CROSSBAR DIAL TELEPHONE SWITCHING SYSTEM 103 



called office appear. This connection is made through the office Hnk 

 frame connector circuit, one of which is provided for each office Hnk 

 frame. Through this connector the marker is extended to the test 

 leads of any desired trunk group on the office link frame and to the 

 crossbar switches of the frame. When so connected the marker has 

 exclusive control of the trunks and switches of the frame and other 

 markers which desire connection to the same frame are deprived of 

 access until the connected marker releases. 



2. The marker next tests the outgoing trunks to the called office and 

 selects an idle one. If, as determined from the route relay, the trunks 

 are divided over more than one frame, the marker will connect to 

 the second group of trunks on the second office link frame in case the 

 first group of trunks is found to be busy.. 



3. The marker also connects by means of a connector circuit to 

 the district link frame associated with the district junctor to which 

 the calling line is connected. The identification of this frame was 

 obtained from the sender and the sender link control circuit as pre- 

 viously mentioned. Through the connector circuit of the district link 

 frame the marker is extended to the control leads of the district 

 junctor circuit and the crossbar switches of the district link frame. 

 As in the case of the office link frame, only one marker is connected to 

 a frame at a time. 



4. The marker after selecting an idle trunk circuit which appears 

 in a horizontal circuit path on one of the secondary switches of the 

 office link frame, then proceeds with the selection of an idle channel 

 through the switches of the two switch frames. A number of these 

 connecting channels is provided between the district junctor and the 

 outgoing trunk. Each channel consists of a "district link" on the 

 district link frame, of an "office link" on the office link frame, and an 

 "office junctor" connecting the district Hnk frame to the office link 

 frame. The marker tests a group of these channels simultaneously 

 and selects an idle one. It then operates the switch magnets which 

 will connect these three paths of a channel, and the district junctor 

 and the outgoing trunk together, thereby establishing a connection 

 from the district junctor to the outgoing trunk. 



5. When the marker has completed this operation it checks the 

 connection to insure that it has been properly established and that 

 it is capable of being held under control of the district junctor, before 

 releasing itself from the connection. 



6. The marker performs these functions in approximately .5 second, 

 then releases and becomes available for use on other calls. 



It will be observed that the three links involved in establishing the 



