466 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 



in the section on Switching Network. The marking and switch operating 

 voltage is apphed to the hne terminal of the switches through a line 

 cut-off relay, which operates on the increased current which flows in 

 this circuit immediately after the diodes in the switch crosspoints have 

 been shorted out. The operation of the line cut-off relay releases the 

 originating actuator and receiver which were connected through back 

 contacts of this relay and, in turn causes the release of the trunk num- 

 ber group. 



The next step is to send the called line number over the outgoing 

 trunk so that the distant office may complete the connection to the called 

 subscriber. An outward actuator is provided for this purpose. A relay 

 in series with the marking path in the outgoing trunk circuit operates 

 to connect the outward actuator directly to the trunk. The trunk-to- 

 actuator connector circuits include gas tube lockout to insure that only 

 one trunk is connected to the actuator at a time. During the short delay 

 of awaiting an actuator that may occur during heavy traffic periods the 

 established switching network connection is held under control of direct 

 current supervision from the trunk circuit. The outward actuator, when 

 connected, transmits 50-cycle current through the switching network 

 to the calling subscriber's subset and maintains the connection by moni- 

 toring the 50-cycle current flow. This 50-cycle current causes the sub- 

 scriber's set to transmit again the called number repetitively through 

 the switches and outgoing trunk to the associated incoming trunk at the 

 called office. In this paper it is assumed that all other offices connecting 

 to this one are of the same type as this one or are arranged to transmit 

 and receive, when required, the signaling pulse code used in this office. 

 The arrangements in this office for completing incoming calls, including 

 calls originating within this office itself, are shown in Fig. 12. 



Operation of the connector relay which connects the outgoing trunk 

 to an actuator signals the incoming trunk circuit in the terminating 

 office to connect to an incoming receiver circuit for receiving the re- 

 petitive dialing signals. Connection between the incoming trunk and 

 signal receiver is made through a lockout circuit which insures that 

 only one trunk is connected to the receiver. When the incoming receiver 

 has absorbed the office code, registered the called line number and 

 checked the registration, it causes the incoming trunk to transmit a 

 reverse battery pulse to the outgoing trunk as a number-received signal. 

 This reversal causes the outgoing trunk to dismiss the outw^ard actuator 

 and to trip the latch in the subscriber's subset to the talking position 

 with direct current talking and supervisory battery supplied from the 

 outgoing trunk. At the same time the incoming receiver connects to 

 the subscriber number group for making an idle-busy-vacant test of 



