THROWDOWN MACHINE FOR TRAFFIC STUDIES 329 



a channel before allowing time to advance. In case of a mismatch the 

 match operator depresses a mismatch key. This operates a memryo 

 relay which will cause the marker to follow the alternate sequence in- 

 dicated by the side branch at Position 2 in Fig. 13. As a safety pre- 

 caution, the MISMATCH key is made effective only at the time a request 

 for a match is made so that accidental operation at other times will not 

 disturb the circuit action. With a mismatch recorded, the sequence 

 switch advances to Position 3 and at the proper time displays signals 

 to release the line link frame, trunk link frame and register. Thus the 

 call advances with the possible alternates of all registers busy at Posi- 

 tion 4 or a second mismatch at Position 5. The call proceeds to one of 

 its possible conclusions where frames are released and the marker be- 

 comes idle. 



The dial tone call which has been described is the least complex call 

 handled by the machine. The intraoffice call which was diagramed in 

 Fig. 4 is the most complex. It requires 22 sequence switch positions to 

 represent events and may have 92 possible sequences depending on 

 conditions encountered. To take care of variations in sequence in all 

 calls a total of nine memory relays is provided in each marker. 



The circuit equipment consists, largely, of telephone type electro- 

 magnetic relays and rotary stepping switches. Approximately 800 relays 

 are used. The total number of switches is 57. Of these 47 are of the 22- 

 position, 6-circuit type while the remainder are of the 44-position, 3-cir- 

 cuit type. This equipment is mounted in the two cabinets shown in 

 Fig. 14 and in additional units located within the operating positions. 

 Time indications are given by four-digit message registers, approximately 

 40 being used. The random circuit consists of a gas tube counting ring 

 with several control relays. Output indications are given by miniature 

 neon lamps. Signals are given to the operators by telephone switchboard 

 lamps, 822 being used. Manual equipment used by the operators in sig- 

 naling to the circuits consists of keys, switches and telephone plugs and 

 jacks. The machine contains 187 keys and switches, 60 cords equipped 

 with plugs and 509 jacks. 



PREPARATION FOR A THROWDOWN RUN 



There are two phases in the preparation for a throwdown run. One of 

 these is the tentative engineering of an office of the size to be tested. 

 The other is the preparation of data to represent traffic handled by this 

 office. The first of these follows rather closely the general procedure 

 that would be used in planning the installation of a new switching office. 



