker system of control is its ability to make two or more attempts to establish a path over alternate switches and trunks when the normally used paths are busy. Before it releases from a connection, it checks the circuit to ensure that the proper connection has been made. It operates an alarm when trouble conditions are encountered. The operating time of a marker is considerably less than one second, therefore, only a few markers of each type are required.