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THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



smtch causing the clock to stop and the signals associated with Position 1 

 of the sequence switch to be displayed. Signals at the assignment position 

 identify the particular marker and instruct the assignment operator to 

 obtain a trunk Hnk frame and a register. Three conditions may occur: 

 (1) a trunk hnk frame frame and register may be idle and available, (2) 

 a register may be idle but the frame on which it appears is busy, be- 

 ing held b}^ another marker, or (3) all registers may be busy. 



In condition (1) the assignment operator obtains the frame and register 

 according to the operating procedures and operates an ok key at her 

 position. This extinguishes her signals and passes a signal to the marker 

 operator instructing her to record the present time in the space provided 

 for trunk seizure on the call slip. The proper space is indicated by one 

 of a row of lamps beside the call slip. The marker operator then operates 

 the START key for this marker causing the marker timer to return to 

 normal and the sequence switch to advance to Terminal 2. The clock 

 starts if no other marker is waiting to display signals. 



In condition (2) the assignment operator observes that there will be 

 a delay in obtaining a trunk link frame. She inserts a connector cord for 

 this marker in a ''delay" jack and operates a delay key. This extin- 

 guishes her signals and passes a signal to the marker operator to record 



SEQUENCE 

 SWITCH 

 POSITION 







1 



EVENT 



MARKER SEIZURE 



SEIZE TRUNK LINK FRAME 

 TEST REGISTERS 



ALL REGISTERS BUSY 



SEIZE LINE LINK FRAME 

 MAKE CHANNEL MATCH 



release line link frame 

 and trunk link frame 



seize trunk link frame 

 test registers 

 (second trial) 



seize line link frame 

 make channel match 



release after 

 all registers busy 



release after 

 second mismatch 



MISMATCH 



ALL REGISTERS BUSY 



NORMAL RELEASE )- — 



Fig. 13— Possible sequences of a dial tone call. 



