TRANSLATORS AND IDENTIFIERS IN SWITCHING SYSTEMS 593 



between the input and output codes permitted the translating arrange- 

 ment to be made a part of other equipment. 



(3) In our latest crossbar system the idea of not using the numerical 

 digits of the called number as the switching control code has been carried 

 still further. There are no terminals numbered as subscribers' telephone 

 numbers. The switches obtain access to the called subscribers by con- 

 necting to terminals for ''line equipment numbers". The line equipments 

 correspond to subscribers' Hnes and are associated with subscribers' num- 

 bers on an entirely arbitrary basis. The equipment numbers are not four- 

 digit numbers but each is a series of five 1- or 2-digit numbers (a mixed 

 base number) which indicate the locations of the equipments on the frames. 



Here again use is made of translation to convert the dialed decimal 

 number to the non-decimal number forming the switching instructions the 

 common equipment must have in order to reach a called subscriber. In 

 this case, however, the simple, fixed, systematic type of translator used 

 with the panel system cannot be employed, as the associations of the input 

 and output codes are entirely arbitrary and may be changed from time to 

 time to make changes in number assignments, and so the type of translator 

 employed is of the changeable type with arbitrary correspondence. This 

 type of translator, especially when used for large ofl&ces having 10,000 or 

 more numbers (input codes) is decidedly a large scale affair and too costly 

 for permanent association with each circuit unit making use of it. The 

 translating equipment is, therefore, made common and is sectionalized in 

 groups called number groups each handling several hundred numbers and 

 operating independently. 



(4) In automatic equipments arranged for handling toll calls dialed by 

 operators or subscribers, translation is an extremely important feature 

 especially where the networks are as large and complicated as those of the 

 Bell System. Our latest crossbar toll switching system has many important 

 features and economic advantages made possible by the ingenious use of 

 translation. 



In automatic toll switching practice a numerical code of three to six 

 decimal digits is sent to the switching equipment in the originating toll 

 office to indicate the particular geographical area in which the called num- 

 ber is located. The area may be nearby or far away, trunking may involve 

 only a few paths in series or a number of intermediate offices and many 

 interswitch paths. The switching equipment must determine the necessary 

 course of action from the 3- to 6-digit code which has been received, and 

 this is done through the use of a translator. 



In the case of our newest toll crossbar office, the output code of the 



