MACHINE SWITCHING TELEPHONE SYSTEM 63 



removed from the switchhook preparatory to dialing, the line is 

 selected by a "line tinder" and connected to an idle "sender" by 

 means of a "sender-selector." 



Upon completion of these operations which take but a fraction of 

 a second, the dial tone is sent to the calling subscriber as previously 

 mentioned. When the subscriber dials, electrical impulses on a 

 decimal basis are transmitted to the sender which receives and regis- 

 ters them, translating them in turn to the proper basis for the control 

 of the selectors which are not operated on a decimal basis. The 

 sender automatically causes the particular "district selector" which 

 is permanently associated with the line finder originally used, to select 

 a trunk to the ofhee desired. 



Assuming that the call is for a subscriber in the same office, Aca- 

 demy, the trunk chosen will terminate at an "incoming selector" 

 frame and the sender above referred to will cause the call to be routed 

 through the incoming selector to a final selector, and thence to the 

 particular line desired. When the connection is thus completed, 

 audible signals will be sent back to the calling subscriber to indicate 

 that the station is being rung or that the line is busy. 



It the call had been for a subscriber in another machine switching 

 office, namely, Pennsylvania, the call would be routed from the district 

 selector to the office desired, either directly or through an "office 

 selector" in case the total number of trunks to all offices is too large 

 to be placed on the district selector multiple. These trunks terminate 

 on incoming selectors at the Pennsylvania office which select the sub- 

 scriber's line through final selectors, as described above. 



If the call is for a subscriber connected to, say, the Worth Office, 

 which is a manual office, the call would be routed from a district 

 selector directly or through an office selector to the "B" board in the 

 Worth Office, where the number desired appears in front of the oper- 

 ator at a "call indicator position" in the form of visible numbers on 

 the keyshelf. The operator is advised of the trunk to which the call 

 is connected by suitable signals, and the call is completed by plugging 

 this trunk into the desired subscriber's line. 



Calls originating in a manual office and intended for a machine 

 switching office reach the machine switching office over trunks from 

 the "A" operators in the manual office. At the machine switching 

 end these trunks terminate in incoming selectors, which have access 

 to the final selectors on which the subscriber's lines are located. The 

 selectors are under the control of a special group of senders, and 

 operators are provided with suitable keys for setting up in these 

 senders the number of the desired subscriber. These operators at 



