THROWDOWN MACHINE FOR TRAFFIC STUDIES 323 



Three time detectors are provided in the throwdown machine. One 

 each is used for setting originating times of subscriber starts and of 

 incoming calls. The third is used for releasing held items. Since the 

 holding times of these items are measured in hundreds of time units the 

 last two digits of the time interval are dropped, and only four switches 

 are required. 



It has been mentioned that the ratio of basic machine (clock) time to 

 real time is in the order of 70 to 1. However, in operation, the flow of 

 time is halted frequently to permit actions by the operators. The average 

 interval between stops in the traffic runs which have been processed is 

 less than 10 time units. Thus the machine time is only a small fraction 

 of the time consumed in processing a traffic sample. The ratio of total 

 processing time to real time has turned out in practice to be betw^een 

 1000 and 2000 to 1 depending on the nature of the traffic sample being 

 tested. 



GENERAL PLAN OF THE CONTROL CIRCUITS 



The major part of the throwdown machine circuitry is associated 

 with the marker sequence and timing controls and the gate preferencing 

 arrangement. The circuit plan followed in these two cases will be briefly 

 described in order to illustrate how the throwdown functions were 

 implemented. 



The gate circuits simulate the action of the marker connector circuits 

 of the No. 5 crossbar system which control the access of line link frames 

 and registers to the markers. These circuits assign traffic to idle markers 

 according to the preference rules used in the actual system. The circuits 

 resemble corresponding circuits of the system. They employ two relays 

 per connector and one relay per marker and are arranged with cross- 

 connection terminals so that the preference order and number of con- 

 nectors can be varied as required. 



Each call handled by a marker consists of a series of events occurring 

 in time sequence with time intervals between events corresponding to 

 the "work time" consumed by the marker in performing required func- 

 tions. The sequence of events is not fixed at the start of a particular 

 call but may be altered from stage to stage depending on the particular 

 busy and idle conditions encountered. A block diagram of the control 

 circuits used for simulating this action is shown in Fig. 12. They con- 

 sist of a number of individual circuits provided on the basis of one per 

 marker together with common circuits whose use is shared by all markers. 



The fundamental plan is based on the use of two rotary stepping 



