THROWDOWN MACHINE FOR TRAFFIC STUDIES 327 



on the call slip that a delay has been encountered. The marker operator 

 then operates the start key for this marker. This returns the timer to 

 normal but since a delay condition has been established in the marker 

 circuit by the actions of the assignment operator it does not advance 

 the sequence switch but allows it to remain in Position 1. The marker 

 in a delay condition does not permit its timer switch to step but removes 

 the halting signal from the clock to allow time to advance and other 

 markers to be ser^'ed. All signals for this marker are extinguished during 

 this time. As time advances some other marker ^vill release a trunk link 

 frame. This passes a signal through the delay jack to the delayed marker 

 causing it to display again the signals requesting a trunk link frame and 

 a register associated with sequence switch Position 1. The operators 

 and circuits then proceed exactly as when these signals were first 

 displayed. 



In condition (3), the assignment operator observes that all registers 

 are busy and operates her all busy key. This operates a memory relay 

 in the marker circuit recording that the all busy condition has been 

 encountered and that the future progress of the call should follow the 

 sequence indicated in Fig. 13 by the side branch at Position 1. With all 

 registers busy it is impossible for the marker to establish a connection. 

 As the side branch shows, the alternative is to release and restore to 

 normal. (Later attempts to serve this subscriber will be made until an 

 idle register is obtained.) Thus, with the all busy condition recorded on 

 the memory relays, the circuit will cause the sequence switch to advance, 

 running over positions representing intermediate actions and coming to 

 rest in Position 6 where it is prepared to display signals for the release 

 of the marker. The operation of the all busy key also started the clock 

 and restored the timer switch to normal so that it could measure suit- 

 able work time before displaying release signals. 



The call progresses through successive events in a manner similar to 

 that described above. After obtaining a trunk link frame and a register 

 as in condition (1), the sequence switch stands in Position 2 while the 

 timer switch counts work time preceding a request for a line Unk frame. 

 During this time other markers may request service causing the clock 

 to halt, interrupting the advance of time in all circuits until the opera- 

 tors have completed the required actions. After this marker has counted 

 the specified time, a signal is passed through Position 2 of the sequence 

 switch causing a request for a line link frame to be displayed at the 

 marker position. A delay is handled as before, the marker waiting until 

 the busy frame is released by some other marker. When the frame is 

 obtained, a signal at the match position requests that operator to match 



