CROSSBAR DIAL TELEPHONE SWITCHING SYSTEM 111 



No changes are required in the panel selectors to function with the 

 crossbar office. 



On a call for a subscriber in a manual office, the call would be routed 

 through the switches of the district link and the office link frames as 

 previously described and connected to a trunk circuit on the office 

 link frame which terminates in the "B" switchboard in the manual 

 office. The subscriber sender of the crossbar office then transfers the 

 called number by impulses transmitted over the interoffice trunk 

 circuit to the operator's position equipment in the manual office. 

 The called number appears in the form of visible numbers on the 

 operator's keyshelf. The operator completes the connection by 

 "plugging" the associated trunk circuit, which terminates on a cord 

 and plug, into the called subscriber line jack. 



A call originating in a panel dial office for a subscriber line in a 

 crossbar office reaches the crossbar office through an incoming trunk 

 circuit as in the case where the call originated in a crossbar office. 

 The call from the panel office is then handled by the crossbar office 

 terminating sender and marker in exactly the same manner as described 

 for calls originating in the same crossbar office. 



A call originating in a manual office for a line connected to the 

 crossbar office reaches the crossbar office over an incoming trunk 

 circuit from an "A" operator's position in the manual office. These 

 incoming trunks in the crossbar office are similar to the incoming 

 trunks previously described. In this case, however, the incoming 

 trunk is connected to a terminating "B" sender and by means of this 

 sender to a "B" board operator in the crossbar office. The "B" 

 operator will obtain the called number verbally from the distant 

 "A" operator and then, by means of the keyset on her position, 

 register the called number in the terminating sender. The terminating 

 sender will then select a terminating marker and the connection will 

 be established in exactly the same manner as described for a call 

 originating in a crossbar office. 



Maintenance Facilities 

 Automatic routine testing circuits are provided for testing all the 

 principal circuit units, such as the district junctors, incoming trunks 

 and senders. These test circuits automatically put each circuit, one 

 after the other, through all of its functions on all classes of calls to 

 insure that it performs satisfactorily. It tests the important relays 

 of the circuits to insure that they have the proper adjustment to 

 handle the worst circuit conditions. In case any circuit fails to meet 

 the test conditions, the test is stopped and an alarm given to the 

 maintenance force. 



