594 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



translator actually consists of many different numbers in various bases, 

 each indicating some different item of information required in order to 

 complete the call. The information includes switching instructions for 

 interswitch paths and intertoU routes of the preferred combination and 

 also indicates where alternate combinations may be found if the preferred 

 choices are busy or out of order. 



Because of the large number of possible codes, translators suitable for 

 this application present special design problems. 



Typical Translators 



Before undertaking an analysis of the general concepts used in trans- 

 lation, it may be well to review some of the typical translation methods 

 which have been used in the field. In the following descriptions, details not 

 necessary in illustrating the general method are omitted. 



Fixed Translators 



Figure 1 shows the principles of a fixed, systematic translation scheme 

 employed in early panel and other systems for deriving from decimal 

 numbers the switching instructions for controlling some of the non-decimal 

 selections. 



This is one of the solutions for case (2) of the examples of use just men- 

 tioned. The selection of a called subscriber's number by the terminating 

 equipment in the called central office unit is governed by the last four 

 decimal digits of the number, but the process required with the panel ar- 

 rangement is in part non-decimal. The numbers are grouped in banks of 

 100, which means that, once switching has proceeded this far, the wanted 

 number can be sehcted in the bank on a decimal basis as indicated directly 

 by the tens and units digits of the number. Other groupings of final and 

 preceding equipment involved are not decimal, so the preceding selections 

 must be made on the basis of non-decimal switching control codes ob- 

 ined by the common control equipment through the translation process. 



The switching code wanted in this case consists of three numbers for 

 controlling selections called incoming brush (IB), incoming group (IG) and 

 final brush (FB), and must be derived from the combination of the thousands 

 and hundreds digits of the called subscriber's number as recorded on the 

 register switches by the calling subscriber's dial. This can be done because 

 the non-decimal arrangement of the switching equipment is orderly and 

 there is, therefore, a systematic relationship between the input and output 

 codes.2 



It will be noted that the input code consists of a ground on one lead in 



' Oscar Myers, Codes and Translations, A .I.E.E. Transactions, Vol. 68, 1949. 



