104 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1956 



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10 with Madison and Milwaukee, Wisconsin, in area 414 and Belle 

 Plaine Crossbar Tandem in Chicago, Illinois, in area 312. An economical 

 trunking plan may provide for direct circuits from Chicago to each 

 place. If only three-digit translation were provided in the Chicago 

 switching equipment, the route to both places would be selected as a 

 result of the translation of the 414 area code alone and, therefore, calls 

 to central offices reached through Madison, would need to be routed 

 via Milwaukee. This involves not only the extra trunk mileage, ])ut 

 also the use of an extra switching point. With six-digit translation, both 

 the area code and the central office code are analyzed, making it 

 possible to select the direct route to either city. 



Six-digit translation in crossbar tandem will involve primarily the 

 use of a foreign area translator and a marker. The translator will have 

 a capacity for translation of five foreign areas and for 60 routes to each 

 area. Since the translator holding time is very short, one translator is 

 sufficient to handle all of the calls requiring six-digit translation, but 

 two are always provided for hazard and maintenance reasons. 



On a call requiring six-digit translation the first three digits are 



CASE 2 



DIGITS RECEIVED 



OUTPULSING 

 CONTROL 







DIGITS CODE CONVERTED 

 AA AB AC 



;: PS1 



X' 



PS2 ;:PS3 ;:S4 ):S6 ~:S6 ;;S7 ::S8 



10 



59 ;:S10 



CASE 3 



DIGITS RECEIVED 



DIGITS PREFIXED 

 AB AC 



B' 



C 



OUTPULSING 

 CONTROL 



i PS2 : : P 



B 



PS3 •:SI ':S2 ::S3 :;S4 : : S5 :'S6 ■;S7 



Fig. 9 — Method used for outpulsing digits. 



