CROSSBAR DIAL TELEPHONE SWITCHING SYSTEM 97 



thus taking advantage of the flexibiHty of the crossbar switch by pro- 

 viding twenty horizontal paths instead of ten on each switch. The 

 incoming links, on each half of these secondary switches, have access 

 to "line junctors" appearing on the verticals of these switches. 

 These line junctors are in turn distributed over the secondary switches 

 of all the line link frames in the office. There will be at least one 

 line junctor as shown, from each secondary switch on an incoming 

 link frame to a secondary switch on every line link frame in the office, 

 or a minimum of ten line junctor paths between any incoming link 

 frame and any line link frame. The number of the line junctors 

 between these frames will vary depending upon the number of frames 

 required in an office. The line junctors on the verticals of each of 

 the line link frame secondary switches in turn have access to ten 

 line links on the horizontal paths. These ten line links are, as described 

 above, distributed over the primary switches of the line link frame, 

 one to each primary switch. These line links then have access to the 

 called subscriber lines which appear on the verticals of the primary 

 switches. With this arrangement of switches and the three groups 

 of interconnecting link paths, any incoming trunk can be connected 

 to any called line on the line link frame shown, or by means of other 

 groups of line junctors, to a called line on any other line link frame 

 in the office. 



Terminating markers are employed for selecting the paths through 

 these switches to connect an incoming trunk to a called subscriber 

 line. The marker, as will be explained later, records information 

 which permits it to connect to the test wire and holding magnet of a 

 called line and to the test wires and switch magnets of the groups 

 of incoming links, line junctors and line links through which the 

 incoming trunk may be connected to the called line. The marker 

 simultaneously tests these three groups of paths and "marks" an 

 incoming link, a line junctor and a line link which are idle and are 

 accessible to one another, and then operates the switch magnets to 

 connect these three paths and the incoming trunk and the called line 

 together. The paths are selected in an ordered arrangement, so that 

 the lowest numbered incoming links, line junctors and line links are 

 preferred and are used as long as they are available. This increases 

 the efficiency of the paths as compared with a random selection, since 

 it reduces the chance that one or two of them although idle cannot be 

 used because the third one is busy. 



A double primary and secondary trunk arrangement similar to the 

 one shown in Fig. 10 is employed for connecting district junctors to 

 outgoing trunks in the originating end of the office. 



