1058 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER, 1953 



pretranslation time. Pretranslation does not occur if the office code as 

 well as the area code is registered in the sender before the decoder is 

 connected. This often occurs during periods of heavy traffic. On six-digit 

 translation, two cards must be translated, the three-digit area code 

 followed by the six-digit destination code card. 



SIX DIGIT TRANSLATION IN FOREIGN AREA TRANSLATOR (fAT) 



This type of call requires approximately 560 milliseconds. The area 

 code card in the decoder translator gives the information for selecting 

 the particular FAT in which the six-digit card is located. The trans- 

 lation time will be extended if there is a delay, due to another decoder 

 using the FAT. Pretranslation time, as stated above is not included. 



SIX-DIGIT TRANSLATION-PRINCIPAL CITY AND VACANT CODE ROUTING (fAT) 



In this case translation requires approximately 615 milliseconds. This 

 is for routings to areas where there is a principal city (PC), usually an- 

 other CSP, through which all calls to that area can be completed, although 

 in the area there are other destinations reached over direct high usage 

 trunks. In this case, to save cards and perhaps translators, the six-digit 

 cards for all destinations reached directly through the PC are deliber- 

 ately omitted. The time given is for a call to such a destination. The 

 three-digit card for the area has on it information for the proper routing 

 of the call to the principal city. For those destinations where the six- 

 digit cards are omitted, as well as for vacant codes in such areas, the 

 call is routed to the principal city. Pretranslation and foreign area trans- 

 lator delay times, if any, are not included. 



THREE-DIGIT CARD-TO-CARD TRANSLATION 



This type of card-to-card operation is used where there are several 

 sub-groups of trunks or routes to the destination and the decoders do 

 not have facilities for determining which group of trunsk has an idle 

 trunk. The routing information for each trunk group must be presented 

 successively to the marker in selecting an idle trunk. 



The translation time, considering that an idle trunk is selected from 

 information on the first card, is approximately 330 milliseconds, assum- 

 ing no marker delays. When the trunks for the first card are found 

 busy and routing is made from the second card, the total time is about 

 550 milliseconds. This increases to about 770 milliseconds for routings 



