AUTOMATIC SWITCHING SYSTEM 459 



switches so as to pro\'ido one path from each primary switch to each 

 secondary switch. 



Connections are made between the secondary hne frame switches and 

 the secondary trunk frame switches to provide talking paths between 

 each Hne frame and each trunk frame. A direct metalUc connection is 

 made for the two talking conductors of each path but the control lead 

 from each secondary line switch outlet is connected to an individual 

 control circuit, called a junctor, and the control lead from a secondary 

 trunk switch outlet associated with the same talking path is connected 

 to the same control circuit or junctor. The size of the switches on each 

 type of frame and the number of frames in each particular office will be 

 determined by the number of subscribers and other offices connecting 

 to this office and the calling habits of the subscribers served. 



The operation of the switching network may be explained by reference 

 to Fig. 10 which shows the control lead diagram of a skeletonized switch- 

 ing network of a large size office. This figure shows two line frames, 

 each of which has two primary switches and two secondary switches. 

 Three vertical inlets are provided on each primary switch and two ver- 

 tical outlets on each secondary switch. The figure also shows two trunk 

 frames, each of which has two primary switches and two secondary 

 switches. The trunk switches provide two vertical trunk inlets on the 

 primary switches and two vertical outlets on the secondary switches. 

 Eight junctors are required as indicated. This switching network' then 

 serves to interconnect twelve subscribers with eight trunk appearances. 

 This is the actual size built in the experimental model. 



As shown in Fig. 10 each control lead path between a primary and a 

 secondary switch on both the line and trunk frames is connected through 

 a high value of resistance to a — 45-volt power supply. In addition each 

 control lead path from a secondary switch terminates in a similar re- 

 sistor connected to a — 105-volt power supply. In a junctor involved 

 in an established connection, such as junctor 5 of Fig. 10, the control 

 leads connect to a —24- volt source through low resistance relay wind- 

 ings. A talking path is shown as fully established between line C on line 

 frame 2 and trunk D on trunk frame 2. This connection is held by the 

 current flowing from the — 24-volt source in junctor 5 through the opera- 

 ted reed crosspoints in the line frame to a ground in the line circuit and 

 in the same manner through the operated reed crosspoints in the trunk 

 frame to a ground in the trunk circuit. The —24-volt potential^on the 

 junctor leads and the resulting — 12-volt potential on the primary-to- 

 secondary switch link leads are effective path busy indications for sub- 

 sequent path selection operations in the network. 



