THROWDOWN MACHINE FOR TRAFFIC STUDIES 345 



to call on a substantially random basis. Thus, when the operator deter- 

 mines the trunk frame ^vithin which she ^vill hunt, she observes the 

 LEFT and RIGHT lamps below the array for the indication as to whether 

 to hunt from left to right or \'ice versa. 



TRAFFIC ASSIGNMENT 



One of the important functions of the assignment operator is to deter- 

 mine the assignment of all calls at the time of marker release. For this 

 purpose she is furnished with traffic assignment keys and indicators 

 which appear to the right of her position. An adequate understanding 

 of this feature requires a somwhat detailed explanation. 



With the aid of the traffic assignment controls and indicators, shown 

 to the right of Fig. 21, the assignment operator performs the following 

 specific functions : 



On Dial Tone Calls: The operator determines whether a call reaching 

 a register should be classified as a good call (successful subscriber dial- 

 ing), a PD call (partial dial — incomplete subscriber diahng) or an nd 

 call (no dial — ^no subscriber dialing while connected to a register). A 

 proportion of call sUps are originally marked as pd or nd (and also fs 

 or false start) and on these this determination need not be made. If the 

 call is of the pd or nd type, the operator determines whether it should be 

 subtypes PDl, PD2, PD3 or NDl, ND2, ND3. The subtype affects 

 the assumed time until the subscriber abandons the call. If the call is 

 classified as good type, the operator determines which of several dialing 

 times should be used. If the call is classified as pd, nd or fs type, the 

 operator determines when the call is abandoned and whether or not it 

 is routed to a tone trunk. 



On Calls Completed to a Subscriber: On calls completed via intraoffice, 

 outgoing or incoming trunks, the operator determines whether the 

 call is answered and which of ten holding times should be assigned for 

 subscriber line and trunk. 



On Calls Routed to a Tone Trunk: On calls which are routed to tone 

 trunks or given a tone signal from the register, the operator determines 

 the trunk or register holding time and whether and when the call is 

 re-originated. 



In making these determinations, the operator presses keys which 

 cause a lamp to Hght either beneath a time counter or beside a designa- 

 tion strip. The time counter, set ahead of present time, indicates trunk 

 release time, register return time, etc., while the designation strip class- 

 ifies the calls. The determining factors include the magnitude of dial 



