592 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



through the switching equipment may have to be changed from time to 

 time, provision must be made in the translator so that the correspondence 

 between dialed codes and switching codes can be changed economically 

 when necessary by the operating personnel by making changes in the wiring 

 of the translators or by other means. At present this is generally done by 

 re-arranging jumpers. 



Here then we have an example of a translator of the changeable type 

 with arbitrary correspondence between the input and output codes. 



This type of translation is used with almost all common control systems 

 in the world. With some of these systems it is required because of the non- 

 decimal nature of the switching arrangement. With other types, having 

 decimal switches, it is not required but it is nevertheless used in order to 

 make the trunking arrangements more flexible and efficient. 



Translators of this type are not large in some cases because of the small 

 number of translations needed. A complete translator is sometimes perma- 

 nently associated with each circuit element having need for translation 

 service and the translator may be separately mounted or built into the 

 associated circuit. In other cases one or more translators may be arranged 

 for conamon use by numerous circuits requiring them. 



(2) In some switching systems, for instance the panel type, additional 

 use is made of translation in the switching operations involving the further 

 extension of a call after it has reached the desired central office. The nu- 

 merical code, usually the thousands, hundreds, tens, and units digits dialed 

 by the calling subscriber would, with some types of offices, directly serve 

 to control the switching operation for the final selections; but in panel- type 

 offices the terminations for the subscriber numbers, while arranged in an 

 orderly manner, are not grouped on a decimal basis and a switching control 

 code corresponding to the actual location of the called number must be 

 determined. Here again a translator is used, but the input codes in this 

 case have a definite relation to the output codes which is invariable; so the 

 translator used is of the fixed type with systematic correspondence between 

 the codes. 



This particular application followed from the first American invention 

 relating to translators and marked an important step in the development 

 of switching arrangements not requiring a direct correspondence between 

 dialed numbers and switching operations. This appUcation is now found in 

 many systems. 



When we examine the block diagrams of the switching arrangements for 

 the panel and some other systems with this type of translation we do not 

 find any block for this particular translator, as the systematic correspondence 



