AUTOMATIC Tt)LL SWITCHING SYSTEMS 867 



(lifiits foiward by MF and loaves the coiiiiection to accept another call. 

 This intoi'nialion is relayed from the decodiM" to the sender by way of 

 lh(> niarkei'. The woi'k time of the decoder has becMi in {\w order of a half 

 second. 



The markei- delei-mines tlie identity of the frames on which the in- 

 comiiifi; and outjj;()injj; circuits are located, finds an idle path between the 

 two circuits and sets up the connection. After checking the path through 

 th(> switches to be sure that there are no troubles it Jiotifies the sender 

 that its task has been completed and then leaves the connection. Its 

 work time has also been in the order of a half second. 



In th<> meantime other digits have been coming in to the sender but 

 it does not wait foi' all of them to arrive before advancing the call. When 

 the marker selected the circuit to New York a signal was immediately 

 sent foiward to summon a sender in the New York switching system. 

 The process of attaching the sender in New York was carried on con- 

 currently with the establishment of the coimection through th(> switches 

 in Atlanta. 



When the New York sender is attached a signal is sent to the Atlanta 

 sender to advise it that pulsing may proceed. It immediately sends the 

 area code 207 to New York by MF pulsing and follows it with the 

 remaining digits of the called number, AC4-2345, as they are received 

 from the operator, ending with a start pulse, and then leaves the connec- 

 tion. All common control equipment in Atlanta is now free. 



In New York, as soon as the Maine area code is received it is submitted 

 to the decoder. Upon examination of the code the decoder finds that it is 

 insufficient for routing purposes. New York has a direct circuit group 

 to Portland over which traffic to some offices in Maine is routed, but 

 other offices are reached through Bangor by Avay of Boston. In order to 

 determine which route to take the decoder must know what office is 

 desired. It, therefore, gives the sender a signal saying "come again when 

 you have six digits" and leaves the connection. When the sixth digit 

 arrives the sender again calls for a decoder and gives it the complete 

 code 207-AC4. 



The decoder again translates the area code, which now directs it to the 

 foreign area translator which serves the Maine area, and submits the 

 complete code to that translator. From the ensuing translation it learns 

 that the route is by way of Boston and that all digits should be sent 

 forward by MF. It then calls for a marker and releases the foreign area 

 translator. 



Subseciuent operation is the same as previously described for Atlanta 

 and the complete ten-digit number now arrives at Boston. At that point 



