Abstract: A line identifying system for an automatic switching system of the common control type employs a line identifier adapted to be connected to any of a plurality of switch frames through a connector, which cuts off the operating circuit for a connector relay corresponding to a switch frame upon receipt of instructions from the line identifier and prepares the operating circuit of the connector relay corresponding to the switch frame upon receipt of instructions from a switch controller.

Abstract: A telephone switching system of the stored program control type comprising a calling line identifier for identifying the position of a calling subscriber on the switching network and a called line busy status detector for detecting the free or busy status of a called line designated by a central controller. The central controller reads and utilizes the information identified and detected by the above-mentioned two devices respectively, thereby to eliminate the need for memories in the central controller to store the status of all subscribers' lines.