TRANSLATORS AND IDENTIFIERS IN SWITCHING SYSTEMS 591 



corresponding outputs or the association may be changeable through 

 movable jumpers or other means. Thus we have two major types of 

 translators— ^^.reJ and changeable. 



(2) In most applications the input and output codes have no natural cor- 

 respondence but require arbitrary translation determined by the 

 designers of the system or those who operate it. Translation is of the 

 systematic type where there is a definite relationship between the 



, input and output codes. The relationship may be purely mathematical 



I or may follow from some of the peculiarities of the switching system. 



(3) The input and output codes may be of the same numbering base with 

 the same or a different number of places. Often the two codes are of 

 different numbering systems and one or both may consist of mixed 

 base numbers. 



As discussed later, many devices we do not call translators do in fact have 

 a translating function, but they have been designed with a different point 

 of view and have accordingly been given different but suitable functional 

 names. However, the vagaries of telephone switching nomenclature have in 

 some cases resulted in giving other names to elements clearly having the 

 same functions as elements earlier or elsewhere called translators. The more 

 important variants will be pointed out as we go along. One of these, the 

 term ''code converter," seems more appropriate than the original term. 



Examples of Use 



It may now be in order to give a few examples of the kinds of uses made 

 of translators in automatic switching systems. 



(1) Let us assume we have a common control system in a multi-office 

 city. When a subscriber dials the digits of a local number which we call 

 the "office code", indicating the central office unit in which the called 

 subscriber is located, this number is received by the switching equipment 

 of the originating office as a decimal number with three digits or less. The 

 switching equipment, in extending the call to the central office indicated, 

 may have to set up connections at numerous stages of switches, some in 

 distant offices, which are not indicated by the dialed code. The switching 

 operations which must be performed by the control equipment to reach the 

 desired office are indeed represented by a numerical code, but it may be a 

 number quite different from the dialed number and have no natural relation 

 to it. For this purpose a translator is used to convert the dialed number to 

 the required new code comprising the instructions for the switching oper- 

 ations which must be performed. In British practice a translator used in 

 this way is sometimes called a ''route table." 



Since the routing of calls corresponding to any particular office code 



