AUTOMATIC SWITCHING SYSTEM 



465 



the trunk number group a matrix of cold cathode gas tubes combines 

 the three digits of an office code to estabUsh a single lead control path 

 to the equipuKMit appearances of the trunks. This translator feature 

 l)ermits an arhitrar}^ assignment between trunk locations and directory- 

 listed office codes. Another circuit, the subscriber number group, simi- 

 ilarly includes translation of a called line directory number into the 

 switching network line eciuipnient nunil)er. Over such a control path a 

 test is made of the idle, busy, or vacant condition of any designated 

 trunk or line, and this same control path is used, together with other 

 control leads to the switching network, to establish a connection through 

 the switching network to this trunk or line. 



If the test through the number group discloses an idle trunk, the 

 control terminal of the trunk appearance on the reed-diode switches is 

 "marked" with voltage over the same busy-testing path and the control 

 lead of the calling line appearance is similarly ''marked" over a path 

 extenchng through the receiver-actuator connector. These marks from 

 opposite ends of the switching network cause the selection of an idle 

 junctor located in the connecting leads between line and trunk frames. 

 The selected junctor in turn functions to make the marks effective in 

 operating the switch crosspoints of all four switch stages as described 



SUBSCRIBER 

 NUMBER-GROUP 



CALLED LINE 



LINE 

 CIRCUIT 



TERMINATING 

 RECEIVER 



CALLING LINE 



TO 



OTHER 



LINE 



CIRCUITS 



SWITCHING 

 NETWORK 



INCOMING 

 TRUNK 



TO 



OTHER 



TRUNK 



CIRCUITS 



OUTGOING 

 TRUNK 



LINE 

 CIRCUIT 



ACTUATOR 



ORIGINATING 

 RECEIVER 



TRUNK 

 NUMBER-GROUP 



Fig. 12— Block diagram of ECASS. 



