DELAYED EXPONENTIAL CALLS SERVED IN RANDOM ORDER 369 



the long delays occurring on a few of the more unfortunate calls. Even 

 choosmg w = 25 moved the delay curve hardly more than half way from 

 the completely random to the fully queued curve oi w = » . The w = SO 

 selection shows the accomplishment of nearly fully queued results, the 

 latter being given by curve C {w = oo). Thus one would apparently 

 find little value in instructing a team of two operators working at an 

 occupancy of 90 per cent to try to remember the order of arrival of 

 waiting calls unless they could keep track of an unexpectedly large 

 number. 



Electrical storing circuits have long been used to assist the ordering 

 of waiting calls. They have the especial advantage of not becoming 

 confused and losing the order of the calls which have engaged them up to 

 the limit of their storage capacity. In the Bell System two methods of 

 approaching true queueing are in common use. In one method, such as 

 found, for instance, in the No. 3 Information Desk, a nimiber of storage 

 circuits are provided so that as a waiting call is served from the number 

 one storage position, all the others waiting on storage circuits drop down 

 one position. If s such circuits are provided, and more than s calls have 

 been waiting, one of the excess wiU then be chosen at random to oc- 

 cupy the newly vacated sth storage circuit. 



The second method used widely in both local and toll systems is 

 known as gating. In its simplest form a gate opens into a ''corral" 

 where the operators or other service media are located. So long as calls 

 simultaneously demanding service do not exceed the number of operators 

 (trunks, markers, etc.) the gate is ineffective. As soon as one call has to 

 wait, the gate closes until that call obtains service, and then admits to 

 the corral all calls which have accumulated on the outside. The gate 

 again closes until all calls within the corral are served; and so on. Thus 

 the calls are admitted in bunches to the corral. Between bunches there 

 is strict queueing but within bunches when they get inside the gate the 

 calls are substantially served at random. As long as the bunches are 

 small the effect of true queueing is approached. In any event a strong 

 safeguard against excessively long delays on a few unlucky calls is in- 

 troduced. In the Bell System, a variety of gating plans are found such as 

 double gates, gates with additional preferences for certain types of calls, 

 and schemes for placing calls outside the gate again if they cannot be 

 served immediately. Each of these must be studied with its own peculiar 

 characteristics in mind. 



To illustrate the effectiveness of the storage circuit type of automatic 

 queueing arrangement, the 1000 calls of Runs 1 and 2, for the two path 

 case, were processed by a throwdown through a two operator, 20 storage 



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