THROWDOWN MACHINE FOR TRAFFIC STUDIES 333 



tempt. No dial starts represent such situations as a change of mind by 

 the subscriber after Hfting the receiver or accidentally removing the 

 receiver and are not considered to be correlated with later trials. The 

 same is true of false starts which are momentary start signals often 

 hard to explain. A certain number of partial dial and no dial calls are 

 the result of dial tone delays which may occur during heavy load con- 

 ditions. These branch from the ''good call" line in the figure and are due 

 to the subscriber not waiting for dial tone and dialing part of the digits 

 or even the entire number before being connected to a register. The 

 probability of this occurrence will depend on the extent of dial tone 

 delay. After dial tone delay on each call is known, successive uses of the 

 random circuit determine whether the call is partial or no dial type and 

 if the call is to be re-orginated at a later time. Rough estimates of the 

 quantity of this type of traffic could have been made and included in the 

 original traffic data. However, since they depend on the performance 

 of the system there is a tendency toward a ''snowballing" effect and it 

 was thought best to handle it as described in order to detect this effect. 



It can be seen that the exact load on a system is difficult to estimate 

 on the basis of initial starts. The procedure then is to make the best 

 possible estimate of initial starts necessary to produce a given load, 

 taking into consideration all important known factors and, at the con- 

 clusion of a run, make a count to determine the exact number of calls of 

 various types handled. 



When the data for the various calls have been determined from the 

 random numbers, the pertinent information must be transcribed on the 

 call slips. For most calls originated in the office this will requre two call 

 slips. One of these is for the dial tone stage of the call and is used in 

 establishing a connection to a register. The other represents the later 

 stage of the call where the register connects to a marker after dialing is 

 completed and an attempt is made to establish an intraoffice or outgoing 

 connection. The initial time of origination and the calling line number 

 will be recorded on the dial tone slip. The slip for the second stage of the 

 call will carry the calling line number and the called line or outgoing 

 trunk number, but will not carry a time of origination. This is a function 

 of dialing time and is determined at the conclusion of the dial tone 

 stage by the random circuit. It is recorded on the second call slip at 

 that time. The two slips are associated by recording the serial number of 

 the associated slip on the dial tone slip. Incoming call slips carry the 

 origination time, the calling trunk, and the called line numbers. Call 

 slips for partial dial and no dial initial starts carry information similar 

 to that on the dial tone slips. 



