MACHINE SW ITCHING TELEPHONE SYSTEM 



11 



The first step in completing the connection is to choose an idle 

 trunk in the proper direction. To the nearby offices there are groups 

 of direct trunks, whereas the more distant offices are reached through 

 tandem centers described later. 



The line finder leads to the movable element of a panel selector 

 known as a "district selector." This district selector has capacity 

 for 450 working outgoing trunks, the other 50 trunks being used for 

 control purposes. In a small city 450 trunks would be sufficient to 



Fig. 19 — Sender Selector 



reach all points, but in the case of the New York offices 450 outgoing 

 trunks are not sufficient. Accordingly, only a few of the trunk groups 

 outgoing from these offices leave directly from the district selectors. 

 To obtain access to the remaining trunks there are, on every district 

 selector frame, groups of trunks leading to so-called "office selectors." 

 These office selectors are of the panel type and each has a capacity 

 for 450 outgoing trunks. 



The path of a call through a district and office selector will now be 

 traced. The district selector starts upward under the control of the 



