86G THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



of these groups an idle circuit maj^ be found. Let us assume that the 

 circuits to Boston are all busy but there are one or more idle circuits in 

 the New York group. The decoder calls for a marker and tells it which 

 group of leads to test, and also causes the sender to be connected to the 

 particular marker it has selected. 



The marker, following instructions from the decoder, is connected to 

 the appropriate trunk block connector. This is one of a group of common 

 circuits giving access to "blocks" of trunks for allowing the marker to 

 locate an idle trunk. The marker examines the test leads of the individual 

 toll lines to New York and as soon as it has selected an idle circuit it 

 so informs the decoder. The decoder then tells the sender to send all 



/■^^ 



207-AC4-2345 



ATLANTA OUTWARD V 

 OPERATOR KEYS \ 



207- AC4 -234-5 



LEGEND 

 D REGIONAL CENTER 

 A SECTIONAL CENTER 

 ® PRIMARY OUTLET 



FINAL GROUP 



HIGH-USAGE GROUP 



Fig. 2 — Call from Atlanta, Georgia to Alouticello, Maine. 



